The Language of Chemistry

Exercise 1(A)

Question 1.1

The formula of a compound represents

1. an atom
2. a particle
3. a molecule
4. a combination

Answer

a molecule

Reason — The formula of a compound employs symbols to denote the molecule of a compound.

Question 1.2

The correct formula of aluminium oxide is

1. AlO₃
2. AlO₂
3. Al₂O₃
4. Al₃O₂

Answer

Al₂O₃

Reason — The formula of aluminium oxide can be determined as below:

$\text{Al}^{3+} \space \text{O}^{2-} \\[1em] \overset{\phantom{3}{3}}{\text{Al}} \space {\swarrow}\mathllap{\searrow} \space \overset{2}{\text{O}} \Rightarrow \underset{\phantom{2}{2}}{\text{Al}} \space {\swarrow}\mathllap{\searrow} \underset{\phantom{3}{3}}{\text{O}} \\[1em] \text{Al}_2\text{O}_3$

Question 1.3

The valency of nitrogen in nitrogen dioxide (NO₂) is

1. one
2. two
3. three
4. four

Answer

four

Reason — The valency of nitrogen in nitrogen dioxide can be determined from the formula NO₂ as below:

$\text{NO}_2 = \underset{\phantom{1}{1}}{\text{N}} \space {\nearrow}\mathllap{\nwarrow} \space \underset{2}{\text{O}} \Rightarrow \overset{\phantom{2}{2}}{\text{N}} \space {\nearrow}\mathllap{\nwarrow} \space \overset{1}{\text{O}} \\[0.5em]$

But valency of O is 2. Multiplying by 2, we get:

$\overset{{2 \times 2}}{\text{N}} \space {\nearrow}\mathllap{\nwarrow} \space \overset{2 \times 1}{\text{O}} \Rightarrow \overset{\phantom{4}{4}}{\text{N}} \space {\nearrow}\mathllap{\nwarrow} \space \overset{2}{\text{O}} \\[0.5em]$

Therefore, valency of Nitrogen is 4.

Question 2

Match the following : (Refer common names in the beginning of the book)

Answer

Question 3

Select the basic and acidic radicals in the following compounds.

(a) MgSO₄

(b) (NH₄)₂SO₄

(c) Al₂(SO₄)₃

(d) ZnCO₃

(e) Mg(OH)₂

Answer

The basic and acidic radicals in the compounds are given in the table below:

Question 4

Give the formula and valency of :

(a) aluminate

(b) chromate

(c) aluminium

(d) cupric

Answer

The formula and valency are given in the table below:

Question 5

What do the following symbols stand for ?

(a) H

(b) H₂

(c) 2H

(d) 2H₂

Answer

(a) H → One atom of Hydrogen.

(b) H₂ → One molecule of Hydrogen.

(c) 2H → Two atoms of Hydrogen.

(d) 2H₂ → Two molecules of Hydrogen.

Question 6

Write the chemical names of the following compounds :

(a) Ca₃(PO₄)₂

(b) K₂CO₃

(c) K₂MnO₄

(d) Mn₃(BO₃)₂

(e) Mg(HCO₃)₂

(f) Na₄Fe(CN)₆

(g) Ba(ClO₃)₂

(h) Ag₂SO₃

(i) (CH₃COO)₂Pb

(j) Na₂SiO₃

Answer

(a) Ca₃(PO₄)₂ → Calcium Phosphate

(b) K₂CO₃ → Potassium Carbonate

(c) K₂MnO₄ → Potassium Manganate

(d) Mn₃(BO₃)₂ → Manganese (II) borate

(e) Mg(HCO₃)₂ → Magnesium Hydrogen Carbonate

(f) Na₄Fe(CN)₆ → Sodium Ferrocyanide

(g) Ba(ClO₃)₂ → Barium Chlorate

(h) Ag₂SO₃ → Silver Sulphite

(i) (CH₃COO)₂Pb → Lead Acetate

(j) Na₂SiO₃ → Sodium Silicate

Question 7

Write chemical formulae of the sulphates of Aluminium, Ammonium and Zinc.

Answer

(a) Chemical formula of Aluminium Sulphate:

$\text{Al}^{3+} \space \text{SO}_4^{2-} \\[1em] \overset{\phantom{3}{3}}{\text{Al}} \space {\swarrow}\mathllap{\searrow} \space \overset{2}{\text{SO}_4} \Rightarrow \underset{\phantom{2}{2}}{\text{Al}} \space {\swarrow}\mathllap{\searrow} \underset{\phantom{3}{3}}{\text{SO}_4} \\[1em] \text{Al}_2\text{(SO}_4)_3$

∴ Chemical formula of Aluminium Sulphate is Al₂(SO₄)₃

(b) Chemical formula of Ammonium Sulphate:

$\text{NH}_4^{+} \space \text{SO}_4^{2-} \\[1em] \overset{\phantom{3}{1}}{\text{NH}_4} \space {\swarrow}\mathllap{\searrow} \space \overset{2}{\text{SO}_4} \Rightarrow \underset{\phantom{2}{2}}{\text{NH}_4} \space {\swarrow}\mathllap{\searrow} \underset{\phantom{3}{1}}{\text{SO}_4} \\[1em] \text{(NH}_4)_2\text{SO}_4$

∴ Chemical formula of Ammonium Sulphate is (NH₄)₂SO₄

(c) Chemical formula of Zinc Sulphate:

$\text{Zn}^{2+} \space \text{SO}_4^{2-} \\[1em] \text{Dividing by H.C.F. it becomes} \\[1em] \text{Zn}^{1+} \space \text{SO}_4^{1-}\\[1em] \overset{\phantom{22}{1}}{\text{Zn}} \space {\swarrow}\mathllap{\searrow} \space \overset{1}{\text{SO}_4} \Rightarrow \underset{\phantom{2}{1}}{\text{Zn}} \space {\swarrow}\mathllap{\searrow} \underset{\phantom{2}{1}}{\text{SO}_4} \\[1em] \text{ZnSO}_4$

∴ Chemical formula of Zinc Sulphate is ZnSO₄

Question 8

The valency of an element A is 3 and that of element B is 2. Write the formula of the compound formed by the combination of A and B.

Answer

Formula of the compound formed by the combination of A and B:

$\overset{\phantom{3}{3}}{\text{A}} \space {\swarrow}\mathllap{\searrow} \space \overset{2}{\text{B}} \Rightarrow \underset{\phantom{2}{2}}{\text{A}} \space {\swarrow}\mathllap{\searrow} \underset{\phantom{3}{3}}{\text{B}} \\[1em] \text{A}_2\text{B}_3$

∴ Formula of the compound is A₂B₃

Question 9

Give the names of the following compounds.

(a) KClO

(b) KClO₂

(c) KClO₃

(d) KClO₄

Answer

(a) KClO → Potassium hypochlorite

(b) KClO₂ → Potassium Chlorite

(c) KClO₃ → Potassium Chlorate

(d) KClO₄ → Potassium Perchlorate

Question 10

The formula of the sulphate of an element M is M₂(SO₄)₃. Write the formula of its

(a) Chloride

(b) Oxide

(c) Phosphate

(d) Acetate

Answer

Given, formula of sulphate is M₂(SO₄)₃.

$\text{M}_2(\text{SO}_4)_3 = \underset{\phantom{2}{2}}{\text{M}} \space {\nearrow}\mathllap{\nwarrow} \space \underset{3}{\text{SO}_4} \Rightarrow \overset{\phantom{3}{3}}{\text{M}} \space {\nearrow}\mathllap{\nwarrow} \space \overset{2}{\text{SO}_4} \\[0.5em]$

∴ Valency of M is 3.

(a) Formula of Chloride:

$\text{M}^{3+} \space \text{Cl}^{1-} \\[1em] \overset{\phantom{3}{3}}{\text{M}} \space {\swarrow}\mathllap{\searrow} \space \overset{1}{\text{Cl}} \Rightarrow \underset{\phantom{1}{1}}{\text{M}} \space {\swarrow}\mathllap{\searrow} \underset{\phantom{3}{3}}{\text{Cl}} \\[1em] \text{M}\text{Cl}_3$

∴ Formula of chloride of element M is MCl₃

(b) Formula of Oxide:

$\text{M}^{3+} \space \text{O}^{2-} \\[1em] \overset{\phantom{3}{3}}{\text{M}} \space {\swarrow}\mathllap{\searrow} \space \overset{2}{\text{O}} \Rightarrow \underset{\phantom{2}{2}}{\text{M}} \space {\swarrow}\mathllap{\searrow} \underset{\phantom{3}{3}}{\text{O}} \\[1em] \text{M}_2\text{O}_3$

∴ Formula of oxide of element M is M₂O₃

(c) Formula of Phosphate:

$\text{M}^{3+} \space \text{PO}_4^{3-} \\[1em] \text{Dividing by H.C.F. it becomes} \\[1em] \text{M}^{1+} \space \text{PO}_4^{1-} \\[1em] \overset{\phantom{3}{1}}{\text{M}} \space {\swarrow}\mathllap{\searrow} \space \overset{1}{\text{PO}_4} \Rightarrow \underset{\phantom{2}{1}}{\text{M}} \space {\swarrow}\mathllap{\searrow} \underset{\phantom{3}{1}}{\text{PO}_4} \\[1em] \text{MPO}_4$

∴ Formula of phosphate of element M is MPO₄

(d) Formula of Acetate:

$\text{M}^{3+} \space \text{CH}_3\text{COO}^{1-} \\[1em] \overset{\phantom{3}{3}}{\text{M}} \space {\swarrow}\mathllap{\searrow} \space \overset{\phantom{CHCOOO}1}{\text{CH}_3\text{COO}} \Rightarrow \underset{\phantom{1}{1}}{\text{M}} \space {\swarrow}\mathllap{\searrow} \underset{\phantom{3}{3}}{\text{CH}_3\text{COO}} \\[1em] \text{M}\text{(CH}_3\text{COO})_3$

∴ Formula of acetate of element M is M(CH₃COO)₃

Question 11

What is a symbol of an element ? What information does it convey ?

Answer

A symbol is a short form that stands for the atom of a specific element or the abbreviation used for the name of an element.

A symbol conveys the following information:

1. It represents the name of the element.
2. It represents one atom of the element.
3. It represents a definite mass of the element (equal to atomic mass expressed in grams).

Question 12

Why is the symbol S for sulphur, but Na for sodium and Si for silicon ?

Answer

When the first letter of more than one element is the same the elements are denoted by two letters. Sulphur, Sodium and Silicon all have the first letter as S. Therefore, only sulphur is denoted by S, Silicon is denoted by two letter Si, Sodium is denoted by two letter Na taken from its latin name Natrium.

Question 13

Write the full form of IUPAC. Name the elements represented by the following symbols :

Au, Pb, Sn, Hg.

Answer

Full form of IUPAC is International Union of Pure and Applied Chemistry.

The elements represented by the following symbols are:

Au → Gold

Pb → Lead

Sn → Tin

Hg → Mercury

Question 14

If the symbol for Cobalt, Co, were written as CO, what would be wrong with it ?

Answer

When writing symbols, we need to be careful about the case of the letters in the symbol. CO means the compound Carbon Monoxide not Cobalt.

Question 15

What is meant by atomicity ? Name a diatomic element.

Answer

The number of atoms in a molecule of an element is called its atomicity. Hydrogen (H₂) is a diatomic element.

Question 16

(a) Explain the terms 'valency' and 'variable valency'.

(b) How are the elements with variable valency named ? Explain with an example.

Answer

(a) Valency is the combining capacity of an atom or of a radical. The valency of an element or of a radical is the number of hydrogen atoms that will combine with or displace one atom of that element or radical.
Variable valency is the ability of certain elements to have more than one valency or different combining capacities. An atom of an element can sometimes lose more electrons than are present in its valence shell, i.e., there is a loss of electrons from the penultimate shell too. Such element is said to exhibit variable valency.

(b) If an element exhibits two different positive valencies, then the suffix "ous" is used for the lower valency and the suffix "ic" is used for the higher valency. Modern chemists use Roman numerals in place of these trivial names.
For example, Iron can exhibit a valency of +2 or +3. The ion with valency +2 is named as Ferrous ion (Fe²⁺) and with valency +3 is named as Ferric ion (Fe³⁺). Its oxides will be named as Ferrous oxide or Iron (II) oxide [FeO] and Ferric oxide or Iron (III) oxide [Fe₂O₃].

Question 17

(a) What is a chemical formula ?

(b) What is the significance of a formula ? Give an example to illustrate.

Answer

(a) A chemical formula also known as molecular formula employs symbols to denote the molecule of an element or of a compound.

(b) The chemical/molecular formula of a compound has quantitative significance. It represents:

1. both the molecule and the molecular mass of the compound.
2. the respective numbers of different atoms present in one molecule of the compound.
3. the ratios of the respective masses of the elements present in the compound.

For example, the formula CO₂ means that:

1. the molecular formula of carbon dioxide is CO₂.
2. each molecule contains one carbon atom joined by chemical bonds with two oxygen atoms.
3. the molecular mass of carbon dioxide is 44, given that the atomic mass of carbon is 12 and that of oxygen is 16.

Question 18

What do you understand by the following terms ?

(a) Acid radical

(b) Basic radical

Answer

(a) An Acid radical is the radical that remains after an acidic molecule loses a hydrogen ion (H⁺). Acid radicals typically have a negative charge. They are also called electronegative radicals or anions.

(b) A Basic radical is the radical that remains after a base molecule loses a hydroxyl ion (OH^-). Basic radicals typically have a positive charge. They are also called electropositive radicals or cations.

Question 19

Write the basic radicals and acidic radicals of the following and then write the chemical formulae of these compounds.

(a) Barium sulphate

(b) Bismuth nitrate

(c) Calcium bromide

(d) Ferrous sulphide

(e) Chromium sulphate

(f) Calcium silicate

(g) Stannic oxide

(h) Sodium zincate

(i) Magnesium phosphate

(j) Sodium thiosulphate

(k) Stannic phosphate

(l) Nickel bisulphate

(m) Potassium manganate

(n) Potassium ferrocyanide

Answer

Question 20

Give the names of the elements and number of atoms of those elements, present in the following compounds.

(a) Sodium sulphate

(b) Quick lime

(c) Baking soda

(d) Ammonia

(e) Ammonium dichromate

Answer

(a) Sodium sulphate
     Formula: Na₂SO₄
   ∴ It contains 2 atoms of Sodium (Na), 1 atom of Sulphur (S) and 4 atoms of Oxygen (O).

(b) Quick lime
     Formula: CaO
   ∴ It contains 1 atom of Calcium (Ca) and 1 atom of Oxygen (O).

(c) Baking soda
     Formula: NaHCO₃
   ∴ It contains 1 atom of Sodium (Na), 1 atom of Hydrogen (H), 1 atom of Carbon (C) and 3 atoms of Oxygen (O).

(d) Ammonia
     Formula: NH₃
   ∴ It contains 1 atom of Nitrogen (N) and 3 atoms of Hydrogen (H).

(e) Ammonium dichromate
     Formula: (NH₄)₂Cr₂O₇
   ∴ It contains 2 atoms of Nitrogen (N), 8 atoms of Hydrogen (H), 2 atoms of Chromium (Cr) and 7 atoms of Oxygen (O).

Exercise 1(B)

Question 1

What is a chemical equation ? Why it is necessary to balance it ?

Answer

A chemical equation is the symbolic representation of a chemical reaction using the symbols and formulae of the substances involved in the reaction.

An equation must be balanced in order to comply with the "Law of Conservation of Matter", which states that matter is neither created nor destroyed in the course of a chemical reaction. An unbalanced equation would imply that atoms have been created or destroyed.

Question 2

State the information conveyed by the following equation.

Zn(s) + 2HCl (aq) ⟶ ZnCl₂ (aq) + H₂↑

Answer

The given equation tells us:

1. About the reactants involved and the products formed as a result of the reaction and their state. Zinc (Zn) and Hydrochloric acid (HCl) are the reactants. Zinc is in solid state and HCl is in aqueous solution state. The product Zinc Chloride (ZnCl₂) is also in aqueous solution state and Hydrogen is in gaseous state.
2. About the number of molecules of each substance taking part and formed in the reaction. Here one molecule of Zinc and two molecules of Hydrochloric acid react to give one molecule of Zinc chloride and one molecule of Hydrogen gas.
3. About chemical composition of respective molecules. For example, one molecule of Zinc chloride contains one atom of Zinc and two atoms of Chlorine.
4. About molecular mass; that 65 parts by weight of Zinc reacts with 73 parts by weight of Hydrochloric acid to produce 136 parts by weight of Zinc chloride and 2 parts by weight of Hydrogen.
   $\underset{65}{\text{Zn}}\text{(s)} + \underset{73}{\text{2HCl}}\text{(aq)} \longrightarrow \underset{136}{\text{ZnCl}_2}\text{(aq)} + \underset{2}{\text{H}_2}\uparrow$
5. 65 g of Zinc on treatment with 73 g of HCl, will produce 22.4 litres of hydrogen gas at S.T.P.
6. It also proves the law of conservation of mass. According to the above equation, 138 gram of reactants are producing 138 gram of products.

Question 3

What is the limitation of the reaction given in question 2?

Answer

The equation of the given reaction does not tell us:

1. the time taken for the completion of the reaction.
2. whether heat is given out or absorbed during the reaction.
3. the respective concentrations of the reactants and the products.
4. the rate at which the reaction proceeds.
5. whether the reaction is completed or it is not completed.

Question 4

Write chemical equations for the following word equations and balance them.

(a) Carbon + Oxygen ⟶ Carbon dioxide

(b) Nitrogen + Oxygen ⟶ Nitrogen monoxide

(c) Calcium + Nitrogen ⟶ Calcium nitride

(d) Calcium oxide + Carbon dioxide ⟶ Calcium carbonate

(e) Magnesium + Sulphuric acid ⟶ Magnesium sulphate + Hydrogen

(f) Sodium reacts with water to form sodium hydroxide and hydrogen.

Answer

The balanced chemical equations for the word equations are given below:

(a) C + O₂ ⟶ CO₂

(b) N₂ + O₂ ⟶ 2NO

(c) 3Ca + N₂ ⟶ Ca₃N₂

(d) CaO + CO₂ ⟶ CaCO₃

(e) Mg + H₂SO₄ ⟶ MgSO₄ + H₂↑

(f) 2Na + 2H₂O ⟶ 2NaOH + H₂↑

Question 5

Balance the following equations:

(a) Fe + H₂O ⟶ Fe₃O₄ + H₂

(b) Ca + N₂ ⟶ Ca₃N₂

(c) Zn + KOH ⟶ K₂ZnO₂ + H₂

(d) Fe₂O₃ + CO ⟶ Fe + CO₂

(e) PbO + NH₃ ⟶ Pb + H₂O + N₂

(f) Pb₃O₄ ⟶ PbO + O₂

(g) PbS + O₂ ⟶ PbO + SO₂

(h) S + H₂SO₄ ⟶ SO₂ + H₂O

(i) S + HNO₃ ⟶ H₂SO₄ + NO₂ + H₂O

(j) MnO₂ + HCl ⟶ MnCl₂ + H₂O + Cl₂

(k) C + H₂SO₄ ⟶ CO₂ + H₂O + SO₂

(l) KOH + Cl₂ ⟶ KCl + KClO + H₂O

(m) NO₂ + H₂O ⟶ HNO₂ + HNO₃

(n) Pb₃O₄ + HCl ⟶ PbCl₂ + H₂O + Cl₂

(o) H₂O + Cl₂ ⟶ HCl + O₂

(p) NaHCO₃ ⟶ Na₂CO₃ + H₂O + CO₂

(q) HNO₃ + H₂S ⟶ NO₂ + H₂O + S

(r) P + HNO₃ ⟶ NO₂ + H₂O + H₃PO₄

(s) Zn + HNO₃ ⟶ Zn(NO₃)₂ + H₂O + NO₂

Answer

(a) 3Fe + 4H₂O ⟶ Fe₃O₄ + 4H₂

(b) 3Ca + N₂ ⟶ Ca₃N₂

(c) Zn + 2KOH ⟶ K₂ZnO₂ + H₂

(d) Fe₂O₃ + 3CO ⟶ 2Fe + 3CO₂

(e) 3PbO + 2NH₃ ⟶ 3Pb + 3H₂O + N₂

(f) 2Pb₃O₄ ⟶ 6PbO + O₂

(g) 2PbS + 3O₂ ⟶ 2PbO + 2SO₂

(h) S + 2H₂SO₄ ⟶ 3SO₂ + 2H₂O

(i) S + 6HNO₃ ⟶ H₂SO₄ + 6NO₂ + 2H₂O

(j) MnO₂ + 4HCl ⟶ MnCl₂ + 2H₂O + Cl₂

(k) C + 2H₂SO₄ ⟶ CO₂ + 2H₂O + 2SO₂

(l) 2KOH + Cl₂ ⟶ KCl + KClO + H₂O

(m) 2NO₂ + H₂O ⟶ HNO₂ + HNO₃

(n) Pb₃O₄ + 8HCl ⟶ 3PbCl₂ + 4H₂O + Cl₂

(o) 2H₂O + 2Cl₂ ⟶ 4HCl + O₂

(p) 2NaHCO₃ ⟶ Na₂CO₃ + H₂O + CO₂

(q) 2HNO₃ + H₂S ⟶ 2NO₂ + 2H₂O + S

(r) P + 5HNO₃ ⟶ 5NO₂ + H₂O + H₃PO₄

(s) Zn + 4HNO₃ ⟶ Zn(NO₃)₂ + 2H₂O + 2NO₂

Exercise 1(C) — Multiple Choice Type

Question 1

Modern atomic symbols are based on the method proposed by

1. Bohr
2. Dalton
3. Berzelius
4. Alchemist

Answer

Berzelius

Reason — Berzelius suggested that the initial letter of an element written in capitals should represent that particular element. This method suggested by him laid the basis of the IUPAC system of chemical symbols and formulae.

Question 2

The number of carbon atoms in a hydrogen carbonate radical is

1. one
2. two
3. three
4. four

Answer

one

Reason — Hydrogen carbonate radical is represented as HCO₃^-. Thus, it shows that one carbon atom is present in a hydrogen carbonate radical.

Question 3

The formula of iron (III) sulphate is

1. Fe₃SO₄
2. Fe(SO₄)₃
3. Fe₂(SO₄)₃
4. FeSO₄

Answer

Fe₂(SO₄)₃

Reason — Chemical formula of iron (III) sulphate:

$\text{Fe}^{3+} \space \text{SO}_4^{2-} \\[1em] \overset{\phantom{22}{3}}{\text{Fe}} \space {\swarrow}\mathllap{\searrow} \space \overset{2}{\text{SO}_4} \Rightarrow \underset{\phantom{2}{2}}{\text{Fe}} \space {\swarrow}\mathllap{\searrow} \underset{\phantom{2}{3}}{\text{SO}_4} \\[1em] \text{Fe}_2\text{(SO}_4)_3$

∴ Chemical formula of iron (III) sulphate is Fe₂(SO₄)₃

Question 4

In water, the hydrogen-to-oxygen mass ratio is

1. 1 : 8
2. 1 : 16
3. 1 : 32
4. 1 : 64

Answer

1 : 8

Reason — Hydrogen-to-oxygen mass ratio in water can be found as below:

Molecualr formula of water = H₂O

∴ Hydrogen-to-oxygen mass ratio in water

   = $\dfrac{2}{16}$ = $\dfrac{1}{8}$

   = 1 : 8

Question 5

The formula of sodium carbonate is Na₂CO₃ and that of calcium hydrogen carbonate is

1. CaHCO₃
2. Ca(HCO₃)₂
3. Ca₂HCO₃
4. Ca(HCO₃)₃

Answer

Ca(HCO₃)₂

Reason — Chemical formula of calcium hydrogen carbonate:

$\text{Ca}^{2+} \space \text{HCO}_3^{1-} \\[1em] \overset{\phantom{22}{2}}{\text{Ca}} \space {\swarrow}\mathllap{\searrow} \space \overset{1}{\text{HCO}_3} \Rightarrow \underset{\phantom{2}{1}}{\text{Ca}} \space {\swarrow}\mathllap{\searrow} \underset{\phantom{2}{2}}{\text{HCO}_3} \\[1em] \text{Ca}\text{(HCO}_3)_2$

∴ Chemical formula of calcium hydrogen carbonate is Ca(HCO₃)₂

Question 6

The correct atomic symbols for carbon, calcium, copper and cadmium respectively are:

1. Ca, C, Cu, Cd
2. Ca, C, CO, Cd
3. C, Ca, Cu, Cd
4. Ca, Cl, Co, Cd

Answer

C, Ca, Cu, Cd

Reason — Carbon is denoted by the first letter of its name C, Calcium by the first two letters of its name Ca, Cadmium by first and third letters Cd and Copper is denoted by the first two letters of its latin name Cuprum so Cu.

Question 7

Hydrargyrum is the Latin name of:

1. Gold
2. Silver
3. Mercury
4. Platinum

Answer

Mercury

Reason — The term "Hydrargyrum" is derived from the Greek words "hydr-" meaning water and "argyros" meaning silver. In Latin, "Hydrargyrum" is used to refer to the element mercury, which is a silvery, liquid metal.

Question 8

In Zn₃(PO₄)₂, the valency of Zn and Phosphate respectively is:

1. 3 and 2
2. 2 and 6
3. 4 and 6
4. 2 and 3

Answer

2 and 3

Reason — Given the formula Zn₃(PO₄)₂ :

$\text{Zn}_3(\text{PO}_4)_2 = \underset{\phantom{2}{3}}{\text{Zn}} \space {\nearrow}\mathllap{\nwarrow} \space \underset{2}{\text{PO}_4} \Rightarrow \overset{\phantom{3}{2}}{\text{Zn}} \space {\nearrow}\mathllap{\nwarrow} \space \overset{3}{\text{PO}_4} \\[0.5em]$

∴ Valency of Zinc is 2 and Phosphate is 3.

Question 9

In Ca₃(PO₄)_x, the value of x is:

1. 1
2. 2
3. 3
4. 4

Answer

2

Reason — Chemical formula of calcium phosphate:

$\text{Ca}^{2+} \space \text{PO}_4^{3-} \\[1em] \overset{\phantom{22}{2}}{\text{Ca}} \space {\swarrow}\mathllap{\searrow} \space \overset{3}{\text{PO}_4} \Rightarrow \underset{\phantom{2}{3}}{\text{Ca}} \space {\swarrow}\mathllap{\searrow} \underset{\phantom{2}{2}}{\text{PO}_4} \\[1em] \text{Ca}_3\text{(PO}_4)_2$

∴ Chemical formula of calcium phosphate is Ca₃(PO₄)₂ hence x = 2.

Question 10

In C₂H₄, the valency of carbon is:

1. 2
2. 1
3. 4
4. 3

Answer

4

Reason — Given the formula C₂H₄ :

$\text{C}_2\text{H}_4 = \underset{\phantom{2}{2}}{\text{C}} \space {\nearrow}\mathllap{\nwarrow} \space \underset{4}{\text{H}} \Rightarrow \overset{\phantom{3}{4}}{\text{C}} \space {\nearrow}\mathllap{\nwarrow} \space \overset{2}{\text{H}} \\[0.5em]$

∴ Valency of Carbon is 4.

Exercise 1(C) — Very Short Type

Question 1

Fill in the blanks:

(a) Dalton used symbol ............... for oxygen and ............... for hydrogen.

(b) Symbol represents ............... atom of an element.

(c) Symbolic expression for a molecule is called ............... .

(d) Sodium chloride has two radicals. Sodium is a ............... radical while chloride is a ............... radical.

(e) Valency of phosphorus in PCl₃ is ............... and in PCl₅ is ............... .

(f) Valency of Iron in FeCl₂ is ............... and in FeCl₃ it is ............... .

(g) Formula of iron (III) carbonate is ............... .

Answer

(a) Dalton used symbol $\bigcirc$ for oxygen and ${\bigcirc}\mathllap{\bullet\phantom{\space}}$ for hydrogen.

(b) Symbol represents one atom of an element.

(c) Symbolic expression for a molecule is called molecular formula .

(d) Sodium chloride has two radicals. Sodium is a basic radical while chloride is a acidic radical.

(e) Valency of phosphorus in PCl₃ is 3 and in PCl₅ is 5 .

(f) Valency of Iron in FeCl₂ is 2 and in FeCl₃ it is 3 .

(g) Formula of iron (III) carbonate is Fe₂(CO₃)₃ .

Question 2

Complete the following table.

Answer

The completed table is given below:

Question 3

Correct the following statements.

(a) A molecular formula represents an element.

(b) Molecular formula of water is H₂O₂.

(c) A molecule of sulphur is monoatomic.

(d) CO and Co both represent cobalt.

(e) Formula of iron (III) oxide is FeO.

Answer

(a) A molecular formula represents the molecule of an element or of a compound.

(b) Molecular formula of water is H₂O.

(c) A molecule of sulphur is octatomic.

(d) CO represents Carbon Monoxide and Co represents cobalt.

(e) Formula of iron (III) oxide is Fe₂O₃.

Question 4

Give the empirical formula of :

1. Benzene (C₆H₆)
2. Glucose (C₆H₁₂O₆)
3. Acetylene (C₂H₂)
4. Acetic acid (CH₃COOH)

Answer

1. Ratio of C and H atoms in Benzene (C₆H₆) = 6 : 6
   Simplest Ratio = 1 : 1
   ∴ Empirical formula of Benzene (C₆H₆) = CH
2. Ratio of C, H and O atoms in Glucose (C₆H₁₂O₆) = 6 : 12 : 6
   Simplest Ratio = 1 : 2 : 1
   ∴ Empirical formula of Glucose (C₆H₁₂O₆) = CH₂O
3. Ratio of C and H atoms in Acetylene (C₂H₂) = 2 : 2
   Simplest Ratio = 1 : 1
   ∴ Empirical formula of Acetylene (C₂H₂) = CH
4. Ratio of C, H and O atoms in Acetic acid (CH₃COOH) = 2 : 4 : 2
   Simplest Ratio = 1 : 2 : 1
   ∴ Empirical formula of Acetic acid (CH₃COOH) = CH₂O

Exercise 1(C) — Short Answer Type

Question 1

What is the valency of :

(a) fluorine in CaF₂

(b) sulphur in SF₆

(c) phosphorus in PH₃

(d) carbon in CH₄

(e) Manganese in MnO₂

(f) Copper in Cu₂O

(g) Magnesium in Mg₃N₂

(h) nitrogen in the following compounds :

(i) N₂O₃ (ii) N₂O₅ (iii) NO₂ (iv) NO

Answer

(a) Valency of fluorine in CaF₂ is -1.

(b) Valency of sulphur in SF₆ is +6.

(c) Valency of phosphorus in PH₃ is +3.

(d) Valency of carbon in CH₄ is +4.

(e) Valency of manganese in MnO₂ is +4.

(f) Valency of copper in Cu₂O is +1.

(g) Valency of magnesium in Mg₃N₂ is +2.

(h) Valency of nitrogen in the given compounds :

1. N₂O₃ = +3
2. N₂O₅ = +5
3. NO₂ = +4
4. NO = +2

Question 2

Why should an equation be balanced ? Explain with the help of a simple equation.

Answer

An equation must be balanced in order to comply with the "Law of Conservation of Matter", which states that matter is neither created nor destroyed in the course of a chemical reaction. An unbalanced equation would imply that atoms have been created or destroyed.

For example, consider the following unbalanced equation:

KNO₃ ⟶ KNO₂ + O₂

In this equation, there are 3 oxygen atoms on the left side, but 4 oxygen atoms on the right side. This means that the equation is not balanced and does not satisfy the law of conservation of mass.

The balanced form of the equation is:

2KNO₃ ⟶ 2KNO₂ + O₂

Now there are 6 oxygen atoms on both the sides. This means that the law of conservation of mass is satisfied and the equation correctly represents the reaction.

Question 3

Define atomic mass unit.

Answer

Atomic mass unit is defined as 1⁄12 the mass of an carbon atom C-12.

Question 4

Write the balanced chemical equations of the following word equations.

(a) Sodium hydroxide + sulphuric acid ⟶ sodium sulphate + water

(b) Potassium bicarbonate + sulphuric acid ⟶ potassium sulphate + carbon dioxide + water

(c) Iron + sulphuric acid ⟶ ferrous sulphate + hydrogen

(d) Chlorine + sulphur dioxide + water ⟶ sulphuric acid + hydrogen chloride

(e) Silver nitrate ⟶ silver + nitrogen dioxide + oxygen

(f) Copper + nitric acid ⟶ copper nitrate + nitric oxide + water

(g) Ammonia + oxygen ⟶ nitric oxide + water

(h) Barium chloride + sulphuric acid ⟶ barium sulphate + hydrochloric acid

(i) Zinc sulphide + oxygen ⟶ zinc oxide + sulphur dioxide

(j) Aluminium carbide + water ⟶ aluminium hydroxide + methane

(k) Iron pyrites (FeS₂) + oxygen ⟶ ferric oxide + sulphur dioxide

(l) Potassium permanganate + hydrochloric acid ⟶ potassium chloride + manganese chloride + chlorine + water

(m) Aluminium sulphate + sodium hydroxide ⟶ sodium sulphate + sodium meta aluminate + water

(n) Aluminium + sodium hydroxide + water ⟶ sodium meta aluminate + hydrogen

(o) Potassium dichromate + sulphuric acid ⟶ potassium sulphate + chromium sulphate + water + oxygen

(p) Potassium dichromate + hydrochloric acid ⟶ potassium chloride + chromium chloride + water + chlorine

(q) Sulphur + nitric acid ⟶ sulphuric acid + nitrogen dioxide + water

(r) Sodium chloride + manganese dioxide + sulphuric acid ⟶ sodium hydrogen sulphate + manganese sulphate + water + chlorine

Answer

(a) 2NaOH + H₂SO₄ ⟶ Na₂SO₄ + 2H₂O

(b) 2KHCO₃ + H₂SO₄ ⟶ K₂SO₄ + 2CO₂ + 2H₂O

(c) Fe + H₂SO₄ ⟶ FeSO₄ + H₂

(d) Cl₂ + SO₂ + 2H₂O ⟶ H₂SO₄ + 2HCl

(e) 2AgNO₃ ⟶ 2Ag + 2NO₂ + O₂

(f) 3Cu + 8HNO₃ ⟶ 3Cu(NO₃)₂ + 2NO + 4H₂O

(g) 4NH₃ + 5O₂ ⟶ 4NO + 6H₂O

(h) BaCl₂ + H₂SO₄ ⟶ BaSO₄ + 2HCl

(i) 2ZnS + 3O₂ ⟶ 2ZnO + 2SO₂

(j) Al₄C₃ + 12H₂O ⟶ 4Al(OH)₃ + 3CH₄

(k) 4FeS₂ + 11O₂ ⟶ 2Fe₂O₃ + 8SO₂

(l) 2KMnO₄ + 16HCl ⟶ 2KCl + 2MnCl₂ + 5Cl₂ + 8H₂O

(m) Al₂(SO₄)₃ + 8NaOH ⟶ 3Na₂SO₄ + 2NaAlO₂ + 4H₂O

(n) 2Al + 2NaOH + 2H₂O ⟶ 2NaAlO₂ + 3H₂

(o) 2K₂Cr₂O₇ + 8H₂SO₄ ⟶ 2K₂SO₄ + 2Cr₂(SO₄)₃ + 8H₂O + 3O₂

(p) K₂Cr₂O₇ + 14HCl ⟶ 2KCl + 2CrCl₃ + 7H₂O + 3Cl₂

(q) S + 6HNO₃ ⟶ H₂SO₄ + 6NO₂ + 2H₂O

(r) 2NaCl + MnO₂ + 3H₂SO₄ ⟶ 2NaHSO₄ + MnSO₄ + 2H₂O + Cl₂

Exercise 1(C) — Descriptive Type

Question 1

Sodium chloride reacts with silver nitrate to produce silver chloride and sodium nitrate

(a) Write the equation.

(b) Check whether it is balanced, if not balance it.

(c) Find the weights of reactants and products.

(d) State the law that this equation satisfies.

Answer

(a) NaCl + AgNO₃ ⟶ AgCl + NaNO₃

(b) The equation is balanced.

(c) Calculating the weights of reactants and products from the equation:

$\begin{matrix} \text{NaCl} & + & \text{AgNO}_3 & \longrightarrow & \text{AgCl} & + & \text{NaNO}_3 \\ 23 + 35.5 & + & 108 + 14 + 3(16) & & 108 + 35.5 & + & 23 + 14 + 3(16) \\ \Rightarrow 58.5 & + & 170 & & 143.5 & + & 85 \\ \Rightarrow & 228.5 & & & & 228.5 & \end{matrix}$

Thus, weights of reactants = weights of products = 228.5 g

(d) The equation satisfies the law of conservation of mass. It states that the total mass of the substances on either side of the equation is the same.

Question 2

What information does the following chemical equations convey ?

(a) Zn + H₂SO₄ ⟶ ZnSO₄ + H₂

(b) Mg + 2HCl ⟶ MgCl₂ + H₂

Answer

$\text{(a) }\underset{65}{\text{Zn}} + \underset{98}{\text{H}_2\text{SO}_4} \longrightarrow \underset{161}{\text{Zn}\text{SO}_4} + \underset{2}{\text{H}_2} \\[1em]$

The above balanced equation conveys the following information:

1. One molecule of zinc reacts with one molecule of sulphuric acid to produce one molecule of zinc Sulphate and one molecule of hydrogen.
2. 65 g of zinc reacts with 98 g of sulphuric acid to produce 161 g of zinc Sulphate and 2 g of hydrogen.
3. 65 g of zinc reacts with 98 g of sulphuric acid to produce 22.4 litres of hydrogen gas at S.T.P.
4. It also proves the law of conservation of mass. According to the above equation, 163 gram of reactants are producing 163 gram of products.

$\text{(b) }\underset{24}{\text{Mg}} + \underset{73}{\text{2HCl}} \longrightarrow \underset{95}{\text{MgCl}_2} + \underset{2}{\text{H}_2} \\[1em]$

The above balanced equation conveys the following information:

1. One molecule of magnesium reacts with two molecules of hydrochloric acid to produce one molecule of magnesium chloride and one molecule of hydrogen.
2. 24 g of magnesium reacts with 73 g of hydrochloric acid to produce 95 g of magnesium chloride and 2 g of hydrogen.
3. 24 g of magnesium reacts with 73 g of hydrochloric acid to produce 22.4 litres of hydrogen gas at S.T.P.
4. It also proves the law of conservation of mass. According to the above equation, 97 gram of reactants are producing 97 gram of products.

Question 3

(a) What are poly-atomic ions ? Give two examples.

(b) Name and state the fundamental law that every equation must fulfill.

Answer

(a) Polyatomic ions are ions composed of two or more atoms that are covalently bonded together and carry a net electrical charge. Examples — Nitrate ion (NO₃^-) and Sulphate ion (SO₄^2-).

(b) Every equation must fulfill the "Law of Conservation of Matter". It states that matter is neither created nor destroyed in the course of a chemical reaction. Thus, the total mass of the substances on either side of the equation must be the same.

Question 4

Give the information conveyed by the chemical formula of a compound.

Answer

By looking at the chemical formula, we understand the ratio in which different atoms are united to form the molecule.

Question 5

Write the significance of a molecular formula.

Answer

The molecular formula of a compound has quantitative significance. It represents:

1. both the molecule and the molecular mass of the compound.
2. the respective numbers of different atoms present in one molecule of the compound.
3. the ratios of the respective masses of the elements present in the compound.

For example, the formula CO₂ means that:

1. the molecular formula of carbon dioxide is CO₂
2. each molecule contains one carbon atom joined by chemical bonds with two oxygen atoms;
3. the molecular mass of carbon dioxide is 44, given that atomic mass of carbon is 12 and that of oxygen is 16.

Question 6

What do you understand by radicals : What are basic and acidic radicals ? Explain with examples.

Answer

A radical is an atom or a group of atoms of the same or of different elements that behaves as a single unit with a positive or a negative charge.

An Acid radical is the radical that remains after an acidic molecule loses a hydrogen ion (H⁺). Acid radicals typically have a negative charge. They are also called electronegative radicals or anions.

A Basic radical is the radical that remains after a base molecule loses a hydroxyl ion (OH^-). Basic radicals typically have a positive charge. They are also called electropositive radicals or cations.

For example, in the compound ammonium carbonate (NH₄)₂CO₃, ammonium (NH₄⁺) is a basic radical with combining power 1 and carbonate (CO₃^2-) is an acidic radical with combining power 2.

Question 7

Give four examples of compounds with variable valency.

Answer

Exercise 1(C) — Structured/Application/Skill Type

Question 1

Elements X, Y and Z have 3, 7 and 6 electrons in their valence shells respectively. Write the formula of the compound formed between :

(a) X and Y

(b) X and Z

Answer

(a) Valency of X is +3 and Y is -1. Formula of the compound formed between X and Y is :

$\text{X}^{3+} \space \text{Y}^{1-} \\[1em] \overset{\phantom{22}{3}}{\text{X}} \space {\swarrow}\mathllap{\searrow} \space \overset{1}{\text{Y}} \Rightarrow \underset{\phantom{2}{1}}{\text{X}} \space {\swarrow}\mathllap{\searrow} \underset{{3}}{\text{Y}} \\[1em] \text{X}\text{Y}_3$

∴ Chemical formula of the compound formed between X and Y is XY₃

(b) Valency of X is +3 and Z is -2. Formula of the compound formed between X and Z is :

$\text{X}^{3+} \space \text{Z}^{2-} \\[1em] \overset{\phantom{22}{3}}{\text{X}} \space {\swarrow}\mathllap{\searrow} \space \overset{2}{\text{Z}} \Rightarrow \underset{\phantom{2}{2}}{\text{X}} \space {\swarrow}\mathllap{\searrow} \underset{{3}}{\text{Z}} \\[1em] \text{X}_2\text{Z}_3$

∴ Chemical formula of the compound formed between X and Z is X₂Z₃

Question 2

The following figure represents the structural formula of a chemical compound.

Answer the questions given below:

(a) How many Carbon and Hydrogen atoms are present in the compound.

(b) Write the molecular and empirical formulae of the compound.

(c) Calculate the percentage composition of all the elements present in the compound. [At. wt. of C = 12, H = 1]

Answer

(a) 6 Carbon and 12 Hydrogen atoms are present.

(b) Its molecular formula is C₆H₁₂.
As the simplest ration between C and H is 1:2, hence the empirical formula is CH₂

(c) Relative molecular mass of C₆H₁₂
   = (6 x 12) + (1 x 12)
   = 72 + 12
   = 84 g

84 g of C₆H₁₂ contains 72 g of Carbon

∴ 100 g of C₆H₁₂ contains $\dfrac{72 \times 100}{84}$ g of Carbon

= $\dfrac{7200}{84}$ = 85.7 g of Carbon.

84 g of C₆H₁₂ contains 12 g of Hydrogen

∴ 100 g of C₆H₁₂ contains $\dfrac{12 \times 100}{84}$ g of Hydrogen

= $\dfrac{1200}{84}$ = 14.3 of Hydrogen.

∴ In C₆H₁₂, C = 85.7% and H = 14.3%

Exercise 1(C) — Numericals

Question 1

Calculate the molecular mass of the following :

(i) Na₂SO₄.10H₂O

(ii) (NH₄)₂CO₃

(iii) (NH₂)₂CO

(iv) Mg₃N₂

Given atomic mass of Na = 23, H = 1, O = 16, C = 12, N = 14, Mg = 24, S = 32

Answer

(i) Molecular mass of Na₂SO₄.10H₂O
     = 2 x 23 + 32 + 4 x 16 + 10(2 x 1 + 16)
     = 46 + 32 + 64 + 180
     = 322 amu

(ii) Molecular mass of (NH₄)₂CO₃
     = 2(14 + 4 x 1) + 12 + 3 x 16
     = 36 + 12 + 48
     = 96 amu

(iii) Molecular mass of (NH₂)₂CO
     = 2(14 + 2 x 1) + 12 + 16
     = 32 + 12 + 16
     = 60 amu

(iv) Molecular mass of Mg₃N₂
     = 3 x 24 + 2 x 14
     = 72 + 28
     = 100 amu

Question 2

Calculate the relative molecular masses of

(a) CHCl₃

(b) (NH₄)₂Cr₂O₇

(c) CuSO₄.5H₂O

(d) (NH₄)₂SO₄

(e) CH₃COONa

(f) Potassium chlorate, KClO₃

(g) Ammonium chloroplatinate, (NH₄)₂PtCl₆

[At. mass : C = 12, H = 1, O = 16, Cl = 35.5, N = 14, Cu = 63.5, S = 32, Na = 23, K = 39, Pt = 195, Ca = 40, P = 31, Mg = 24, Cr = 52]

Answer

(a) The relative molecular mass of CHCl₃
     = 12 + 1 + 3 x 35.5
     = 12 + 1 + 106.5
     = 119.5 amu

(b) The relative molecular mass of (NH₄)₂Cr₂O₇
     = 2(14 + 4 x 1) + 2 x 52 + 7 x 16
     = 36 + 104 + 112
     = 252 amu

(c) The relative molecular mass of CuSO₄.5H₂O
     = 63.5 + 32 + 4 x 16 + 5(2 x 1 + 16)
     = 63.5 + 32 + 64 + 90
     = 249.5 amu

(d) The relative molecular mass of (NH₄)₂SO₄
     = 2(14 + 4 x 1) + 32 + 4 x 16
     = 36 + 32 + 64
     = 132 amu

(e) The relative molecular mass of CH₃COONa
     = 12 + 3 + 12 + 16 + 16 + 23
     = 82 amu

(f) The relative molecular mass of KClO₃
     = 39 + 35.5 + 3 x 16
     = 39 + 35.5 + 48
     = 122.5 amu

(g) The relative molecular mass of (NH₄)₂PtCl₆
     = 2(14 + 4 x 1) + 195 + 6 x 35.5
     = 36 + 195 + 213
     = 444 amu

Question 3

Find the percentage mass of water in Epsom salt, MgSO₄.7H₂O.

Answer

Relative molecular mass of MgSO₄.7H₂O
   = 24 + 32 + 4 x 16 + 7(2 x 1 + 16)
   = 24 + 32 + 64 + 126
   = 246 amu

246 g of Epsom salt contains 126 g of water of crystallisation

∴ 100 g of Epsom salt contains $\dfrac{126 \times 100}{246}$

= $\dfrac{12600}{246}$ = 51.22 g of water of crystallisation.

∴ % mass of water in Epsom salt, MgSO₄.7H₂O = 51.22%

Question 5

Calculate the percentage of phosphorus in:

(a) Calcium hydrogen phosphate, Ca(H₂PO₄)₂

(b) Calcium phosphate, Ca₃(PO₄)₂

Answer

(a) Relative molecular mass of Ca(H₂PO₄)₂
     = 40 + 2(2 x 1 + 31 + 4 x 16)
     = 40 + 2(2 + 31 + 64)
     = 40 + 194
     = 234 amu

Wt. of P in Ca(H₂PO₄)₂ = 2 x 31 = 62 g

% of P = $\dfrac{\text{Wt. of P}}{\text{Total Wt. of Ca(H}_2\text{PO}_4)_2}\times 100$

= $\dfrac{62}{234}$ x 100 = 26.5%

∴ Phosphorus in Calcium hydrogen phosphate is 26.5%

(b) Relative molecular mass of Calcium phosphate, Ca₃(PO₄)₂
     = 3 x 40 + 2(31 + 4 x 16)
     = 120 + 2(31 + 64)
     = 120 + 190
     = 310 amu

Wt. of P in Ca₃(PO₄)₂ = 2 x 31 = 62 g

% of P = $\dfrac{\text{Wt. of P}}{\text{Total Wt. of Ca}_3\text{(PO}_4)_2}\times 100$

= $\dfrac{62}{310}$ x 100 = 20%

∴ Phosphorus in Calcium phosphate is 20%

Question 6

Calculate the percentage composition of each element in Potassium chlorate, KClO₃.

Answer

Relative molecular mass of KClO₃
   = 39 + 35.5 + 3 x 16
   = 39 + 35.5 + 48
   = 122.5 amu

122.5 g of KClO₃ contains 39 g of Potassium

∴ 100 g of KClO₃ contains $\dfrac{39 \times 100}{122.5}$ g of Potassium

= $\dfrac{39000}{1225}$ = 31.83 g of Potassium

122.5 g of KClO₃ contains 35.5 g of Chlorine

∴ 100 g of KClO₃ contains $\dfrac{35.5 \times 100}{122.5}$ g of Chlorine

= $\dfrac{35500}{1225}$ = 28.98 g of Chlorine

122.5 g of KClO₃ contains 48 g of Oxygen

∴ 100 g of KClO₃ contains $\dfrac{48 \times 100}{122.5}$ g of Oxygen

= $\dfrac{48000}{1225}$ = 39.18 g of Oxygen

∴ In KClO₃ : K = 31.83%, Cl = 28.98% and O = 39.18%

Question 7

Urea is a very important nitrogenous fertilizer. Its formula is CON₂H₄. Calculate the percentage of carbon in urea.

(C= 12, O = 16, N = 14 and H = 1)

Answer

Relative molecular mass of CON₂H₄
   = 12 + 16 + 2 x 14 + 4 x 1
   = 12 + 16 + 28 + 4
   = 60 amu

Wt. of C in CON₂H₄ = 12 g

% of C = $\dfrac{\text{Wt. of C}}{\text{Total Wt. of CON}_2\text{H}_4}\times 100$

= $\dfrac{12}{60}$ x 100 = 20%

∴ Carbon in Urea is 20%