Acids Bases Salts Class 10 Science Important Questions

Please refer to Acids Bases Salts Class 10 Science Important Questions given below. These solved questions for Acids Bases Salts have been prepared based on the latest CBSE, NCERT and KVS syllabus and books issued for the current academic year. We have provided important examination questions for Class 10 Science all chapters.

Class 10 Science Acids Bases Salts Important Questions

Very Short Answer Questions

Question. Which among distilled water, tap water and sea water is the best conductor of electricity?
Answer : Sea water is a better conductor due to the presence of ions.

Question. Name the acids present in (i) nettle sting, (ti) curd.
Answer : (i) HCOOH, Formic acid,
(ii) Lactic acid, CH₃-CH(OH)-COOH

Question. Name a salt which does not contain water of crystallisation.
Answer : NaHCO3 is a salt that does not contain water of crystallisation.

Question. Write the name and chemical formula of the product formed by heating gypsum at 373 K.
Answer : Plaster of Paris, CaSO₄. 2 1H₂O

Question. The pH of a sample of vegetable soup was found to be 6.5. How is this soup likely to taste?
Answer : It will be sour in taste.

Question. Which bases are called alkalies? Give one example of alkali.
Answer : Those bases which are soluble in water are called alkalies e.g., NaOH, KOH.

Question. Write the name and chemical formula of the product formed by action of chlorine on slaked lime.
Answer : CaOCl2, Bleaching powder, Calcium oxy-chloride.

Question. Write a balanced chemical equation for the reaction between sodium carbonate and hydrochloric acid indicating the physical state of reactants and the products.
Answer : Na₂CO₃(s) + 2HCl (dill) → 2NaCl (aq) + CO₂(g) + H₂O(l) 

Question. Name the acid and base that have constituted the salt ammonium nitrate.
Answer : Acid: HNO3,
Base: NH4OH (i.e., Nitric acid, Ammonium hydroxide).

Question. Write chemical equation for the reaction of zinc metal on sodium hydroxide.
Answer : Zn(s) + 2NaOH(aq) Heat Na₂ZnO2(aq) + H₂(g)

Question. Three acidic solutions A, B and C have pH = 0, 3 and 5 respectively.
a. Which solution has the highest concentration of H+ ions?
b. Which solution has the lowest concentration of H+ ions?
Answer : a. The solution with pH = 0 has highest concentration of H+ ions.
b. The solution with pH = 5 has lowest concentration of H+ ions.

Question. What is meant by p and H in pH?
Answer : p stands for ‘potenz’ in German meaning power, H stands of hydrogen.

Question. Define alkalies and give an example.
Answer : Water soluble bases are called alkalies e.g., NaOH.

Question. Mention the range of pH for identification of a base.
Answer : 7.1 to 14 is the pH range for bases.

Question. Suggest one way to reduce alkaline nature of the soil.
Answer : Add ammonium nitrate (Acidic salt) to neutralise alkaline nature of soil.

Question. Oxides of metals are basic while those of non-metals are acidic. Explain.
Answer : Metal oxides dissolve in water to form base basic in nature. On the other hand non-metals dissolve in water to form acids, acidic in nature.

Question. During summer season, a milkman usually adds a very small amount of baking soda to fresh milk. Give one reason.
Answer : Baking soda is basic in nature, it will not allow milk to turn sour due to the formation of lactic acid.

Question. Curd is not kept in copper and brass utensils, why?
Answer : Curd contains lactic acid which can make poisonous compounds with brass and copper vessels.

Question. How chloride of lime differs from calcium chloride?
Answer : CaOCl₂ is the chloride of lime whereas CaCl₂ calcium chloride.

Question. What is meant by water of crystallisation in a substance?
Answer : The water molecules associated with a crystalline solid are called water of crystallisation.

Question. Write the chemical name and chemical formula of washing soda.
Answer : Na₂CO₃.10H₂O, sodium carbonate deca-hydrate is washing soda.

Question. Fresh milk has pH = 6. When it changes to curd will its pH value increase or decrease?
Answer : pH value will decrease when milk changes to curd.

Question. How does flow of acid rain water into river makes the survival of aquatic life in the river difficult?
Answer : Acidic water makes aquatic species uncomfortable.
Aquatic species are more comfortable in the pH 7 to 7.8.

Question. How does the pH change when solution of a base is diluted?
Answer : When solution of a base is diluted, its pH decreases.

Short Answer Questions

Question. Crystals of a substance changes their colour on heating in a closed vessel but regained it after sometime, when they were allowed to cool down.
a. Name one such substance.
b. Explain the phenomenon involved.
Answer : 
a. CuSO4.5H2O (Hydrated copper sulphate)
b. CuSO4.5H2O Heat CuSO4 + 5H2O
Blue (Dirty white)
The colour changes due to the loss of molecules of water of crystallisation. Colour is regained by absorbing water molecules from the atmosphere containing water vapours.

Question. (a) Write the name given to the bases that are highly soluble in water. Give an example.
(b) Why does bee sting causes pain and irritation?
Rubbing of baking soda on the sting area gives relief. How?
Answer : 
(a) Highly soluble bases are called alkalies e.g., KOH.
(b) Bee sting contains HCOOH, formic acid which causes irritation. Baking soda (basic) neutralises HCOOH, therefore it gives relief from pain on rubbing it on sting area,

Question. Write the chemical name of Plaster of paris. Write a chemical equation to show the reaction between Plaster of paris and water.
Answer : 
CaSO₄ . 1/2H₂O₂ → (Calcium sulphate hemihydrate)
CaSO₄ . 1/2H₂O +3/2 H₂O →CaSO₄.2H₂O

Question. You have two solutions A and B. The pH of solution ‘A’ is 6 and the pH of solution ‘B’ is 8. Which solution has more hydrogen ion concentration? Which one of this is acidic and which one is basic?
Answer : ‘A’ has more H+ ion concentration.
‘A’ is acidic while ‘B’ is basic.

Question. Give suitable reasons to justify the following statement: An aqueous solution of sodium chloride is neutral but an aqueous solution of sodium metal is basic.
Answer : Sodium chloride is made up of a strong base, NaOH and a strong acid, HCl. Therefore, its aqueous solution is neutral in nature.
Sodium metal reacts with water to form NaOH(Base) and H2 gas:
2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g)

Question. State in brief the preparation of washing soda from baking soda. Write balanced chemical equation of the reaction involved.
Answer : When sodium hydrogen carbonate (Baking soda) is heated sodium carbonate is formed which on crystallisation forms washing soda:
(Baking soda)
2NaHCO₃ → Heat Na₂CO₃ + CO₂ + H₂O
Na2CO₃+ 10H₂O → Na₂CO₃ . 10H₂O 
(Washing soda)

Question. What is colour of FeSO4.7H2O crystals? How does this colour change upon heating? Give a balanced chemical equation for the change.
Answer : FeSO₄.7H₂O is pale green in colour. It becomes dirty white on heating.
FeSO₄.7H₂O → FeSO₄ + 7H₂O
If it is heated strongly Fe₂O₃ and SO₂, SO₃ gases will be formed .
2FeSO₄ →Heat Fe₂O₃ + SO₂ + SO₃

Question. Classify the following salts into acidic, basic and neutral salts: Potassium sulphate, ammonium chloride,
sodium carbonate, sodium chloride
Answer : 
Acidic: Ammonium chloride,
Basic: Sodium carbonate,
Neutral: Potassium sulphate, sodium chloride.

Question. 2 mL of sodium hydroxide solution is added to a few pieces of granulated zinc metal taken in a test tube.
When the contents are warmed, a gas evolves which is bubbled through a soap solution before testing. Write the equation for the chemical reaction involved and the test to detect the gas. Name the gas which will be evolved when the same metal reacts with dilute solution of a strong acid.
Answer : Zn(s) + 2NaOH warm→ Na2ZnO2 + H2
                                       Sodium zincate
Test: Bring a burning splinter near the gas. If it burns with ‘pop’ sound, the gas liberated is hydrogen.
Zn + H2SO4(dil) → ZnSO4(aq) + H2
Hydrogen gas will be evolved by reaction of the same metal with dilute H2SO4, strong acid.

Question. The pH of a salt which is used to make tasty and crispy pakoras is 14. Identify the salt and write a chemical equation for its formation. List its two uses.
Answer :  The salt is NaHCO3, sodium hydrogen carbonate.
NH3(g) CO₂(g) NaCl (g) H₂O(l) → NaHCO₃(s) NH₄Cl 
Uses:
a. It is used as an antacid.
b. It is used in soda-acid fire extinguishers.
No salt has pH = 14. NaHCO₃ has pH = 8.4.

Question. (a) Why does aqueous solution of an acid conduct electricity?
(b) How does the concentration of H3O+ ions change when a solution of an acid is diluted?
(c) Which one has a higher pH, a concentrated or a dilute solution of hydrochloric acid?
(d) What would to be the gas evolved on adding dilute to hydrochloric acid to
(i) Solid sodium carbonate placed in a test tube?
(ii) Zinc metal in a test tube?
Answer : 
a. It contains ions which carry current.
b. H₃O⁺ ions will decrease when it is 7 diluted.
c. Dilute solution has higher pH than concentrated.
d. (i) CO₂ gas will be formed:
Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂
(ii) Hydrogen gas will be formed:
Zn + 2HCl → ZnCl₂ + H₂

Question. pH has a great importance in our daily life. Explain by giving three examples.
Answer : 
a. pH of our stomach is 2.0 and it is needed for the digestion of proteins in our body.
b. Blood has pH = 7.36 to 7.42 which must be maintained for proper health.
c. pH of soil is determined and suitable chemicals are added so as to make it suitable for growth of crops.

Question. Answer the following questions:
a. State the colour of phenolphthalein in soap solution.
b. Name the by-product of chlor-alkali process which is used for the manufacture of bleaching powder.
c. Name one indicator which specifies the various levels of H+ ion concentration.
Answer : 
a. Phenolphthalein will turn pink in soap solution.
b. Chlorine is the by-product of chlor-alkali process which is used in the manufacture of bleaching powder.
c. Universal indicator specifies the various levels of H+ ion concentration.

Question. a. Define a universal indicator. Mention its one use.
b. Solution ‘A’ gives pink colour when a drop of phenolphthalein indicator is added to it. Solution ‘B’ gives a red colour when a drop of methyl orange is added to it. What type of solutions are ‘A’ and ‘B’ and which of these will have higher pH?
c. Name one salt whose solution has pH greater than 7 and one salt with pH less than 7.
Answer : 
a. Universal indicator is mixture of indicators used to find pH of solution. It is used to measure levels of H+ ion concentration.
b. ‘A’ is basic in nature, ‘B’ is acidic in nature. ‘A’
will have higher pH than ‘B’. It should be greater than 7.
c. Na₂CO₃ is the salt whose pH is more than, CuSO₄ is the salt whose pH is less than 7.

Question. A student dropped few pieces of marble in dilute HCl contained in a test tube. The evolved gas was passed through lime water.
a. What change would be observed in lime water?
b. Write a balanced chemical equation for the above change.
Answer : 
a. Lime water will turn milky.
b. Ca(OH)₂(aq) + CO₂(g) → CaCO₃(s) + H₂O(l)

Question. A white powder is added while baking breads and while making cakes to make them soft and fluffy.
What is the name of that powder? What are the main ingredients in it? What are the functions of each ingredient?
Answer : The powder is baking powder. It consist of sodium hydrogen carbonate and tartaric acid. 
NaHCO3 gives CO2 on heating which makes the bread cake soft and fluffy. Tartaric acid neutralises Na2CO3 which is bitter in taste.

Question. HCl and HNO3 show acidic characteristics in aqueous solution while alcohol and glucose solutions do not.
Give reasons.
Answer : 
HCl and HNO3 form H+ or H3O+ ions in aqueous solution whereas alcohol and glucose do not dissociate into ions.
HCl + H₂O → H₃O+ + Cl-
HNO₃ + H₂O → H3O+ + NO₃ –

Question. What is bleaching powder chemically? Give a reaction for its preparation. State one of its use.
Answer : 
Bleaching powder is chemically CaOCl₂, calcium oxychloride
Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O
(Dry slaked lime)
It is used as a disinfectant i.e., it makes water fit for drinking.

Question. What are olfactory indicators? Dry HCl gas does not change the colour of dry blue litmus. Give reason.
Answer : 
Olfactory indicators: They give different smell in acids and bases.
Dry HCl(g) does not form ions, so there is no effect on litmus.

Question. Answer the following:
a. Why is Plaster of paris written as CaSO4 . 1/2H2O ? How is it possible to have a half water molecule attached with CaSO4?
b. Why is sodium hydrogen carbonate an essential ingredient in antacids?
Answer : a. It has one molecule of water associated with 2 molecules of CaSO4. Water molecules are present as water of crystallisation.
b. It is a mild base and it can neutralise hyper acidity without harming our body.

Question. What happens when chlorine is passed over slaked lime at 313 K? Write chemical equation of the reaction involved and state two uses of the product.
Answer : Bleaching powder, CaOCl2 is formed:
Ca(OH)2 + Cl2 →3313 K CaOCl2 + H2O
a. It is used as an oxidising agent.
b. It is used as a disinfectant.

Question. What is meant by ‘water of crystallisation’ of a substance? Describe an activity to show that blue copper sulphate crystals contains water of crystallisation.
Answer : The molecules of water associated with a crystalline substance are called ‘water of crystallisation.’
CuSO₄ + 5H₂O → CuSO_` + 5H₂O 
When hydrated copper sulphate is heated its colour changes from blue to dirty white and water droplets are formed. If we add little quantity of water to anhydrous CuSO4, we get blue colour again. It is those presence of molecules water of crystallisation which was lost on heating.
Activity: To study the effect of heat on hydrated crystalline salts.
i. Take 2 g of CuSO4 5H2O $ in a test tube.
ii. Observe the initial colour of the salt.
iii. Heat the test tube at top of burner carefully as shown in the diagram.
iv. Record your observations.
v. Cool the crystals and add few drops of water.
vi. Record your observations again.

Observations: Blue colour of CuSO4 . 5H2O is changed to dirty white anhydrous CuSO4 and water droplets were formed. On adding water, blue colour of salt was restored.
Conclusion: CuSO4 5H2O $ is a hydrated salt which loses water of crystallisation, which on heating becomes dirty white and regains its colour when it comes in contact with water.
Chemical reactions involved:

CuSO₄ . 5H₂O(S) Heat→ CuSO₄ (s) + 5H₂O(l)
(Blue)                           Dirty white
CuSO₄(s) + 5H₂O(l) Heat→ CuSO₄ 5H₂O

Question. Write the chemical formulae of washing soda and baiting soda. Which one of these two is an ingredient of antacids? How does it provide relief in stomachache?
Answer : Na2CO₃ . 10H₂O $ is washing soda, NaHCO₃ is baking soda. NaHCO₃ is an ingredient of antacid. It neutralises hyper acidity in stomach and gives relief.

Question. What is baking powder? How does it make the cake soft and spongy?
Answer : Baking powder is made up of NaHCO3 and tartaric acid. NaHCO₃, on heating gives CO₂ which makes the cake soft and spongy.

Long Answer Questions

Question. Write chemical equations when zinc granules react with
a. Sulphuric acid,
b. Hydrochloric acid,
c. Aluminium chloride,
d. Sodium hydroxide,
e. Nitric acid
Answer : 
a. Zn(s) + H₂SO₄(dil.) → ZnSO₄(aq) + H₂(g)
b. Zn(s) + 2HCl(dil) → ZnC(aq) + H₂(g)
c. Zn(s) + AlCl₃(aq) → No reaction
d. Zn(s) + 2NaOH(aq) → Na₂ZnO₂(aq) + H₂(g)
e. 3Zn(s) + 8HNO₃(dil) →3Zn(NO₃)₂(aq) + 2NO(g) + 4H₂O(l)

Question. The metal salt ‘A’ is blue in colour. When salt ‘A’ is heated strongly over a burner, then a substance ‘B’ present in it is eliminated and a white powder ‘C’ is
left behind. When a few drops of a liquid ‘D’ is added to powder ‘C’, it becomes blue again.
a. Identify A, B, C and D.
b. Write the chemical equations involved.
c. Give an example of the salt which also shows the above property.
Answer : 

c. FeSO₄.7H₂O is a salt which also shows this property.

Question. a. Write the chemical name and chemical formula of washing soda.
b. How is chlorine obtained from sodium chloride?
Give equations for the reactions involved.
c. Give an example of the salt which also shows the above property.
Answer : 
a. Na₂CO₃ 10H₂O → , Sodium carbonate decahydrate.
b. NaCl + H₂O + NH₃ + CO₂ → NaHCO₃ + NH₄Cl
2NaHCO3 → Heat Na₂CO₃ + H2O + CO₂ Heat

Na2CO3 + 10H₂O → Na₂CO₃ + 10H₂O . CO₂ gas is passed through ammonical brine to get back NaHCO₃. NaHCO₃ on heating again gives Na₂CO₃ which on crystallisation gives washing soda. 
c. Na₂CO₃ is salt of NaOH (Strong base) and H₂CO₃(Weak acid), therefore it is a basic salt. It is used for softening hard water.

Question. a. Identify the acid and the base whose combination forms the common salt that you use in your food.
Write its chemical formula and chemical name of the salt.
b. What is rock salt? Mention its colour and the reason due to which it has this colour.
c. What happens when electricity is passed through brine? Write chemical equation for it.
Answer : 
a. NaOH (Sodium hydroxide) and HCl (Hydrochloric acid) form common salt. NaCl is common salt,sodium chloride.
b. Rock salt is sodium chloride found in the form of rocks. It is yellowish in colour due to the presence of impurities.
c. Sodium hydroxide, H₂ gas and chlorine gas will be formed:
2NaCl (aq) + 2H₂O(l)  → 2NaOH(aq) + H₂(g) + Cl₂(g)

Question. a. Explain why is hydrochloric acid a strong acid and acetic acid, a weak acid. How can it be verified?
b. Explain why aqueous solution of an acid conducts electricity.
c. You have four solutions A, B, C and D. The pH of solution A is 6, B is 9, C is 12 and D is 7.
(1) Identify the most acidic and most basic solutions respectively.
(2) Arrange the above four solutions in the increasing order of H⁺ ion concentration.
(3) State the change in colour of pH paper on dipping in solution C and D.
Answer : a. Hydrochloric acid is a strong acid because it is completely ionised in its aqueous solution. Acetic acid is only partially ionised. HCl reacts with Mg vigorously whereas acetic acid reacts less vigorously.
b. Aqueous solution of acid contain ions which carry current, it conducts electricity.
c. (1) With pH = 6 ‘A’ is most acidic,With pH = 12, ‘C’ is most basic.
(2) C < B < D < A is the increasing order of H⁺ ion concentration.
(3) pH paper will turn blue in ‘C’ with pH = 12, basic pH paper will turn green in D with pH = 7, neutral.

Question. (a) Dry pellets of a base ‘X’ when kept in open absorbs moisture and turns sticky. The compound is also formed by chlor-alkali process. Write the chemical name and formula of X. Describe chloralkali process with balanced chemical equations.
Name the type of reaction occurs when X is treated with dilute hydrochloric acid. Write the relevant chemical equation.
(b) While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?
Answer :  a. ‘X’ is NaOH. It is a base which is hygroscopic i.e., absorbs moisture from the atmosphere and turns sticky. It is also formed by the electrolysis of aqueous solution of brine by chlor alkali process:
2NaCl (aq) + 2H₂O(l)  →Heat 2NaOH(aq) + H₂ (g Heat 
Neutralisation reaction will take place between NaOH and HCl:
NaOH + HCl $ NaCl + H₂O
b. It is because the process is highly exothermic. If we add H₂O to acid, the glass container may break due to excess heat evolved.

Question. a. Explain the following chemical properties of acids with the help of balanced chemical equations only:
(1) when an acid reacts with a metal carbonate,
(2) when an acid reacts with a metal bicarbonate,
(3) when an acid reacts with a metal oxide.
b. You are given three solutions A, B and C with pH values, 2,10 and 13 respectively. Which solution has the highest hydrogen ion concentration among the three and state the nature ‘acidic or basic’ of each solution.
Answer : 
a. (1) Na₂CO₃ + H₂SO₄(dil) → Na₂SO₄ + H₂O + CO₂
(2) 2NaHCO3 + H2SO₄(dil) → Na₂SO₄+ H₂O + CO₂
(3) MgO + H₂SO₄ → MgSO₄ + H₂O
b. ‘A’ has more H+ ion concentration among the three.
A’ is acidic.
‘B’ is basic.
‘C’ is strongly basic.

Question. a. A metal compound ‘X’ reacts with dilute H2SO4 to produce effervescence. The gas evolved extinguishes a burning candle. If one of the compound formed is calcium sulphate, then what is ‘X’ and the gas evolved? Also write a balanced chemical equation for the reaction which has occurred.
b. (i) Name one antacid. How does it help to relieve indigestion in stomach?
(ii) A farmer treats the soil with quicklime or calcium carbonate. What is the nature of the soil? Why does the farmer treat the soil with quicklime?
Answer : 
This is is calcium carbonate
CaCO₃(s) + H₂SO₄(dill) → CaSO₄(aq) + H₂O(l) + CO₂(g) 
The gas evolved is carbon dioxide (CO₂).
b. (i) NaHCO₃(baking soda) is an antacid. If neutralises excess of HCl in stomach and gives relief.
(ii) The nature of soil is acidic. The farmer treats the soil with quicklime (basic in nature) to neutralise the acidity of soil and make it fit for crops.

Question. a. Tooth enamel is one of the hardest substance in our body. Explain the changes in pH of mouth which indicates tooth decay. How does tooth paste help in preventing it?
b. What is the nature of salt if pH of its aqueous solution is greater than 7? Name the acid and base that would be used to prepare the following salts:
(i) Potassium sulphate, (ii) Ammonium chloride
Answer : a. Tooth enamel is made up of Ca₃(PO₄)₂ calcium phosphate. pH = 5.5 causes tooth decay because Ca₃(PO₄)₂ reacts with acid. Tooth paste are basic, neutralises the acid in mouth and prevents tooth decay.
b. The salt is basic if pH > 7.
(i) KOH and H₂SO₄ are needed to prepare K₂SO₄.
(ii) NH₄OH and HCl are needed to prepare NH₄Cl.

Question. (a) A salt is produced by reaction between an acid and a base. Identify the acid and base from which the following salts have been formed:
(i) Na₂SO₄, (ii) NH₄Cl, (Hi) KNO₃, (iv) NaCl
(b) Which one of these will have pH less than 7 and why?
Answer : (a) (i) Na₂SO₄ is prepared from NaOH and H₂SO₄
(ii) NH₄Cl is formed by NH₄OH and HCl.
(iii) KNO₃ is formed by KOH and HNO₃.
(iv) NaOH is formed by NaOH and HCl.
(b) NH₄Cl has pH less than 7 because it is a salt of weak base NH4OH and strong acid, HCl, therefore the salt is acidic.

Question. What are strong acids and weak acids? In the following list of acids, separate strong acids from weak acids: hydrochloric acid, citric acid, acetic acid, nitric acid, formic acid, sulphuric acid.
Answer : Strong acids are those acids which are completely ionised in aqueous solution e.g.-,
HCl(aq) → H+(aq) + Cl-(aq)
Weak acids do not ionise completely in aqueous solution:
CH₃COOH(aq) ⇌ CH₃OO-(aq) + H+(aq)
Strong acids: Hydrochloric acid, Nitric acid, Sulphuric acid.
Weak acids: Citric acid, Acetic acid, Formic acid.