Answer the following in brief.

Question 13 Marks

If 10 volumes of dihydrogen gas react with 5 volumes of dioxygen gas, how many volumes of water vapour would be produced?

Answer

If 10 volumes of dihydrogen gas react with 5 volumes of dioxygen gas, then 10 volumes of water vapour would be produced.

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Question 23 Marks

Classify the following as element and compound.
i. Mercuric oxide
ii. Helium gas
iii. Water
iv. Table salt
v. Iodine
vi. Mercury
vii. Oxygen
viii. Nitrogen

Answer

No.	Material	Element or compound
i.	Mercuric oxide	Compound
ii.	Helium gas	Element
iii.	Water	Compound
iv.	Table salt	Compound
V.	lodine	Element
vi.	Mercury	Element
vii.	Oxygen	Element
viii.	Nitrogen	Element

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Question 33 Marks

Which are mixtures and pure substances from the following?
i. Sea water
ii. Gasoline
iii. Skin
iv. A rusty nail
v. A page of textbook
vi. Diamond

Answer

No.	Material	Pure substance or mixture
i.	Seawater	Mixture
ii.	Gasoline	Mixture
iii.	Skin	Mixture
iv.	A rusty nail	Mixture
V.	A page of textbook	Mixture
vi.	Diamond	Pure substance

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Question 43 Marks

i. One dozen means how many items? ii. One gross means how many items?

Answer

i. One dozen means 12 items. ii. One gross means 144 items.

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Question 53 Marks

State the law of multiple proportions.

Answer

The law states that, “When two elements A and B form more than one compounds, the masses of element B that combine with a given mass of A are always in the ratio of small whole numbers”.

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Question 63 Marks

What is meant by molar volume of a gas ?

Answer

The volume occupied by one mole of a gas at standard temperature $\left(0^{\circ} C \right)$ and pressure $(1 atm)( STP )$ is called as molar volume of a gas. The molar volume of a gas at STP is $22.4 dm ^3$.

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Question 73 Marks

What is the SI unit of amount of a substance ?

Answer

The SI unit for the amount of a substance is mole (mol).

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Question 83 Marks

How many particles are present in $1$ mole of a substance ?

Answer

The number of particles in one mole is $6.0221367 \times 10^{23}$.

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Question 93 Marks

How many grams does an atom of hydrogen weigh ?

Answer

The mass of a hydrogen atom is $1.6736 \times 10^{-24} g.$

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Question 103 Marks

Point out the difference between 12 g of carbon and 12 u of carbon.

Answer

12 g of carbon is the molar mass of carbon while 12 u of carbon is the mass of one carbon atom.

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Question 113 Marks

Find the formula mass of
i. KCl
ii. AgCl
Atomic mass of K = 39 u, Ag =108 u and Cl = 35.5 u.

Answer

i. Formula mass of KCl
= Average atomic mass of K + Average atomic mass of Cl
= 39 u + 35.5 u = 74.5 u

ii. Formula mass of AgCl
= Average atomic mass of Ag + Average atomic mass of Cl
= 108 + 35.5 = 143.5 u
Ans:
i. Formula mass of KCl = 74.5 u
ii. Formula mass of AgCl = 143.5 u

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Question 123 Marks

Give reason: Dalton’s atomic theory explains the law of multiple proportion.

Answer

The law of multiple proportion states that, “When two elements A and B form more than one compounds, the masses of element B that combine with a given mass of A are always in the ratio of small whole numbers
According to Dalton’s atomic theory, compounds are formed when atoms of different elements combine in fixed ratio.

Hence, Dalton’s atomic theory explains the law of multiple proportion.

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Question 133 Marks

Give reason: Dalton’s atomic theory explains the law of conservation of mass.

Answer

The law of conservation of mass states that, “Mass can neither be created nor destroyed” during chemical combination of matter.
According to Dalton’s atomic theory, chemical reactions involve only the reorganization of atoms. Therefore, the total number of atoms in the reactants and products should be same and mass is conserved during a reaction.

Hence, Dalton’s atomic theory explains the law of conservation of mass.

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Question 143 Marks

Why are fractional units of the $SI$ units of length often used? Give two examples of the fractional units of length. How are they related to the $SI$ unit of length?

Answer

$i.$ Some properties such as the atomic radius, bond length, wavelength of electromagnetic radiation, etc. are very small and therefore, fractional units of the $SI$ unit of length are often used to express these properties.
$ii.$ Fractional units of length: Nanometre $(nm),$ picometre $(pm),$ etc.
$iii.$ Nanometre $(nm)$ and picometre $(pm)$ are related to the $SI$ unit of length $(m)$ as follows:
$1 nm = 10^{-9} m, 1 pm = 10^{-12}m$

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Question 153 Marks

Give reason: The mass of a body is more fundamental property than its weight.

Answer

Mass is an inherent property of matter and is the measure of the quantity of matter of a body.
The mass of a body does not vary with respect to its position.
On the other hand, the weight of a body is a result of the mass and gravitational attraction
Weight varies because the gravitational attraction of the earth for a body varies with the distance from the centre of the earth.

Hence, the mass of a body is more fundamental property than its weight.

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Question 163 Marks

Explain the following terms:
i. Organic chemistry
ii. Inorganic chemistry
iii. Physical chemistry

Answer

i. Organic chemistry: It deals with properties and reactions of compounds of carbon.
ii. Inorganic chemistry: It deals with the study of all the compounds which are not organic.
iii. Physical chemistry: It deals with the study of properties of matter, the energy changes and the theories, laws and principles that explain the transformation of matter from one form to another. It also provides basic framework for all the other branches of chemistry.

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Question 173 Marks

Which are mixtures and pure substances from the following?
iv. A rusty nail
v. A page of textbook
vi. Diamond

Answer

No.	Material	Pure substance or mixture
iv.	A rusty nail	Mixture
V.	A page of textbook	Mixture
vi.	Diamond	Pure substance

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Chemistry Answer the following in brief.

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