Chemical equation and reaction 3
1. Translate the following statements into chemical equations and balance them:
[CCE 2016]
Lead nitrate reacts with sulphuric acid to form a precipitate of lead sulphate and nitric acid.
Pb(NO3)2(aq) + H2SO4(aq) → PbSO4(s) + 2HNO3(aq)
Magnesium burns in the presence of nitrogen to form magnesium nitride.
3Mg(s) + N2(g) →Δ Mg3N2(s)
Aluminium metal strip is added in hydrochloric acid to produce aluminium chloride and hydrogen gas.
2Al(s) + 6HCl(aq) → 2AlCl3(aq) + 3H2(g)
2. Write the balanced chemical equations for the following reactions:
[NCERT Exemplar]
Sodium carbonate on reaction with hydrochloric acid in equal molar concentrations gives sodium chloride and sodium hydrogen carbonate.
Na2CO3 + HCl → NaCl + NaHCO3
Sodium hydrogencarbonate on reaction with hydrochloric acid gives sodium chloride, water and liberates carbon dioxide.
NaHCO3 + HCl → NaCl + H2O + CO2
Copper sulphate on treatment with potassium iodide precipitates cuprous iodide (Cu2I2), liberates iodine gas and also forms potassium sulphate.
2CuSO4 + 4KI → Cu2I2 + 2K2SO4 + I2
3. Write the balanced chemical equations for the following reactions and identify the type of reaction in each case.
[NCERT Exemplar]
Nitrogen gas is treated with hydrogen gas in the presence of a catalyst at 773 K to form ammonia gas.
N2(g) + 3H2(g) −→773KCatalyst 2NH3(g) Combination reaction
NaOH(aq) + CH3COOH(aq) → CH3COONa(aq) + H2O(l)
Double displacement reaction/Neutralisation reaction
Ethanol is warmed with ethanoic acid to form ethyl acetate in the presence of concentrated H2SO4.
C2H5OH(l) + CH3COOH(l) → CH3COOC2H5(l) + H2O(l)
Double displacement reaction/Esterification reaction
Ethene is burnt in the presence of oxygen to form carbon dioxide, water and releases heat and light.
C2H4(g) + 3O2(g) → 2CO2(g) + 2H2O(g) + Heat + Light Redox reaction/Combustion reaction
Thermit reaction, iron (III) oxide reacts with aluminium and gives molten iron and aluminium oxide.
Fe2O3(s) + 2Al(s) → Al2O3(s) + 2Fe(l) + Heat Displacement reaction
Magnesium ribbon is burnt in an atmosphere of nitrogen gas to form solid magnesium nitride.
3Mg(s) + N2(g) → Mg3N2(s) Combination reaction
Chlorine gas is passed in an aqueous potassium iodide solution to form potassium chloride solution and solid iodine.
2KI(aq) + Cl2(g) → 2KCl(aq) + I2(s) Displacement reaction
Ethanol is burnt in air to form carbon dioxide, water and releases heat.
C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(l) + Heat Combustion reaction
Name the type of chemical reaction represented by the following equation:
[CCE 2016]
CaO + H2O → Ca(OH)2
Combination reaction
3BaCl2 + Al2(SO4)3 → 2AlCl3 + 3BaSO4
Double displacement reaction
2FeSO4 →Heat Fe2O3 + SO2 + SO3
Thermal decomposition reaction
4. Translate the following statements into chemical equations and then balance the equations:
Phosphorus burns in oxygen to give phosphorus pentoxide.
P4 + 5O2 → 2P2O5
Aluminium metal replaces iron from ferric oxide, Fe2O3, giving aluminium oxide and iron.
2Al + Fe2O3 → Al2O3 + 2Fe
Carbon disulphide burns in air to give carbon dioxide and sulphur dioxide.
CS2 + 3O2 → CO2 + 2SO2
Barium chloride reacts with zinc sulphate to give zinc chloride and barium sulphate.
BaCl2 + ZnSO4 → ZnCl2 + BaSO4
5. What is observed when a solution of potassium iodide is added to a solution of lead nitrate taken in a test tube?
What type of reaction is this?
Write a balanced chemical equation to represent the above reaction.
(i) A yellow precipitate of lead iodide (PbI2) is formed.
(ii) Precipitation reaction/Double displacement reaction.
(iii) Pb(NO3)2(aq)Leadnitrate+2KI(aq)Potassiumiodide→PbI2(s)Leadiodide(Yellowppt.)+2KNO3(aq)Potassiumnitrate
(i) What happens when silver nitrate solution is added to sodium chloride solution? Write the equation for the reaction which takes place.
(ii) Name the type of reaction involved.
(i) When silver nitrate solution is added to sodium chloride solution, a white precipitate of silver chloride is formed along with sodium nitrate solution.
AgNO3(aq)+NaCl(aq)→AgCl(s)(Whiteppt.)+NaNO3(aq)
(ii) This is double displacement reaction and precipitation reaction.
(i) What is the colour of ferrous sulphate crystals? How does this colour change after heating?
(ii) Name the products formed on strongly heating ferrous sulphate crystals. What type of chemical reaction occurs in this change?
(i) The colour of ferrous sulphate crystals is green. On heating, FeSO4.7H2O first decomposes to form anhydrous ferrous sulphate (FeSO4) which is white in colour.
(ii) The products formed on strongly heating ferrous sulphate crystals are ferric oxide, sulphur dioxide and sulphur trioxide.
2FeSO4(s)Greenish−blue→HeatFe2O3(s)Brown+SO2(g)+SO3(g)
This is a type of thermal decomposition reaction.
6. Identify the oxidising agent (oxidant) in the following reactions.
[NCERT Exemplar]
Pb3O4 + 8HCl → 3PbCl2 + Cl2 + 4H2O
Pb3O4
2Mg + O2 → 2MgO
O2
CuSO4 + Zn → Cu + ZnSO4
CuSO4
V2O5 + 5Ca → 2V + 5CaO
V2O5
3Fe + 4H2O → Fe3O4 + 4H2
H2O
CuO + H2 → Cu + H2O
CuO
Solid calcium oxide was taken in a container and water was added slowly to it.
7. State the two observations made in the experiment.
Following are the two observations:
(a) Calcium oxide (CaO) reacts vigorously with water to form slaked lime.
(b) The container becomes hot because a large amount of heat is released during this reaction.
8. Write the name and chemical formula of the product formed.
The product formed is slaked lime for which the chemical formula is Ca(OH)2.
CaO(s)Calciumoxide+H2O(l)Water→Ca(OH)2(aq)Slakedlime(Calciumhydroxide)
9. A substance X, which is an oxide of a group 2 element, is used intensively in the cement industry. This element is present in bones also. On treatment with water it forms a solution which turns red litmus blue. Identify X and also write the chemical reactions involved.
[NCERT Exemplar]
X is calcium oxide, also called quick lime. It reacts with water to form calcium hydroxide which is basic in nature. So, it turns red litmus blue.
CaO(s) + H2O(l) → Ca(OH)2(aq)
10. A magnesium ribbon is burnt in oxygen to give a white compound X accompanied by emission of light. If the burning ribbon is now placed in an atmosphere of nitrogen, it continues to burn and forms a compound Y.
(i) Write the chemical formulae of X and Y.
(ii) Write the balanced chemical equation when X is dissolved in water.
[NCERT Exemplar]
2Mg + O2 → 2MgO + Light
3Mg + N2 → Mg3N2
(i) X is MgO; Y is Mg3N2
(ii) MgO + H2O → Mg(OH)2
11. Identify the type of reaction in the following examples:
Na2SO4(aq) + BaCl2(aq) → BaSO4(s) + NaCl(aq)
Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)
Displacement reaction
2H2(g) + O2(g) → 2H2O(l)
12. During the reaction of some metals with dilute hydrochloric acid, following observations were made.
[NCERT Exemplar]
Silver metal does not show any change.
Silver being a less reactive metal than hydrogen does not displace hydrogen from HCl. Hence, it does not react with dilute HCl.
The temperature of the reaction mixture rises when aluminium (Al) is added.
The temperature of the reaction mixture rises when aluminium is added because it is an exothermic reaction.
The reaction of sodium metal is found to be highly explosive.
Reaction of sodium metal is found to be highly explosive because it is an exothermic reaction.
Some bubbles of a gas are seen when lead (Pb) is reacted with the acid.
When lead is treated with hydrochloric acid, bubbles of hydrogen gas are evolved.
Pb(s) + 2HCl(aq) → PbCl2(aq) + H2(g)
A silver article generally turns black when kept in the open for a few days. The article when rubbed with toothpaste again starts shining.
[NCERT Exemplar]
Why do silver articles turn black when kept in the open for a few days? Name the phenomenon involved.
Metals such as silver when attacked by substances around it such as moisture, acids, gases etc, are said to corrode and this phenomenon is called corrosion.
Name the black substance formed and give its chemical formula.
The black substance is formed because silver (Ag) reacts with H2S present in air. It forms thin black coating of silver sulphide (Ag2S).
2Ag + H2S → Ag2S + H2 Black
