AP 10th Class Physical Science 2nd Lesson Questions and Answers Acids, Bases and Salts

AP State Board new syllabus AP Board Solutions Class 10 Physics 2nd Lesson Acids, Bases and Salts Questions and Answers.

10th Class Physical Science 2nd Lesson Acids, Bases and Salts Questions and Answers

10th Class Physics 2nd Lesson Questions and Answers (Exercise)

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
10 ml of NaOH will neutralise = 8 ml of HCl
10 ml of NaOH will neutralise = \(\frac{8}{10}\) × 20 = 16 ml of HCl.

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

Question 5.
Write word equation 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 fillings.
Answer:

Question 6
Compounds such as alcohols and glucose also contain hydrogen but are not categorised as acids. Describe an Activity to prove it. (Activity 2.8) (TP No. 48)
Answer:
Aim : To prove that alcohols and glucose do not conduct electricity in their solution form.
Procedure :

1. Fix two iron nails on a cork and place this cork in a beaker.
2. Connect the nails to the two terminals of a 6 volt battery through a switch and bulb a as shown in Figure.
3. Now add some dilute hydrochloric
   acid in the beaker and switch on the current. Take the observation. Acid solution in water conducts electricity
4. Repeat the experiment separately with alcohol and glucose solution.

Observation : You will observe that in case of dilute hydrochloric acid bulb glows but when glucose or alcohol solution is taken in beaker, the bulb does not glow.
Conclusion:

1. Alcohol and glucose do not conduct electricity suggesting that they do not form ions.
2. Dilute hydrochloric acid solution conducts electricity suggesting that it forms ion and the electric current is carried through the solution by ions.

Question 7.
Why does distilled water not conduct electricity, whereas rain water does ?
Answer:
Distilled water does not contain any ionic compounds like acids, bases or salts. Therefore, it does not dissociate into ions as it is a.weak electrolyte. Salts are present in rain water which help in dissociation of rain water into ions which help in conduction of electricity.

Question 8.
Why do acids not show acidic behaviour in the absence of water ?
Answer:
It is because adds do not dissociate into ions in absence of water. But when an acid is dissolved in water, it forms hydrogen ions and hence, show acidic behaviour,

Question 9.
Five solutions A,B,C,D and E when tested with universal indicator showed pH as 4, 1, 11,7 and 9, Which solution is
a) neutral ?
b) strongly alkaline ?
c) strongly acidic ?
d) weakly acidic ?
e) weakly alkaline ?
Arrange the pH increasing order of hydrogen-ion concentration.
Answer:
a) ‘D’ with pH = 7 is neutral
b) ‘C’ with pH = 11 is strongly alkaline
c) ‘B’ with pH = 1 is strongly acidic
d) ‘A’ with pH = 4 is weakly acidic
e) ‘E’ with pH = 9 is weakly alkaline
C, E, D, A, B is increasing order of H⁺ ion concentration.

Question 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 v will the fizzing occur more vigorously and why?
Answer:
Fizzing occurs more vigorously in hydrochloric acid (A) than in acetic acid (B) because HCl is stronger acid than acetic acid. HCf dissociates into H⁺ and Cl^– ions completely whereas acetic acid partially dissociates into its ions.

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:
pH will decrease form 6
Reason : Curd is more acidic than milk. When milk changes into curd, lactose (organic sugar) present in milk gets converted into lactic acid due to the fermentation process.

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 to set as curd ?
Answer:
a) It is done to increase the shelf life of milk.
b) The alkaline milk takes a longer time to set into curd because lactic acid being formed has to neutralise the alkali present in it.

Question 13.
Plaster of Paris should be stored in a moisture-proof container. Explain why ?
Answer:
Plaster of Paris changes into a hard solid mass on mixing with water. This solid mass is of gypsum

Due to this reason, Plaster of Paris is always stored in a moisture – proof container.

Question 14.
What is a neutralisation reaction ? Give two examples.
Answer:
The reaction in which a base reacts with an acid is called neutralisation reaction.
Examples : NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l)
HCl(aq) + NHOH(aq) → NH₄Cl(aq) + H₂O (l)

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

1. It is used in glass, soap and paper industries.
2. It is used in the manufacture of sodium compounds.
3. It is used as a cleaning agent for domestic purposes.
4. It is used for removing permanent hardness of water.

Uses of Baking soda:

1. It is used in soda – acid fire extinguishers.
2. It is used as an ingredient in antacids, as it neutralises excess acid in the stomach.

10th Class PS 2nd Lesson Questions and Answers (InText)

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:
Divide the red litmus paper in three parts and dip each part in three test tubes. The test tube in which red litmus paper turns blue contains basic solution. The blue litmus paper so obtained is dipped into the remaining two solutions. The one which turns blue litmus paper red again is an acidic solution. The third tube in which there is no change of colour contains water.

Page No. 48

Question 2.
Why should curd and sour substances not be kept in brass and copper vessels ?
Answer:
Curd and sour substances are acidic and acids react with brass and copper and so are not kept in brass and copper vessels.

Question 3.
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:

1. H₂ gas is liberated when an acid reacts with a metal.
2. Illustration : Set up an apparatus as shown in figure. Take some zinc granules in the test tube. Add some 5 ml dilute hydrochloric acid slowly. Soon the reaction between zinc and hydrochloric acid starts and hydrogen gas is evolved.
   Zn + HCl → ZnCl₂ + H₂
3. Test for H₂ gas : H₂ gas is not soluble in water. When passed through soap solution, it gets trapped into bubbles which burn with explosion.

Question 4.
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:
Since the end product is calcium chloride and the gas formed extinguishes a burning candle, it is CO₂, the metal compound A must be calcium carbonate. Hence, the reaction between calcium carbonate and hydrochloric acid is as follows.

Page No. 54

Question 5.
Why do HCl, HNO₃, etc., show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character ?
Answer:
H⁺ ions in aqueous solution are responsible for acidic character. HCl, HNO₃ etc. generate H⁺ ions in water while alcohol and glucose do not do so, and hence do not show acidic character.

Question 6.
Why does an aqueous solution of an acid cortduct electricity ?
Answer:
Acids give ions in aqueous solution and in solution current is carried through ions. Thus aqueous solution of an acid conducts electricity.

Question 7.
Why does dry HCl gas not change the colour of the dry litmus paper ?
Answer:
Dry HCl gas does not generate H* ions and hence does not change the colour of dry litmus paper.

Question 8.
While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid ?
Answer:
When an acid is mixed with water, there is evolution of a large amount of heat. Therefore, acid is slowly added to water. If on the other hand, water is added to acid, it might spill on your body and cloths due to explosion and evolution of sudden and large amount of heat.

Question 9.
How is the concentration of hydronium ions (H₃O⁺) affected when a solution of an acid is diluted ?
Answer:
Concentration of hydronium ions (H₃O⁺) decreases when a solution of an acid is diluted.

Question 10.
How is the concentration of hydroxide ions (OH^–) affected when excess base is dissolved in a solution of sodium hydroxide ?
Answer:
Concentration of hydroxide ions (OH⁺) increases. When excess base is dissolved in a solution of sodium hydroxide.

Page No. 60

Question 11.
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:
Solution A has more hydrogen ion concentration. Solution A is slightly acidic and solution B is slightly basic.

Question 12.
What effect does the concentration of H⁺ (aq) ions have on the nature of the solution?
Answer:
More the concentration of H⁺ ion, higher the acidic nature of the solution.

Question 13.
Do basic solutions also have H⁺ (aq) ions ? If yes, then why are these basic ?
Answer:
Yes, basic solutions also have H⁺ ions. However, their concentration is less as compared to the OH^– ions that makes the solution basic.

Question 14.
Under what sdil 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) ?
Answer:
Plants work well in the pH range 6 – 8. So, when the soil becomes acidic farmers treat the soil fields with bases like quick lime or slaked lime or chalk.

Page No. 70

Question 15.
What is the common name of the compound CaOCl₂ ?
Answer:
Bleaching powder.

Question 16.
Name the substance which on treatment with chlorine yields bleaching powder.
Answer:
Dry slaked lime (Ca(OH)₂).

Question 17.
Name the sodium compound which is used for softening hard water.
Answer:
Washing soda, i.e., sodium carbonate (Na₂CO₃.10H₂O)

Question 18.
What will happen if a solution of sodium hydrogen carbonate is heated ? Give the equation of the reaction involved.
Answer:
Sodium hydrogen carbonate on heating gives sodium carbonate and CO gas is evolved.
2NaHCO₃ → Na₂CO₃ + CO₂ + H₂O

Question 19.
Write an equation to show the reaction between Plaster of Paris and water.
Answer:

Group Activity

(I) Prepare your own indicator

• Crush beetroot in a mortar.
• Add sufficient water to obtain the extract.
• Filter the extract by the procedure learnt by you in earlier classes.
• Collect the filtrate to test the substances you may have tasted earlier.
• Arrange four test tubes in a test tube stand and label them as A, B, C and D. Pour 2 ml each of lemon juice solution, soda-water, vinegar and baking soda solution in them respectively.
• Put 2 – 3 drops of the beetroot extract in each test tube and note the colour change if any. Writ your observation in a Table.
• You can prepare indicators by using other natural materials like extracts of red cabbage leaves, coloured petals of some flowers such as Petunia, Hydrangea and Geranium.

(II) Preparing a soda-acid fire extinguisher
The reaction of acids with metal hydrogencarbonates is used in the fire extinguishers which produce carbon dioxide.

• Take 20 ml of sodium hydrogencarbonate (NaHCO₃) solution in a wash-bottle.
• Suspend an ignition tube containing dilute sulphuric acid in the wash-bottle (Figure).

• Close the mouth of the wash-bottle.
• Tilt the wash-bottle so that the acid from the ignition tube mixes with the sodium hydrogencarbonate solution below.
• You will notice discharge coming out of the nozzle.
• Direct this discharge on a burning candle. What happens ?

Answer:
Student’s Activity.

AP 10th Class Physical Science Chapter 2 Questions and Answers (Lab Activities)

Activity – 2.1 (Page. No. 40)

Question 1.
How do you test a solution for its nature ? Explain with an activity.
Answer:
Aim : To test the given samples with the help of red litmus solution, blue litmus solution, phenolphthalein and methyl orange indicators.
Materials required : HCl, H₂SO₄, HNO₃, CH₃COOH, NaOH, Ca(OH)₂, KOH, Mg(OH)₂, NH₄OH red litmus solution, blue litmus solution, phenolphthalein, methyl orange indicators and test tubes.
Procedure:

1. Take each of the above solutions in separate test tubes.
2. Test the nature of these solutions by adding a drop of red litmus solution, blue litmus solution, phenolphthalein and methyl orange indicators.
3. Observe the change ¡n colour and record your observations in observation table.

Sample Solution	Red Litmus Solution	Blue Litmus Solution	Phenolphthalein Solution	Methyl Indicator
Hydrochloric Acid (HCl)	No colour change	Red	Colourless	Pink
Sulphuric Acid (H2SO4)	No colour change	Red	Colourless	Pink
Nitric Acid (HNO3)	No colour change	Red	Colourless	Pink
Acetic Acid (CH3COOH)	No colour change	Red	Colourless	Pink
Sodium Hydroxide (NaOH)	Blue	No colour change	Pink	Yellow
Calcium Hydroxide (Ca(OH)2)	Blue	No colour change	Pink	Yellow
Potassium Hydroxide (KOH)	Blue	No colour change	Pink	Yellow
Magnesium Hydroxide (Mg(OH)2)	Blue	No colour change	Pink	Yellow
Ammonium Hydroxide (NH4OH)	Blue	No colour change	Pink	Yellow

Observation : Acidic substances turn blue litmus red. Basic substances turn red litmus blue. Phenolphthalein remains colourless in acidic substances whereas it becomes pink in basic substances. Methyl orange becomes pink in acidic substances and yellow in basic substances.
Conclusion: HCl, H₂SO₄, HNO₃ and CH₃COOH are acidic in nature while NaOH, Ca(OH)₂, KOH, Mg(OH)₂ and NH₄OH are basic in nature.

Activity 2.2 (Page. No. 40)

Question 2.
What are olfactory indicators? How do you prepare an olfactory indicator ? Explain with an activity.
Answer:
Aim: To test some substances whose odour changes in acidic or basic media (olfactory indicators)
Procedure:

1. 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.
2. Take two of these cloth strips and check their odour.
3. 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.
4. Rinse both cloth strips with water and again check there odour.
5. Now take some dilute vanilla essence and clove oil and Check their odour.
6. 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.
7. Similarly, test the change in the odour of clove oil with dilute HCl and dilute NaOH solutions and record observations.

Observations :

1. Both the cloth strips give characteristic smell of onion, with drops of dilute HCl, smell of onion remains but it is destroyed when drops of NaOH are added. After washing with water, there was no smell.
2. Vanilla essence and clove oil give characteristic pleasant smell. This smell is not affected by dilute HCl but disappers in the presence of dil. NaOH.

Activity – 2.3 (Page. No. 42)

Question 3.
How do you prove that acids react with metals and release hydrogen gas ?
Answer:
Aim : To show acid react with metal to liberate hydrogen gas.
Materials required : Zinc granules, Dilute H₂SO₄, Test tube, Stand, Delivery tube, Soap solution, Candle.

Procedure :

1. Set the apparatus as shown in Figure.
2. Take about 5 ml of dilute sulphuric acid in a test tube and add a few pieces of zinc granules to it.
3. You observe effervescence on the surface of zinc granules.
4. Pass the gas being evolved through the soap solution.
5. H₂ gas evolved gets trapped in soap solution forming bubbles.
6. Take a burning candle near a gas filled bubble.

Observation : Gas bubbles breakup with a pop sound due to burning of hydrogen gas.
Conclusion; Repeat this activity with some more acids like H₂SO₄, HNO₃ and CH₃COOH, similar observations will be seen.

Activity – 2.4 (Page. No. 44)

Question 4.
How do you prove that bases react with metals and release hydrogen gas ?
Answer:
1) Place a few pieces of granulated zinc metal in a test tube.
2) Add 2 ml of sodium hydroxide solution and warm the contents of the test tube.
3) You can observe bubbles filled with gas on the surface of zinc granules.
4) Pass the gas being evolved through the soap solution.
5) Take a burning candle near gas-filled bubbles.
6) The burning candle is put off with a pop sound.
7) Do the same with other metals.
8) Record your observations.
9) The reaction that takes place can be written as follows.

10) We can conclude that some bases react with some metals and release hydrogen gas.

Activity – 2.5 (Page. No. 44)

Question 5.
How do you prove that all metal carbonates and hydrogen carbonates react with acids and release carbon dioxide ?
Answer:

Aim : To show acid reacts with metal carbonate and metal hydrogen carbonate to liberate carbon dioxide.
Materials required Na₂CO₃, NaHCO₃, dilute HCl, test tubes, lime water.
Procedure :

1. Take two test tubes, label them as A and B.
2. 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.
3. Add about 2 ml of dilute HCl to both the test tubes.
4. CO₂ is evolved with effervesence when sodium carbonate or sodium bicarbonate reacts with dilute acids. So, similar observations is made in test tube A and test tube B.
   Na₂CO₃(s) + 2HCl(aq) → 2NaCl(aq) + H₂O(l) + CO₂(g)
   NaHCO₃(s) + HCl(aq) → NaCl(aq) + H₂O(l) + CO₂(g)

Observations:
1) Pass the gas produced in each case through lime water as shown in figure.
2) On passing carbon dioxide produced through lime water a milky precipitate of calcium carbonate is formed

3) On passing excess carbon dioxide the following reaction takes place

Activity – 2.6 (Page. No. 46)

Question 6.
What is neutralisation reaction ? Explain through an activity.
Answer:
Aim : To study the acids and bases react each other.
Procedure :

1. Take about 2 ml of dilute NaOH solution in a test tube and add two drops of phenolphthalein solution.
2. The colour of phenolphthalein is pink in NaOH solution.
3. Add dilute HCl solution to the above solution
4. On adding dilute HCl, pink colour slowly disappears.
5. This is because NaOH present is neutralized by acid.
6. Now add a few drops of NaOH to the above mixture.
7. On adding NaOH again, pink colour reappears.
8. This is because the solution becomes alkaline again due to excess of NaOH over HCl.

Observation : We have observed that effect of a base is nullified by an acid and vice-versa. The reaction taking place is written as
NaOH_(aq) + HCl_(aq) → NaCl_(aq) + H₂O_(l)

Activity – 2.7 (Page. No. 46)

Question 7.
How do you say metallic oxides are basic oxides ?
Answer :
Aim : To study the neutralisation reaction of copper oxide with dil. HCl.
Materials required : Copper oxide, dil. HCl.
Procedure : Take a small amount of copper oxide in a beaker and add dilute hydrochloric acid slowly while stirring.
Observation : Copper oxide reacts with dil. HCl and blue coloured solution of copper chloride is formed.
CuO_(s) + 2HCl_(aq) → CuCl_2(aq) + H₂O
Conclusion: The general reaction between a metal oxide and an acid can be written as
Metal oxide + Acid → Salt + Water

Activity – 2.9 (Page. No. 50)

Question 8.
Hydrogen ions in HCl are produced in the presence of water. Prove it.
Answer:
Aim : To show that HCl aqueous solution is acidic whereas dry HCl is not.
Materials required : NaCl, Cone. H₂SO₄, Test tube, Cork, Delivery tube, Tongs.
Procedure :

1. Take about 1 g solid NaCl in a clean and dry test tube and set up the apparatus as shown in figure.
2. Add some concentrated sulphuric acid to the test tube.
3. Reaction takes place and hydrochloric acid gas is produced
   2NaCl_(s) + H₂SO₄ → Na₂SO_4(aq) + 2HCl_(g)↑
4. Test the gas evolved successively with dry and wet blue litmus paper.

Observation : The gas no effect on dry litmus paper, but wet litmus paper turns to red.
Conclusion : Hydrogen ions in HCl are produced in the presence of water and thus only HCl solution is acidic whereas dry HCl is not.

Activity – 2.10 (Page. No. 52)

Question 9.
Prove that the process of dissolving an acid or a base in water is a highly exothermic one.
Answer:
Aim : To show that dissolution of acid in water is an exothermic process.
Materials required : Water in beaker, cone. H₂SO₄
Procedure :

1. Take 10 ml water in a beaker.
2. Add a few drops of concentrated H₂SO₄ to it and swirl the beaker slowly.
3. Touch the base of the beaker, the temperature rises.
   Observation Dissolution of acid in water is an exothermic process.

Activity – 2.11 (Page. No. 56)

Question 10.
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 ?
Answer:

1. Test the pH values of solutions given in table.
2. Record your observations.
3. What is the nature of each substance on the basis of your observations ?

S.No.	Solution	Colour of pH Paper	Approximate pH Value	Nature of Substance
1)	Saliva (before meal)	Light green	7.4	Basic
2)	Saliva (after meal)	Pale yellow	5.8	Acidic
.3)	Lemon juice	Pink red	2.5	Acidic
4)	Colourless aerated drink	Pale yellow	6	Acidic
5)	Carrot juice	Light orange	4	Acidic
6)	Coffee	Orange yellow	5	Acidic
7)	Tomato juice	Dark orange	4.1	Acidic
8)	Tap water	Green	7	Neutral
9)	1M NaOH	Dark blue, violet	13 – 14	Basic
10)	1M HCl	Red	1	Acidic

Activity – 2.12 (Page. No. 58)

Question 11.
Write the procedure of find the pH of soil.
Answer:

1. Put about 2 g soil in a test tube and add 5 ml water to it.
2. Shake the contents of the test tube.
3. Filter the contents and collect the filtrate in a test tube.
4. Check the pH of this filtrate with the help of universal indicator paper.

Conclusion : The pH of soil is near 7, plants will grow well.

Activity – 2.13 (Page. No. 60)

Question 12.
Write the chemical formulae of the salts given below. Potassium sulphate, sodium sulphate, calcium sulphate, magnesium sulphate, copper sulphate, sodium chloride, sodium nitratd, sodium carbonate and ammonium chloride.

1. Identify the acids and bases from which the above salts may be obtained.
2. Write the family of the salts like sodium salts, chloride salts, etc.,

The following families can be identified.

Family of Sulphate Salts : K₂SO₄, Na₂SO₄, CaSO₄, MgSO₄, CuSO₄
Family of Chloride Salts : NaCl, NH₄Cl
Family of Sodium Salts : Na₂SO₄, NaCl, NaNO₃, Na₂CO₃

Question 13.
How do you determine the nature of the salts ?
Answer:

Activity – 2.15 (Page. No. 68)

Question 14.
What is water of crystallisation? Write procedure to observe water of crystallisation in copper sulphate.
Answer:
Aim : To show crystaline salts contain water of crystallization.
Materials required : Copper sulphate crystals (CuSO₄.5H₂O), Boiling tube Burner, A pair of tongs.
Procedure :

1. Heat a few crystals of copper sulphate in a dry boiling tube.
2. The colour of copper sulphate after heating is white.
3. Water droplets in boiling tube are seen due to condensation of water of crystallization of copper sulphate.
4. Add 2 – 3 drops of water on the sample of copper sulphate obtained after heating.

Observation : On adding 2 – 3 drops of water on the sample of copper sulphate, obtained after heating, the blue colour of copper sulphate is restored.