KSEEB SOLUTIONS FOR CHAPTER 1 CHEMICAL REACTIONS AND EQUATIONS

DOWNLOAD KSEEB SOLUTIONS FOR CHAPTER ;-1 Chemical Reactions and Equations,CLASS 10 S.S.L.C SCIENCE PART-1 English medium Karnataka state board,the Answers Are Prepared By Our Teachers Which Are Simple ,Pointwise,Easy To Read And Remember ,And Are As Per The Scheme Of Evaluation And Key-Answer Sheets SO that any one can get full marks at their exams.

CHAPTER ;-1 Chemical Reactions and Equations

1.Why should a magnesium ribbon be cleaned before burning in air?

answer:-

Cleaning the magnesium ribbon before burning removes any impurities or oxide layers on its surface.
Impurities or oxide layers can hinder the reaction between magnesium and oxygen.
Cleaning ensures a better surface area for reaction and more efficient burning.
A clean surface promotes a more vigorous reaction and better observation of the chemical change.

2.Write the balanced equation for the following chemical reactions.

(i) Hydrogen + Chlorine → Hydrogen chloride

(ii) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride

(iii) Sodium + Water → Sodium hydroxide + Hydrogen

answer:-

(i) Hydrogen + Chlorine → Hydrogen chloride

H2(g) + Cl2(g) → 2HCl(g)

(ii) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride

3BaCl2(aq) + Al2(SO4)3(aq) → 3BaSO4(s) + 2AlCl3(aq)

(iii) Sodium + Water → Sodium hydroxide + Hydrogen

2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)

3.Write a balanced chemical equation with state symbols for the following reactions.

(i) Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride.

(ii) Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water.

answer:-

(i) Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride.

BaCl2(aq) + Na2SO4(aq) → BaSO4(s) + 2NaCl(aq)

(ii) Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water.

NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)

1.A solution of a substance ‘X’ is used for whitewashing.

(i) Name the substance ‘X’ and write its formula.

(ii) Write the reaction of the substance ‘X’ named in (i) above with water.

answer:-

(i) Substance ‘X’ is calcium hydroxide.

Formula: Ca(OH)2

(ii) Reaction of calcium hydroxide with water:

Ca(OH)2(aq) + H2O(l) → Ca(OH)2(aq) (slaked lime)
This reaction produces slaked lime, which is used for whitewashing walls.

2.Why is the amount of gas collected in one of the test tubes in Activity 1.7 double of the amount collected in the other? Name this gas.

answer:-

The gas collected in one of the test tubes is oxygen.
The amount of gas collected in one test tube is double because water (H2O) decomposes into hydrogen (H2) and oxygen (O2) gas during electrolysis, and the ratio of the volume of hydrogen to oxygen produced is 2:1 according to the chemical equation.
Thus, the volume of oxygen collected is double the volume of hydrogen collected.

1.Why does the colour of copper sulphate solution change when an iron nail is dipped in it?

answer:-

The colour of copper sulphate solution changes because of a displacement reaction.
Iron displaces copper from the copper sulphate solution, forming iron sulphate and depositing copper metal.
The reaction is represented as: Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)
The blue colour of copper sulphate fades because copper ions are replaced by iron ions.

2.Give an example of a double displacement reaction other than the one given in Activity 1.10.

answer:-

An example of a double displacement reaction is the reaction between sodium hydroxide (NaOH) and hydrochloric acid (HCl) to form sodium chloride (NaCl) and water (H2O).
The balanced chemical equation for this reaction is: NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)

3.Identify the substances that are oxidised and the substances that are reduced in the following reactions.

(i) 4Na(s) + O2 (g) → 2Na2O(s)

(ii) CuO(s) + H2 (g) → Cu(s) + H2O(l)

answer:-

(i) 4Na(s) + O2(g) → 2Na2O(s)

Oxidised: Sodium (Na) is oxidised to sodium oxide (Na2O).
Reduced: Oxygen (O2) is reduced to sodium oxide (Na2O).

(ii) CuO(s) + H2(g) → Cu(s) + H2O(l)

Oxidised: Copper oxide (CuO) is reduced to copper (Cu).
Reduced: Hydrogen (H2) is oxidised to water (H2O).

EXERCISES

1.Which of the statements about the reaction below are incorrect? 2PbO(s) + C(s) → 2Pb(s) + CO2 (g)

(a) Lead is getting reduced.

(b) Carbon dioxide is getting oxidised.

(d) Lead oxide is getting reduced.

(i) (a) and (b)

(ii) (a) and (c)

(iii) (a), (b) and (c)

(iv) all

Answer: (iii) (a), (b) and (c)

2.Fe2O3 + 2Al → Al2O3 + 2Fe

The above reaction is an example of a

(a) combination reaction.

(b) double displacement reaction

(d) displacement reaction.

Answer:

Answer: (d) displacement reaction.

3.What happens when dilute hydrochloric acid is added to iron fillings? Tick the correct answer.

(a) Hydrogen gas and iron chloride are produced.

(b) Chlorine gas and iron hydroxide are produced.

(d) Iron salt and water are produced.

Answer: (a) Hydrogen gas and iron chloride are produced.

4.What is a balanced chemical equation? Why should chemical equations be balanced?

Answer:

A balanced chemical equation is one where the number of atoms of each element is the same on both the reactant and product sides.

Chemical equations should be balanced to follow the law of conservation of mass, which states that mass cannot be created or destroyed in a chemical reaction

5.Translate the following statements into chemical equations and then balance them.

(a) Hydrogen gas combines with nitrogen to form ammonia.

(b) Hydrogen sulphide gas burns in air to give water and sulpur dioxide.

(d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.

Answer;-

a)H2(g) + N2(g) → NH3(g)

b)H2S(g) + O2(g) → H2O(g) + SO2(g)

c)BaCl2(aq) + Al2(SO4)3(aq) → AlCl3(aq) + BaSO4(s)

d)K(s) + H2O(l) → KOH(aq) + H2(g)

6.Balance the following chemical equations.

(a) HNO3 +Ca(OH)2 → Ca(NO3 ) 2 + H2O

(b) NaOH + H2 SO4 → Na2 SO4 + H2O

(d) BaCl2 + H2 SO4 → BaSO4 + HCl

Answer:

a) 2HNO3 + Ca(OH)2 → Ca(NO ) + 3 2 2H2O

b) 2NaOH + H2SO4 → Na2SO4 + 2H2O

c) NaCl + AgNO3 → AgCl + NaNO3

d) BaCl2 + H2SO4 → BaSO4 + 2HCl

7.Write the balanced chemical equations for the following reactions.

(a) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water

(b) Zinc + Silver nitrate → Zinc nitrate + Silver

(d) Barium chloride + Potassium sulphate → Barium sulphate + Potassium chloride

Answer:

a) Ca(OH) (aq) + 2 CO2(g) → CaCO3(s) + H2O

b) Zn + 2AgNO3 → Zn(NO 3)2+ 2Ag

c) 2Al + 3CuCl2 → 2AlCl3 + 3Cu

d) BaCl2 + K2SO4 → BaSO4 + 2KC

8.Write the balanced chemical equation for the following and identify the type of reaction in each case.

(a) Potassium bromide(aq) + Barium iodide(aq) → Potassium iodide(aq) + Barium bromide(s)

(b) Zinc carbonate(s) → Zinc oxide(s) + Carbon dioxide(g)

(d) Magnesium(s) + Hydrochloric acid(aq) → Magnesium chloride(aq) + Hydrogen(g)

Answer:

a) 2KBr(aq) + BaI2(aq) → 2KI(aq) + BaBr2(s)- Double displacement reaction

(b) ZnCO3(s) → ZnO(s) + CO2(g)- Decomposition reaction

(d) Mg(s) + 2HCl(aq) → MgCl2 (aq) + H2(g)- – Single displacement reaction

9.What does one mean by exothermic and endothermic reactions? Give examples.

Answer:

Exothermic reactions release heat energy, while endothermic reactions absorb heat energy.

Examples:

Exothermic reaction: Burning of natural gas (CH4 + 2O2 → CO2 + 2H2O)

Endothermic reaction: Melting of ice (H2O(s) → H2O(l))

10Why is respiration considered an exothermic reaction? Explain.

Answer:

Respiration is considered an exothermic reaction because it releases energy in the form of heat during the breakdown of glucose molecules in the presence of oxygen.

11.Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.

Answer:

Decomposition reactions involve the breakdown of a single compound into two or more simpler substances. They are called the opposite of combination reactions because in combination reactions, two or more substances combine to form a single compound.

Equation for decomposition reaction:

Thermal decomposition of limestone: CaCO3(s) → CaO(s) + CO2(g)

12.Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.

Answer:

Equations for decomposition reactions with energy supplied in the form of heat, light, or electricity:

Heat: 2Pb(NO3)2(s) → 2PbO(s) + 4NO2(g) + O2(g)
Light: 2AgBr(s) + sunlight → 2Ag(s) + Br2(g)
Electricity: 2H2O(l) → 2H2(g) + O2(g) (during electrolysis)

13.What is the difference between displacement and double displacement reactions? Write equations for these reactions.

Answer:

Displacement reactions involve the replacement of one element in a compound by another more reactive element,

whereas double displacement reactions involve the exchange of ions between two compounds to form two new compounds.

Equations:

Displacement reaction: Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s)

Double displacement reaction: Na2SO4(aq) + BaCl2(aq) → BaSO4(s) + 2NaCl(aq)

14.In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved.

Answer:

Reaction: 2AgNO3(aq) + Cu(s) → 2Ag(s) + Cu(NO3)2(aq)

Explanation:Silver ions in the silver nitrate solution are displaced by copper metal, leading to the formation of silver metal and copper(II) nitrate solution. This reaction helps in the recovery of silver during the refining process.

15.What do you mean by a precipitation reaction? Explain by giving examples.

Answer:

Precipitation Reaction: A reaction in which an insoluble solid forms (precipitate) when two soluble compounds in aqueous solution are mixed.

Example: Mixing solutions of sodium sulfate (Na2SO4) and barium chloride (BaCl2) results in the formation of insoluble barium sulfate (BaSO4) precipitate according to the equation:

Na2SO4(aq) + BaCl2(aq) → BaSO4(s) + 2NaCl(aq) .

16.Explain the following in terms of gain or loss of oxygen with two examples each.

(a) Oxidation

(b) Reduction

Answer:

(a) Oxidation: It involves the gain of oxygen or the loss of hydrogen by a substance.

Example 1: 2Cu(s) + O2(g) → 2CuO(s)
Example 2: 2Mg(s) + O2(g) →2MgO(s)

(b) Reduction: It involves the loss of oxygen or the gain of hydrogen by a substance.

Example 1:CuO(s) + H2(g) →Cu(s) + H2O(l)
Example 2: Fe2O3(s) + 3CO(g) → 2Fe(s) + 3CO2(g)

17.A shiny brown coloured element ‘X’ on heating in air becomes black in colour. Name the element ‘X’ and the black coloured compound formed.

Answer:

Element X: Copper ( Cu )

Black Compound Formed: Copper(II) oxide ( CuO )

18.Why do we apply paint on iron articles?

Answer:

Reason: To prevent corrosion or rusting of iron articles.

Explanation: Paint forms a protective layer over the surface of iron, preventing it from coming into contact with moisture and oxygen in the air, which are the primary causes of corrosion.

19.Oil and fat containing food items are flushed with nitrogen. Why?

Answer:

Reason: To prevent rancidity.

Explanation: Nitrogen gas displaces oxygen from the packaging, creating an oxygen-free environment. This prevents oxidation of fats and oils, which leads to rancidity.

20.Explain the following terms with one example each.

(a) Corrosion

(b) Rancidity

Answer:

(a) Corrosion: The gradual degradation of metals due to chemical reactions with their environment.

Example: Rusting of iron ( 4Fe(s) + 3O2(g) →2Fe2O3(s) )

(b) Rancidity: The development of undesirable odors and flavors in fats and oils due to oxidation.

-Example: Rancid butter or oils in stored food.

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