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JAC Board Class 9th Science Solutions Chapter 5 The Fundamental Unit of Life

JAC Class 9th Science The Fundamental Unit of Life InText Questions and Answers

Page 59

Question 1.
Who discovered cells and how?
Answer:
Robert Hooke discovered cells in 1665. He observed the cells in thin slices of cork. They appeared like small compartments when viewed under the microscope.

Question 2.
Why is the cell called structural and functional unit of life?
Answer:
A cell is capable of carrying out all the life functions such as nutrition, excretion, respiration, etc Hence, a cell is called the functional unit of life. Additionally, the cell is the smallest unit of life and all the living beings are made up of cells. Therefore, a cell is called the structural unit of life.

Page 61

Question 1.
How do substances like CO, and water move in and out of the cell? Discuss.
Answer:
Substances move in and out of the cell because of diffusion. Diffusion is the random movement of particles in order to attain concentration equilibrium. The movement of water molecules through a semi – permeable membrane is called osmosis. It is important to note that plasma membrane is a semi – permeable membrane. Water always moves from its higher concentration to its lower concentration.

Question 2.
Why is the plasma membrane called a selectively permeable membrane?
Answer:
Plasma membrane allows passage to some selected substances. Hence, it is called a selectively permeable or semi- permeable membrane.

Page 63

Question 1.
Fill in the gaps in the following table illustrating difference between prokaryotic and eukaryotic cells.

Answer:

• Prokaryotic cell (b): Nuclear region is poorly defined due to absence of a nuclear membrane and is known as nucleoid.
• Eukaryotic cell (d): Membrane bound cell organelles are present.

Page 65

Question 1.
Can you name the two organelles we have studied that contain their own genetic material?
Answer:
Mitochondria and chloroplast contain their own genetic material.

Question 2:
If the organisation of a cell is destroyed due to some physical or chemical influence, what will happen?
Answer:
Various parts of a cell are responsible for various functions. They work in tandem
to continue life in the cell. In case, the organisation of a cell is destroyed due to some physical or chemical influence, the cell will die.

Question 3.
Why are lysosomes known as suicide bags?
Answer:
Lysosomes contain digestive enzymes. In case of a rupture in lysosomes, the enzymes are released in the cytoplasm and end up digesting the contents of the cell. This results in cell death. Due to this, lysosomes are also known as suicide bags of cells.

Question 4.
Where are proteins synthesised inside the cell?
Answer:
The proteins are synthesised in the ribosomes present on RER (rough endoplasmic reticulum). They are also known as protein factories.

JAC Class 9th Science The Fundamental Unit of Life Textbook Questions and Answers

Question 1.
Make a comparison and write the ways in which plant cells are different from animal cells.
Answer:

Question 2.
How is a prokaryotic cell different from a eukaryotic cell?
Answer:

Question 3.
What would happen if the plasma membrane ruptures or breaks down?
Answer:
Plasma membrane provides a container for the cell organelles and cytoplasm. Moreover, plasma membrane also protects the contents of a cell from external environment. In case the plasma membrane ruptures or breaks down, the cell contents would be exposed to the external environment. This would prove lethal for the cell and the cell would cease to exist.

Question 4.
What would happen to the life of a cell if there was no Golgi apparatus?
Answer:
If Golgi apparatus is not present, the packaging and transport of materials would cease to happen. Various substances would not be transformed into useful materials of the cell. Plasma membrane will also be affected The secretory activities of the cell would also cease to occur. Hence, the cell will eventually die off.

Question 5.
Which organelle is known as the powerhouse of the cell? Why?
Answer:
Mitochondrion is known as the powerhouse of the cell. The reason for this is the fact that cellular respiration takes place in mitochondria and the energy released after that, gets stored in mitochondria in the form of ATP. As ATP instantly provides energy, they are called energy currency of the cell.

Question 6.
Where do the lipids and proteins constituting the cell membrane get synthesised?
Answer:
Lipids are synthesised in the endoplasmic reticulum (smooth ER). Protein is synthesised in ribosomes which are usually present on the rough ER.

Question 7.
How does Amoeba obtain its food?
Answer:
Amoeba obtains its food through a process called phagocytosis. The cell membrane of amoeba is projected into numerous finger – like outgrowths called pseudopodia Amoeba surrounds a food particle by pseudopodia and makes a food vacuole after engulfing the food.

Question 8.
What is osmosis?
Answer:
Osmosis is the process of movement of water molecules from a region of higher water concentration, through a semi – permeable membrane, to a region of lower water concentration.

Question 9.
Carry out the following osmosis experiment:
Take four peeled potato halves and scoop each one out to make potato cups, one of these potato cups should be made from a boiled potato. Put each potato cup in a trough containing water. Now,
(a) Keep cup A empty.
(b) Put one teaspoon sugar in cup B.
(c) Put one teaspoon salt in cup C.
(d) Put one teaspoon sugar in the boiled potato cup D.
Keep these for two hours. Then, observe the four potato cups and answer the following:
1. Explain why water gathers in the hollowed portion of B and C.
2. Why is potato A necessary for this experiment?
3. Explain why water does not gather in the hollowed out portions of A and D.
Answer:

1. Water gathers in the hollowed portion of potato B and C because: Living plasma membrane of potato cells act as semi – permeable membrane. There is higher concentration of water in trough than the hollowed portions of B and C. So water, by the process of osmosis, moves into the hollowed portions of potato cups B and C.
2. Potato cup A is kept empty to act as control set – up.
3.  potato is necessary because
   • (a) As the potato cup A is empty, water does not gather in hollowed out portions of A.
   • (b) In the potato cup D, the potato cell membrane lose semi – permeability due to boiling. So, no water movement occurs from the trough into the potato cup D.

Question 10.
Which type of cell division is required for growth and repair of body and which type is involved in formation of gametes?
Answer:
Growth and repair of body – Mitosis. Formation of gametes – Meiosis.

JAC Class 9 Science Solutions

JAC Board Class 9th Science Solutions Chapter 4 Structure of the Atom

JAC Class 9th Science Structure of the Atom InText Questions and Answers

Page 47

Question 1.
What are canal rays?
Answer:
Canal rays are radiations which are positively charged. They were the key in the discovery of proton, another positively charged sub – atomic particle.

Question 2.
If an atom contains one electron and one proton, will it carry any charge or not?
Answer:
Since an electron is a negatively charged particle and the proton, a positively charged one, the net charge becomes neutral as both particles neutralise each

Page 48

Question 1.
On the basis of Thomson’s model of an atom, explain how the atom is neutral as a whole.
Answer:
According to Thomson’s model of an atom:

1. an atom consists of a positively charged sphere in which the negatively charged electrons are embedded.
2. the number of protons and electrons are equal in an atom, thereby, neutralising their charge keeping the overall system neutral.

Question 2.
On the basis of Rutherford’s model of an atom, which sub-atomic particle is present in the nucleus of an atom?
Answer:
As per Rutherford’s model of atom, the positively charged protons are the ones that are present in the nucleus of an atom.

Question 3.
Draw a sketch of Bohr’s model of an atom with three shells.
Answer:
Bohr’s model of an atom with three shells:

Question 4.
What do you think would be the observation if the α – particle scattering experiment is carried out using a foil of a metal other than gold?
Answer:
When any other metal foil is used instead of gold, the observation would remain the same. This is because the structure of an atom, when considered individually, remains the same.

Page 49

Question 1.
Name the three subatomic particles of an atom.
Answer:
An atom consists of three subatomic particles:

1. Protons : Positively charged
2. Electrons : Negatively charged
3. Neutrons : Neutral in nature (no charge)

Question 2.
Helium atom has an atomic mass of 4u and two protons in its nucleus. How many neutrons does it have?
Answer:
Atomic mass of He = 4u
Atomic mass = number of (protons + neutrons)
4 = 2 + number of neutrons Number of neutrons = 4 – 2
= 2 Helium atom has 2 neutrons.

Page 50

Question 1.
Write the distribution of electrons in carbon and sodium atoms.
Answer:
1. Carbon atom:
Atomic number = 6
Number of protons = 6 = Number of electrons
Distribution of electrons = K – 2, L – 4.

2. Sodium atom:
Atomic number = 11
Number of protons = 11 = Number of electrons
Distribution = K – 2, L – 8, M – 1.

Question 2.
If K and L shells of an atom are full, then what would be the total number of electrons in the atom?
Answer:
Number of electrons K shell can hold = 2 Number of electrons L shell can hold = 8
Hence, when both the shells are full, the total number of electrons present = 2 + 8 ⇒ 10 electrons.

Page 52

Question 1.
How will you find the valency of chlorine, sulphur and magnesium?
Answer:
Valency is the combining capacity of the atom of an element.
1. Chlorine: Atomic number = 17
Number of protons = Number of electrons = 17
Distribution: K – 2, L – 8, M – 7 Chlorine needs 1 electron to complete its outermost orbit shell. Its valency is – 1 (gains 1 electron).

2. Sulphur: Atomic number = 16 Number of protons = Number of electrons = 16
Distribution: K – 2, L – 8, M – 6 Sulphur needs 2 electrons to complete its outermost shell. Its valency is – 2 (gains 2 electrons).

3. Magnesium: Atomic number = 12
Number of protons = Number of electrons = 12
Distribution: K – 2, L – 8, M – 2 Magnesium needs to donate 2 electrons from its outermost shell to become stable. Its valency is + 2 (donate 2 electrons).

Question 2.
If the number of electrons in an atom is 8 and number of protons is also 8, then
(a) what is the atomic number of the atom?
(b) what is the charge on the atom?
Answer:
Number of electrons = 8, Number of protons = 8
(a) Atomic number of the atom = Number of protons = 8

(b) As the number of electrons is equal to the number of protons on the atom, their charges neutralise each other. Therefore, the atom does not possess any charge.

Question 3.
With the help of the table 4.1, find out the mass number of oxygen and sulphur atom.
Answer:

1. Oxygen: Number of protons = 8 Number of neutrons = 8 Atomic number = 8
   Mass number = Number of (protons + neutrons) = 8 + 8 = 16u.
2. Sulphur: Number of protons = 16 Number of neutrons = 16 Atomic number = 16
   Mass number = Number of (protons + neutrons) = 16 + 16 = 32u.

Page 53

Question 1.
For the symbols H, D and T, tabulate three subatomic particles found in each of them.
Answer:
The symbols H, D and T, tabulate three subatomic particles:

Question 2.
Write the electronic configuration of any one pair of isotopes and isobars.
Answer:
(a) Isotopes : Isotopes are atoms which have the same number of protons but the number of neutrons differs. This leads to the variation in mass number too.
Example :
The simplest example is the carbon molecule which exists as \({ }_{6} \mathrm{C}^{12}\) and \({ }_{6} \mathrm{C}^{14}\) but when their electronic configuration is noticed, both have K – 2, L – 4.

(b) Isobars : Isobars are the atoms having the same mass number but differ in the atomic numbers. Electronic configuration of an isobar pair is as follows:
Example :
⁴⁰Ca₂₀: K – 2, L – 8, M – 8, N – 2
⁴⁰Ar₁₈ : K – 2, L – 8, M – 8

JAC Class 9th Science Atoms and Molecules Textbook Questions and Answers

Question 1.
Compare the properties of electrons, protons and neutrons.
Answer:
The properties of electrons, protons and neutrons:

Question 2.
What are the limitations of J.J. Thomson’s model of an atom?
Answer:
According to J.J. Thomson’s model of an atom, the electrons are embedded all over in the positively charged sphere. But experiments done by the other scientists show that protons are present only in the centre of the atom and electrons are distributed around it.

Question 3.
What are the limitations of Rutherford’s model of atom?
Charged bodies, when move in circular motion, emit radiations. Thus, electrons revolving round the nucleus, as suggested by Rutherford, will lose energy and will come closer and closer to the nucleus and will finally merge into the nucleus. This means that atoms are quite unstable which is not true.

Question 4.
Describe Bohr’s model of atom.
Answer:
(a) The nucleus of an atom is present in the centre.
(b) Negatively charged electrons revolve around this nucleus.
(c) Discrete orbits of electrons are present inside the atom.
(d) While revolving in the orbit, the electrons do not radiate energy.
(e) These discrete orbits are represented as K, L, M, N orbits or denoted by

Question 5.
Compare all the proposed models of an atom given in this chapter.
Answer:

Question 6.
Summarise the rules for writing of distribution of electrons in various shells for the first 18 elements.
Answer:
(a) Generally, the maximum number of electrons that can be accommodated in a shell is given by the formula: 2n², where n = 1, 2, 3 … .

(b) Maximum number of electrons in different shells are:
K shell (n = 1), 2n² = 2(1)² = 2
L shell (n = 2), 2n² = 2(2)² = 8
M shell (n = 3), 2n² = 2(3)² = 18
N shell (n = 4), 2n² = 2(4)² = 32.

(c) The electrons are not taken in unless the inner shells are completely filled.

Question 7
Define valency by taking examples of silicon and oxygen.
Answer:
Valency is the combining capacity of an atom. Take the examples of silicon and oxygen:

In the atoms of oxygen, the valence electrons are 6.
To fill the orbit, 2 electrons are required In the atom of silicon, the valence electrons are 4.
To fill this orbit 4 electrons are required Hence, the  combining capacity of oxygen is 2 and of silicon is 4, i.e., valency of oxygen = 2 and valency of silicon = 4.

Question 8.
Explain with examples.
(a) Atomic number
(b) Mass number
(c) Isotopes
(d) Isobars
Give any two uses of isotopes.
Answer:
(a) Atomic number : The atomic number of an element is the total number of protons present in the atom of that element. For example, nitrogen has 7 protons in its atom. Thus, the atomic number of nitrogen is 7.

(b) Mass number : The mass number of an element is the. sum of the number of protons and neutrons present in the atom of that element. For example, the atom of boron has 5 protons and 6 neutrons. So, the mass number of boron is 5 + 6 =11.

(c) Isotopes : These are atoms of the same element having the same atomic number, but different mass numbers. For example, chlorine has two isotopes with atomic number 17 but mass numbers 35 and 37 represented by \({ }_{17}^{35} \mathrm{Cl}\) \({ }_{17}^{37} \mathrm{Cl}\).

(d) Isobars : These are atoms having the same mass number but different atomic number, i.e, isobars are atoms of different elements having the same mass number. For example,
Ca has atomic number 20 and Ar has atomic number 18 but both of them have mass number 40 represented by \({ }_{20}^{40} \mathrm{Ca}\) and \({ }_{18}^{40} \mathrm{Ar}\) respectively.

Two uses of isotopes:

1. An isotope of uranium is used as a fuel in nuclear reactors.
2. An isotope of cobalt is used in the treatment of cancer.

Question 9.
Na⁺ has completely filled K and L shells. Explain.
Answer:
The atomic number of sodium is 11. So, neutral sodium atom has 11 electrons and its electronic configuration is 2, 8, 1. But Na⁺ has 10 electrons. Out of 10, K – shell contains 2 and L – shell has 8 electrons. Thus, Na⁺ has completely filled K and L shells.

Question 10.
If bromine atom is available in the 79 form of, say, two isotopes \({ }_{35}^{79} \mathrm{Br}\) (49.7%) and \({ }_{35}^{81} \mathrm{Br}\) (50.3%), calculate the average atomic mass of bromine atom.
Answer:
The atomic masses of two isotopic atoms are 79 (49.7%) and 81 (50.3%).
Thus, total mass = (79 × \(\frac{49.7}{100} \) ) + (81 × \(\frac{50.3}{100} \)) = 39.263 + 40.743 = 80.006u.

Question 11.
The average atomic mass of a sample of an element X is 16.2 u. What are the percentages of isotopes \({ }_{8}^{16} \mathrm{X}\) and \({ }_{8}^{18} \mathbf{X}\) in the sample?
Answer:
It is given that the average atomic mass of the sample of element X is 16.2 u. Let the % of isotope \({ }_{8}^{16} \mathrm{X}\) be y%. Thus, the % of isotopes \({ }_{8}^{18} \mathbf{X}\) will be (100 – y) %. Therefore,
16 × \(\frac{\mathrm{y}}{100}\) + \(\frac{18 \times(100-y)}{100}\) = 16.2
\(\frac{16 y}{100}\) + \(\frac{18(100-y)}{100}\) = 16.2
\(\frac{16 y+1800-18 y}{100}\) = 16.2
1800 – 2y = 1620 or 2y = 1800 – 1620 = y – 90
Therefore, the % of isotope \({ }_{8}^{16} \mathrm{X}\) is 90%.
And, the % of the isotope \({ }_{8}^{18} \mathbf{X}\) is (100 – 90) % = 10%.

Question 12.
If Z = 3, what would be the valency of the element? Also, name the element.
Answer:
Z = atomic number = 3 (given) Electronic configuration = K – 2, L – 1 Thus, valency = 1 The element with atomic number 3 is lithium.

Question 13.
The composition of the nuclei of two atomic species X and Y are given as under

Give the mass number of X and Y. What is the relation between the two species?
Answer:
Mass number of X = Protons + Neutrons = 6 + 6 = 12
Mass number of Y = Protons + Neutrons = 6 + 8 = 14
Since the atomic numbers of both the species are the same, they are the same element. Also, since they have different number of neutrons, their mass number is different and they are the isotopes.

Question 14.
For the following statements, write T for true and F for false.
(a) J. J. Thomson proposed that the nucleus of an atom contains only nucleons.
(b) A neutron is formed by an electron and a proton combining together. Therefore, it is neutral.
(c) The mass of an electron is about 1/2000 times that of proton.
(d) An isotope of iodine is used for making tincture iodine, which is used as a medicine.
Answer:
(a) False
(b) False
(c) True
(d) False
Put tick against correct choice and cross against wrong choice in questions 15, 16 and 17.

Question 15.
Rutherford’s alpha – particle scattering experiment was responsible for the discovery of:
(a) Atomic nucleus
(b) Proton
(c) Electron
(d) Neutron
Answer:
(a) Atomic nucleus.

Question 16.
Isotopes of an element have:
(a) the same physical properties
(b) different number of neutrons
(c) different number of protons
(d) different atomic number
Answer:
(b) different number of neutrons.

Question 17.
Number of valence electrons in Cl^– ion are:
(a) 16
(b) 8
(c) 17
(d) 18
Answer:
(b) 8.

Question 18:
Which one of the following is a correct electronic configuration of sodium?
(a) 2, 8
(b) 8, 2, 1
(c) 2, 1, 8
(d) 2, 8, 1
Answer:
(d) 2, 8, 1.

Question 19.
Complete the following table.

Answer:

JAC Class 9 Science Solutions

JAC Board Class 9th Science Solutions Chapter 3 Atoms and Molecules

JAC Class 9th Science Atoms and Molecules InText Questions and Answers

Page 32

Question 1.
In a reaction, 5.3g of sodium carbonate reacted with 6g of ethanoic acid. The products were 2.2g of carbon dioxide, 0.9g water and 8.2g of sodium ethanoate. Show that these observations are in agreement with the law of conservation of mass. Sodium carbonate + Acetic acid → Sodium acetate + Carbon dioxide + Water
Answer:

This shows that during a chemical reaction, mass of reactants mass of products. Hence the given observation are in agreement with the law of conservation of mass.

Question 2.
Hydrogen and oxygen combine in the ratio of 1 : 8 by mass to form water. What mass of oxygen gas would be required to react completely with 3g of hydrogen gas?
Answer:
Ratio of H : O by mass in water is:
Hydrogen : Oxygen → H₂O ⇒ 1 : 8 = 3 : x or x = 24g
24 g of oxygen gas would be rcquircd to react completely with 3g of hydrogen.

Question 3.
Which postulate of Dalton’s atomic theory is the result of the Law of consersatlon of mass?
Answer:
Awms are indivisible particles, which can neither be created nor destroyed in a chemical rcacuon.

Question 4.
Which postulate of Dalton’s atomic theory can explain the law of definite proportions?
Answer:
“The relative number and kind of atoms are constant in a given compound”

Page 35

Question 1.
Define the atonik mass unit.
Answer:
A unit of mass used in express atomic and molecular weights, equal to one twelfth (1/12th.) of the mass of an stom of carbon – 12 The relative atomic masses of all elements have been found with respect to an atom of carbon – 12.

Question 2.
Why Is it not possible to see an atom with naked eyes?
Answer:
The size of an atom is very small, Further, atoms of most elements do not exist independently. The radius of an atom is of the order of 10^-10m.

Page 39

Question 1.
Write down the formulae of
(a) sodium oxide
(b) aluminium chloride
(c) sodium sulphide
(d) magnesium hydroxide
Answer:
(a) Sodium oxide — Na₂O
(b) Aluminium chloride — AlCl₃
(c) Sodium sulphide — Na₂S
(d) Magnesium hydroxide — Mg(OH)₂

Question 2.
Write down the names of compounds represented by the following formulae:
(a) Al₂(SO₄)₃
(b) CaCl₂
(c) K₂SO₄
(d) KNO₃
(e) CaCO₃
Answer:
(a) Al₂(SO₄)₃ : Aluminium sulphate
(b) CaCl₂ : Calcium chloride
(c) K₂SO₂ : Potassium sulphate
(d) KNO₃ : Potassium nitrate
(e) CaCO₂ : Calcium carbonate

Question 3.
What Is meant by the term chemical formula?
Answer:
The chemical formula of a compound is the symbolic representation of its composition. It gives the number and kinds of atoms which are chemically united in a given compound. For example, chemical formula of sodium chloride is NaCl.

Question 4.
How many atoms are present in a
(a) H₂S molecule and
(b) \(\mathrm{PO}_{4}^{3-}\) ion?
Answer:
(a) H₂S → 3 atoms are present: 2 atoms of hydrogen and 1atom of sulphur.
(b) \(\mathrm{PO}_{4}^{3-}\) → 5 atoms are present: 1 atom of phosphorus and 4 atoms of oxygen.

Page 40

Question 1.
Calculate the molecular masses of H₂, O₂ C₁₂, CO₂, CH₄, C₂H₆, C₂H₄, NH₃, CH₃OH.
Answer:
The molecular masses are:
H₂ → 1 + 1 = 2u
O₂ → 16 + 16 = 32u
Cl₂ → 35.5 + 35.5 = 71u
CO₂ → p 12 + 32 = 44u
CH₄ → 12 + 4 = 16u
C₂H₆ → (12 × 2) + (1 × 6) = 30u
C₂H₄ → (12 × 2) + (1 × 4) = 28u
NH₃ → (1 × 14) + (1 × 3) = 17u
CH₃OH → (1 × 12) + (1 × 3) + (1 × 16)(1 × 1) = 32u.

Question 2.
Calculate the formula unit of masses of ZnO, Na₂O, K₂CO₃, given atomic masses of Zn = 65u, Na = 23u, K = 39u, C = 12u and O = 16u.
Answer:
The formula Unit mass of:
(a) ZnO = 65u + 16u = 81u
(b) Na₂O = (23u × 2) + 16u = 46u + 16u = 62u
(c) K₂CO₃ = (39u × 2) + 12u + (16u × 3)
= 78u + 12u + 48u
= 138u.

Page 42

Question 1.
If 1 mole of carbon atoms weigh 12grams, what Is the mass (in grams) of 1 atom of carbon?
Answer:
1 mole of carbon atoms = 6.022 × 10²³ atoms
Now, 12/6.022 × 10²³ atoms of carbon weigh = 12g
One atom of carbon weighs = \(\frac{12}{6.023}\) × 10²³
= 1.99 × 10^-23g.

Question 2.
Which has more number of atoms 100 grams of sodium or loo grams of iron (given atomic mass of Na = 23u, Fe 56u)?
Answer:
23 gram atomic unit or 23g sodium (1 mole) = 6.022 × 10²³ atoms
100 gram atomic unit or 100g sodium = \(\frac{6.022 \times 10^{23} \times 100}{23}\)
= 2.617 × 10²⁴ atoms Again 56 gram atomic unit or 56 g iron (1 mole) 6.022 × 10²³
100 gram atomic unit or 100 g iron = \(\frac{6.022 \times 10^{23} \times 100}{56}\)
= 1. 075 × 10²⁴ atoms Thus, 100 g of sodium has more atoms than 100g of iron

JAC Class 9th Science Atoms and Molecules Textbook Questions and Answers

Question 1.
A 0.24g sample of compound of oxygen and boron was found by analysis to contain 0.096g of boron and 0.144g of oxygen. Calculate the percentage composition of the compound by weight.
Answer:
Percentage (%) of boron in the sample
\(\frac{0.096}{0.24}\) × 100 = 40%
Percentage (%) of oxygen in the sample
\(\frac{0.144}{0.24}\) × 100 = 60%
The sample of compound contains 40% boron and 60% oxygen by weight.

Question 2.
When 3.0g of carbon is burnt in 8.00 g oxygen, 11.00g of carbon dioxide is produced. What mass of carbon dioxide will be formed when 3.00g of carbon Is burnt In 50.00g of oxygen? Which law of chemical combination will govern your answer?
Answer:
When 3.0g of carbon is burnt in 8.00g oxygen, 11.00g carbon dioxide is produced. It means all of carbon and oxygen are used up and carbon and oxygen are combined in the ratio of 3 : 8 to form carbon dioxide. Thus when there is 3g carbon and 50.0g oxygen, then also only 8g oxygen will be used and 11.0g carbon dioxide will be formed. The remaining oxygen is not used up. This indicates law of defmite proportions which Say that in compounds, the combining elements are present in definite proportions by mass.

Question 3.
What are polyatomic ions? Give examples.
Answer:
The ions which contain more than one atom (same kind or may be of different kind) and behave as a single unit are called polyatomic ions. For example:

1. Ammonium ion NH is a compound ion which is made up of two types of atoms joined together, viz., nitrogen and hydrogen.
2. Carbonate ion CO is a compound ion which is made up of two types of atoms joined together, viz., carbon and oxygen.

Question 4.
Write the chemical formulae of the following:
(a) Magnesium chloride
(b) Calcium oside
(c) Copper nitrate
(d) Aluminium chloride
(e) Calcium carbonate
Answer:
(a) Magnesium chloride : MgCl
(b) Calcium oxide : CaO
(e) Copper nitrate : Cu(NO₃)₂
(d) Aluminium chloride : AlCl₃
(e) Calcium carbonate: CaCO₃

Question 5.
Give the names of the elements present in the following compounds:
(a) Quick lime
(b) Hydrogen bromide
(c) Baking powder
(d) Potassium sulphate
Answer:
(a) Quick lime : Calcium and oxygen
(b) Hydrogen bromide : Hydrogen and bromine
(c) Baking powder : Sodium, hydrogen. carbon and oxygen
(d) Potassium sulphate : potassium. sulphur and oxygen

Question 6.
Calculate the molar mass of the following substances.
(a) Ethvne, C₂H₂
(b) Sulphur molecule, S₈
(c) Phosphorus molecule, P₄ (Atomic mass of phosphorus = 31u)
(d) Hydrochloric acid, HCl
(e) Nitric acid, HNO₃
Answer:
(a) Ethyne, C₂H₂ = (2 × 12) + (2 × 1) = 26g
(b) Sulphur molecule, S₈ = 8 × 32 = 256g
(c) Phosphorus molecules, P₄ = 4 × 31 = 124g
(d) Hydrochloric acid, HCl = (1 × 1) + (1 × 35.5) = 36.5g
(e) Nitric acid, HNO₃ = (1 × 1) + (1 × 14) + (3 × 16) = 63g

Question 7.
What is the muss of
(a) 1 mole of nitrogen atoms?
(b) 4 moles of aluminium atoms (atomic mass of aluminium 27u)?
(c) 10 moles of sodium sulphite (Na₂SO₃)?
Answer:
(a) 1 mole of nitrogen atoms 14u = 14g
(b) 4 moles of aluminium atoms = 4 × 27 = 108u = 108g
(c) 1 mole of sodium sulphite = (2 × 23) + (1 × 32) + (3 × 16) = 126u = 126g
10 moles of sodium sulphite = 10 × 126 = 1260g.

Question 8.
Convert Into mole.
(a) 12g of oxygen gas
(b) 20g of water
(c) 22 g of carbon dioxide
Answer:
(a) Given mass of oxygen gas = 12g
Molar mass of oxygen gas (O₂) = 32g
Mole of oxygen gas = \(\frac{12}{32}\)
= 0.375 mole.

(b) Given mass of water = 20g
Molar mass of water(H₂O) (2 × 1) + 16= 18g
Mole of water = \(\frac{20}{18}\)= 1.11 mole.

(c) Given mass of carbon dioxide = 22g
Molar mass of carbon dioxide (CO₂) (1 × 12) + (2 × 16) = 12 + 32 = 44g
Mole of carbon dioxide = \(\frac{22}{44}\)
= 0.5 mole.

Question 9.
What is the mass of
(a) 0.2 mole of oxygen atoms?
(b) 0.5 mole of water molecules?
Answer:
(a) Mole of oxygen atoms = 0.2 mole
Molar mass of oxygen atoms = 16g
Mass of oxygen atoms 16 × 0.2 = 3.2g.

(b) Mole of water molecule 0.5 mole
Molar mass of water molecules = (2 × 1) + 16 = 18g
Mass of H₂O = 18 × 0.5 = 9g.

Question 10.
Calculate the number of molecules of sulphur (S₈) present In 16 g of solid sulphur.
Answer:
Molar mass of sulphur (S₈) = 256 g = 6.022 × 10₂₃ molecules
Given mass of sulphur = 16g
Molecules of sulphur = \(\frac{16 \times 6.022 \times 10^{23}}{256}\)
\(=\frac{96.35 \times 10^{23}}{256}\) = 0.376 × 10²³ molecules.

Question 11.
Calculate the number of aluminium ions present In 0.051 g of aluminium oxide.
Hint: The mass of an ion is the same as that of an atom of the saine element Atomic mass of Al = 27u
Answer:
1 mole of aluminium oxide, Al₂O₃ = (2 × 27) + (3 × 16) = 102u = 102g
102 g of Al₂O₃ has = 6.022 × 10₂₃ Al₂O₃ molecules
0.051 g of Al₂O₃has = \( \frac{6.022 \times 10^{23} \times 0.051}{102}\)
= 3.01 × 10₂₀ molecules
1 molecule of Al₂O₃ gives = 2 Al³⁺ ions
Hence, 0.051g Al₂O₃ gives = 2 × 3.01 × 10²⁰ Al³⁺ ions
= 6.022 × 10²⁰ aluminium ions.

JAC Class 9 Science Solutions

JAC Board Class 9th Science Solutions Chapter 2 Is Matter Around Us Pure

JAC Class 9th Science Is Matter Around Us Pure InText Questions and Answers

Page 15

Question 1.
What is meant by a pure substance?
Answer:
A pure substance consists of a single type of particles and it cannot be separated into other kinds of matter by any separation process.

Question 2.
List the points of difference between ho-mogeneous and heterogeneous mixtures.
Answer:
Differences between homogeneous and heterogeneous mixtures:

Page 18

Question 1.
Differentiate between homogeneous and heterogeneous mixtures with examples.
Answer:
See answer 2 above.

Question 2.
How are sol, solution and suspension different from each other?
Answer:
Comparison among properties of true solution, colloidal solution and suspension:

Question 3.
To make a saturated solution, 36g of sodium chloride is dissolved in lOOg of water at 293K. Find its concentration at this temperature.
Answer:
Mass of solute (sodium chloride) = 36g
Mass of solvent (water) = 100 g
Mass of solution = Mass of solute + Mass of solvent = 36g + 100g =136g
\(\frac{ Mass of solute}{Mass of solution}\) × 100 ⇒ \(\frac{36 \times 100}{136}\)
= 26.47%

Page 24

Question 1.
How will you separate a mixture containing kerosene and petrol (difference in their boiling points is more than 25°C), which are miscible with each other?
Answer:
Set up the apparatus as shown in the figure. Take the given mixture in a distillation flask. Heat the mixture slowly, keeping a close watch at the thermometer. At a certain point, temperature becomes constant. Petrol vaporises first as it has lower boiling point. It condenses in the condenser and is collected from the condenser outlet. Stop heating when the temperature further starts rising. Kerosene is left behind in the distillation flask.

Question 2.
Name the technique to separate:
(a) Butter from curd
(b) Salt from sea – water
(c) Camphor from salt
Answer:
(a) Butter from curd – Centrifugation
(b)Salt from sea – water – Evaporation
(c) Camphor from salt – Subiimation

Question 3.
What type of mixtures are separated by the technique of crystallisation?
Answer:
Crystallisation technique is used to purify a solid with some impurities in it. For example, purification of salt obtained from sea – water.

Page 25

Question 1.
Classify the following as chemical or physical changes: cutting of trees, melting of butter in a pan, rusting of almirah, boiling of water to form steam, passing of electric current, through water and the water breaking down into hydrogen and oxygen gases. making of fruit salad with raw fruits, dissolving common salt in water, burning of paper and wood
Answer:

1. Physical change:
   • Cutting of trees
   • Melting of butter in a pan
   • Boiling of water to form steam
   • Dissolving common salt in water
   • Making a fruit salad with raw fruits
2. Chemical change:
   • Rusting of almirah
   • Passing of electric current through water and the water breaking down into hydrogen and oxygen gases
   • Burning of paper and wood

Question 2.
Try segregating the things around you as pure substances or mixtures.
Answer:

1. Pure substances: Water, sugar, gold, copper wire, salt, ice, etc.
2. Mixtures: Steel, plastic, paper, talc, milk, air, ink, soda water, lemonade, bread, etc.

JAC Class 9th Science Is Matter Around Us Pure Textbook Questions and Answers

Question 1.
Which separation techniques will you apply for the separation of the following?
(a) Sodium chloride from its solution in water.
(b) Ammonium chloride from a mixture containing sodium chloride and ammonium chloride.
(c) Small pieces of metal in the engine oil of a car.
(d) Different pigments from an extract of flower petals.
(e) Butter from curd.
(f) Oil from water.
(g) Tea leaves from tea.
(h) Iron pins from sand.
(i) Wheat grains from husk.
(j) Fine mud particles suspended in water.
Answer:
(a) Crystallisation/Evaporation

(b) Sublimation

(c) Filtration

(d) Chromatography

(e) Centrifugation

(f) Separating funnel

(g) Filtration

(h) Magnetic separation

(i) Winnowing

(j) Decantation/Sedimentation

Question 2.
Write the steps you would use for making tea Use the words solution, solvent, solute, dissolve, soluble, insoluble, filtrate and residue.
Answer:
Take a cup of water in a kettle as solvent and heat it. When the solvent boils, add sugar in it which is the solute. Heat it till entire sugar dissolves. Water and sugar form a solution. Then, add some tea leaves in this solution. Boil the contents, add milk which is also soluble in this mixture, and boil again. Filter the tea with the help of a strainer. The tea collected in cup is the filtrate and the tea leaves collected in the strainer is residue.

Question 3.
Pragya tested the solubility of three different substances at different temperatures and collected the data as given below (results are given in the following table, as grams of substance dissolved in 100 grams of water to form a saturated solution).

(a) What mass of potassium nitrate would be needed to produce a saturated solution of potassium nitrate in 50 grams of water at 313 K?
(b) Pragya makes a saturated solution of potassium chloride in water at 353K and leaves the solution to cool at room temperature. What would she observe as the solution cools? Explain.
(c) Find the solubility of each salt at 293K. Which salt has the highest solubility at this temperature?
(d) What is the effect of change of temperature on the solubility of a salt?
Answer:
(a) Mass of potassium nitrate (KNO₃) needed to produce a saturated solution of KNO₃ in 100 grams of
water at 313 K = 62 g
Mass of KNO₃ needed in 50 g of
water at 313 K = \(\frac{62.0 \times 50}{100}\)
= 31.0g

(b) As solution cools, potassium chloride gets crystallised. This is because the solubility of a solid decreases with decrease in temperature.

(c) At 293K, solubility of KNO₃ is 32, NaCl is 36, KCL is 35 andNH₄Cl is 37. Ammonium chloride has the highest solubility at 293 K temperature.

(d) As the temperature increases, solubility increases and vice – versa.

Question 4.
Explain the following giving examples.
(a) saturated solution
(b) pure substance
(c) colloid
(d) suspension
Answer:
(a) Saturated solution: A solution in which no more solute can be dissolved at a given temperature is called a saturated solution.

(b) Pure substance: A pure substance consists of a single type of particles. It always has the same colour, taste or texture at a given temperature and pressure. For example, pure water is always colourless, odourless and tasteless.

(c) Colloid: A colloid is a solution in which the size of solute particles is bigger than those of a true solution. These particles cannot be seen with naked eyes as they are stable, e.g., ink, blood, smoke, milk, fog and cloud.

(d) Suspension: Suspension is a heterogeneous mixture. The particles of a suspension are greater than 1000 nm and are visible to naked eyes, e.g., chalk powder in water, paints, etc.

Question 5.
Classify each of the following as a homogeneous or a heterogeneous mixture: soda water, wood, air, soil, vinegar, filtered tea.
Answer:

1. Homogeneous mixtures: Soda water, vinegar, filtered tea.
2. Heterogeneous mixtures: Wood, soil, air.

Question 6.
How would you confirm that a colourless liquid given to you is pure water?
Answer:
By finding the boiling point of the given colourless liquid. If the given colourless liquid boils at exactly 373K at 1 atmosphere pressure, then it is pure water. This is because pure substances have fixed melting and boiling points.

Question 7.
Which of the following materials fall in the category of a ‘pure substance’?
(a) Ice
(b) Milk
(c) Iron
(d) Hydrochloric acid
(e) Calcium oxide
(f) Mercury
(g) Brick
(h) Wood
(i) Air
Answer:
Pure substances are: ice (a compound), iron (an element), hydrochloric acid (a compound), calcium oxide (a compound) and mercury (an element).

Question 8.
Identify the solutions among the following mixtures.
(a) Soil
(b) Sea water
(c) Air
(d) Coal
(e) Soda water
Answer:
Solutions are sea water, soda water and air.

Question 9.
Which of the following will show “Tyndall effect”?
(a) Salt solution
(b) Milk
(c) Copper sulphate solution
(d) Starch solution
Answer:
Milk and starch solution are colloids and will show Tyndall effect.

Question 10.
Classify the following into elements, compounds and mixtures.
Sodium, Soil, Sugar solution, Silver, Calcium carbonate, Tin, Silicon, Coal, Air, Soap, Methane, Carbon dioxide, Blood
Answer:

• Elements: Sodium, Silver, Tin, Silicon
• Compounds: Calcium carbonate, Meth – ane, Carbon dioxide
• Mixtures: Sugar solution, Soil, Coal, Air, Blood, Soap

Question 11.
Which of the following are chemical changes?
(a) Growth of a plant
(b) Rusting of iron
(c) Mixing of iron filings and sand
(d) Cooking of food
(e) Digestion of food
(f) Freezing of water
(g) Burning of a candle
Answer:
Chemical changes are growth of a plant, rusting of iron, cooking of food, digestion of food, burning of a candle.

JAC Class 9 Science Solutions

JAC Board Class 9th Science Solutions Chapter 1 Matter in Our Surroundings

JAC Class 9th Science Matter in Our Surroundings InText Questions and Answers

Page 3

Question 1.
Which of the following are matter? Chair, air, love, smell, hate, almonds, thought, cold, cold – drink, smell of perfume.
Answer:
Chair, air, almonds and cold – drink.

Question 2.
Give reasons for the following observation: The smell of hot sizzling food reaches you several metres away, but to get the smell from cold food you have to go close.
Answer:
Particles of matter are continuously moving. They possess kinetic energy. As the temperature rises, particles move faster. Thus, particles that carry smell of hot sizzling food move faster than the smell of the cold food. Therefore, the smell of hot sizzling food can reach us several metres away, but to get the smell from a cold food we have to go close.

Question 3.
A diver is able to cut through water in a swimming pool. Which property of matter does this observation show?
Answer:
This shows that the particles of matter have space between them. This space is maximum in gases and minimum in solids. Thus, one cannot cut through a solid easily but a diver is able to cut easily through water.

Question 4.
What are the characteristics of the particles of matter?
Answer:
The characteristics of the particles of matter are as follows:
(a) Particles of matter have intermolecular space.
(b) Particles of matter have intermolecular forces of attraction.
(c) Particles of matter are moving continuously.

Page 6

Question 1.
The mass per unit volume of a substance is called density = \(\frac{ mass}{volume}\) . Arrange the following in order of increasing density – air, exhaust from chimneys, honey, water, chalk, cotton and iron.
Answer:
Air, exhaust from chimneys, cotton, water, honey, chalk, and iron

Question 2.
(a) Tabulate the differences in the characteristics of states of matter,
(b) Comment upon the following: rigidity, compressibility, fluidity filling a gas container, shape, kinetic energy and density.
Answer:
(a) The differences in the characteristics of states of matter are

(b) Rigidity: It is the property of matter to resist change in its shape, e.g. solids are rigid.

• Compressibility: It is a property by which matter can be reduced to lower volume on application of force.
• Fluidity: It is the property of matter to flow.
• Filling a gas container: Gases completely fill the volume of the container in which they are kept, at any volume while solids and liquids do not.
• Shape: It indicates definite boundaries.
• Kinetic energy: It is the energy possessed by the particles of matter due their motion.
• Density: It is mass per unit volume. Higher density means more mass is confined in a lesser volume.

Question 3.
Give reasons:
(a) A gas fills completely the vessel in which it is kept.
(b) A gas exerts pressure on the walls of the container.
(c) A wooden table should be called a solid.
(d) We can easily move our hand in air but to do the same through a solid block of wood we need a karate expert.
Answer:
(a) The molecules of gases are free to move. Gas molecules have the least amount of attraction between them.Thus, the molecules of gases completely fill the vessel in which they are kept.

(b) The molecules of gas are in continuous motion. They collide with each other and with the walls of container. These collisions of the gas molecules with the walls of the container exert pressure on the walls of the container.

(c) A wooden table has a definite shape and size. Also, it is a non-compressible rigid body. Thus, a wooden table has all the characteristics of a solid.

(d) The molecules of air have least amount of attraction between them. Thus, one can easily move one’s hand in air and push the molecules of air apart. However, the molecules of solid have maximum amount of attraction between them. A greater amount of force is required to move the molecules of a solid apart. Thus, a much greater force is required to move our hand through a solid block of wood.

Question 4.
Liquids generally have lower density as compared to solids. But you must have observed that ice floats on water. Find out why.
Answer:
Ice is a solid but its density is lower than water due to its structure. The molecules in ice make a cage like structure with lot of vacant spaces. This makes ice float on water.

Page 9

Question 1.
Convert the following temperature to Celsius scale: (a) 300 K (b) 573 K.
Answer:
Celsius scale = Kelvin scale – 273
(a) Celsius scale = 300 – 273 = 27°C
(b) Celsius scale = 573 – 273 = 300°C

Question 2.
What is the physical state of water at:
(a) 250°C
(b) 100°C?
Answer:
The physical state of water at:
(a) 250°C is gaseous
(b) 100°C might be gaseous or liquid. Steam and water coexist at 100°C.

Question 3.
For any substance, why does the temperature remain constant during the change of state?
Answer:
During the change of state, temperature remains constant because heat given to the matter is used up in changing the state of matter. This is called latent heat.

Question 4.
Suggest a method to liquefy atmospheric gases.
Answer:
Atmospheric gases liquefy at very low temperatures. It is not possible to attain such low temperatures. However, atmospheric gases can be liquefied by compressing them. When the atmospheric gases are compressed, the molecules of gases come closer to each other and as we keep on compressing the gases, the molecules keep coming closer and closer to each other. When the pressure on the atmospheric gases becomes large enough, the gases liquefy. Thus, atmospheric gases can be liquefied by compressing them.

Page 10

Question 1.
Why does a desert cooler cool better on a hot dry day?
Answer:
On a hot dry day, there is high temperature and low humidity. Both these factors are responsible for increasing the rate of evaporation. This also means better cooling.

Question 2.
How does the water kept in an earthen pot (matka) become cool during summer?
Answer:
The earthen pot has lots of tiny pores in it. The water oozes out through these pores and gets evaporated at the surface of the pot, by absorbing heat from the water kept in it, thereby causing cooling effect.

Question 3.
Why does our palm feel cold when we put some acetone or petrol or perfume on it?
Answer:
Acetone, petrol and perfume evaporate at low temperatures. When some acetone, petrol, or perfume is dropped on the palm, it takes heat from the palm and evaporates, thereby making the palm cooler.

Question 4.
Why are we able to sip hot tea or milk faster from a saucer rather than a cup?
Answer:
Hot tea or milk in a saucer has larger surface area than in a cup. The rate of evaporation is faster with increased surface area. The cooling of tea or milk in a saucer takes place sooner than in a cup. Hence, we are able to sip hot tea or milk faster from a saucer rather than a cup.

Question 5.
What type of clothes should we wear in summer?
Answer:
During summer, we should wear cotton clothes because we perspire more to maintain the temperature of our body. Cotton is a good absorber of sweat. It allows the sweat to evaporate faster, thereby giving a cooling effect.

JAC Class 9th Science Matter in Our Surroundings Textbook Questions and Answers

Question 1.
Convert the following temperatures to the Celsius scale, (a) 293 K (b) 470 K
Answer:
Celsius scale = Kelvin scale – 273
a. Celsius scale = 293 – 273 = 20°C
b. Celsius scale = 470 – 273 = 197°C

Question 2.
Convert the following temperatures to the kelvin scale, (a) 25°C (b) 373°C.
Answer:
Kelvin scale = Celsius scale + 273
a. Kelvin scale = 25 + 273 = 298 K
b. Kelvin scale = 373 + 273 = 646 K

Question 3.
Give reason for the following observations.
(a) Naphthalene balls disappear with time without leaving any solid.
(b) We can get the smell of perfume sitting several metres away.
Answer:
(a) Naphthalene balls show the property of sublimation. Evaporation of naphthalene takes place easily and so it disappears during the course of time without leaving any residue,

(b) Perfume contains volatile solvent, i.e., gaseous particles, which have high speed and large space between them and diffuse faster and can reach people sitting at a distance.

Question 4.
Arrange the following substances in increasing order of forces of attraction between the particles water, sugar, oxygen.
Answer:
Oxygen < Water < Sugar

Question 5.
What is the physical state of water at ……… (a) 25°C (b) 0°C (c) 100°C?
Answer:
(a) Liquid
(b) Solid or liquid
(c) Liquid or gas

Question 6.
Give two reasons to justify
(a) Water at room temperature is a liquid.
(b) An iron almirah is a solid at room temperature.
Answer:
(a) Water is liquid at room temperature because:

1. At room temperature water has a definite volume, but it does not have a definite shape.
2. At room teperature water can flow easily.

(b) Iron almirah is solid at room temperature because:

1. At room temperature iron amirah has a definite volume as well as a definite shape.
2. At room temperature, iron almirah is very rigid.

Question 7.
Why is ice at 273 K more effective in cooling than water at the same temperature?
Answer:
Ice at 273 K will absorb heat energy or latent heat from the medium to overcome the intermolecular forces to become water. Hence, it cools more effectively than water at the same temperature.

Question 8.
What produces more severe burns, boiling water or steam?
Answer:
Steam at 100°C will produce more severe bums as extra heat is hidden in the form of latent heat in steam, whereas the boiling water does not have this hidden heat.

Question 9.
Name the processes A, B, C, D, E and F in the following diagram showing change in state of matter. Increase heat and decrease pressure

Answer:
A → Liquefaction/melting/fusion
B → Vaporisation/evaporation
C → Condensation
D → Solidification
E → Sublimation
F → Sublimation

JAC Class 9 Science Solutions