Chapter 3 Chemical Formulae and Equations

Relative Atomic Mass and Relative Molecular Mass

No.ElementSymbolRAM

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5

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8

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14

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16

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18

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Exercise 1Calculate the relative molecular masses of the following substances

Chemistry Form 41

1. Pusat Tuisyen Minda Inspirasi

2. Bromine gas, Br2

3. Sulphur, S8

4. Methane, CH4

5. Glucose, C6H12O6

6. Zinc oxide, ZnO

7. Copper hydroxide, Cu(OH)2

8. Magnesium nitrate, Mg(NO3)2

9. Sodium carbonate, Na2CO3

10. Hydrogen gas, H2

11. Oxygen gas, O2

12. Water, H2O

13. Propane, C3H8

14. Ethanol, C2H5OH

15. Ammonia, NH3

16. Sodium chloride, NaCl

17. Potassium oxide, K2O

18. Copper chloride, CuCl2

19. Zinc nitrate, Zn(NO3)2

20. Aluminium sulphate, Al2(SO4)3

21. Copper sulphate, CuSO4

22. Benzoic acid, C6H5COOH

23. Sulphuric acid, H2SO4

24. Hydrochloric acid, HCl

25. Nitric acid, HNO3

Number of moles & number of particles

1 mole of ANY substance

= 6.02 x 1023 particles (atoms, molecules, ions)

Number of molesAvogadro constantNumber of particles

Example 1Find the number of atoms in(a) 0.4 moles of iron, Fe(b) 0.1 moles of oxygen gas, O2

Example 2(a) Find the number of atoms in 0.5 moles of aluminium, Al(b) Find the number of molecules in 1.2 moles of hygrogen gas, H2(c) Find the number of oxide ions in 0.6 moles of oxide ions, O2-

Example 3A gas jar contains 0.2 moles of carbon dioxide, CO2. Find(a) The number of CO2 molecules(b) The number of atoms in the gas jar(c) The number of carbon, C atoms(d) The number of oxygen, O atoms

Example 40.4 moles of copper chloride, CuCl2 is dissolved in a beaker of water. The copper chloride, CuCl2 dissolves into ions. Calculate a) the number of copper chloride, CuCl2 molecules present at firstb) the number of ions presentc) the number of copper, Cu2+ ions presentd) the number of chloride, Cl- ions present

Example 50.3 moles of zinc bromide, ZnBr2 is dissolved in a beaker of water. Calculate a) the number of ZnBr2 molecules present at firstb) the number of ions presentc) the number of zinc, Zn2+ ions presentd) the number of bromide, Br- ions present

Example 6Calculate the number of particles in(a) 0.75 moles of aluminium atoms, Al(b) 1.2 moles of chloride ions, Cl-(c) 0.07 moles of carbon dioxide molecules, CO2

Example 7Calculate the number of atoms in(a) 0.2 moles of sulphur dioxide gas, SO2(b) 0.125 moles of methane gas, CH4

Example 8Calculate the number of moles of the following substances:(a) 6x1021 iron atoms, Fe(b) 7.5x1023 carbon monoxide molecules, CO

Example 9How many moles of water contain 3.01x1023 water molecules?

Example 10What is the number of moles of atoms represented by 3.01x1022 carbon atoms and 1.806x1023 lead atoms?

Example 11Calculate the number of moles of the following substances:(a) 6x1022 sodium ions(b) 1.8x1024 H2S molecules

Number of moles & mass of substances

Mass

RAM / RMMNumber of moles

Example 1Calculate the mass of(a) 1.5mol of zinc, Zn(b) 0.25mol of lithium hydroxide, LiOH(c) 4mol of nitrogen monoxide, NO[Relative atomic mass: Zn, 65; Li, 7; O, 16; H, 1; N, 14]

Example 2Calculate the mass of 0.5mol of magnesium oxide, MgO.[Relative atomic mass: Mg, 24; O, 16]

Example 3Find the mass of 0.5mol of copper.[Relative atomic mass: Cu, 64]

Example 4What us the mass of 0.04mol hydrated copper (II) sulphate, CuSO4.5H2O?[Relative atomic mass: Cu, 64; S, 32; O, 16; H, 1]

Example 5Calculate the number of moles in(a) 3.2g of copper, Cu(b) 3.72g of phosphorus molecules P4(c) 8.88g of magnesium nitrate, Mg(NO3)2[Relative atomic mass: Cu, 64; P, 31; Mg, 24; N, 14; O, 16]

Example 6What is the number of moles of 4.97g of sodium sulphate, Na2SO4?[Relative atomic mass: Na, 23; S, 32; O, 16]

Example 7What is the number of moles of potassium chloride, KCl in 3.725g of potassium chloride crystals?[Relative atomic mass: K, 39; Cl, 35.5]

Example 8Calculate the number of moles of atoms in 1.2g of magnesium.[Relative atomic mass: Mg, 24]

Example 9Find the number of moles of molecules in 1.7g of ammonia gas, NH3.[Relative atomic mass: N, 14; H, 1]

Example 10How many moles of atoms are there in 20g of neon?[Relative atomic mass: Ne, 20]

Example 11A gas jar contains 4g of bromine gas, Br2. Find the number of moles of atoms in 4g of bromine gas. Given that the relative atomic mass of Br is 80.

Example 12Calculate the number of moles of atoms in 0.22g of carbon dioxide, CO2.[Relative atomic mass: CO2, 44]

Example 13A gas jar contains 2.8g of nitrogen gas/(a) Calculate the number of moles of nitrogen gas.(b) Calculate the number of moles of nitrogen atoms.[Relative atomic mass: N, 14]

Example 14Liquefied petroleum gas tank contains 9.68g of propane gas, C3H8.(a) Find the number of moles of propane gas(b) Find the number of moles of carbon atoms[Relative atomic mass: C, 12; H, 1]Number of moles & volume of substances

Number of molesRAM / RMMMass

Example 1Calculate the volume, in dm3, of each of the following gases at STP. Given that the molar volume is 22.4dm3mol-1 at STP.(a) 7 mol of hydrogen gas(b) 3.5mol of sulphur dioxide gas(c) 0.25mol of chlorine gas

Example 2Calculate the volume, in cm3, of each of the following gases at room conditions. Given that the molar volume is 24dm3mol-1 at room conditions.(a) 3mol of nitrogen gas(b) 0.5mol of ammonia gas(c) 0.025mol of ethane gas

Example 3Find the volume, in dm3, of 0.4mol carbon dioxide gas at room temperature and pressure. [1mol of gas occupies 24dm3 at room temperature and pressure]

Example 4Calculate the volume, in cm3, of 0.16mol of helium gas at room conditions.[1 mol of gas occupies 24dm3 at room conditions]

Example 5What is the volume, in cm3, of 0.24mol of carbon monoxide gas at STP? Given that 1 mol of gas occupies 22.4dm3 at STP.

Example 6A balloon is filled with 0.5mol of nitrogen dioxide gas. Calculate the volume of nitrogen gas, in dm3, present in the balloon at STP.[1 mol of gas occupies 22.4dm3 at STP]

Example 7Calculate the number of moles of the following gases at STP. Given that 1 mol of gas occupies 22.4dm3 at STP.(a) 582.4cm3 of neon gas(b) 224cm3 of carbon dioxide gas

Example 8Calculate the number of moles of the following gases at room conditions.[1 mol of gas occupies 24000cm3 at room conditions](a) 16.8dm3 of methane gas(b) 0.4464dm3 of ozone

Example 9An aquarium air pump can produce 2.4dm3 of gas per minute at room temperature. What is the number of moles of the gas produced in 1 minute?[1 mol of gas occupies 24000cm3 at room conditions]

Example 10What is the number of moles of 1320cm3 of ammonia gas at room conditions?[1 mol of gas occupies 24000cm3 at room conditions]

Example 11Find the number of moles of 89.6dm3 of oxygen gas present in a gas container at STP.[1 mol of gas occupies the volume of 22.4dm3 at STP]

Example 12Given that there is 336cm3 of sulphur trioxide gas in a container at STP. What is the number of moles of sulphur trioxide gas?[1 mol of gas occupies the volume of 22.4dm3 at STP]

Chemical Formulae Empirical formula

A chemical formula is used to represent a chemical substance using symbols of the elements and the number of elements present in the substance.

NH4CO2H2O

There are two types of chemical formulae:(a) Empirical formulaGives the simplest whole number ratio of atoms of each element present in the compound.

(b) Molecular formulaGives the actual number of atoms present in one molecule of the compound.

Example 12.24g of iron combines chemically with 0.96g of oxygen to form an oxide. What is the empirical formula of the oxide? [RAM: O, 16; Fe, 56]

Example 2A sample of lead oxide contains 4.14g of lead and 0.32g of oxygen. What is the empirical formula of the sample? [RAM: O, 16; Pb, 207]

Example 32.36g of cobalt combines chemically with 1.92g of sulphur to form cobalt sulphide. What is the empirical formula of cobalt sulphide? [ RAM: Co, 59; S, 32]

Example 4A potassium compound has a percentage composition as the following:K, 31.84%; Cl, 28.98%; O, 39.18%What is the empirical formula of the potassium compound? [RAM: O, 16; Cl, 35.5; K, 39]

Example 5An oxide of copper contains 88.98% copper by mass. Find the empirical formula of the oxide of copper. [RAM: Cu, 64; O, 16]

Example 6A compound has the percentage composition as follows.

Na, 33.33%N, 20.29%O, 46.38%

What is the empirical formula of the compound?[RAM: Na, 23; N, 14; O, 16]

Example 73.5g of a hydrocarbon contains 3g of carbon. What is the empirical formula of the hydrocarbon?[RAM: H, 1; C, 12]

Chemical Formulae Empirical formula

An ionic compound consists of a ____________ and an _____________.

Because of the combination of _______________ and ______________ charges, an ionic compound is _______________.

Cation (positive ion)

CationFormulaCharge

Lithium ion

Sodium ion

Potassium ion

Hydrogen ion

Silver ion

Ammonium ion

Copper (II) ion

Iron (II) ion

Lead (II) ion

Manganese (II) ion

Tin (II) ion

Calcium ion

Magnesium ion

Zinc ion

Aluminium ion

Iron (III) ion

Chromium (III) ion

Anion (negative ion)

AnionFormulaCharge

Flouride ion

Chloride ion

Bromine ion

Iodide ion

Hydroxide ion

Manganate (VII) ion

Nitrate ion

Oxide ion

Carbonate ion

Sulphate ion

Thiosulphate ion

Chromate (VI) ion

Dichromate (VI) ion

Aluminium ion

Some common covalent compoundsName of gasChemical formulaName of acidChemical formula

Bromine gasHydrochloric acid

Nitrogen gasSulphuric acid

Chlorine gasNitric acid

Hydrogen gasEthanoic acid

Oxygen gasPhosphoric acid

Ammonia gas

Carbon dioxide gas

Nitrogen dioxide gas

Sulphur dioxide gas

Sulphur trioxide gas

Example Construct the formula of the following substances:(a) Sodium chloride

(b) Aluminium oxide

(c) Iron (II) hydroxide

(d) Zinc chloride

(e) Copper (II) sulphate

(f) Calcium carbonate

(g) Ammonium sulphate

(h) Calcium phosphate

(i) Sodium sulphate

(j) Magnesium hydroxide

(k) Magnesium chloride

(l) Potassium sulphate

(m) Aluminium hydroxide

(n) Tin (II) oxide

(o) Zinc nitrate

(p) Lead (II) iodide

(q) Iron (III) bromide

(r) Ammonium chloride

Chemical Equations

A chemical equation shows us a chemical reaction in _____________ and _____________.

We use __________________ and symbols to denote the chemicals and the actions.

All chemical equations must be ________________. This means that the amount of _____________ must equal the amount of ______________.

SymbolMeaningExamples

produces / becomes / forms / decomposes

reversible reaction

solid

liquid

gas

aqueous solution

heat

Example 1Write a balanced chemical equation for each of the following reactions

(a) A solution of silver nitrate is added to a solution of sodium chloride. A precipitate of silver chloride and a solution of sodium nitrate are produced

(b) When solid lead (II) carbonate is heated strongly, it decomposes into solid lead (II) oxide and carbon dioxide gas is released

(c) Nitrogen gas reacts with hydrogen gas to produce ammonia gas

(d) Solid calcium oxide dissolves hydrochloric acid, producing calcium chloride solution and water

(e) Sulphur trioxide gas + water sulphuric acid

Example 2Balance the following chemical equations:

(a) Na (s) + Br2 (g) NaBr (s)

(b) H2 (g) + O2 (g) H2O (l)

(c) Zn (s) + AgNo3 (aq) Zn(NO3)2 (aq) + Ag (s)

(d) Zn(NO3)2 (s) ZnO (s) + NO2 (g) + O2 (g)

Example 3The reaction between zinc powder and copper (II) sulphate solution produces zinc sulphate solution and copper deposit. Write a balanced chemical equation.

Example 4Decomposition of green powder of copper (II) carbonate produces black residue of copper (II) oxide and carbon dioxide gas.

Example 5Liquid oleum, H2S2O7, is formed when sulphur trioxide gas reacts with concentrated sulphuric acid. Write the chemical equation for this reaction.

Example 6Hydrochloric acid reacts with marble chips to form calcium chloride solution, carbon dioxide gas and water.

Example 7When sodium sulphate is added to excess lead (II) nitrate solution, a white precipitate of lead (II) sulphate and sodium nitrate are formed. Write the chemical equation for the reaction.

Example 8Write a balanced chemical equation for the reaction between ammonia solution and sulphuric acid. Given that the product formed is ammonium sulphate, write the chemical equation for the reaction.

Example 9Dissolving sodium oxide in water produces alkaline solution of sodium hydroxide. Form a balanced chemical equation.

Example 10Sulphuric acid neutralizes potassium hydroxide solution to form potassium sulphate salt and water. Form a balanced chemical equation for this reaction.

Example 11Combustion of magnesium powder in excess oxygen produces white powder of magnesium oxide. What is the balanced chemical equation for this reaction?

Example 12Decomposition of hydrogen peroxide solution produces water and oxygen gas. Write out the balanced chemical equation for this reaction.

Example 13Complete combustion of ethanol, C2H5OH produces carbon dioxide gas and water. Write the balanced chemical equation for this reaction.

Example 14Combustion of propane, C3H8 produces carbon dioxide gas and water.

Chemical Equations Stoichiometry

Stoichiometry is the calculation of the quantities of ________________ and _______________ involved in a chemical reaction.

Example 1Potassium reacts with chlorine to form potassium chloride.2K (s) + Cl2 (g) 2KCl (s)What is the mass of potassium chloride formed when 7.8g of potassium reacts with excess chlorine gas? [Relative atomic mass: K, 39; Cl, 35.5]

Example 23.9g of element X reacts completely with oxygen.4X (s) + O2 (g) 2X2O (s)(a) Calculate the number of moles of element X.(b) Calculate ht maximum mass of X2O formed.[Relative atomic mass: X, 39; O, 16]

Example 3Complete combustion of methane gas, CH4 produces carbon dioxide and water. What is the mass of water produced when 3.2g of methane is burnt completely?[Molar mass of methane, 16gmol-1; molar mass of water, 18gmol-1]

Example 4Excess copper is added to 1.7g of silver nitrate solution to produce copper (II) nitrate solution and silver.(a) Write a balanced equation for the reaction.(b) Find the mass of silver that is displaced from silver nitrate solution.[Relative atomic mass: Ag, 108; N, 14; O, 16]

Example 5The following equation shows the reaction between iron and chlorine.2Fe + 3Cl 2FeCl3

4.48g of iron burns completely in chlorine. What is the mass of the product?[Relative atomic mass: Cl, 35.5; Fe, 56]

Example 6A chemical reaction is represented by the following equation.2Mg (s) + O2 (g) 2MgO (s)If 6g of magnesium oxide is produced in the reaction, calculate the mass of oxygen required in the reaction.[Relative atomic mass: Mg, 24; O, 16]

Example 7The following equation shows the thermal decomposition of zinc nitrate at STP.2Zn(NO3)2 (s) 2ZnO (s) + 4NO2 (g) + O2 (g)

What is the number of moles of nitrogen gas formed when 3.78g of zinc nitrate is heated strongly?[Molar mass of Zn(NO3)2, 189gmol-1]

Example 8Magnesium reacts with sulphuric acid to form magnesium sulphate and hydrogen gas. If 4.8g of magnesium sulphate is produced, calculate the mass of magnesium needed in the reaction.[Relative atomic mass: Mg, 24; S, 32; O, 16]

Example 9Silver nitrate reacts with potassium chloride to form a white precipitate of silver chloride and potassium nitrate. Find the mass of silver nitrate needed if 2.87g of silver chloride precipitate is formed.[Relative atomic mass: Ag, 108; Cl, 35.5; N, 14; O, 16]

Example 10The chemical equation below is about the neutralization reaction between x g of hydrochloric acid, HCl and 14g of potassium hydroxide solution, KOH.HCl (aq) + KOH (aq) KCl (aq) + H2O (l)What is the mass of hydrochloric acid?[Relative atomic mass: H, 1; Cl, 35.5; K, 39; O, 16]

Example 110.5mol of copper (II) oxide reacts completely with sulphuric acid to form copper (II) sulphate and water.(a) Write the chemical equation for the reaction.(b) Calculate the mass of sulphuric acid needed to completely react with 0.5mol of copper (II) oxide.[Relative atomic mass: H, 1; S, 32; O, 16]

Example 12When excess zinc is added to 18.9g of nitric acid, hydrogen gas is produced. Calculate the volume, in dm3, of hydrogen gas produced at room conditions.[Relative atomic mass: H, 1; N, 14; O, 16; molar volume, 24dm3 at room conditions]

Example 13Burning of 0.72g of carbon produces carbon dioxide gas. Calculate the volume, in cm3, of carbon dioxide gas formed in the reaction at room conditions.[Relative atomic mass: C, 12; molar volume, 24dm3 mol-1]

Example 14The following equation shows the decomposition of hydrogen peroxide solution to form oxygen gas and water:2H2O2 (l) 2H2O (l) + O2 (g)Find the mass of hydrogen peroxide that is required to produce 840cm3 of oxygen gas at room conditions.[Relative atomic mass: H, 1; O, 16; 1 mol of gas occupies 24dm3 at room conditions]

Example 15When heated under STP, sodium bicarbonate, NaHCO3 decomposes to form sodium carbonate, carbon dioxide, and water.If 0.28dm3 of carbon dioxide gas is released, what is the mass of sodium bicarbonate?[1 mol of gas occupies 22.4dm3 at STP]

Example 16Write the chemical equation for the reaction between copper (II) oxide and hydrogen gas to produce water and copper. Then, calculate the volume, in cm3, of hydrogen gas that is required to form 2.5mol of water at STP.[Molar volume, 22.4dm3mol-1]

Example 17Reaction between nitrogen gas and hydrogen gas is represented by the following equation:N2 (g) + 3H2 (g) 2NH3 (g)Based on the equation, find the volume, in cm3, of hydrogen gas that produces 3.01x1022 molecules of ammonia at room conditions.[NA, 6.02x1023; 1 mol of gas occupies 24dm3 at room conditions]

Example 18When calcium carbonate, CaCO3 reacts with nitric acide, HNO3, carbon dioxide gas, CO2, calcium nitrate solution, Ca(NO3)2 and water H2O are produced.In the reaction, 2g of calcium carbonate reacts with 1.89g of nitric acid to form carbon dioxide gas. Find the volume, in dm3, of carbon dioxide gas produced at room conditions.[Relative atomic mass: Ca, 40; C, 12; O, 16; H, 1; N, 14; molar volume, 24dm3 mol-1 at room conditions]

Example 19Magnesium reacts with lead (II) oxide to form magnesium oxide and lead. If 3.12g of magnesium reacts with 44.6g of lead (II) oxide, calculate the mass of lead produced.[Relative atomic mass: Pb, 207; O, 16; Mg, 24]

Example 20Urea, CO(NH2)2 and water are produced when carbon dioxide reacts with ammonia. Find the mass of urea produced if 26.4g of carbon dioxide reacts with 25.5g of ammonia.[Relative atomic mass: C, 12; O, 16; N, 14; H, 1]

Example 21The reaction between 30g of zinc oxide and 0.2mol of sulphuric acid is represented by the following equation:ZnO (s) + H2SO4 (aq) ZnSO4 (aq) + H2O (l)Find the mass of zinc oxide left unreacted.[Relative atomic mass: Zn, 65; O, 16]