NCERT Class 10 Science First Chapter Chemical Reactions and Equations Solution
NCERT Class 10 Science Chapter 1 Solution: Dear students Here in this post we are posted First Chapter Chemical Reactions and Equations full exercise questions & answer by our Science teacher. This Solution is helpful for CBSE English medium students. Download this 1st Chapter Science solution & prepare your homework.
Questions (Text book page no:6)
1) Why should a magnesium ribbon be cleaned before burning in air?
Ans: Magnesium get oxidised when kept in air for long time and forms a layer of magnesium oxide on it. This layer does not allow magnesium to burn properly. Hence it is to be cleaned before burning in air.
2.) Write the balanced equation for the following chemical reactions.
(i) Hydrogen + Chlorine → Hydrogen chloride
H2 + Cl2 —> 2HCl
(ii) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride
3BaCl2+ Al2(SO4)3 —> 3BaSO4 (↓) + 2AlCl3
(iii) Sodium + Water → Sodium hydroxide + Hydrogen
2Na+ 2H2 —> 2NaOH+ H2 (↑)
(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.
BaCl2 (aq) + NaSO4 (aq) —> BaSO4 (↓) + 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)
Questions (Text book page no:10)
1.) A solution of a substance ‘X’ is used for whitewashing
(i) Name the substance ‘X’ and write its formula.
Ans: Calcium oxide is a substance used for white washing. It is also known as Quick lime. Its formula is CaO.
(ii) Write the reaction of the substance ‘X’ named in (i) above with water.
Ans: CaO (l) + H2O —> Ca(OH)2 (aq)
(Calcium oxide) (Calcium hydroxide)
(Calcium hydroxide is known as slaked lime)
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.
Ans: In Activity 1.7, water is electrolysed to give hydrogen gas at cathode and oxygen gas at anode.
The reaction is as follows:
2 H2O (l) —> 2 H2(g) + O2 (g)
Thus, two molecules of water on electrolysis gives two molecule of hydrogen gas and one molecule of oxygen gas. So, we can say that the amount of gas collected in one test tube is the double of the amount collected in the other.
Questions (Text book page no:13)
1.) Why does the colour of copper sulphate solution changes when an iron nail is dipped in it ?
Ans: As compared to copper, the iron has more reactivity and present in upper part or above the copper. Therefore the iron called as more reactive metal, it’ll displace the copper which is less reactive metal, so the colour of copper sulphate solution changes when an iron nail is dipped in it.
2.) Give an example of double displacement reaction other than the one given in activity 1.10.
Ans: Double displacement reaction can be defined as when there is presence of two reactants, these two reactants will share the ions between them and leads to formation of new product. The example can be taken as when there is reaction between two substrates such as lead nitrate and potassium iodide. The resultant product will potassium nitrate with yellow precipitate formation due to lead iodide.
Pb(NO3)2 (aq) + KI (aq) —> PbI2 (s) + KNO3 (aq)
3.) Identify the substances that are oxidized 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)
Ans :
(i) In the first reaction Na will get oxidized and O2 will be reduced substance.
(ii) In the second reaction, H2 is oxidizing and copper will be oxidizing substance.
EXERCISES
(Q1) Which of the statements about the reaction below are incorrect?
2PbO (s) + C (s) → 2Pb (s) + Co2 (g)
Ans: (i) (a) & (b).
Reason: Carbon is oxidised by formation of Co2 & PbO is reduced by formation of Pb.
(Q2) Fe2 O3+2Al → Al2O3+2Fe
The above reaction is an example of
Answer: (d) Displacement reaction.
Reason: Al displaces Fe, due to higher reactivity of Fe.
(Q3) What happens when dilute hydro chloric acid is added to iron fillings? Tick the correct answer.
Answer: (a) Hydrogen gas & iron chloride are produced
Reason: Fe(s) + dil HCL → FeCl2 + H2 (g) ↑
Or
Fe (s) + 2HCL → FeCl2 + H2 (g) ↑
(Q4) What is balanced chemical equation? Why should chemical equations be balanced?
Answer: The total number of atoms of each element is the same on both sides of the arrow is called as balanced chemical equation.
– The chemical equations should be balanced because, according to the law of conservation of mass, mass neither be created not destroyed in a chemical reaction.
– Hence, the total mass of reactant & product in the reaction is same.
– Thus the number of atoms of each elements remains same, before & after a chemical reaction.
Alternative Answer –
When we write the chemical equation,we must notice that the amount of atom of each element that are present in left hand side or before chemical reaction is equal to amount of atoms that are present in right hand side or after chemical reaction then it is known as balanced chemical equation.
Because when we practically do the chemical reaction,we notice that the amount of atom of substance before the chemical reaction is same as the amount of atom of substance after the chemical reaction that means there will be no change in the amount of atom of substance because of that chemical equation should be balanced.
(Q5) Translate the following statements into the chemical equations & then balance them.
(a) Hydrogen gas combine with nitrogen to form ammonia.
Ans: H2 (g) + N2 (g) → NH3 (g)
Balanced chemical equations
3H2 (g) + N2 (g) → 2 NH3 (g)
(b) Hydrogen Sulphide gas burns in air to give water & sulfur dioxide.
Ans: H2 S (g) + O2 (g) → 2H2O (l) + SO2 (g)
Balanced chemical equation
2H2 S (g) + 3O2 (g) → 2H2O (l) + 2So2 (g)
(c) Barium chloride reacts with aluminum sulphate to give aluminum chloride & a precipitate of barium sulphate.
Ans: BaCl2 + Al2 (SO4)3 → 2AlCl3 + 3BaSO4
Balanced chemical equation
3BaCl2 + Al2 (So4)3 → 2AlCl3 + BaSo4
(d) Potassium metal reacts with water to give potassium & hydrogen gas.
Ans: K (s) + H2 O (l) → KoH + H2 (g)
Balanced chemical equation:
2K (s) + 2H2O (l) → 2KoH + H2 (g)
Alternative Answer –
(a) 3H2(g)+N2(s) → 2 NH3(g)
(b) 2H2S(g)+3O2(g) ⟶ 2H2O(l)+2SO2
(c) 3BaCl2+Al2(SO4)3 → 2AlCl3 + 3BaSO4
(d) 2K(s)+2H2O(l) → 2KOH(aq)+H2(g)
(Q6) Balance the following chemical equations:
(a) HNo3 + Ca(OH)2 → Ca(No3)2 + H2o
Ans: 2HNo3 + Ca(OH)2 → Ca(NO3)2 + 2H2O
(b) NaoH + H2SO4 → Na2SO4 + H2O
Ans: 2NaOH + H2SO4 → Na2SO4 + 2H2O
(c) Nacl + AgNo3 → Agcl + NaNo3
Ans: Nacl + AgNo3 → Agcl + NaNo3
Already balanced chemical reaction
(d) Bacl2 + H2So4 → BaSo4 + HCL
Ans: Bacl2 + H2So4 → BaSo4 + 2HCL
Alternative Answer –
(a) 2HNO3+Ca(OH)2 → Ca(NO3)2+2H2O
(b) 2NaOH+H2SO4 → Na2SO4+2H2O
(c ) NaCl+AgNO3 → AgCl+NaNO3
(d) BaCl2+H2SO4 → BaSO4+2HCl
(Q7) Write the balanced chemical equations for the following reactions.
(a) Calcium hydroxide + carbon dioxide → Calcium carbonate + water
Ans: Ca (OH)2 + Co2 → CaCo3 + H2O
(b) Zinc + Silver nitrate → Zinc nitrate + silver
Ans: Zn + 2 AgNo3 → Zn (NO3)2 + 2Ag
(c) Aluminum + Copper chloride → Aluminium chloride + copper
Ans: 2Al + 3CuCl2 → 2AlCl3 + 3Cu
(d) Barium chloride + potassium sulphate → Barium sulphate + potassium chloride
Ans: BaCl2 + K2So4 → BaSo4 + 2KCL
Alternative Answer –
(a) Ca(OH)2+CO2→CaCO3+H2O
(b) Zn+ 2AgNO3 → Zn(NO3)2+2Ag
(c ) 2Al+3CuCl2 → 2AlCl3+3Cu
(d) BaCl2+K2SO4 → BaSO4+2KCl
(Q8) Write the balanced chemical equation for the following & identify the type of reaction in each case.
(a) Potassium bromide (aq) + barium iodide (aq) → Potassium iodide (aq) + Barium bromide (s)
Answer: 2KBr (aq) + BaI2 (aq) → 2KI (aq) + BaBr2 (Aq)
- This reaction is double displacement type
(b) Zinc Carbonate (s) → Zinc oxide (s) + carbon dioxide (g)
Answer: ZnCo3 → Zno + Co2
- This reaction is decomposition type
(c) Hydrogen + chlorine (g) → Hydrogen chloride (g)
Ans: H2 (g) + Cl2 (g) → 2HCL (g)
- This reaction is combination type.
(d) Magnesium (s) + hydrochloric acid (aq) → Magnesium chloride (aq) + hydrogen (g)
Ans: Mg (s) + 2HCL (aq) → Mg Cl2 (aq) + H2 (g)
This reaction is displacement type.
Alternative Answer –
(a) 2KBr(aq)+Bal2(aq) → 2KI(aq)+ BaBr2(s)
Double displacement reaction.
(b) ZnCO3(s) → ZnO(s)+CO2(g)
Decomposition reaction.
(c ) H2(g)+Cl2(g) → 2HCl(g)
Combination reaction.
(d) Mg(s)+ 2HCl(aq) → MgCl2(aq)+ H2(g)
Displacement reaction.
(Q9) What does one mean by exothermic & endothermic reactions? Give examples.
Ans: Exothermic reactions:
The reactions in which heat is released along with formation of product is called as exothermic reaction.
Ex:- (1) Burning of natural gas
CH4 (g) + 2O2 (g) → Co2 (g) + 2H2O (g)
(2) Reaction between hydrochloric acid & sodium hydroxide produce sodium chloride & water.
HCL + NaOH → NaCl + H2O + heat
Endothermic reaction:
The reactions in which energy is absorbed in the form of heat or sunlight is called as endothermic reaction
Ex: In photosynthesis process, plants converts carbon dioxide & water into glucose & oxygen in presence of sunlight.
6Co2 (g) + 6H2O (l) sunlight> C6H12O6 + 6O2 (g) + Glucose
Alternative Answer –
In an chemical reaction, we got finally energy or after reaction we get energy then it is known ans exothermic reaction.
CH4(g)+2O2(g) → CO2(g)+2H2O(g)+energy
In an chemical reaction we lost the energy which is already present in initial state of the chemical reaction then it is known as endothermic reaction.
2AgBr(s) → sunlight →2Ag(s)+Br2(g)
In case you are missed :- NCERT Solution for Acids, Bases and Salts
(Q10) Why is respiration considered an exothermic reaction? Explain
Ans: Energy in our body is obtained from food that we cat. During digestion the complex substances are broken down into simple substances like glucose.
In respiration process this glucose combines with oxygen in the cells & it release energy. This released energy is used for various functions of our body.
In the respiration process energy is released, Hence it is considered as exothermic reaction.
Ex: C6H12O6 + 6O2 (g) → 6 Co2 (g) + 6H2O (l)
Glucose Oxygen Carbon dioxide + Energy
Alternative Answer –
We know that exothermic process means an chemical reaction which gives energy at last where as respiration is the process in which food is undergo digest and provide the energy for body at last there for respiration is considered as exothermic reaction.
C6H12O6(aq) + 6O2(aq) → 6CO2(aq) + 6H2O(l) + energy
Above chemical reaction shows how energy created in our body, Normally we consume the food lik vegetables and rice,when these types of food enter our stomach and digest ,then it gives glucose from the carbohydrates and glucose with the contract of oxygen will form energy in our body.
(Q11) Why are decomposition reactions called the opposite of combination reaction? Write equations for these reactions
Ans: Decomposition reactions are those reactions in which a single substance break into two or more than two products.
– These reactions are endothermic reactions it requires energy. It absorbs energy in the form of heat.
- Whereas, its exact opposite combination reactions. Combination reactions are those in which two or more substances combine to form a single product. These reactions are exothermic energy is released.
Example:
* Decomposition reactions:
Alternative Answer –
Any one product when it is contact of heat or any other,and break down to two or more than two products then it known an decomposition reaction. Where as when two or more than two chemical products or many combinations of chemical products are react and give only one product then it is known as combination reaction.
Here above two definition shows that Decomposition reactions is opposite of Combination reactions.
For example:
Decomposition reaction:
CaCO3(s) → Heat→ CaO(s) + CO2(g)
Combination reaction:
C(s)+O2(g)→CO2(g)
(Q12) Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.
Ans: Decomposition reactions requires energy in the form of heat known as thermal decomposition, light known as photolysis & electricity known as electrolysis.
The examples of these reactions are as follows
Alternative Answer –
(a) 2FeSO4(s) → Heat → FeO3(s)+ SO2(g)+SO3(g)
(b) 2AgCl(s) → Sunlight → 2Ag(s)+Cl2(g)
Q13) What is the difference between displacement & double displacement reaction? Write equations for these reactions.
Displacement reaction |
Double displacement reaction |
(1) In these reactions the ions of more active elements displaces the ions of less active element. |
(1) In these reactions, both the reactants exchanges their ions between them. |
(2) During displacement reactions change in color takes place. |
(2) During double displacement reaction precipitation is formed |
(3) These reactions are usually slow and require more time for complete the reaction. |
(3) These reactions are usually fast & require very less time.
|
Ex: – Zn (s) + Cuso4 (Aq) → ZnSo4 (Aq) + Cu(s) In this reaction Zinc is more reactive than Cu. Hence it displace copper from its compound . |
Ex: Na2 So4 (Aq) + Bacl2 (Aq) (Sodium sulphate) ↓ (Barium chloride) BaSo4 (s) + 2 NaCl (Barium sulphate (Sodium chloride) In this reaction sodium sulphate & barium chloride exchange their ions by the formation of barium sulphate (ppt) & sodium chloride. |
Alternative Answer –
Displacement reaction |
Double displacement reaction |
An chemical equation in which one is solid and another one is aqueous solution after the chemical reaction solid compound will be displaced from aqueous solution then it is known as displacement reaction. | An chemical reaction in which after the chemical reaction the aqueous solutions are exchange there ions and gives solid compound with an aqueous solution then it is known as double displacement reaction. |
Zn(s)+CuSO4(aq) → ZnSO4(aq)+Cu(s) ( Copper sulphate). (Zinc sulphate) | Na2SO4(aq)+BaCl2(aq)→BaSO4(s)+2NaCl(aq) |
(Q14) In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved.
Ans: The reaction involved is as follows
Cu (s) + 2 AgNo3 (Aq) → Cu (No3)2 + 2 Ag (s)
Copper Silver nitrate copper nitrate Silver
Alternative Answer –
2AgNO3(aq)+Cu(s)→Cu(NO3)2(aq)+2Ag(s)
This is an Displacement reaction.
(Q15) What do you mean by a precipitation reaction is called as precipitation reaction.
Ans: The reaction in which precipitate is produced is called as precipitation reaction.
Example: Double displacement reactions are precipitation reactions.
When Sodium Sulphate reacts with barium chloride it produce white precipitate of barium sulphate along with sodium chloride.
Na2So4 (Aq) + Bacl2 (Aq) → BaSo4 (s) + 2Nacl (Aq)
(Sodium sulphate) (Barium chloride) (Barium sulphate) sodium chloride
↓
White ppt
Alternative Answer –
In an chemical reaction,if we get a white substance which is insoluble in water then it is known as white precipitate.Any chemical reaction process which involves white precipitate is known as precipitation reaction.
Na2SO4(aq)+BaCl2(aq) → BaSO4(s)+2NaCl(aq)
When Barium chloride aqueous solutions is added to sodium sulphate, after chemical reaction it gives Barium sulphate and sodium chloride.In this process there is a white precipitate of Barium sulphate will be formed, therefore it is clear that it is an precipitation reaction.
(16) Explain the following in terms of gain or loss of oxygen with two examples each.
Ans:
Oxidation:
If a substance gains oxygen during a reaction, such reactions are known as oxidation reaction.
Example:
In example Cu (Copper) gains oxygen & convert it into copper oxide
Reduction:
If a substance loses a oxygen during a reaction, such reactions are known as reduction reaction.
Example:
In above reaction Cuo is converted into Cu with the removal of oxygen in the form of water.
Alternative Answer –
a) Oxidation:
In the process of chemical reaction if chemical substance gains oxygen after the chemical reaction then the process is known as oxidation.
2Cu + O2 →heat→ 2CuO
The above chemical equation shows that when copper powder react with oxygen in the presence of heat it gives copper(II) oxide in this process we clearly notice that the product copper(II) oxide is gains the oxygen after the chemical reaction,then this process is clearly an oxidation reaction.
CuO +H2 →heat→Cu+H2O
The above chemical reaction shows that when CuO react whith hydrogen in presence of heat it gives copper and water in this case after the chemical reaction hydrogen gains the oxygen and became water, there for it is also an oxidation reaction.
b) Reduction:
In the process of chemical reaction if chemical substance loses oxygen after the chemical reaction then the process is known as Reduction.
CuO+H2 → heat → Cu+H2O
The above chemical reaction shows that when copper oxide is heated with hydrogen then it gives copper and water in this process after reaction the compound CuO loses its oxygen and became copper with water.
ZnO+C → Zn+CO
The above chemical reaction shows that when zinc oxide is react with carbon then it gives zinc and carbon monoxide,in this case after chemical reaction zinc oxide is loses oxygen and became zinc therefore it is an Reduction process.
(Q17) A shiny brown coloured element ‘x’ on heating in air becomes black in colour. Name the element ‘x’ & the black coloured compound formed.
In above reaction a shiny brown coloured element ‘X’ is Cu (Copper) & the black coloured compound is Cuo (Copper Oxide)
Alternative Answer –
The shiny brown colored element is copper and when we heat copper in air it becomes black coloured,and the black coloured compound is copper oxide.
2Cu(s)+O2(g) → heat → 2CuO(s)
(Q18) Why do we apply paint on iron articles?
Ans: We apply paint on iron articles to prevent corrosion of iron. Due to various components of atmosphere like moisture, oxygen, the oxidation of iron takes place which results oxidation of iron takes place which results iron rusts that is known as corrosion. Corrosion damages the iron articles.
If we apply paint on iron articles iron does not comes in direct contact with moisture & oxygen. Hence corrosion does not occurs.
Alternative Answer –
Iron particles are rusted with time, after this process iron will loose it’s strength.To pause this process we paint on the iron articles because doing from this they do not loose their strength.
(Q19) Oil & fats containing food items are flushed with nitrogen why?
Ans: Oil & fats containing food items are flushed with nitrogen because, oil & fats are easily oxidised. They becomes food rancid, their smell & taste changes.
Nitrogen is antioxidant, it prevents the food from getting oxidise, as a result which rancidity does not takes place & food remains safe.
Alternative Answer –
When we keep the food openly in air for a long time,then the food become rancid and food change its taste and smell. Therefore we add fat and oil in food because it prevents oxidation process. And nitrogen also makes slow down the process of oxidation,thats why the oil and fat containing food items are flushed with nitrogen.
(Q20) Explain the following terms with one example each.
(a) Corrosion
(b) Rancidity
Ans: (a) Corrosion: When the surface of metal comes in contact with air, acid moisture, the metal get corrodes this process is known as corrosion.
Example:
Ag + H2S + O2 → Ag2S + H2 O
Silver (Black colour)
When silver react with H2S & O2 from atmosphere it corrodes silver (Ag) & forms black colour coating on them.
(b) Rancidity: The process of slow oxidation of oil & fats present in the food resulting in changes of smell & taste is known as rancidity.
Example: When potato chips containing fats & oils are exposed for considerable time to a moisture, it starts giving unpleasant taste & odour.
Alternative Answer –
- Corrosion:
Normally we observed when iron articles are new it looks shiny,but after sometimes later we notice that reddish-brown coloured powder is on the iron articles same process is happens for other metals also. The reaction in which metal is react with moisture and acids that are present in air or surrounded by the metal is called corrod and such process is called corrosion.
Corrosion is a serious problem which couses serious damages to ships cars and buses and all matalic mades.And every year lots of money is spent for correct the problem that are cousing from corrosion.
Ex: if black particles are coted on the silver,it means that the silver is covered by the corrosion process.
- Rancidity:
When fat and oil foods are covered by the process oxidation it changes it smell and taste. If any food contaning the quantity of fat and oil then the fat and oil prevents the process of oxidation. And nitrogen is the gas which contains the power to slow down the the process of oxidation in this reason we flushed the oil and fat containing food items with nitrogen.
Ex:Nitrogen gas is filled in the bags of chips because nitrogen gas is helpful in preventing the oxidation process of the chips.
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