NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts

These NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts Questions and Answers are prepared by our highly skilled subject experts to help students while preparing for their exams.

Acids, Bases and Salts NCERT Solutions for Class 10 Science Chapter 2

Class 10 Science Chapter 2 Acids, Bases and Salts InText Questions and Answers

In-text Questions (Page 18)

Question 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?
Answer:
We dip the red litmus paper in any one of the three test tubes. If there is no change in the colour of the litmus paper, it means this test tube contains water or acidic solution.

If the colour of the red litmus paper turns blue, it means this test tube contains basic solution.

Now, again we dip this litmus paper in any one of the remaining two test tubes. If we do not observe any change in the colour of the litmus paper it is surely water and if a colour change is noticed, then it will be an acidic solution.

In-text Questions (Page 22)

Question 1.
Why should curd and sour substances not be kept in brass and copper vessels?
Answer:
Brass is an alloy of copper and zinc, Brass and copper vessels reacts with atmospheric oxygen and to form metal oxides. The nature of metal oxides is basic. Curd and sour substances contains acids, e.g., curd contains lactic acid and orange contains citric acid. If we keep curd and sour substances in brass and copper vessels the layer of oxides present on the surface of brass and copper reacts with the acids present in curd and sour substances to form salt and water and taste of sour substances chages from sour to bitter. So curd and sour substance are not be kept in brass and copper vessels.

Question 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?
Answer:
Hydrogen has is usually liberated when an acid reacts with a metal.
e.g.
NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts 1
This gas buns with a pop sound when a burning candle is placed near the evolved gas.

Question 3.
A 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.
Answer:
Metal compound ‘A’ is CaCO3
NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts 2

NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts

In-text Questions (Page 25)

Question 1.
Why do HCl, HNO3, etc show acidic character in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character?
Answer:
A substance is said to be an acid, when it produces H+ ions in its aqueous solution and turns blue litmus paper into red. HCl, HNO3, etc. ionise in their aqueous solutions and produce H+ ions. They turn the colour of blue litmus paper into red. When electric current is passed through the aqueous solutions of acids, the H+ ions reach the cathode and form hydrogen. But in their aqueous solutions alcohol and glucose do not produce H+ ions and they do turn blue litmus into red. So they do not show acidic character in their aqueous solution.

Question 2.
Why does an aqueous solution of an add conduct electricity?
Answer:
Acids are ionised in their aqueous solution and produce H+ (aq) ions. These ions are responsible for the flow of electricity in the aqueous solutions of acids. H+ ions migrates towards cathode and gain electron to produce hydrogen gas. So when electricity is passed through the aqueous solution of an acid, hydrogen gas is liberated at cathode.

So an aqueous solution of an acid conducts electricity because it contains H+ (aq) ions or hydronium ions.

Question 3.
Why does dry HCl gas not change the colour of the dry litmus paper?
Answer:
The separation of H+ ion from HCl molecules cannot occur in the absence of water. In fact H+ ion is an atom that has lost an eletron, it is simply isolated proton and is smallest positive ion. It is attracted very strongly towards electrons of anything. So the separation of H+ ion from HCl molecules cannot occur and the reaction.
H – Cl(g) H+ → + Cl

cannot occur in the absence of water, because highly concentrated positive charge of TP would join back with the Cl ion to get back electron and reform covalent ‘H – Cl‘ molecules. It means dry HCl does not contain H+ ions so it does not change the colour of the dry litmus paper.

Question 4.
While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid ?
Answer:
The process of dissolving an add or a base in water is a highly exothermic process. Be careful while mixing concentrated sulphuric acid with water During dilution of an acid, the acid must always be added slowly to water with constant stirring. It water is added to a concentrated acid the heat generated may cause the mixture lo splash out from the container and cause bums. The glass container may also break due to heal release during dilution. So it is recommended that the acid should be added to water and not water to the acid.

Question 5.
How is the concentration of hydronium ions (H3O)+ affected when a solution of an acid is diluted?
Answer:
An aqueous solution of an acid contains the specific number of H3O+ ions per unit volume. These H3O+ ions are responsible for the acidic character of an acid. When water is added in an acid it results in decrease in inconcentration of H3O+ ions per unit volume of the acid because the specified volume of an acid contains the definite no. of H3O+ ions, when its volume increases by addition of water, the no. of H3O+ ions decreases per unit volume of the acid. So we can say that on dilution the concentration of H3O+ ions decreases per unit volume of the acid.

Question 6.
How is the concentration of hydroxide ions (OH) affected when excess base is dissolved in a solution of sodium hydroxide?
Answer:
A solution of sodium hydroxide contain Na+ and OH ions. When a base is dissolved in a solution of sodium hydroxide, it results in increase of concentration of OH ions per unit volume because added base is ionised and produce a large no. of hydroxide ions (OH) in the solution of sodium hydroxide.

NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts

In-text Questions (Page 28)

Question 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?
Answer:
The hydrogen ion concentration of a solution is calculated by the formula :
[H+] = 10-pH
∴ The conc. of H+ ions in solution ‘A’ = 10-6
and the conc, of H+ ions in solution ‘B’ = 10-8
So solution ‘A’ has more hydrogen ion concentration than ‘B’.
Solution A’ is acidic and solution ‘B’ is basic.

Question 2.
What effect does the concentration of H+(aq) ions have on the nature of the solution?
Answer:
On the basis of concentration of H+ (aq) ions in a solution we can justify the nature of the solution i.e., whether it is acidic, basic or neutral. A solution which has the concentration of H+ (aq) ion equal to 10-7 mole/litre will be neutral and if the concentration is slightly less than 10-7 then it will be basic and if the cone, of H+ (aq) ions in a solution is slightly higher than 10-7 then it will be acidic.

Question 3.
Do basic solutions also have H+(aq) ions? If yes, then why are these basic?
Answer:
Yes, basic solutions also have H+ (aq) ions and similarly acidic solutions have OH (aq). because acids or bases shows acidic or basic character in water. Distilled water also has 10-7 mol/L, H+ and 10-7 mole/L, OH ions at 298K.

If an aqueous solution has an equal concentration of hydrogen ions and hydroxide ions in it, it is said to be neutral. Now, if an aqueous solution has more of hydrogen ions and less of hydroxide ions, it will be acidic solution. On the other hand, if an aqueous solution has more of hydroxide ions and less of hydrogen ions it will be basic in nature.

Question 4.
Under what soil condition do you think a fanner would treat the soil of his fields with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate)?
Answer:
If the soil has acidic nature, then famer would treat the soil of his fields with quick lime or slaked lime or chalk to maintain its pH near about neutral.

In-text Questions (Page 33)

Question 1.
What is the common name of the compound CaOCl2?
Answer:
Bleaching powder.

Question 2.
Name the substance which cm treatment with chlorine yields bleaching powder,
Answer:
Dry slaked lime : Ca(OH)2
Chlorine : Cl2

Question 3.
Name the sodium compound which is used for softening hard water.
Answer:
Washing soda : Sodium carbonate (Na2CO3)

NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts

Question 4.
What will happen if a solution of sodium hydrocarbonate is heated? Give the equation of the reaction involved.
Answer:
On heating sodium hydrocarbonate, it produces sodium carbonate, carbondioxide and water.
NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts 3

Question 5.
Write an equation to show the reaction between Plaster of Paris and water,
Answer:
NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts 4

Class 10 Science Chapter 2 Acids, Bases and Salts Textbook Questions and Answers

Page No. 34

Question 1.
A solution turns red litmus blue, its pH is likely to be:
(a) 1
(b) 4
(c) 5
(d) 10
Answer:
(d) 10

Question 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
Answer:
(b) HCl

Question 3.
10 mL of a solution of NaOH is found to be completely neutralised by 8 mL of a given solution of HCl. If we take 20 mL of the same solution of NaOH, the amount of HCl solution (the same solution as before) required to neutralise it will be:
(a) 4 mL
(b) 8 mL
(c) 12 mL
(d) 16 mL
Answer:
(d) 16 mL

Question 4.
Which one of the following types of medicines is used for treating indigestion ?
(a) Antibiotic
(b) Analgesic
(c) Antarid
(d) Antiseptic
Answer:
(c) Antacid.

Question 5.
Write word equations and then balanced equations for the reactions taking place when:
(a) dilute sulphuric add 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 fillings.
Answer:
(a) Dilute sulphuric acid reacts with zinc granules to form zinc sulphate and hydrogen.
Sulphuric acid + Zinc → Zinc Sulphate + Hydrogen
H2SO4 + Zn → ZnSO4 + H2

Step I.

Element No. of atoms in Reactants No. of atoms in Products
H 2 2
S 1 1
O 4 4
Zn 1 1

The above equation is a balanced equation because it contains the equal no. of atoms of different elements in reactants to the no. of atoms of different elements in products.

(b) Hydrochloric add + Magnesium → Magnesium chloride + Hydrogen
HCl + Mg → MgCl2 + H2
Step I.

Element No. of atoms in Reactants No. of atoms in Products
H 1 2
Cl 1 2
Mg 1 1

Step II. Balance hydrogen and chlorine by multiplying ‘HCl’ with ‘2′ we get
2 HCl + Mg → MgCl2 = H2

(c) Sulphuric acid + Aluminium → Aluminium sulphate + Hydrogen
H2SO4 + Al → Al2(SO4)3 + H2
Step I.

Element No. of atoms in Reactants No. of atoms in Products
H 2 2
S 1 3
O 4 12
Al 1 2

Step II. Balance oxygen by multiplying ‘H2SO4‘ with ‘3’ we get:
3H2SO4 + Al → Al2(SO4)3 + H2
Step III. Balance aluminium by multiplying ‘Al’ in reactants side with ‘2’ we get;
3H2SO4 + 2Al → Al2(SO4)3 + H2
Step IV. Balance hydrogen by multiplying ‘H2‘ in product side with ‘3’ we get:
3H2SO4 + 2Al → Al2(SO4)3 + 3H2
This is a balance equation.

(d) Hydrochloric acid + Iron → Iron (III) chloride + Hydrogen
HCl + Fe → FeCl3 + H2
Step I.

Element No. of atoms in Reactants No. of atoms in Products
H 1 2
Cl 1 3
Fe 1 1

Step II. Balance chlorine by multiplying ‘FeCl3‘ with ‘2’ and ‘HCl’ with ‘6’ we get:
6HCl + Fe → 2FeCl3 + H2
Step III. Balance hydrogen and iron by multiplying ‘Fe’ with ‘2’ and ‘H2‘ with ‘3’ we get:
6HCl + 2Fe → 2FeCl3 + 3H2
This is a balance equation.

NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts

Question 6.
Compounds such as alcohols and glucose also contain hydrogen but are not categorised as adds. Describe an activity to prove it.
Answer:
A substance is said to be an acid when it can produce H+ ions in its aqueous solution and turns blue litmus paper to red.

HCl, HNO3 etc. are ionized in their aqueous solution and furnished H+ ions. When electricity is passed through aqueous solutions of acids, hydrogen liberates at cathode.

Compounds such as alcohols and glucose contain hydrogen but they do not ionise in their aqueous solution and not produce H+ ions, and they do not turn blue litmus to red so they are not categorised as acids.

Activity: Take four test tubes namely, A, B, C and D. Add ethyl alcohol (alcohol) aq. solution of glucose ; hydrochloric acid and nitric acid, 2 mL of each in test tube A, B, C and D respectively. Now add 1-2 drops of blue litmus solution in each test tube. We observe that the colour of test tube ‘A’ and ‘B’ remain unchanged however the colour of test tube and ‘C’ and ‘D’ turns red. If proves that alcohol and glucose are not categorised as acid.

Question 7.
Why does distilled water not conduct electricity, whereas rainwater does ?
Answer:
Distilled water does not contain ions (H+ or OH) or it contains a very poor concentration of H+ or OH ions ≈ 1 × 10-7 moles per litre. So it does not conduct electricity, whereas rainwater has some acidic character due to the presence of acids such as H2SO4, HNO3 etc. So rainwater has a sufficient amount or concentration of H+ ions, so it conducts electricity.

Question 8.
Why do acids not show acidic behaviour in the absence of water ?
Answer:
A substance is said to be an acid when it can furnish H+ ions in its aqueous solution. The separation of H+ ions from the molecules of an acid cannot occur in the absence of water. The molecule of water are polar in nature, so the negative pole of ‘H2O’ molecule pull the H+ ions from acids towards itself and separate them from acids e.g,
HCl + H2O → H3O+ + Cl. Hydrogen ions cannot exist alone, but they exist after combining with water molecules. Thus hydrogen ions must always be shown as H+ (aq) of hydronium ion (H3O+).

In absence of water ‘H+‘ are does not furnish by an acid so it does not show acidic behaviour.

Question 9.
Five solutions A, B, C, D and E when tested with universal indicater 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.
Answer:
(a) Solution ‘D’ is neutral because it has pH 7.
(b) Solution ‘C’ is strongly alkaline because it has pH 11.
(c) Solution ‘B’ is strongly acidic because it has pH 1.
(d) Solution ‘A’ is weakly acidic because it has pH 4.
(e) Solution ‘E’ is weakly alkalin because it has pH 9.

Hydrogen ion concentration is inversely proportional to the pH of the solution. It means, higher the ‘pH’ lower will be the hydrogen ion concentration.

The ‘pH’ of the given solution can be arranged m increasing order of hydrogen-ion concentration as follows :
pH : 11 > 9 > 7 > 4 > 1
Hydrogen ion concentration : C < E < D < A < B

Question 10.
Equal lengths of magnesium ribbons are taken in test tubes A and B. Hydrochloric acid (HCl) is added to test tube A which acetic acid (CH3COOH) is added to test tube B. In which test tube will the fizzing occurs more vigorously and why ?
Answer:
Fizzing occurs more vigourosly in test tube A’ because hydrochlonic acid is a strong acid while acetic acid is a weak acid.

Magnesium metal reacts with acids and produce repective salt and hydrogen gas.
NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts 5

Question 11.
Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd ? Explain your answer.
Answer:
The fresh milk has a pH of 6. Milk has slightly sweet taste But when it turns into curd its taste has changed from lightly sweet taste to intense sour taste. It means its pH has changed. The intense sour taste of curd is the presence of the strong acidic character. So when milk changes into curd its pH decreases because acidic character increases.

NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts

Question 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 a set as curd ?
Answer:
(a) Milk contains lactose and pH of milk is approximately 6. The micro-organism which converts milk into curd work effectively in slightly acidic medium. Baking soda has slightly alkaline nature. So milkman adds small quantity of baking soda to protect it from curding because in alkaline medium micro-organism do not function properly and thus milk is prevented from rancidity or curding. So milkman makes milk alkaline.

(b) The process of converting milk into curd takes place in slightly acidic medium, Micro-organism converts lactose of milk into lactic acid. But in alkaline medium curding takes place very slowly, so this milk takes long to set as curd.

Question 13.
Plaster of Paris should be stored in moisture-proof container. Explain why ?
Answer:
Plaster of Paris (CaSO4. \(\frac {1}{2}\)H2O) has a very remarkable Property of setting into a hard mass on wetting with water or moisture. The setting of Plaster of Paris is due to its hydration to form crystals of gypsum which set to form a hard, solid mass as follows :
NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts 6
So, to protect the hydration of Plaster of Paris it is stored in moisture proof container.

Question 14.
What is a neutralisation reaction ? Given two examples.
Answer:
Neutralisation reaction : A reaction in which an acid reacts with a base and to form a salt and water is called neutralisation reaction.
Examples:
(i)
NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts 7
(ii)
NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts 8

Question 15.
Given two important uses of washing soda and baking soda.
Answer:
Uses of washing soda :

  • Washing soda is used in laundary. In other words, washing soda is used as a cleansing agent for domestic purposes. It is a main component of many dry soap powders.
  • It is used in the manufacture of many useful sodium compounds like caustic soda, borax, glass and soap.

Uses of baking soda :
(i) Baking soda (sodium hydrogen carbonate) is used as an antacid in medicine to remove acidity of the stomach.

(ii) Baking soda is used in making powder. Baking powder contains baking soda in acid like tartaric acid. When baking powder is mixed in the dough for preparing cake or bread is heated, sodium hydrogen carbonate present it decomposes it give carbon dioxide and sodium carbonate. This carbon dioxide gas bubbles out causing the cake or bread to rise and becomes light and spongy. The tartaric acid present in baking powder reacts with sodium carbonate and neutralises it. If tartaric acid is not present in baking power, then the cake will taste bitter due to the presence of sodium carbonate in it.

Class 10 Science Chapter 2 Acids, Bases and Salts Textbook Activities

Activity 2.1 (Page 18)

  • Collect the following samples from the science laboratory-hydrochloric acid (HCl), sulphuric acid (H2SO4), nitric acid (HNO3), acetic add (CH3COOH), sodium hydroxide (NaOH), calcium hydroxide [Ca(OH)2], potassium hydroxide (KOH), magnesium hydroxide [Mg(OH)2], and ammonium hydroxide (NH4OH).
  • Put a drop of each of the above solutions on a watch-glass and test with a drop of the following indicators as shown in Table 2.1.
  • What change in colour did you observe with red litmus, blue litmus, phenolphthalein and methyl orange solutions for each of the solutions taken?
  • Tabulate your observations in Table 2.1.

Table 2.1
NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts 9

Activity 2.2 (Page 18)

  • Take some finely chopped onions in a plastic bag along with some strips of clean cloth. Tie up the bag tightly and leave overnight in the fridge. The cloth strips can now be used to test for acids and bases.
  • Take two of these cloth strips and check their odour.
  • Keep them on a clean surface and put a few drops of dilute HCl solution on one strip and a few drops of dilute NaOH solution on the other.
  • Rinse both cloth strips with water and again check their odour.
  • Note your observations.
  • Now take some dilute vanilla essence and clove oil and check their odour.
  • Take some dilute HCl solution in one test tube and dilute NaOH solution in another. Add a few drops of dilute vanilla essence to both test tubes and shake well. Check the odour once again and record changes in odour, if any.
  • Similarly, test the change in the odour of clove oil with dilute HCl and dilute NaOH solutions and record your observations.

Observations: Vanilla indicator.

NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts

Activity 2.3 (Page 19)

  • Set the apparatus as shown in Fig.
  • Take about 5 mL of dilute sulphuric acid in a test tube and add a few pieces of zinc granules to it.
  • What do you observe on the surface of zinc granules?
  • Pass the gas being evolved through the soap solution.
  • Why are bubbles formed in the soap solution?
  • Take a burning candle near a gas filled bubble.
  • What do you observe?
  • Repeat this Activity with some more acids like HCl, HNO3, and CH3COOH,
  • Are the observations in all the cases the same or differed ?

NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts 10
Observation : Bubbles of hydrogen gas are evolved from the surface of zinc granules. When hydrogen gas is passed through a soap solution it forms bubbles because hydrogen is lighter than soap solution and it filled in the bubbles of soap. Hydrogen gas burns with a pop sound.

Hydrogen evolves vigorously with acids like HCl and HNO3 but releases slowly with CH3COOH.

Activity 2.4 (Page 20)

  • Place a few pieces of granulated zinc metal in a test tube.
  • Add 2 mL of sodium hydroxide solution and warm the contents of the test tube.
  • Repeat the rest of the steps as in Activity 2.3 and record your observations.

Observations : Zinc reacts with ‘NaOH’ to forms sodium zincate and hydrogen.
NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts 11
Hydrogen bums with a pop near the candle.

Activity 2.5 (Page 20)

NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts 25

  • Take two test tubes, label them as A and B.
  • Take about 0.5 g of sodium carbonate (Na2CO3) in test tube A and about 0.5 g of sodium hydrogen carbonate (NaHCO3) in test tube B.
  • Add about 2 mL of dilute HCl to both the test tubes.
  • What do you observe?
  • Pass the gas produced in each case through lime water (calcium hydroxide solution) as shown in Fig. and record your observations.

Observations : Sodium carbonate (Na2CO3) and sodium bicarbonate (NaHCO3) reacts with dilute HCl to form NaCl, H2O and CO2, Carbondioxide evolves with effervescence.

Test Tube A:
Na2CO3(s) + 2 HCl (aq) → 2NaCl (aq) H2O(l) + CO2
Test Tube B:
NaHCO3 (s) + HCl (aq) → NaCl (aq) + H2O(l) + CO2 (↑)

On passing carbondioxide gas through lime water e.g. aq. Ca(OH)2, it turns milky.
NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts 12
On Passing carbondioxide for long time through lime water, the milky colour of water disapperas due to the formation of soluble Ca(HCO3)2 (aq).
NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts 13

Activity 2.6 (Page 21)

  • Take about 2 mL of dilute NaOH solution in a test tube and add two drops of phenolphthalein solution.
  • What is the colour of the solution?
  • Add dilute HCl solution to the above solution drop by drop.
  • Is there any colour change for the reaction mixture?
  • Why did the colour of phenolphthalein change after the addition of an acid?
  • Now add a few drops of NaOH to the above mixture.
  • Does the pink colour of phenolphthalein reappear?
  • Why do you think this has happened?

Observation : (i) The colour of the solution is pink because phenolphthalein given pink colour in basic medium.
(ii) As dil. HCl is added drop by drop in the above solution it turns pink to colourless.
(iiï) The colour of the phenolphthalein change after the addition of an acid because in neutral or acidic medium phenolphthaLein does not give any colour.
(iv) Yes the pink colour of phenolphthalein reappears because when NaOH is added in the neutral mixture it becomes basic and in basic medium phenolphthalein gives pink colour.

NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts

Activity 2.7 (Page 21)

  • Take a small amount of copper oxide in a beaker and add dilute hydrochloric acid slowly while stirring.
  • Note the colour of the solution. What has happened to the copper oxide?

Observation : We observe that the colour of the solution becomes blue-green and the copper oxide dissolves. The blue-green colour of the solution is due to the formation of copper (II) Chloride.
NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts 14

Activity 2.8 (Page 22)

  • Take solutions of glucose, alcohol, hydrochloric acid, sulphuric acid, etc.
  • Fix two nails on a cork, and place the cork in a 100 mL beaker.
  • Connect the nails to the two terminals of a 6 volt battery through a bulb and a switch, as shown in Fig,

NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts 15

  • Now pour some dilute HCl in the beaker and switch on the current,
  • Repeat with dilute sulphuric acid.
  • What do you observe?
  • Repeat the experiment separately with glucose and alcohol solutions. What do you observe now? Does the bulb glow in all cases?

The Bulb will start glowing in the case of acids like HCl, H2SO4 etc. But in case of glucose and alcohol bulb does not glow because these solutions do not conduct electricity. The electric current in carried through the solution by ions. Since the cation present in acids is H+, this suggests that acid produce hydrogen ions in solution, which are responsible for their acidic character.

Activity 2.9 (Page 23)

  • Take about 1g solid NaCl in a clean and dry test tube and set up the apparatus as shown in Fig.
  • Add some concentrated sulphuric acid to the test tube.
  • What do you observe ? Is there a gas coming out of the delivery tube?
  • Test the gas evolved successively with dry and wet blue litmus paper.
  • In which case does the litmus paper change colour?
  • On the basis of the above Activity, what do you infer about the acidic character of: (i)dry HCl gas (ii) HCl solution?

NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts 16
Note : If the climate is very humid, you will have to pass the gas produced through a guard tube (drying tube) containing calcium chloride to dry the gas.
Observation : A pungent smelling gas is evolved from the test tube.
2NaCl + H2SO4 → Na2SO4 + HCl (g)
The colour of dry blue litmus paper remain unchanged while the colour of wet blue litmus paper turns red.

This activity suggests that .hydrogen ions in HCl are produced in the presence of water. The separation of K+ ion from HCl molecules cannot occur in the absence of water.
HCl + H2O → H3O+ + Cl

Hydrogen ions cannot exist alone, but they exist after combining with water molecules. Thus hydrogen ions must always be shown as H+(aq) or hydronium ion (H3O+).
H+ + H2O → H3O+

NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts

Activity 2.10 (Page 24)

  • Take 10 mL water in a beakér.
  • Add a few drops of concentrated H2SO4 to it and swirl the beaker slowly.
  • Touch the base of the beaker.

Question 1.
Is there a change in temperature?
Answer:
Yes, there is a change in temperature. Temperature of the beaker increases.

Question 2.
Is this an exothermic or endothermic process?
Answer:
This is an enothermic reaction

Question 3.
Repeat the above Activity with sodium hydroxide pellets and record your observations.
Answer:
When sodium hydroxide pellets are added in water, the temperature of beaker increases. This is also an exothermic reaction.

Activity 2.11 (Page 26)

  • Test the pH values of solutions given in Table.
  • Record your observations.
  • What is the nature of each substance on the basis of your observations?

Observations :

NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts 17

Activity 2.12 (Page 27)

  • Put about 2g soil in a test tube add 5 mL water to it.
  • Shake the contents of the test tube.
  • Filter the contents and collect the filtrate in a test tube.
  • Check the pH of this filtrate with the help of universal indicator paper.
  • What can you conclude about the ideal soil pH for the growth of plants in your region?

Observations:
(i) The pH of the sample of soil is about 7.6. It means it is alkaline in nature.
(ii)The pH of good soils should be about 7 but due to pollution the pH increases or decreases. For the normal growth of plants pH should be 6 to 8.

Activity 2.13 (Page 28)

  • Write the chemical formulae of the salts given below. Potassium sulphate, sodium sulphate, calcium sulphate, magnesium sulphate, copper sulphate, sodium chloride, sodium nitrate, sodium carbonate and ammonium chloride.
  • Identify the acids and bases from which the above salts may be obtained.
  • Salts having the same positive or negative radicals are said to belong to a family. For example, NaCl and Na2SO4 belong to the family of sodium salts. Similarly, NaCl and KCl belong to the family of chloride salts. How many families can you identify among the salts given in this Activity?

Answer:
NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts 18
(i) Sulphate Family
K2SO4, Na2SO4, CaSO4, MgSO4, Cu4SO4
(ii) Chloride Family NaCl, NH2Cl
(iii) Sodium Family
Na2SO4, NaCl, NaNO3, Na2CO3

NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts

Activity 2.14 (Page 29)

  • Collect the following salt, samples – sodium chloride, potassium nitrate, aluminium chloride, zinc sulphate, copper sulphate, sodium acetate, sodium carbonate and sodium hydrogen carbonate (some other salts available can also be taken).
  • Check their solubility in water (use distilled water only).
  • Check the action of these solutions on litmus and find the pH using a pH paper.
  • Which of the salts are acidic, basic or neutral?
  • Identify the acid or base used to form the salt.
  • Report your observations in Table 2.4.

Observations:
NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts 19

Activity 2.15 (Page 32)

  • Heat a few crystals of copper sulphate in a dry boiling tube.
  • What is the colour of the copper sulphate after heating?
  • Do you notice water droplets in the boiling tube? Where have these come from?
  • Add 2-3 drops of water on the sample of copper sulphate obtained after heating.
  • What do you observe? Is the blue colour of copper sulphate restored?

NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts 20
Observation : Copper sulphate crystals have blue colour which seems to be dry but contain water of crystallisation. When we heat the crystals, this water is removed and the salt turns white.

Yes we noticed some water droplets in the boiling tube. Hydrated copper sulphate contains ‘5’ molecules of water of crystallisation per molecule- It has chemical formula CuSO4, 5H2O. On heating, this water of molecules is removed and form water droplets in the boiling tube.

When 2-3 water droplets are added in the anhydrous CuSO4, we find that the blue colour of the crystals reappears.

Class 10 Science Chapter 2 Acids, Bases and Salts Additional Important Questions and Answers

Very Short Answer Type Questions

Question 1.
What is litmus solution ?
Answer:
Litmus solution is a purple dye, extracted from lichen.

Question 2.
Define an acid.
Answer:
A substance which is furnished H+caq ions in their aqueous solution, e.g. Hd, H2SO4 etc.

Question 3.
What is a base ?
Answer:
Base is a substance which is produced OHcaq ions in their aqueous solution e.g. NaOH, KOH etc.

Question 4.
What is an alkali ?
Answer:
Water soluble base is called alkali, e.g. NaOH, KOH etc.

Question 5.
A substance change blue litmus to red. What is the nature of the substance ?
Answer:
Acidic.

NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts

Short Answer Type Questions

Question 1.
What are non-electrolytes ? Give some examples.
Answer:
A compound which does not conduct electricity when dissolved in water or in molten state is called a non-electrolyte.

For example, an aqueous solution of sugar does not conduct electricity, so it is a non-electrolyte. Other examples of non-electrolytes are glucose, urea, benzene, acetone, etc.

Question 2.
What are strong acids ? Explain.
Answer:
An acid which completely dissociated in its aqueous solution and produces a large number of hydrogen ions is called a strong acid.
e.g. Hydrochloric acid, sulphuric acid and nitric acid.
NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts 21

Question 3.
What are weak acids ? Explain.
Answer:
An acid which is partially ionised dissociated in its aqueous solution and produces a small number of hydrogen ions is called a weak acid.
NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts 22

Long Answer Type Questions

Question 1.
How washing soda is prepared ? Give its properties and uses.
Answer:
The Solvay proces gives us anhydrous sodium carbonate Na2CO3, which is called soda ash, Soda ash is obtained by heating sodium carbonate. Now, washing soda contains 10 molecules of water of crystallization. So, anhydrous sodium carbonate is dissolved in water and recrystallized to get washing soda crystals containing 10 molecules of water crystallization :
NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts 23

Properties:

  • It is a transparent crystalline solid.
  • It is fairly soluble in water.
  • The solution of washing soda in water is alkaline which turns red litmus to blue.
  • When washing soda crystals are heated strongly, they lose all the water of crystallization and form soda ash.
    NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts 24

Uses:

  • Sodium carbonate is used in laundry as washing soda.
  • It is a component of many dry soap powders.
  • It is used for softening of hard water.
  • It is used in the manufacture of many useful sodium compounds like caustic soda, borax, glass and soap.
  • It is also used in the manufacture of paper.

NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts

Multiple Choice Questions

Question 1.
The pH of distilled water is:
(a) 7
(b) 8
(c) 10
(d) 6.8
Answer:
(a) 7

Question 2.
The chemical formula of P.O.P is:
(a) CaSO4
(b) CaSO4. \(\frac {1}{2}\)H2O
(c) CaSO4.H2O
(d) CaSO4.2H2O
Answer:
(b) CaSO4. \(\frac {1}{2}\)H2O

Question 3.
The Plaster of Paris is prepared by heating;
(a) Gypsum
(b) Limestone
(c) Lime
(d) Soda ash
Answer:
(a) Gypsum

Question 4.
The chemical formula of gypsum is :
(a) CaSO4
(b) CaSO4.\(\frac {1}{2}\)H2O
(c) CaSO4. \(\frac {3}{2}\)H2O
(d) CaSO4.2H2O
Answer:
(d) CaSO4.2H2O

Question 5.
Baking powder contains baking soda and:
(a) Oxalic acid
(b) Tartaric acid
(c) Carbonic acid
(d) Methanoic acid
Answer:
(b) Tartaric acid

error: Content is protected !!