NCERT Solution Science Class 10 Chapter 2 Acids, Bases and Salts
NCERT Solution Science Class 10 Chapter 2 Acids, Bases and Salts all questions and answers. Science Class 10 2nd Chapter Acids, Bases and Salts exercise solution and experts answer. As one of online learning platforms, we (netex.) are excited to offer the NCERT Solution Science Class 10 Chapter 2. This solution is designed to help students who are looking to brush up on their Science concepts on Chapter 2 Acids, Bases and Salts.
Page no: 18
1) You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution, respectively. If you are given only red litmus paper, how will you identify the contents of each test tube?
Ans 1- If the red litmus turns into blue, then it is a basic solution. If it remains as it is i.e no change in colour of red litmus, that indicates acidic solution. The slightly change in colour such as light purple, then it is a distilled water.
Page no: 22
1.) Why should curd and sour substances not be kept in brass and copper vessels?
Ans 1- Sour substances and curd(Lactic acid) contains acid. When it is kept in brass or copper metal then the acid content in the food reacts with metals and produce hydrogen gas with formation of harmful products and make them unfit for human body.
2.) Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the presence of this gas?
Ans 2- When acid reacts with metals, the hydrogen gas is liberated.
Eg: Take 5ml of dil. sulphuric acid in a test tube and add some zinc granules in it. Pass the gas being evolved through the soap solution. Formation of bubbles will takes place in the soap solution.
Test for gas: Take a burning candle near the mouth of the gas filled bubble. The pop sound will produce which indicates that it is a hydrogen gas.
3.) Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride.
Ans3- CaCO3(s) + 2HCl(aq) gives CaCl2(aq) + CO2(g) + H2O(l)
Page no: 25
1.) Why do HCl, HNO3 , etc., show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character?
Ans 1- When HCl and HNO3 are mixed in water they produce H+ ions in water which shows their acidic character.
i.e HCl -> H+ + Cl-
whereas glucose and alcohols do not dissociate into H+ ions. Hence, they do not show acidic character.
2.) Why does an aqueous solution of an acid conduct electricity?
Ans 2- The aqueous solution of an acid contains H+ ions or H3O+ ions which is responsible for the conduction of electricity.
3.) Why does dry HCl gas not change the colour of the dry litmus paper?
Ans 3- Dry HCl gas does not change the colour of litmus paper because it as no H+ ions present in it.
4.) While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?
Ans 4- The process of dissolving an acid to water is highly exothermic. If we add water to an acid, the mixture may splash out and cause burn due to excessive heat. Even the beaker can also break. Therefore, acid is added to water with constant stirring.
5.) How is the concentration of hydronium ions (H3O+ ) affected when a solution of an acid is diluted?
Ans 5- When acid is added to water, there is a fixed number of hydronium ions present in water per unit volume. On dilution, the number of hydronium ions get decrease and hence conc. of hydronium ions also decreases.
6.) How is the concentration of hydroxide ions (OH – ) affected when excess base is dissolved in a solution of sodium hydroxide
Ans 6- When excess base is dissolved in the solution of sodium hydroxide, the no. of hydroxide ions increases in the solution and thus concentration of hydroxide ions also increases.
Page 28:
1.) You have two solutions, A and B. The pH of solution A is 6 and pH of solution B is 8. Which solution has more hydrogen ion concentration? Which of this is acidic and which one is basic?
Ans 1- Solution A has more hydrogen ions as it is acidic in nature because its pH value is below 7.
Solution A is acidic because of pH value 6 i.e below 7 and solution B is basic in nature because its pH is more than 7 i.e 8.
2.) What effect does the concentration of H+ (aq) ions have on the nature of the solution?
Ans 2- Water contains same no. of hydrogen and hydroxyl ions. But the acid consists of more hydrogen ions( H+). More the hydrogen ions present in a solution, stronger is the acid.
Eg: HCl ( Hydrochloric acid) is a strong acid and CH3COOH (acetic acid) is a weak acid because of the difference in the concentration of hydrogen ions.
3.) Do basic solutions also have H+ (aq) ions? If yes, then why are these basic?
Ans 3- When a base is dissolved in water, it produces both H+ ions and OH- ions. But the concentration of hydroxyl ions is more than that of hydrogen ions. Therefore, it is basic in nature.
4.) Under what soil condition do you think a farmer would treat the soil of his fields with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate)?
Ans 4- Generally, the plants grows in normal pH i.e close to 7. If the soil is treated with quick lime and slaked lime that means the soil is highly acidic in nature i. e their pH is below 7. To maintain the pH of soil for better growth of plants we add base such as quick lime(CaO) or slaked lime( Ca(OH)2 ) and Calcium carbonate(CaCO3)
Page no- 33
1.) What is the common name of the compound CaOCl2 ?
Ans 1 – CaOCl2 is bleaching powder.
2.) Name the substance which on treatment with chlorine yields bleaching powder.
Ans 2- Slaked lime or Calcium hydroxide is a substance when treated with Chlorine gives bleaching powder.
3.) Name the sodium compound which is used for softening hard water.
Ans 3- Sodium carbonate or washing soda (Na2CO3. 10H2O) is used to remove hardness of water.
4.) What will happen if a solution of sodium hydrocarbonate is heated? Give the equation of the reaction involved.
Ans 4- When sodium bicarbonate is heated, it produce sodium carbonate , water and Carbon dioxide.
Reaction: 2NaHCO3 + Heat -> Na2CO3 + H2O + CO2
5.) Write an equation to show the reaction between Plaster of Paris and water
Ans 5- Reaction: CaSO4.1/2 H2O + 1^1/2 H2O 👉🏻 CaSO4. 2H2O
On reaction with water, gypsum is formed.
Exercise Questions
1.) A solution turns red litmus blue, its pH is likely to be
(a) 1 (b) 4 (c) 5 (d) 10 2.
Ans 1- d) 10
Reason: As red litmus turns into blue which indicates that the substance is basic in nature i.e pH value is between the 8 to 14. Therefore, option C.
2.) A solution reacts with crushed egg-shells to give a gas that turns lime-water milky. The solution contains
(a) NaCl (b) HCl (c) LiCl (d) KCl
Ans2- C) HCl
Reason- As egg shell contains CaCO3, when HCl reacts with CaCO3 it liberate Carbon dioxide gas which turns lime water milky.
CaCO3 + 2HCl → CaCl2 + H20 + CO2
3.) 10 mL of a solution of NaOH is found to be completely neutralized by 8 mL of a given solution of HCl. If we take 20 mL of the same solution of NaOH, the amount HCl solution (the same solution as before) required to neutralize it will be
(a) 4 mL (b) 8 mL (c) 12 mL (d) 16 mL
Ans3- d) 16ml
Reason: 10ml NaOH is neutralized by 8ml HCl
So, 20ml NaOH is neutralized by = 8×20/10 = 16ml
4.) Which one of the following types of medicines is used for treating indigestion?
(a) Antibiotic (b) Analgesic (c) Antacid (d) Antiseptic
Ans4- a) Antacid is a mild base given to a person who is suffering from acidity. Being base, it reacts with acid to form salt and water. The excess acid is neutralized and get relief easily.
5.) Write word equations and then balanced equations for the reaction taking place when –
(a) dilute sulphuric acid reacts with zinc granules.
(b) dilute hydrochloric acid reacts with magnesium ribbon.
(c) dilute sulphuric acid reacts with aluminium powder.
(d) dilute hydrochloric acid reacts with iron filings.
Ans 5- a) H2SO4(l) + Zn(s) gives ZnSO4(s) + H2(g)
b) 2HCl(l) + Mg(s) gives MgCl2(s) + H2(g)
c) 3H2SO4(l) +2 Al(s) gives Al2(SO4)3 (s) + 3H2 (g)
d) 2HCl(l) + Fe(s) gives FeCl2(s) + H2(g)
6.) Compounds such as alcohols and glucose also contain hydrogen but are not categorised as acids. Describe an Activity to prove it.
Ans 6- Fix two nails on the cork and set up into the 100 ml beaker. Connect the nail to 6v battery, a bulb and the switch. Now pour the aqueous solution of either glucose or alcohol in the beaker till the nail get dipped in it. Switch on the current. As bulb does not glow. This activity shows that they contains hydrogen but cannot conduct electricity.
Alternative Answer –
When metals are react with acids it produces hydrogen gas. Cation and anion oh H+ ion are present in acids in the form of Cl– in HCl,NO3– in HNO3,CH3COO– in CH3COOH,SO42- in H2SO4,H+ aqueous solution means it produce hydrogen ions and it is responsible for acidic properties. The aqueous solution which are gives H+ ions are called acids but alcohol and glucose are the substance which are not gives H+ ions, but these substance have hydrogen because of that glucose and alcohol type of compounds are not categorised as acids even they also have hydrogen.
Take a 100ml of beaker and fix the two nails on cork and connect the switch,a bulb and 6 volt battery to two terminals of the nails and add the hydrochloric acid, Sulphuric acid glucose and alcohol seperately and switch on the current and then notice that the bulb is glowing or not. If bulb is start to glowing it means the solution is acid,but we notice that when we add the solutions of glucose and alcohol seperately in the breaker the bulb is not glow. It means that electric charge does not flow, that means glucose and alcohol does not conduct any electric charge therefore glucose and alcohol are not to be considered as acids even they contain hydrogen.
7.) Why does distilled water not conduct electricity, whereas rain water does?
Ans 7- Distilled water does not conduct electricity because it is neither acidic nor basic in nature i.e it does not contains ions(pure form of water). To conduct electricity free ions are needed which is present in rain water and not in distilled water.
Alternative Answer –
If water contains ions and it contains the capacity of disolvese the salts then it conduct electricity. Here distilled water does not have the capacity to disolve salt and it does not contains ions whereas rainy water contains the power to disolve salts and it contains ions therefore distilled water not conduct electricity whereas rainy water does.
In case you are missed :- Previous Chapter Solution
8.) Why do acids not show acidic behaviour in the absence of water?
Ans8- The acidic behaviour of acids is determined by the presence of hydrogen ions. More the hydrogen ions release more acidic in nature is the acid. But it produce hydrogen ions only in the presence of water.
Alternative Answer –
Water has capacity to separate the charges and solvate that disolvese ions and other polar materials and it also has large dipole moment therefore we called also water as polar solvent. In this reason water separate the ions that are present in side the acid but in case of absence of water acids are not show acidic behaviour.
9) Five solutions A,B,C,D and E when tested with universal indicator showed pH as 4,1,11,7 and 9, respectively. Which solution is (a) neutral? (b) strongly alkaline? (c) strongly acidic? (d) weakly acidic? (e) weakly alkaline? Arrange the pH in increasing order of hydrogen-ion concentration.
Ans9- a) D as pH is 7
b) C pH is 11
c) B pH is 1
d) A pH is 4
e) E pH is 9
Increasing order- C< E< D< A<B
Alternative Answer –
The given five solutions are
A=4 B=1 C=11. D=7. E=9
When H+ ion concentration increases acidic nature is increases.
When H+ ion concentration decreases basic nature is increases.
B → pH= 1 → strongly acidic(c)
A → pH= 4 → weakly acidic(d)
D → pH= 7 → neutral(a)
E → pH= 9 → weakly alkaline(e)
C → pH= 11 → strongly alkaline(b)
10.) Equal lengths of magnesium ribbons are taken in test tubes A and B. Hydrochloric acid (HCl) is added to test tube A, while acetic acid (CH3COOH) is added to test tube B. Amount and concentration taken for both the acids are same. In which test tube will the fizzing occur more vigorously and why?
Ans 10- In test tube A fizzing occurs vigorously because of the facts that HCl is a strong acid. So it reacts fastly with Magnesium metal and displaces hydrogen atoms. Acetic acid being weak acid takes time to displace hydrogen atoms.
Test tube A reaction: 2HCl(l) + Mg(s) → MgCl2(s) + H2(g)
Alternative Answer –
A test tube which contains Hydrochloric acid (HCl) will be fizzing occur more vigorously that is test tube A. Because the hydrochloric acid is more stronger than the acetic acid and when Magnesium ribbons are react with HCl it produces hydrogen gas at fast speed due to occurence of fizzing.
11.) Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd? Explain your answer.
Ans 10- In test tube A fizzing occurs vigorously because of the facts that HCl is a strong acid. So it reacts fastly with Magnesium metal and displaces hydrogen atoms. Acetic acid being weak acid takes time to displace hydrogen atoms.
Test tube A reaction: 2HCl(l) + Mg(s) → MgCl2(s) + H2(g)
Alternative Answer –
In ph scale below 7 pH values are called acids. And fresh milk has pH value 6 therefore it is considered as acid. When milk coverded by bacterial action it becomes curd and after milk became curd
the acidity will be increases and the pH value becomes decreases. After milk converted to curd the lactose become lactic acid and it’s pH value is below 6 therefore when milk become curd then it’s pH value also change.
12.) A milkman adds a very small amount of baking soda to fresh milk. (a) Why does he shift the pH of the fresh milk from 6 to slightly alkaline? (b) Why does this milk take a long time to set as curd?
Ans12- i) Its pH is 6 i.e acidic in nature. So it get easily converted into curd in less time. To prevent the formation of curd, milkman add baking soda to shift its pH from acidic to basic.
ii) Due to alkaline nature of fresh milk( addition of baking soda), the milk takes longer time to set as a curd.
Alternative Answer –
(a) In a pH scale the values are below 7 are called acids. In this scale fresh milk is pointed in the place of 6.The milk become curd due to bacterial action in this process lactose become lactic acid and the pH value of milk when it become curd is below 6 that means it is more acidic, therefore the milkman add small amount of Baking soda in milk to prevent the process of milk becoming the curd.
(b) When milkman add small amount of Baking soda then it becomes sightly more alkaline then others and Baking soda prevent the process of milk becoming the curd and it’s acidity will be neutralized. because of that milk take a long time to set as curd.
13.) Plaster of Paris should be stored in a moisture-proof container. Explain why?
Ans13- It should be stored in moisture proof container because it get easily reacts with water molecule present in the moisture and converts into hard solid mass that is gypsum.
CaSO4.1/2 H20 + 1^1/2H20 →CASO4.2H2O
Alternative Answer –
When gypsum is heated about 373K then it realise it water molecules then it becomes plaster of Paris. The chemical name of the plaster of Paris is calcium Sulphate hemihydrate. If we please plaster of Paris in the contact of moisture or water again it becomes hard material called gypsum, that’s why it should be stored in moisture proof container. Normally it is used to make sculpture and supporting fractured bones in the right position. The chemical formula of plaster of Paris is CaSO4.½(H2O).
If plaster of Paris in contact of moisture or water then it become Gypsum
CaSO4.½(H2O)+ 1 ½( H2O) → CaSO4.2H2O
14.) What is a neutralization reaction? Give two examples.
Ans14- The reaction between acid and base to give a salt and water is called neutralization reaction.
Equation: Acid + Base gives Salt + Water
Examples:
1) H2SO4+ 2NaOH → Na2SO4 + 2H2O
2) HCl + KOH → KCl + H2O
Alternative Answer –
An chemical reaction which gives salt and water from the reaction between acid and base is called neutralisation reaction.
The general syntax for the neutralisation reaction is
Base + Acid → salt + water
Ex:
1] NaOH (aq) + HCl (aq) → NaCl (aq) + H2O (l)
2] Mg(OH)2 (aq) + 2HCl (aq) → MgCl2 (aq) + 2H2O(l)
15.) Give two important uses of washing soda and baking soda.
Ans 15- • Uses of washing soda
i) It is used for removing permanent hardness of water.
ii) It is used as cleaning agent for domestic purpose.
Uses of Baking soda
i) It is used as a soda – acid fire extinguishers.
ii) It is an ingredient in antacid, due to its alkaline nature.
Alternative Answer –
Washing soda
- Normally it can be used in the form of washing powder to cleaning.
- It is used as manufacturing of paints.
Baking soda
- To make breads, cakes and other baking foods.
- To treat the health and skin problems.
In case you are missed :- Next Chapter Solution
Other chapter solution link