Chapter 1 - The Language of Chemistry

EXERCISE-1(A)

Question 1

What is a symbol? What information does it convey?

Answer 1 A symbol is the short form which stands for the atom of a specific element or the abbreviations used for the names of elements It represents a specific element. (i)It represents one atom of an element.

(ii)A symbol represents how many atoms are present in its one gram (gm) atom. (iii) It represents the number of times an atom is heavier than one atomic mass unit (amu) taken as a standard.

Question 2

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

Answer 2 In most cases, the first letter of the name of the element is taken as the symbol for that element and written in capitals (e.g. for Sulphur, we use the symbol S). In cases where the first letter has already been adopted, we use a symbol derived from the Latin name (e.g. for sodium/Atrium, we use the symbol Na). In some cases, we use the initial letter in capital together with a small letter from its name (e.g. for silicon, we use the symbol Si).

Question 3

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

Au, Pb, Sn, Hg

Answer 3 The full form of IUPAC is International Union of Pure and Applied Chemistry.

Names of the elements:

Question 4 If the symbol for Cobalt, Co, were written as CO, what would be wrong with it?

Answer 4 Au - Gold

Pb - Lead

Sn - Tin

Hg - Mercury

Co stands for Cobalt. If we write CO, then it would mean that it is a compound containing two non-metal ions, i.e. carbon and oxygen, which forms carbon monoxide gas.

Question 5 What do the following symbols stand for? (a) H (b) H2 (c) 2H (d) 2H2

Answer 5 (a) One Hydrogen atom (b) Hydrogen molecules (c) Two Atom of hydrogen

(d) Two molecules of hydrogen.

Question 6

What is meant by atomicity? Name the diatomic element.

Answer 6 The number of atoms of an element that join together to form a molecule of that element is known

as its automatically.

Diatomic molecules: H2, O2, N2, Cl2

Question 7

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

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

Answer 7 (a) i Valence of Na is +1 because it can lose one electron. Ii Valence of O is -2 because it can accept two electrons.

Variable valence: It is the combining capacity of an element in which the metal loses more

electrons from a shell next to a valence shell in addition to electrons of the valence shell.

(b) If an element exhibits two different positive valences, then

i. for the lower valence, use the suffix -OUS at the end of the name of the metal

ii. for the higher valency, use the suffix -IC at the end of the name of the metal.

Example:

Element Lower valence Higher valency

Ferrum (Iron) Ferrous (Fe2+) Ferric (Fe3+)

Question 8

Give the formula and valence of: (a) Acuminate …………………. (b) Chromate ………….…….. . (c) Aluminum ………………. . (d) Cupric ………………….

Answer 8

Name Formula Valency

a. Aluminates AlO2 -2

b. Chromate CrO4 -2

c. Aluminum Al +3

d. Cupric Cu +2

Question 9

(a) What are chemical formulas? What is the significance of formula? Give an example to

illustrated.

Answer 9

(a) a set of chemical symbols showing the elements present in a compound and their relative properties. (b) Significance of the molecular formula:

It represents both molecule and molecular mass of the compound. It represents the respective number of different atoms present in one molecule of the compound. It represents the ratios of the respective masses of the elements present in the compound.

Question 10 What do you understand by the following terms?

(a) Acid radical (b) Basic radical

Answer 10

(a) Acid radical: The electronegative or negatively charged radical is called an acid radical.

Examples: Cl-, O2-

(b) Basic radical: The electropositive or positively charged radical is called a basic radical. Examples: K+, Na+

Question 11 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 11

Acidic radical Basic radical

a. MgSO4 SO4- Mg+

b. (NH4)2SO4 SO4- NH4

+

c. Al2(SO4)3 SO4- Al3+

d. ZnCO3 CO3- Zn2+

e. Mg(OH)2 OH- Mg2+

Question 12

Write chemical formula of the sulphate of Aluminum, Ammonium and Zinc.

Answer 12 Valences of aluminum, ammonium and zinc are 3, 1 and 2, respectively. The valences of sulphate is 2. Hence, chemical formulae of the sulphates of aluminum, ammonium and zinc are Al2(SO4)3, (NH4)2SO4 and ZnSO4.

Question 13

The valence 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 13

Formula of the compound = A2B3

Question 14

Match the following:

Compound Formula

a. Boric acid i. NaOH

b. Phosphoric acid ii. SiO2

c. Nitrous acid iii. Na2CO3

d. Nitric acid iv. KOH

e. Sulphurous acid v. CaCO3

f. Sulphuric acid vi. NaHCO3

g. Hydrochloric acid vii. H2S

h. Silica (sand) viii. H2O

i. Caustic soda (sodium hydroxide)

ix. PH3

j. Caustic potash (potassium hydroxide)

x. CH4

k. Washing soda (sodium carbonate)

xi. NH3

l. Baking soda (sodium bicarbonate)

xii. HCl

m. Lime stone. (calcium carbonate)

xiii. H2SO3

n. Water xiv. HNO3

o. Hydrogen sulphide xv. HNO2

p. Ammonia xvi. H3BO3

q. Phosphine xvii. H3PO4

r. Methane xviii. H2SO4

Answer 14

Compound Formula (Ans)

a. Boric acid xvi. H3BO3

b. Phosphoric acid xvii. H3PO4

c. Nitrous acid xv. HNO2

d. Nitric acid xiv. HNO3

e. Sulphurous acid xiii. H2SO3

f. Sulphuric acid xviii. H2SO4

g. Hydrochloric acid xii. HCl

h. Silica (sand) ii. SiO2

Caustic soda

(sodium hydroxide)

i. NaOH

Caustic potash (potassium

hydroxide) iv. KOH

Washing soda

(sodium carbonate)

iii. Na2CO3

Baking soda (sodium bicarbonate)

vi. NaHCO3

Lime stone (calcium carbonate)

v. CaCO3

n. Water viii. H2O

o. Hydrogen sulphide vii. H2S

p. Ammonia xi. NH3

q. Phosphine ix. PH3

r. Methane x. CH4

Question 15

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 manganite (n)Potassium Ferro cyanide

Answer 15

Compounds Acidic radical

Basic radical

Chemical formulae

Barium sulphate SO42- Ba2+ BaSO4

Bismuth nitrate NO3- Bi3+ Bi(NO3)3

Calcium bromide Br- Ca2+ CaBr2

Ferrous sulphide S2- Fe2+ FeS

Chromium sulphate SO42- Cr3+ Cr2(SO4)3

Calcium silicate SiO42- Ca2+ Ca2SiO4

Potassium ferrocyanide [Fe(CN)6]4- K1+ K4[Fe(CN)6]

Stannic oxide O2- Sn2+ SnO2

Magnesium phosphate (PO4)3- Mg2+ Mg3(PO4)2

Sodium zincate ZnO2- Na1+ Na2ZnO2

Stannic phosphate (PO4)3- Sn4+ Sn3(PO4)4

Sodium thiosulphate (S2O3)2- Na1+ Na2S2O3

Potassium manganate MnO42- K1+ K2MnO4

Nickel bisulphate HSO41- Ni3+ Ni(HSO4)3

Question 16 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 16 Chemical names of compounds:

a. Ca3(PO4)2 - Calcium phosphate b. K2CO3 - Potassium carbonate c. K2MnO4 - Potassium manganite d. Mn3(BO3)2 - Manganese (II) borate e. Mg(HCO3)2 - Magnesium hydrogen carbonate f. Na4Fe(CN)6 - Sodium Ferro cyanide g. Ba(ClO3)2 - Barium chlorate h. Ag2SO3 - Silver sulphite i. (CH3COO)2Pb - Lead acetate j. Na2SiO3 - Sodium silicate

Question 17 Give the names of the following compounds. (a) KCLO (b) KCLO2

(c) KCLO3

(d) KCLO4

Answer 17 (a)Potassium hypochlorite (b)Potassium chlorate (c)Sodium chlorate (d)Sodium perchlorate

Question 18

Complete the following statements by selecting the correct option :

(a) The formula of a compound represents i. an atom ii. a particle iii. a molecule iv. a combination

Answer 18 (a) iii. The formula of a compound represents a molecule.

(b)Complete the following statements by selecting the correct option :

The correct formula of aluminum oxide is i. AlO3 ii. AlO2 iii. Al2O3

(b) iii. The correct formula of aluminum oxide is Al2O3.

(c)Complete the following statements by selecting the correct option : The valence of nitrogen in nitrogen dioxide (NO2) is I .one ii. two ii .three iv. four

(c) iv. The valence of nitrogen in nitrogen dioxide (NO2) is four.

Question 19 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 (NaHCO3) d. Ammonia e. Ammonium dichromate

Answer 19

a. Sodium sulphate - Na2SO4

There are two sodium atoms, one Sulphur atom and four oxygen atoms. b. Quick lime - CaO

There is one calcium atom and one oxygen atom. 1) Baking soda - NaHCO3

There is one sodium, carbon and hydrogen atom and three oxygen atoms. d. Ammonia - NH3

There is one nitrogen atom and three hydrogen atoms. e. Ammonium dichromate - (NH4) Cr2O7

There two ammonium atoms, two chromium atoms and seven oxygen atoms.

Question 20

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 20 The valence of metal M is 3. So, the formulae are as follows:

a. Chloride - MCl3 b. Oxide - M2O3 c. Phosphate - M(PO4) d. Acetate - M(CH3COO)3

TOLL FREE

EXERCISE -1(B)

Question 1

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

Answer 1 A chemical equation is the symbolic representation of a chemical reaction using the symbols and formulae of the substances involved in the reaction. A chemical equation needs to be balanced because a chemical reaction is just a rearrangement of atoms. Atoms themselves are neither created nor destroyed during the course of a chemical reaction. The chemical equation needs to be balanced to follow the law of conservation of mass.

Question 2

State the information conveyed by the following equation: Zn(s) + 2HCl (aq) → ZnCl2 (aq) + H2 ↑

Answer 2 A solid metal zinc reacts with hydrochloric acid in the aqueous state to produce zinc chloride in the aqueous state and hydrogen gas.

Question 3

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

Answer 3 The chemical equation given in question 2 does not give the time taken for the completion of the reaction.

Also, it does not give information about whether heat is absorbed or evolved during the reaction.

Question 4

Write the 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 Sodium reacts with water to form sodium hydroxide and hydrogen

Answer 4 (a)C + O2→ CO2 (b )N2 + O2→ 2NO (c) 3Ca + N2→ Ca3N2 (d)CaO + CO2→ CaCO3 (e)Mg + H2SO4→ MgSO4 + H2↑

(f)Na + H2O → NaOH + 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 5 Balanced chemical equations: (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 + H2O + SO2 (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)

Question 1 Fill in the blanks: (a) Dalton used symbol _____ for oxygen _____ for hydrogen. (b)Symbol represents _____ atom(s) of an element. (c)Symbolic expression for a molecule is called _____. . (d)Sodium chloride has two radicals. Sodium is a _____ radical while chloride is _____ radical. (e)Valence of carbon in CH4 is _____, in C2H6 _____, in C2H4 ___ and in C2H2 is ____. (f)Valence of Iron in FeCl2 is _____ and in FeCl3 it is ____. (g)Formula of iron (ill) carbonate is _____.

Answer 1 Dalton used symbol [O] for oxygen,[H] for hydrogen. Symbol represents gram atom(s) of an element. Symbolic expression for a molecule is called molecular formula.

Sodium chloride has two radicals. Sodium is a basic radical, while chloride is an acid radical. Valence of carbon in CH4 is 4, in C2H64, in C2H44 and in C2H2 is 4. Valence of iron in FeCl2 is 2 and in FeCl3 it is 3. Formula of iron (III) carbonate is Fe2 [CO3]3.

Question 2

Complete the following table.

Answer 2

Acid Radicals

Basic Radicals

Chloride Nitrate Sulphate Carbonate Hydroxide Phosphate

Magnesium MgCl2 Mg(NO3)2 MgSO4 MgCO3 Mg(OH)2 Mg3(PO4)2

Sodium NaCl NaNO3 Na2SO4 Na2CO3 NaOH Na3PO4

Acid Radicals

Basic Radicals

Chloride Nitrate

Sulphate Carbonate Hydroxide Phosphate

Magnesium MgCl2 Mg(NO3)2 MgSO4 MgCO3 Mg(OH)2 Mg3(PO4)2

Sodium

Zinc

Silver

Ammonium

Calcium

Iron (II)

Potassium

Zinc ZnCl2 Zn(NO3)2 Zn(SO4)2 ZnCO3 Zn(OH)2 Zn3(PO4)2

Silver AgCl AgNO3 Ag2SO4 AgCO3 AgOH Ag3PO4

Ammonium NH4Cl NH4NO3 (NH4)2SO4 (NH4)2CO3 NH4OH (NH4)3PO4

Calcium CaCl2 CaCO3 CaSO4 CaCO3 Ca(OH)2 Ca3(PO4)2

Iron (II) FeCl2 Fe(NO3)2 FeSO4 FeCO3 Fe(OH)2 Fe3(PO4)2

Potassium KCl KNO3 K2SO4 K2CO3 KOH K3PO4

Question 3

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 which this equation satisfies.

Answer 3 a. NaCl + AgNO3 → NaNO3 + AgCl↓ b. It is a balanced equation. c. Weights of reactants: NaCl - 58.44, AgNO3 - 169.87 Weights of products: NaNO3 - 84.99, AgCl - 143.32 NaCl + AgNO3 → NaNO3 + AgCl (23+35.5) + (108+14+48) → (23+14+48) + (108+35.5) 58.5 + 170 → 85 + 143.5 228.5 g → 228.5 g

e. Law of conservation of mass: Matter is neither created nor destroyed in the course of a chemical reaction.

Question 4

What information does the following chemical equation convey?

(a) Zn + H2SO4 → ZnSO4+ H2

The actual result of a chemical change. Substances take part in a reaction, and substances are formed as a result of the reaction. (i)Here, one molecule of zinc and one molecule of sulphuric acid react to give one molecule of zinc sulphate and one molecule of hydrogen.

(ii) Composition of respective molecules, i.e. one molecule of sulphuric acid contains two atoms of hydrogen, one atom of sulphur and four atoms of oxygen. (iii) Relative molecular masses of different substances, i.e. molecular mass of

Zn = 65 H2SO4 = (2+32+64) = 98 ZnSO4 = (65+32+64) = 161 H2 = 2 (iv) 22.4 liters of hydrogen are formed at STP.

(b) Mg + 2HCl → MgCl2+ H2

This equation conveys the following information: (i)Magnesium reacts with hydrochloric acid to form magnesium chloride and hydrogen gas.

(ii) 24 g of magnesium reacts with 2(1 + 35.5) = 73 g of hydrochloric acid to produce (24 + 71), i.e. 95 g of magnesium chloride.

(iii)Hydrogen produced at STP is 22.4 liters.

Question 5

(a)What are polyatomic ions? Give two examples.

(b) Name the fundamental law that is involved in. every equation

Answer 5

(a) A polyatomic ion is a charged ion composed of two or more covalently bounded atoms.

(b) Fundamental laws which are involved in every equation:

(i) A chemical equation consists of formulae of reactants connected by a plus sign (+) and arrow (→) followed by the formulae of products connected by the plus sign (+). (i) The sign of an arrow (→) is to read 'to form'. It also shows the direction in which the

reaction is predominant. The fundamental law followed by every equation is 'Law of Conservation of Mass'.

Question 6

What is the valence of?

(a)Fluorine in CaF2

(b) Sulphur in SF6

(c) Phosphorus in PH3

(d) Carbon in C4

(e) Nitrogen in the following compounds:

(i) N2O5 (ii) N2O3 (iii) NO2 (iv) NO

(f) Manganese in MnO2

(g) Copper is Cu2O

(h) Magnesium in Mg3

Answer 6

(a) Fluorine in CaF2 is -1.

(b) Sulphur in SF6 is -6.

(c) Phosphorus in PH3 is +3.

(d) Carbon in CH4 is +4.

(e) Valence of nitrogen in the given compounds: (i) N2O3 = N is +3

(ii) N2O5 = N is +5 (iii) NO2 = N is +4 (iv) NO = N is +2

Question 7

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

Answer 7 According to the law of conservation of mass, 'matter can neither be created nor can it be destroyed'. This is possible only if the total number of atoms on the reactants side is equal to the total number of atoms on the products side. Thus, a chemical reaction should always be balanced. e.g. KNO3 → KNO2 + O2 In this equation, the number of atoms on both sides is not the same, and the equation is not balanced. The balanced form of this equation is 2KNO3 → 2KNO2 + O2

Question 8

Write the balanced chemical equations of the following word equation.

(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 8 (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)

(h) BaCl2 + H2SO4 → BaSO4 + 2HCl

(i) 2ZnS + 3O2 → 2ZnO + 2SO2

(j) Al4C3 + 12H2O → 4Al(OH)3 + 3CH4

(k) 4FeS2 + 11O2 → 2Fe2O3 + 8SO2

(l) 2KMnO4 + HCl → 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 + HNO3 → H2SO4 + NO2 + H2O

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

Question 9

(a)Define atomic mass unit.

(b) 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 9 (a)Atomic mass unit (amu) is equal to one-twelfth the mass of an atom of carbon-12 (atomic mass of carbon taken as 12).

(b)

(ii) Given atomic mass of Cu = 63·5, H = 1, O= 16, C = 12, N = 14, Mg = 24, S = 32

Molecular mass of (NH4)2CO3 = (2 × 14) + (8 × 1) + 12 + (3 × 16) = 28 + 8 + 12 + 48 = 96

(iii) Given atomic mass of Cu = 63·5, H = 1, O= 16, C = 12, N = 14, Mg = 24, S = 32

Molecular mass of (NH2)2CO = (14 × 2) + (4 × 1) + 12 + 16 = 28 + 4 + 12 + 16 = 60

(iv) Given atomic mass of Cu = 63·5, H = 1, O = 16, C = 12, N = 14, Mg = 24, S = 32

Molecular mass of Mg3N2 = (3 × 24) + (2 × 14) = 72 + 28 = 100

Question 10

Choose the correct answer from the options given below.

(a)Modern atomic symbols are based on the method proposed by

(I). Bohr (ii). Dalton (iii.) Berzelius (iv.) Alchemist

(b) The number of carbon atoms in a hydrogen carbonate radical is

(I). One

(II). Two (III). Three (IV). Four

(c) The formula of iron (III) sulphate is (i). Fe3SO4 (ii) Fe (SO4)3 (iii). Fe2 (SO4)3 (iv.) FeSO4

(d) In water, the hydrogen-to-oxygen mass ratio is

(I) 1: 8 (Ii) 1: 16 (Ii) 1: 32 (IV) 1: 64

(e) The formula of sodium carbonate is Na2CO3 and that of calcium hydrogen carbonate is

(i) CaHCO3

(ii) Ca (HCO3)2

(iii). Ca2HCO3

(iv). Ca (HCO3)3

Answer 10

(a) Iii. Berzelius

(b)I. One

(c) Iii. Fe2 (SO4)3

(d) i. 1:8 (e) Ii. Ca (HCO3)2

Question 11

(a)A molecular formula represent an elements.

(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 11

Question 12

Calculate the relative molecular masses of:

(a)CHCL3 (b) (NH4)2Cr2O7 (c) CuSO4.5H2O

(d) (NH4)2SO4 (e) CH3COONa (f) potassium chlorate

(g) Ammonium chloroplatinate (NH4)2 SO4

[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,]

Answer 12

Question 13

Give the empirical formula of:

(a) Benzene (C6H6) (b) Glucose (C6H12O) (c)

(c) Acetylene (C2H2) (d) Acetic acid (CH3COOH)

Answer 13

Question 14

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

Answer 14

Question 15

Calculate the percentage of phosphorous in :

(a)Calcium hydrogen phosphate Ca(H2PO4O2)

(b) Calcium phosphate Ca3 (PO4)2

Answer 15

Question 16

Calculate the percentage composition of each element in Potassium chlorate, KCLO3.

Answer 16

Question 17

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 17