Acids Bases Salts Class 10 Science Exam Questions

Exam Questions Class 10

Please refer to Acids Bases Salts Class 10 Science Exam Questions provided below. These questions and answers for Class 10 Science have been designed based on the past trend of questions and important topics in your class 10 Science books. You should go through all Class 10 Science Important Questions provided by our teachers which will help you to get more marks in upcoming exams.

Class 10 Science Exam Questions Acids Bases Salts

Class 10 Science students should read and understand the important questions and answers provided below for Acids Bases Salts which will help them to understand all important and difficult topics.

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?


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: The pH of a salt which is used to make tasty and crispy pakoras is 14. Identify the salt and write achemical equation for its formation. List its two uses.


The salt is NaHCO3, sodium hydrogen carbonate.
NH3(g) CO2(g) NaCl (g) H2O(l)→ NaHCO3(s) NH4Cl 
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: pH has a great importance in our daily life. Explain by giving three examples.


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 ofcrops.

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 than7 and one salt with pH less than 7.


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. Define pH scale. Draw a figure showing variation of pH with change in concentration of H+(aq) and OH-(aq) ions.
b. Mention the pH of acidic, basic and neutral solutions respectively.


a. pH scale is a scale which is used for measuring
hydrogen ion concentration in a solution.  EMAGE
b. pH < 7 is for acidic solution, pH > 7 basic solution,
pH = 7 for neutral solution.

Question: a. The blue colour of crystals of a substance on heating in a closed test tube gets changed but the colour was regained after sometime on cooling. Name that substance and write its chemical formula. Explain the phenomenon involved.
b. Write name and chemical formulae of two such compounds whose one unit is associated with 10 and 2 water molecules respectively


a. Hydrated copper sulphate, CuSO4.5H2O is the name and chemical formula of that substance.
It loses water of crystallisation on heating and regains these molecules of water on exposure to the atmosphere:
CuSO4·5H2OHeat→ CuSO4+5H2O
Blue                    (Dirty while)

CuSO4(s) 5H2O(l)→CuSO4· 5H2 O
b. Na2CO3.10H2O, washing soda (Sodium carbonate decahydrate) has 10 molecules of water of crystallisation. CaSO4.2H2O, gypsum, chemically
calcium sulphate dihydrate has 2 molecules of water of crystallisation.

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.


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: Explain the action of dilute hydrochloric acid on the following with suitable chemical equations:
a. Magnesium ribbon,
b. Sodium hydroxide,
c. Crushed egg shells.


a. Mg(s) + 2HCl(dil) → MgCl2(aq) + H2(g)
b. NaOH(aq) + HCl(dil) →  NaCl(aq) + H2O(l)
c. CaCO3 (s) 2HCl (dil) → CaCl2 (g)+ CO2 (g)+ H2O(1) 

Question: a. Define olfactory indicators. Name two substances which can be used as olfactoiy indicators. 
b. Choose strong acids from the following:


a. Olfactory indicators: They give different smell in acidic and basic medium e.g., onion, clove, vanilla.
b. HNO3 and H2SO4 are strong acids among the given acids.

Question: You are provided with magnesium ribbon and sulphur powder. Explain with the help of activity that metal
oxides are basic and oxides of non-metals are acidic in nature.


Bum magnesium ribbon with the help of tongs to form white ash. Dissolve the ash in hot water. Add red litmus which turns blue, showing that MgO is a
basic oxide.
2Mg(s) + O2(g) → 2MgO(s)
MgO(s) + H2O(Hot) → Mg(OH)2(aq)
Heat sulphur taken in a iron spatula and pass the gas through water. Add blue litmus into it. It will turn red showing SO2 is an acidic oxide.
S + O2 → SO2
SO2 + H2O → H2SO3 (Sulphurous acid)

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?


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? 


p stands for ‘potenz’ in German meaning power, H stands of hydrogen.

Question: Write chemical equation for the reaction of zinc metal on sodium hydroxide.


Zn(s) + 2NaOH(aq) Heat → Na2ZnO2(aq) + H2(g)

Question: Mention the range of pH for identification of a base. 


7.1 to 14 is the pH range for bases.

Question: Define alkalies and give an example. 


 Water soluble bases are called alkalies e.g., NaOH.

Question: How chloride of lime differs from calcium chloride?


CaOCl2 is the chloride of lime whereas CaCl2 calcium chloride.

Question: What is meant by water of crystallisation in a substance? 


The water molecules associated with a crystalline solid are called water of crystallisation.

Question: What effect does an increase in concentration of it is diluted?


pH of the solution increases when it is diluted

Question: Name a gas evolved when dilute HCl reacts with sodium hydrogen carbonate. How is it recognised? 


Carbon dioxide, it turns lime water milky. In this way, CO2 gas is recognised.

Question: Write the chemical name and chemical formula of washing soda


 Na2CO3.10H2O, sodium carbonate deca-hydrate is washing soda.

Question: Why does 1 M HCl solution have a high concentration of H+ ions than 1 M CH3COOH solution? 


It is because 1M HCl is a strong acid and it is completely ionised in aqueous solution whereas CH3COOH is a weak acid, so it is only partially ionised.

Question: Write the chemical equation representing the action of atmospheric CO2 gas on bleaching powder when left exposed in open. 


CaOCl2 + CO2 $ CaCO3 + Cl2

Question: How will you test for the gas which is liberated when hydrochloric acid reacts with an active metal? 


Bring a burning matchstick near the gas. If it is burnt with ‘pop’ sound, the gas is H2.

Question: What are olfactory indicators? 


Those indicators whose smell changes in acidic and basic solutions. 

Question: How is the pH of solution of an acid influenced when family. 


NaCl, Na2CO3 are two salts belonging to sodium family.

Question: Which gas is evolved when dilute hydrochloric acid reacts with zinc metal?


Write the molecular formula of this gas. Dihydrogen gas, H2.

Question: Dry HCl gas does not change the colour of dry blue litmus. Give reason to justify it.


 Dry HCl (g) does not form ions, therefore it does not affect dry blue litmus.

Question: Why is HCl a stronger acid than acetic acid?


 HCl is completely ionised in aqueous solution whereas acetic acid is only partially ionised in aqueous solution.

Question: Name the chemicals used in acid fire extinguisher and the gas evolved from it when it is used?


NaHCO3 (Sodium hydrogen carbonate) and H2SO4 (Sulphuric acid). The gas evolved is carbon dioxide.

Question: At what pH rain water is said to be acidic ? 


 When pH < 5.5, the rain water becomes acidic. 

Question: Which is a stronger acid, with pH = 5 or with pH=2? .


The acid with pH = 2 is a stronger acid

Question: What is meant by term pH of solution? The pH of rain water collected from two cities A’ and ‘B’ were found to be 6.0 and 5.0 respectively. The water of which city will be more acidic?


pH of solution is defined as negative logarithm of H+ ion concentration. It determines the strength of acid and base. Rainwater with pH = 5 is more acidic.

Question: A few drops of sulphuric acid are added to water before electrolysis, why?


 Water is not a good conductor of electricity. Few drops of sulphuric acid makes it better conductor of electricity.

Question: A compound which is prepared from gypsum has the property of hardening when mixed with a proper quantity of water. Identify the compound and write its chemical formula.


CaSO4.1/2H2O (Plaster of Paris), Calcium sulphate hemihydrate.

Question: Which among distilled water, tap water and sea water is the best conductor of electricity?


 Sea water is a better conductor due to the presence of ions.

Question: Write the names of two salts belonging to sodium family.


NaCl, Na2CO3 are two salts belonging to sodium family.

Question: Name a salt which does not contain water of crystallisation.


 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.   


Plaster of Paris, CaSO4.1/2H2O

Question: Name the acids present in (i) nettle sting, (ti) curd.


(i) HCOOH, Formic acid, (ii) Lactic acid, CH3-CH(OH)-COOH

Question: Which bases are called alkalies? Give one example of alkali. 


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. Ans   


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. 


Na2CO3(s) 2HCl (dill) 2NaCl (aq) CO2(g) H2O(l) + $ + +

Question: Name the acid and base that have constituted the salt ammonium nitrate.


 Acid: HNO3, Base: NH4OH (i.e., Nitric acid, Ammonium hydroxide).

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


It will be sour in taste. 

Question: Suggest one way to reduce alkaline nature of the soil.


Add ammonium nitrate (Acidic salt) to neutralise alkaline nature of soil.

Question: What is the action of litmus on
a. dry ammonia gas
b. solution of ammonia gas in water?


a. There is no effect of dry litmus on dry ammonia gas.
b. Solution of ammonia will turn red litmus blue.

Question: State the observations you would make on adding sodium hydroxide to an aqueous solution of
a. ferrous sulphate,
b. aluminium chloride.


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.


Sodium chloride is made up of a strong base, NaOH and a strong acid, HCl. Therefore, its aqueous solutionis neutral in nature.
Sodium metal reacts with water to form NaOH(Base) and H2 gas:

Question: Name the acid present in the following:
a. Tomato,
b. Vinegar,
c. Tamarind


a. Tomato contains oxalic acid.
b. Vinegar contains acetic acid.
c. Tamarind contains tartaric acid.

Question: Explain how antacid works.


Antacids are weakly basic in nature. They neutralise excess of HCl present in our stomach and gives us relief from hyper-acidity.

Question: 15mL of water and 10mL of sulphuric acid are to be mixed in a beaker 
a. State the method that should be followed with reason.
b. What is this process called?


a. Acid should be added to the water slowly with constant cooling because the reaction is highly exothermic.
b. This process is called dilution

Question: State what does pH of solution signify? Three solutions A, B and C have pH values of 6, 2 and 10 respectively. Which one of these solutions is highly acidic? Which solution will turn red litmus blue?


pH of solution signifies the nature of the solution i.e., it is weakly acidic, strongly 1 acidic, neutral, weakly basic, strongly basic. 
‘B’ with pH = 2 is strongly acidic.
‘C’ with pH = 10 will turn red litmus blue.

Question: Define an acid and a base. Name one weak acid and one strong acid.


Acid is a substance which gives H+ ions in an aqueous solution.
Base is substance which gives OH- ions in the aqueous solution.
CH3COOH is a weak acid, H2SO4 is a strong acid

Question: Equal lengths of magnesium ribbon are taken in test tube ‘A’ and ‘B’. Hydrochloric acid (HCl) is added to test tube A’ while acetic acid (CH3COOH) is added to test tube ‘B’. In which test tube, will fizzing occur more vigorously and why?


The fizzing will occur more vigorously in test tube ‘A’ because HCl is a strong acid and reacts faster than acetic acid which is a weak acid.

Question: What is universal indicator? State the purpose for which this indicator is used.


Universal indicator is a mixture of a number of
indicators. It is used to determine pH of a solution.

Question: Explain why sodium hydroxide solution cannot be kept in aluminium containers? Write the equation for the reaction that may take place for the same. 


It because ‘Al’ reacts with NaOH to form sodium meta-aluminate and hydrogen gas:
2Al + 2NaOH + 2H2O $ NaAlO2+3H2

Question: A student detected the pH of four unknown solutions A, B, C and D as follows: 11, 5, 7 and 2. Predict the nature of these solutions.


pH = 11 is basic
pH = 5 is acidic
pH = 7 is neutral
pH = 2 is strongly acidic

Very Short Answers Type Questions

Question: What is observed when a pinch of sodium hydrogen carbonate is added to 2 ml of acetic acid taken in a test tube ? Write chemical equation for the reaction involved in this case.
Answer : CO2 gas is evolved with brisk effervescence when sodium hydrogen carbonate is added to acetic acid.

Acids Bases Salts Class 10 Science Exam Questions

Question: Blue litmus solution is added to two test tubes A and B containing dilute HCl and NaOH solution respectively. In which test tube a colour change will be observed ? State the colour change and give its reason.
Answer : Test tube A will show colour change because acids turn blue litmus to red. So the final colour of test tube would be red.

Question: What is observed when 2 ml of dilute hydrochloric acid is added to 1 g of sodium carbonate taken in a clean and dry test tube ? Write chemical equation for the reaction involved.
Answer : A brisk effervescence would be observed if HCl is added to Na2CO3 due to the evolution of CO2 gas.
Na2 CO3 + HCl → NaCl + H2O + CO2.

Question: A teacher provided acetic acid, water, lemon juice, aqueous solution of sodium hydrogen carbonate and sodium hydroxide to students in the school laboratory to determine the pH values of these substances using pH papers. One of the students reported the pH values of the given substances as 3, 12, 4, 8 and 14 respectively. Which one of these values is not correct ? Write its correct value stating the reason.
Answer : The value of pH for water is not correct. The correct value of pH of water is 7 because it has almost equal concentration of H+ and OH due to which it is neutral.

Question: In the laboratory of a school, the sample of hard water is not available “to study the comparative cleaning capacity of a sample of soap in soft and hard water”. Which salt from the laboratory can be added to tap water to make it hard ? In the experiment how is cleaning capacity of soap compared ?
Answer : (a) Sulphate, chloride or hydrogen carbonate of calcium or magnesium can be added to tap water to make it hard.
(b) By adding equal amount of soap to water taken in two test tubes, shaking vigorously and comparing the length of lather or foam formed in each test tube. The cleaning capacity of soap is compared.

Question: If someone is suffering from the problem of acidity after overeating, which of the following would you suggest as remedy ? Lemon juice, Vinegar, Baking soda solution. Give reason for your choice.
Answer : Baking soda solution. The solution being basic in nature, it neutralises excess acid in the stomach.

Question: How is the neutralisation of a carbonate with an acid different from the neutralisation of an oxide or a hydroxide ?
Answer : Neutralisation of a carbonate with an acid produces carbon dioxide gas but not with an oxide or hydroxide.

Question: A gas is liberated immediately with a brisk effervescence, when you add acetic acid to sodium hydrogen carbonate powder in a test tube. Name the gas and describe the test that confirms the identity of the gas.
Answer : CH3COOH + NaHCO3 → CH3COONa + CO2 + H2O
Gas evolved is CO2. It is tested by passing CO2 in lime water which turns milky due to formation of insoluble CaCO3.
Ca(OH)2 + CO2 → CaCO3↓ + H2O

Question: What happens when phenolphthalein is added to an acidic solution ?
Answer : There is no change in colour as it remains colourless.

Question: On adding dilute hydrochloric acid to copper oxide powder, the solution formed is blue-green.
(a) Predict the new compound formed which imparts a blue-green colour to solution.
(b) Write a balanced chemical equation of the reaction which takes place.
(c) On the basis of the above reaction, what can you say about the nature of copper oxide ? 
Answer : (a) The new compound formed is Copper (II) chloride, CuCl2.
(b) CuO(s) + 2HCl(aq) → CuCl2(aq) + H2O(l)
(c) Copper oxide is basic in nature.

Question: A substance X which is used as an antacid reacts with dilute hydrochloric acid to produce a gas Y which is used in one type of fire-extinguisher. Name the substance X and gas Y. Write a balanced equation for the chemical reaction which takes place.
Answer : Substance X is sodium hydrogen carbonate; gas Y is carbon dioxide.
NaHCO3 + HCl → NaCl + CO2 + H2O

Question: Why do acids not show acidic behaviour in the absence of water ?
Answer : Acids do not show acidic behaviour in the absence of water because the dissociation of hydrogen ions from an acid occurs in the presence of water only. It is the hydrogen ions that are responsible for the acidic behaviour.

Question: (a) Why is it wrong to treat a bee sting with vinegar ?
(b) Why is it wrong to treat a wasp sting with baking soda solution ?

Answer : (a) Bee injects acid into the skin. Vinegar is acetic acid so it can’t be used to treat bee sting.
(b) Since baking soda is basic in nature so it can’t be used to treat wasp sting because wasp injects alkaline liquid into the skin.

Question: Name one animal and one plant whose stings contain formic acid (or methanoic acid).
Answer : Animal that contains formic acid–ant. Plant that contains formic acid–nettle plant.

Short Answers Type Questions

Question: What would a student report nearly after 30 minutes of placing duly cleaned strips of aluminium, copper, iron and zinc in freshly prepared iron sulphate solution taken in four beakers ?
Answer : Aluminium displaces the iron from iron sulphate and the colour of two solution changes from green to colourless.
No change takes place when copper strip is dipped in iron sulphate solution.
No change will be observed when iron strips are dipped in iron sulphate solution.
The colour of the solution changes from green to colourless when zinc is added to iron sulphate solution.

Question: Identify the acid and the base from which sodium chloride is obtained. Which type of salt is it ? When is it called rock salt ? How is rock salt formed ?
Answer : NaCl is made by reacting an acid and a base. The base is NaOH (sodium hydroxide). So,
HCl + NaOH → NaCl + H2O
It is a neutralisation reaction.
It is known as rock salt in crystalline form.
It is the result of the evaporation of ancient oceans millions of years ago. Sometimes pressure from deep inside the Earth forces up large masses of rocks to form salt like domes.

Question: On heating blue coloured powder of copper (II) nitrate in a boiling tube, black copper oxide, O2 and a brown gas X is formed.
(a) Identify the type of reaction and the gas X.
(b) Write balanced chemical equation of the reaction.
(c) Write the pH range of aqueous solution of the gas X.
Answer : (a) Decomposition reaction :
The gas X is nitrogen dioxide (NO2)

Question: On heating blue coloured powder of copper (II) nitrate in a boiling tube, black copper oxide, O2 and a brown gas X is formed.
(a) Identify the type of reaction and the gas X.
(b) Write balanced chemical equation of the reaction.
(c) Write the pH range of aqueous solution of the gas X.
Answer : (a) Decomposition reaction :
The gas X is nitrogen dioxide (NO2)

Acids Bases Salts Class 10 Science Exam Questions

(c) Oxides of non-metals are acidic. Therefore, aqueous solution of this gas would be acidic. The pH would be less than 7 or 6.9.

Question: (a) While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid ?
(b) Dry hydrogen chloride gas does not change the colour of dry litmus paper why ?
Answer :
(a) The process of mixing the concentrated acid with water is highly exothermic. So, when a concentrated acid is added to water then heat is easily absorbed by the large amount of water. Thus it is recommended to add acid to water and not water to the acid.
(b) Dry hydrogen chloried does not contain any hydrogen ions in it, so it does not show acidic behaviour and thus does not change the colour of dry litmus paper.

Question: Complete and balance the following chemical equations : 
(i) NaOH(aq) + Zn(s) →
(ii) CaCO3(s) + H2O(l) + CO2(g) →
(iii) HCl(aq) + H2O(l) →
Answer :

Acids Bases Salts Class 10 Science Exam Questions

(ii) Calcium carbonate will react with water that is saturated with carbon dioxide to form the soluble calcium bicarbonate.
CaCO3(s) + CO2 (g) + H2O (l) → Ca (HCO3)2(aq)
(iii) HCl + H2O → H3O+ + Cl

Question: (a) What is produced if an acid is added to a base ?
(b) Why does dry HCl gas not change the colour of dry litmus paper ?
(c) What colour does phenolphthalein indicator turn when added to an alkali (such as sodium hydroxide) ?
Answer : (a) Salt and water.
(b) Dry HCl gas does not change the colour of dry litmus paper because it has no hydrogen ions (H+ions) in it which can impart acidic properties to it.
(c) Pink.

Question: The pH of a salt 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 commonly used to make tasty and crispy pakoras is baking soda i.e., sodium hydrogen carbonate (NaHCO3).
Chemical equation for its formation :
NaCl + H2O + CO2 + NH3 → NH4Cl + NaHCO3
Uses of Baking Soda :
(a) It is used in fire extinguisher.
(b) It is also used as ingredient of antacid.

Question: Complete the following chemical equations :
(a) CH3COOH + Na2CO3
(b) CH4 + O2
(c) 2C2H5OH + Na →
Answer :

Acids Bases Salts Class 10 Science Exam Questions

Question: What happens when an acid reacts with a base ?
Explain by taking the example of hydrochloric acid and sodium hydroxide. Give equation of the chemical reaction which takes place. What is the special name of such a reaction ?
Answer : When an acid reacts with a base, then a salt and water are formed. When hydrochloric acid reacts with sodium hydroxide solution, then a neutralisation reaction takes place to form sodium chloride and water.
NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)
Such a reaction is termed as neutralisation reaction.

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 obtained.
Answer : Bleaching powder is formed.
Ca(OH)2 + Cl2 → CaOCl2 + H2O
(a) It is used as bleaching agent in paper and textile industries.
(b) It is used as disinfectant in purification of drinking water.

Question: How following metals react with acids : magnesium, zinc, iron and copper?
Answer : (a) Magnesium react vigorously with acids. 
(b) Zinc reacts less vigorously with acids than magnesium.
(c) Iron react slowly.
(d) Copper does not react at all.

Question: (a) If you are asked to report your observations about the following two properties of acetic acid, what would you report ?
(i) Odour
(ii) Effect on litmus
(b) If you take a pinch of sodium hydrogen carbonate powder in a test-tube and add drop-by-drop acetic acid to it, what would you observe immediately ?
List any two main observations.  
Answer : (a) (i) Smells like vinegar.
(ii) Turns blue litmus red.
(b) (i) Brisk effervescence will be observed.
(ii) Evolution of colourless gas.

Question: How is sodium hydroxide manufactured in industries?
Name the process. In this process a gas X is formed as by-product. This gas reacts with lime water to give a compound Y, which is used as a bleaching agent in the chemical industry. Identify X and Y and write the chemical equation of the reaction involved.
Answer : Sodium hydroxide is manufactured by the electrolysis of concentrated aqueous solution of sodium chloride

Acids Bases Salts Class 10 Science Exam Questions

The process of manufacture of sodium hydroxide by electrolysis process is called chlor-alkali process. Gas X is chlorine gas and compound Y is calcium oxychloride (Bleaching powder)

Acids Bases Salts Class 10 Science Exam Questions

Question: Identify the acid and base which form sodium hydrogen carbonate. Write chemical equation in support of your answer. State whether this compound is acidic, basic or neutral. Also write its pH value.
Answer : The acid and base that forms sodium hydrogen carbonate are as follows :
Acid – H2CO3
Base – NaOH
The chemical equation for its formation will be :

Acids Bases Salts Class 10 Science Exam Questions

The compound will be basic and its pH value will be around 8 or in the range between 7 and 10.

Question: Which gas is usually liberated when an acid rea cts with a metal ? Illustrate with an example. How will you test for the presence of this gas ?
Answer : Hydrogen gas is usually liberated when an acid reacts with a metal.
Take few pieces of zinc granules and add 5 ml of dilute
H2SO4. Shake it and pass the gas produced into a soap solution. The bubbles of the soap solution are formed.
These soap bubbles contain hydrogen gas.
Zn     +     2H2SO4     →     Zn(SO4)2 + 2H2
Zinc     Sulphuric acid         Zinc Sulphate 
We can test the evolved hydrogen gas by burning it with a pop sound when a candle is brought near the soap bubbles.

Question: You have been provided with three test-tubes. One of these test-tubes contains distilled water and the other two contain an acidic and a basic solution respectively.
If you are given only blue litmus paper, how will you identify the contents of each test-tube ? 
Answer : 
Acidic solution will turn blue litmus red. This red litmus will turn blue in basic solution. Distilled water will have no effect on any type of litmus paper.

Question: A group of students measured the pH of some substances they found in their homes. Their results are given in the following table :
(a) What would the students have used to measure the pH ?
(b) Which solution is the most acidic ?
(c) Which solution is the most alkaline ?
(d) Which solutions are neutral ?
(e) Which solution can be used to treat wasp stings ?
(f) Which solution can be used to treat bee stings ?
Answer : (a) Universal indicator paper is used to measure the pH.
(b) Lemon juice with pH = 2.5 is the most acidic.
(c) Household ammonia with pH = 12 is the most alkaline.
(d) Salt solution and sugar solution with pH = 7 are neutral.
(e) Vinegar (acid) can be used to treat wasp stings since it injects an alkaline liquid into the skin.
(f) Baking soda can be used to treat bee stings since, it injects methanoic acid into the skin.

Question: 1g of solid sodium chloride is taken in a clean and dry test tube and 2 ml of conc. sulphuric acid is added to it. If the gas evolved is tested first with dry and then with wet blue litmus paper, in which case will the litmus paper change colour ? Give reason for your answer. What inference can be drawn about the nature of the evolved gas ? Support your answer with chemical equation for the reaction.
Answer : 
Wet blue litmus paper will change the colour because hydrogen ions are produced by HCl in the presence of water. It has acidic nature and the reaction involved is :
HCl + H2O → H3O+ + Cl

Question: Why should curd and sour substances not be kept in brass and copper vessels ?
Answer : Curd and other sour substances not be kept in brass and copper vessels as they contain acids. When these substances are kept in brass and copper vessels, the metal reacts with the acid to liberate hydrogen gas and harmful products. As a result, food gets spoiled.

Question: (a) For the preparation of cakes, baking powder is used. If at home your mother uses baking soda instead of baking powder, how will it affect the taste of the cake and why ?
(b) How is baking soda be converted into baking powder ?
(c) What makes the cake soft and spongy ?
Answer : (a) The cake will have a bitter taste because of the formation of Na2CO3 or sodium carbonate while baking or heating the cake.
(b) By adding tartaric acid baking soda can be
converted to baking powder.
(c) The CO2 gas liberated makes the cake soft and spongy.

Long Answers Type Questions

Question: In the following schematic diagram for the preparation of hydrogen gas as shown in figure what would happen if following changes are made ?
(a) In place of zinc granules, same amount of zinc dust is taken in the test tube.
(b) Instead of dilute sulphuric acid, dilute hydrochloric acid is taken.
(c) In place of zinc, copper turnings are taken.
(d) Sodium hydroxide is taken in place of dilute sulphuric acid and the tube is heated.
Answer : (a) If in place of zinc granules, same amount of zinc dust is taken, hydrogen gas will evolve with greater speed.
(b) If instead of dilute sulphuric acid, dilute hydrochloric acid is taken, almost same amount of gas is evolved.
(c) Hydrogen gas is not evolved. 
(d) If sodium hydroxide is taken, sodium zincate is formed and hydrogen gas will be evolved.
Zn + 2NaOH → Na2ZnO2 + H2

Question: Write uses of (a) Acids (b) Bases (c) Salts.
Answer : (a) Uses of acid :
(i) Hydrochloric acid is used in many industries like cleaning boilers from inside, cleaning sink and sanitary etc.
(ii) Nitric acid is used for making fertilizers, cleansing of ornaments of gold and silver.(iii) Sulphuric acid is used in cells, car battery etc. It is known as King of Chemicals.
(b) Uses of bases :
(i) Sodium hydroxide is used to make soaps, in paper industry and in textile industry.
(ii) Calcium hydroxide is used to remove acidity of soil. It is an important constituent of lime and pesticides.
(iii) Milk of magnesia (Magneisum hydroxide) is used as an antacid.
(c) Uses of salts :
(i) Calcium carbonate is used to make floors.
(ii) In metallurgy for extraction of iron and in making of cement.
(iii) Silver nitrate is used in photography, Ammonium nitrate is used as explosive and in making fertilizers.
(iv) Alum(K2SO4. Al2SO4. 24H2O) is used to clean water.

Question: For making cake, baking powder is taken. If at home your mother uses baking soda instead of baking powder in cake.
(a) How will it affect the taste of the cake and why ?
(b) How can baking soda be converted into baking powder ?
(c) What is the role of tartaric acid added to baking soda ?
Answer : (a) Baking soda is sodium hydrogen carbonate. On heating, it is converted into sodium carbonate which is bitter to taste. Thus, if baking soda is used the taste of cake changes.
NaHCO3 → Na2CO3 + H2O + CO2
(b) Baking powder is a mixture of baking soda, cream of tartar (a dry acid), and sometimes corn starch.
Therefore, baking soda can be converted into baking powder by the addition of appropriate amount of tartaric acid to it.
(c) Tartaric acid is added to neutralise the sodium carbonate formed on heating by the decomposition of NaHCO3. If it is not added, the cake would taste bitter due to the presence of sodium carbonate in it. Also, CO2 produced during the reaction causes cake to rise making them soft and spongy.

Question: (a) What is ‘pH’ scale ? Explain. How the pH of a neutral solution can be changed to acidic or basic ?
(b) Why is calcium sulphate hemihydrate called ‘Plaster of Paris’ ?
Answer :
(a) The strength of an acid or a base is expressed in terms of hydronium ion concentration. This is expressed on a scale known as ‘pH’ scale. It is a
14 point scale; i.e., it has values ranging from 0 to
14, indicating the value of negative logs of H+ ion concentration of the solution. In the pH scale pH=7
means neutral solution, pH less than 7 means acidic solution and pH more than 7 means basic solution.
pH of a neutral solution can be changed by adding acid or base. If a small amount of acid is added, its pH decreases and solution becomes acidic. If few drops of base is added, its pH increases and solution becomes basic.
(b) Plaster of Paris gets its name from large gypsum deposits in Montmartre in Paris. We know that
Plaster of Paris, which is chemically calcium sulphate hemihydrate is obtained by heating gypsum. So, the origin of the name ‘Plaster of Paris’ is the fact that the source material gypsum is found in large deposits at Montmartre in Paris.

Acids Bases Salts Science Class 10 Science Exam Questions

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