Class 10 Science Chapter 2 Board Questions

Class 10 Science Chapter 2 Board Questions of Acids, Bases and Salts including last 10 years papers questions, important and frequently asked questions in CBSE Board with suitable answers of 1 mark, 2 marks, 3 marks and 5 marks questions with equations and answers.

These set of questions contains last 5 years CBSE Questions with answers, important questions from last ten years, questions from CBSE Sample papers which are related to Class 10 Science Chapter 2 Acids, Bases and Salts for new academic session 2020-21.

Class 10 Science Chapter 2 Board Questions 2020-21

Class:10
Subject:Science
Contents:Board Questions – 10 Years Papers

Class 10 Science Chapter 2 Board Questions with Answers

Class 10 Science Chapter 2 Board Questions with answers including last 5 years papers and all questions from last 5 years papers for the preparation of academic session 2020-21. Answers of all questions are given just below of all questions. For NCERT Solutions 2020-21 visit to NCERT Sols main page or you may download Tiwari Academy Apps working Offline as well as Online.

10th Science Chapter 2 Board Questions Set – 1 (1 Mark)

How will you test for the gas which is liberated when hydrochloric acid react with an active metal? [CBSE 2012]

Bring a burning matchstick near the gas. It burns with pop sound showing that it hydrogen.

Write the name and chemical formula of the products formed by heating Gypsum at 373K. [CBSE 2010]

CaSO4 .2 H2O → CaSO4 .1/2 H2O + 3/2 H2O

The PH of the sample of the vegetable soup was found to be 6.5. How is this soup like to taste? [CBSE 2010]

The taste will be slightly sour as it is weakly acidic.

Which base are called alkalies? Give an example of alkalies. [CBSE 2010]

Soluble bases are called alkalis.

Write the name and the chemical formula of the product formed by the action of chlorine on slaked lime? [CBSE 2010]

Ca(OH)2 + Cl2 → CaOCl2 + H2O

Write a balanced chemical equation for the reaction between sodium carbonate and hydrochloric acid indicating the physical state of the reactant and the products? [CBSE 2010]

Na2CO3 + 2HCL → 2NaCl + CO2 + H2O

Write a balanced chemical equation for a neutralization reaction. Mentioning the physical state of the reactant and the product? [CBSE 2010]

NaOH + HCL → NaCl + H2O

During summer season a milkman usually adds a very small amount of baking soda to fresh milk. Give one reason. [CBSE 2009]

Milkman adds a very small amount of baking soda so as to prevent spoilage of milk. It leads to change in pH which does not allow bacteria and enzymes to act and milk does not become sour due to fermentation.

Curd is not kept in copper and Brass Utensils

Curd and sour substance contain acids which react with brass and copper vessels to form poisonous salts which are harmful for our health.

10th Science Chapter 2 Board Questions Set – 2 (1 Mark)

Name the gas usually liberated when a dilute acid react with a metal. What happen when burning candle is brought near this gas. [CBSE 2009]

H2 gas is liberated. It burns with pop sound it burns with pop sound when burning candle is brought near the gas.

Fresh milk has a pH of 6. When it changes into curd will its pH value increases or decreases why? [CBSE 2009]

Its pH will decrease because curd is sour in taste due to presence of acid in it.

What would be the colour of litmus in a solution of sodium carbonate? [CBSE 2009]

The red litmus will change to blue in sodium carbonate solution.

What effect does an increase in concentration oh H+ in a solution have on the pH of solution? [CBSE 2009]

Higher the concentration lower will be pH of the solution.

Which one of these has a higher concentration of H+ ions? 1 M HCl or 1 M CH3COOH. [CBSE 2009]

1 M HCl has higher concentration of H+ ions.

Why does 1M HCl solution have a higher concentration of H+ ions than 1 M CH3COOH solution? [CBSE 2009]

1 M HCl has higher concentration of H+ ions because it ionises completely in aqueous solution whereas CH3COOH does not as it is weak acid.

Which gas is generally liberated when a dilute solution of hydrochloric acid react with an active metal? [CBSE 2009]

Hydrogen gas is liberated when active metal reacts with dilute hydrochloric acid.
Zn + 2HCl → ZnCl2 + H2

What is the colour of litmus solution of ammonium hydroxide? [CBSE 2009]

Red litmus will turn into blue in ammonium hydroxide.

Flow of Acid Rain into in a River

Flow of acid rain water into the river lower the pH of rainwater which make the aquatic life difficult to survive in rain water. For survival of aquatic lives the suitable pH range must be 7.0 to 7.8.

10th Science Chapter 2 Board Questions Set – 3 (1 Mark)

Which gas is evolved when sodium hydrogen carbonate reacts with hydrochloric acid? [CBSE 2009]

Carbon Dioxide gas is evolved.

On adding dilute hydrochloric acid to copper oxide powder the solution formed is blue-green colour to the solution. Predict the new compound formed which imparts a blue green colour to the solution. [CBSE 2008]

The name of the compound formed is copper chloride gives blue green colour to the solution.
CuO + 2HCl → CuCl2 + H2O

How is the pH of solution of an acid influence when it is diluted? [CBSE 2008]

When acid is diluted H+ Concentrated in mole/L will decrease and pH will increase.

How does the pH of the solution change when a solution of a base is diluted? [CBSE 2008]

pH of a base solution decreases on dilution.

Arrange the following in an increasing order of their pH value: NaOH solution, Blood, lemon juice. [CBSE 2008]

Lemon Juice → Blood → NaOH solution

Why should water be never added dropwise to concentrated sulphuric acid? [CBSE 2007]

It is because the process is highly exothermic and beyond control and bottle may break.

Name the gas evolved when dilute sulphuric acid acts on sodium carbonate? [CBSE 2006]

Carbon dioxide.

A compound which is prepared from gypsum has the property of hardness when mixed with proper quantity of water. Identify the compound and write its chemical formula. [CBSE 2011]

The compound is Plaster of Paris, CaSo4. ½ H2O.

Name a salt which do not water of crystalline. [CBSE 2010]

Sodium hydrogen Carbonate (NaHCO3) does not contain water of crystalline.

Name the acid present(i) Nettle sting (ii) Curd [CBSE 2010]

The acid present are as under:
Nettle Sting – Methanoic Acid
Curd – Lactic Acid

Two Salts Belonging to Sodium Family

1. Sodium Carbonate
2. Sodiumhydrogen Carbonate

10th Science Chapter 2 Previous Years Papers Set – 4 (2 Marks)

What is neutralization reaction? Give one example. [CBSE 2011]

The reaction in which acids reacts with base to form salt and water.,

Example:
NaOH + HCl → NaCl + H2O

State the chemical name of plaster of Paris. Write a chemical equation to show the reaction between Plaster of Paris and water. [CBSE 2011]

Calcium sulphate hemihydrate

CaSO4.½ H2O + 3/2 H2O → CaSO4.2H2O

State in brief preparation of washing soda from baking soda. Write balanced chemical equation involved. [CBSE 2011]

Sodium hydrogen carbonate (baking soda) on heating gives sodium carbonate which on recrystallisation gives washing soda.

2NaHCO3 → Na2CO3 + CO2 + H2O
Na2CO3 + 10.H2O → Na2CO3.10H2O

What is the colour of FeSO4. 7H2O crystals? How does this colour change upon heating? Give balanced chemical equation for the changes. [CBSE 2011]

Pale green is the colour of FeSO4.7H2O crystals. It became dirty white on heating.

FeSO4.7H2O → FeSO4 + 7H2O

Classify the following salts into acidic, basic and neutral: Potassium sulphate, Ammonium chloride, Sodium carbonate, Sodium chloride. [CBSE 2011]

Neutral: Potassium sulphate, Sodium Chloride

Acidic: Ammonium Chloride

Basis: Sodium Carbonate

A student dropped few pieces of marble in dilute HCL contained in a test tube. The evolved gas was passed through lime water. (i) What change would be observed in lime water? (ii) Write the balanced chemical equation for the above change? [CBSE 2011]

(i) Lime water will turn milky due to formation of calcium carbonate.

(ii) Ca(OH)2 + Cl2 → CaCO3 + H2O

What happen when chlorine is passed over slaked lime at 313K? Write chemical equation of the reaction involved and state two uses of the product obtained. [CBSE 2010]

Bleaching powder is formed.
Ca(OH)2 + Cl2 → CaOCl2 + H2O

Uses:
(i) It is used as bleaching agent in paper and textile industry.
(ii) It is used as disinfectant in purification of drinking water.

Baking Powder

Baking powder is a mixture of sodium hydrogen carbonate and tartaric acid. On heating it liberates carbon dioxide which make the cake soft and spongy.

10th Science Chapter 2 Previous Years Papers Set – 5 (2 Marks)

Tooth enamel is one of the hardest substance in our body. How does it undergo damage due to eating chocolates and sweets? Hoe does tooth paste prevent this damage? [CBSE 2009]

Tooth enamel is made up of calcium phosphate. Chocolates and sweets produce acid in our mouth which react with enamel (calcium phosphate) and leads to cavities. We should brush our teeth after every meals as well as after eating sweet etc.

(i) Name the product formed when sodium hydrogen carbonate is heated. (ii) Write the chemical equation for the reaction involved in the above. [CBSE 2009]

(i) When sodium hydrogen carbonate is heated, sodium carbonate carbon dioxide and water are formed.

(ii) 2NaHCO3 → Na2CO3 + CO2 + H2O

A compound X of sodium is commonly used in kitchen for making crispy pakoras. It is also used for curing acidity in the stomach. Identify X What is its chemical formula? State the reaction which take place when it is heated during cooking. [CBSE 2008]

X is sodium hydrogen carbonate. It is used for crispy pakora. It is use for curing acidity in the stomach. Its chemical formula is NaHCO3. It decomposes to sodium carbonate, carbon dioxide and water on heating.
2NaHCO3 → Na2CO3 + CO2 + H2O

Write the chemical formula for bleaching powder. How is bleaching powder prepared? For what purpose it is used in paper factories? [CBSE 2008]

Bleaching powder is CaOCl2. It is prepared by reaction slaked lime [ca(OH)2] with dry chlorine gas.
Ca(OH)2 + Cl2 → CaOCl2 + H2O
It is used as bleaching agent in paper industry.

Given below are the pH value of four different liquids: 7.0, 14.0, 4.0, 2.0. Which of these could be that of (i) Lemon juice (ii) Distilled Water (iii) 1M Sodium Hydroxide Solution (iv) Tomato Juice? [CBSE 2006]

(i) Lemon juice = 2.0

(ii) Distilled Water = 7.0

(iii) 1M Sodium Hydroxide Solution = 14.0

(iv) Tomato Juice = 4.0

Bases are Different from Alkalis

Bases which are soluble in water and produce OH- ions are called alkalis.
Some example are:
Sodium Hydroxide NaOH → Na+ + OH-
Potassium Hydroxide KOH → K+ + OH-

10th Science Chapter 2 Ten Years Papers Set – 6 (3 Marks)

(a) Write the name given to the bases that are highly soluble in water. Give an example. (b) How is tooth decay related to pH? How can it can be prevented? (c) Why does bee sting cause pain and irritation? Rubbing of baking soda on the sting area gives relief How? [CBSE 2012]

(a) Alkali example NaOH (sodium carbonate)

(b) Lower the pH more will be tooth decay. Acids reacts with Ca3(PO4)2 and cause tooth decay. It can be prevented by brushing our teeth after every meal.

(c) It is due to formic acid. Sodium hydrogen carbonate (Baking Soda) neutralize formic acid giving relief.

A white powder is added while baking bread and cakes to make them soft and fluffy. Write the name of the powder? Name its main ingredient. Explain the function of each ingredient. Write the chemical reaction taking place when powder is heated during baking. [CBSE 2012]

Baking Powder.
It is consisting of sodium hydrogen carbonate and tartaric acid. Sodium hydrogen carbonate gives CO2 which makes cake soft and fluffy. Tartaric acid neutralizes the bitterness due to sodium carbonate produced.
2NaHCO3 → Na2CO3 + CO2 + H2O

Sodium hydrogen carbonate is a basic salt. Justify the statement. How it is converted into washing soda? Explain. [CBSE 2012]

Sodium hydrogen carbonate is a salt of sodium hydroxide (strong base) and carbonic acid).
It is basic salt. It is converted into baking soda by heating followed by the crystallization.

What are strong acid and weak acids? Identify the strong and weak acid from the following: Hydrochloric acid, formic acid, acetic acids, nitric acids. [CBSE 2012,2011]

Strong acids are completely ionized in aqueous solution example H2SO4 (sulphuric acid).

Weak acids are partially ionized in aqueous solution for example CH3COOH (Acetic acid).

Strong acids: Hydrochloric acids, Nitric acid

Weak acids: Acetic acid, Formic acid

(a) What is universal indicator? (b) Write the chemical equation involved in the preparation of sodium hydroxide. Name the Process. [CBSE 2011]

(a) Universal indicator is mixture of synthetic indicators which is used to find pH of the solution.

(b) 2NaCl + 2H2O → 2NaOH + H2 + Cl2
It is known as Chlor-Alkali process.

A gas X react with lime water and forms a compound Y which is used as bleaching agent in chemical industry. Identify X and Y. Give the chemical equation of the reaction involved. [CBSE 2011]

X is chlorine Y is bleaching powder.
Ca(OH)2 + Cl2 → CaOCl2 + H2O

Plaster of Paris

Calcium sulphate hemihydrate.
Its prepared by heating gypsum at 373K
CaSO4.2H2O → CaSO4.1/2 H2O + 3/2 H2O
(i) It is used to prepare chalks.
(ii) It is used to make casts and mould.

10th Science Chapter 2 Ten Years Papers Set – 7 (3 Marks)

(i) Name the compound which is obtained from baking soda and is used to remove permanent hardness of water. (ii) Write its chemical formula. (iii) What happen when it is recrystallized from its aqueous solution? [CBSE 2011]

(i) Sodium carbonate is obtained from baking soda and it is used to remove hardness of water.

(ii) Na2CO3

(iii) It changes to washing soda Na2CO3.10H2O

A compound which is prepared from gypsum has the property of hardness when mixed with proper quantity of water. [CBSE 2009](i) Identify the compound (ii) Write the chemical equation for the preparation. (iii) Mention one important use of its compound. [CBSE 2011]

(i) Plater of Paris.

(ii) CaSO4.2H2O→ CaSO4.½ H2O + 3/2 H2O

(iii) It is used for plaster fractured bones.

What is neutralisation reaction? Give two examples. [CBSE 2011]

The reaction between the acid and base to form salt and water is called neutralisation reaction, for example: KOH + HNO3 → KNO3 + H2O
2NaOH + H2SO4 → Na2SO4 + 2H2O

What is tooth enamel chemically? State the condition when it start cording. What happen when food particles left in the mouth after eating degrade? Why does doctor suggest use of tooth powder /toothpaste to prevent tooth decay? [CBSE 2011]

It is made up of calcium phosphate.
It starts corroding by acid formed in mouth. These food particles left in moth to form acids which cause tooth decay. Tooth paste and tooth powder are basic and neutralize acid formed in mouth which prevent tooth decay.

What is baking soda chemically called? Give reaction involved in its preparation. Write one of its uses. [CBSE 2011]

Sodium hydrogen carbonate.
NH3 + CO2 + H2O + NaCl → NaHCO3 + NH4Cl
It is used an antacid.

(a) What is an alkali? Give an example. (b) Why do HCL, HNO3, etc. show acidic characters in aqueous solution while solution of compound like alcohol and glucose do not show acidic character? [CBSE 2011]

(a) Soluble base are called alkalis. Example Sodium hydroxide is an alkali.

(b) HCl, HNO3 ionise in aqueous solution where alcohol and glucose do not show acidic character because they do not ionize in aqueous solution.

Bleaching Power

Chemical name of bleaching powder is calcium oxychloride.
Formula: CaOCl2
On exposure to air, it absorbs moisture.
Uses:
(i) As an oxidising agent in chemical industries.
(ii) For disinfecting drinking water to make it free from germs.

10th Science Chapter 2 Ten Years Papers Set – 8 (3 Marks)

Name the product formed in each case when (a) Hydrochloric acids reacts with caustic soda. (b) Granulated zinc react with caustic soda. (c) Carbon dioxide is passed into lime water. [CBSE 2009]

(a) Sodium chloride and water is formed.
NaOH + HCl → NaCl + H2O

(b) Sodium zincate and H2 are formed.
Zn + 2NaOH → Na2ZnO2 + H2

(c) calcium carbonate and water are formed.
Ca(OH)2 + CO2 → CaCO3 + H2O

(a) Why does aqueous solution of an acid conduct electricity? (b) How does the concentration of hydronium ions [H3O+] change when a solution of an acid is diluted? (c) Which has a higher pH value a concentration or dilute solution of hydrochloric acid? (d) What would you observe on adding dilute hydrochloric acid to (i) solid sodium carbonate placed in a test tube? (ii) Zinc metal in a test tube? [CBSE 2008]

(a) It is because aqueous solution of acid contain ions which carry current.

(b) When solution is diluted, the conc. Of [H3O+] decrease.

(c) Dilute solution of HCl will have higher pH than conc. solution

(d)
(i) Brisk effervescence due to colourless carbon dioxide gas are evolved.
Na2CO3 + 2HCl → 2NaCl + Co2 + H2O
(ii) Bubbles due to colourless odourless hydrogen gas are formed.
Zn + 2HCl → ZnCl2 + H2

While constructing a house, a builder selects marble flooring and marble table top for the kitchen where vinegar and juices of lemon tamarind etc., are more often used for cooking. Will you agree to this selection and why? [CBSE 2010]

No, this selection is wrong.

Vinegar and juices of lemon, tamarind etc., are acidic solution. Acids react with marble flooring and marble table top. Marble is calcium carbonate which react with acids.
For example,
CaCo3 + 2CH3COOH → (CH3COO)2Ca + H2O

Five solution A, B, C, D and E showed pH as 4,7,1,11, and 9 respectively when tested with universal indicators. Which solution is (i) Neutral (ii)Strongly alkaline (iii) Strongly acidic (iv) Weakly acidic and (v) Weakly alkaline. Arrange the PH in increasing order of hydrogen ion concentration. [CBSE 2011]

(i) Solution B is neutral.

(ii) Solution D is strongly alkaline.

(iii) Solution C is strongly acidic.

(iv) Solution A is weakly acidic.

(v) Solution E is weakly alkaline.

You have been provided with three test tube. 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? [CBSE 2011]

(i) Put red litmus papers one by one in each test tube. The test tube in which the red litmus paper turns blue contains a basic solution. There will be no effect on the red litmus paper in the other two test tubes.

(ii) Remove the litmus paper which turned blue and put it one by one in the other test tubes. The tube that turns blue litmus red contains acidic solution.

(iii) The tube which has no effect on the litmus paper contains distilled water.

A student dropped a few pieces of marble in dilute hydrochloric acid, contained in a test tube, the evolved gas was then passed for a long time through lime water. What changes would be observed in lime water? Write balanced equations for both the changes observed. [CBSE 2013]

(i) On adding pieces of marble in the test tube containing dil. HCL, a brisk evolution of CO2 takes place. Carbon dioxide when passed through lime water turns it milky because of the formation of insoluble calcium carbonate.
CaCO3 + 2HCl → CaCl2 + CO2 + H2O
Ca(OH)2 + CO2 → CaCO3 + H2O

(ii) If CO2 is continuously passed for a long time, the mikliness disappears due to the formation of soluble sodium hydrogen carbonate.
CaCO3 + CO2 + H2O → Ca(HCO3)2

Rock Salt

Rock salt is the common name for the mineral “halite”. Its chemical formula is NaCl. It may be white or light blue or yellow depending upon impurities present in it.

10th Science Chapter 2 Ten Years Papers Set – 9 (3 Marks)

(a) Write the formula and chemical name of bleaching powder. (b) Write the chemical equation to represent the action of atmosphere CO2 gas on bleaching powder when exposed in open. (c) Why is bleaching powder used in water treatment plants? [CBSE 2013]

(a) Formula of bleaching powder is CaOCl2 and the chemical name is calcium oxychloride.

(b) Bleaching powder has a tendency to decompose on exposure to atmospheric CO2.
CaOCl2 + CO2 → CaCO3 + Cl2
It releases chlorine gas and loses its activity as a bleaching agent.

(c) It releases chlorine gas which kills bacteria in water and makes it safe for drinking.

(a) Three acidic solutions A, B and C have pH = 0,3 and 5 respectively. (i) Which solutions has highest concentration of H+ ions? (ii) Which solution has the lowest concentration of H+ ions? (b) How concentrated sulphuric acid can be diluted? Describe the process. [CBSE 2015]

(a)
(i) Solution A has the highest concentration of H+ ions.
(ii) Solution C has the lowest concentration of H+ ions.

(b) While diluting concentrated sulphuric acid, water is not added to the acid, rather acid is added to water.
Take some water in a beaker. Add concentrated sulphuric acid I small lots to water. Stir the mixture with glass rod constantly. Cool the beaker under water if it becomes hot.

Define water of Crystallisation with two examples. How will you prove their existence in the examples given by you? [CBSE 2015]

Number of fixed water molecules associated with one formula unit of a substance is called water of Crystallisation.
Examples:
CaSO4.2H2O and CuSO4.5H2O

(i) Gypsum on heating loses half molecules of water and forms plaster of Paris.
CaSO4.2H2O → CaSO4.½ H2O + 1½ H2O
On adding water, it again converts to gypsum.

(ii) Copper sulphate on heating loses water molecules and is converted to white anhydrous CuSO4. On adding water to anhydrous copper sulphate, the blue colour of copper sulphate is restored.
CuSO4.5H2O → CuSO4 + 5H2O

(a) Define olfactory indicators. Name two substances which can be used as olfactory indicators. (b) Choose strong acids from the following: CH3COOH, H2SO4, H2CO3, HNO3 [CBSE 2016]

(a) Indicators which work on the basis of odour are called olfactory indicators. Onion and vanilla can be used as olfactory indicators.

(b) H2SO4 and HNO3 are strong acids out of the four acids given.

Name of type of chemical reaction represented by the following equation: (i) CaO + H2O → Ca(OH)2 (ii) 3BaCl2Al2(so4)3 → 2AlCl3+ 3BaSO4 (iii) 2FeSO4 → Fe2O3 + SO2+SO3 [CBSE 2016]

(i) Combination reaction.

(ii) Double displacement reaction.

(iii) Decomposition reaction.

Universal Indicator

A universal indicator is a mixture of several indicators. It shows different colour at different colour at different concentration of H+ ions concentration.

10th Science Chapter 2 Previous Years Papers Set – 10 (5 Marks)
(a) Identify the acid and base whose combination forms the common salt that you use in your food. Write the formula and the chemical name of this salt. Name the source from where it is obtained. (b) What is rock salt? Mention its colour and reason due to which it has this colour. (c) What happen when electricity is passed through brine? Write the chemical equation for it. [CBSE 2012]

(a) HCl is acid and NaOH is base whose combination forms the common salt.
Its formula is NaCl(Sodium chloride)
It is obtained from sea water.

(b) Rock salt is the common name for the mineral “halite”. Its chemical formula is NaCl.
It may be white or light blue or yellow depending upon impurities present in it.

(c) 2NaCl + 2H2O → 2NaOH + H2 + Cl2

(i) Dry pellets of a base X when kept in absorb moisture and turns sticky. The compound is also formed by Chlor-Alkali process. Write chemical name and formula of X. Describe the Chlor-Alkali process with balanced chemical equation. Name the type of reaction occurs when X is treated with dilute hydrochloric acid, write the chemical equation. (ii) While diluting an acid Why is it recommend that the acid should be added to water and not water to the acid. [CBSE 2012]

(i) X is sodium hydroxide NaOH
When sodium chloride solution (brine solution) is electrolyzed, sodium hydroxide solution is formed H2 and Cl2 gases are liberated. This is Chlor-Alkali process.
2NaCl + H2O → 2NaOH + H2 + Cl2
NaOH + HCl → NaCl2 + H2O
The above reaction is neutralizing reaction.

(ii) It is because process is highly exothermic. If water is acid, bottle of acid will break.

(a) Identifying the compound of calcium which is yellowish white powder and is used for disinfecting drinking water. Write its chemical name and formula? How it is manufactured. Write the chemical equation of the reaction involved. (b) Write the balanced chemical equation of the Chlor-Alkali process? [CBSE 2012]

(a) The compound is bleaching powder(CaCl3)2 Its chemical name is oxychloride. It is manufactured by reaction of solid slaked lime with dry chlorine gas.
Ca(OH)2 + Cl2 → CaOCl2 + H2O

(i) It is used as disinfectant.
(ii) It is used for preparation of chloroform.

(a) Mention the pH range within which our body works. Explain how antacid acids give relief from acidity Write the name of one such acid. (b)Fresh milk has the pH of 6. How does the pH will change as it turns to curd? Explain your answer. (c) A milk man added a very small amount of baking soda to fresh milk Why the milk takes a longer time to set as curd. (d) Mention the nature of the tooth paste how do they prevent tooth decay. [CBSE 2012]

(a) Our stomach has pH equal to 2. Antacids neutralizes excess of acid in our body and give relief from hyperacidity. Sodium hydrogen carbonate is one of the antacids.

(b) pH will decrease as it turns to curd because curd is acidic due to the presence of lactic acid?

(c) It takes longer time to set as curd as bacteria do not work well in presence of sodium hydrogen carbonate that’s why fermentation will take place slowly.

(d) Tooth paste are basic in nature. They neutralize the acids formed in mouth which causes tooth decay.

Crystalisation of Water

Water of crystallisation is the fixed number of water molecules present in one formula unit of the compound.

10th Science Chapter 2 Previous Years Papers Set – 11 (5 Marks)
(a) Define a universal indicator. Mention its one use. (b) Solution A gives pink colour when a drop of phenolphthalein indicators is added to it. Solution B gives red colour when a drop of methyl orange is added to it. What type of solution are A and B and which one of the solution A and B will have a higher pH value? (c) Name one salt whose solution has pH more than 7 and one salt whose solution has pH less than 7. [CBSE 2015]

(a) A universal indicator is a mixture of several indicators. It shows different colour at different colour at different concentration of H+ ions concentration.

(b) Solution A is alkaline in nature.
Solution B is acidic in nature.
Solution A has a higher pH value.

(c) Salts of weak acid and strong base give a solution which has pH less than 7.
Sodium acetate is an example of such salts.
Salts of strong acid and weak base give a solution which has pH less than 7.
Ammonium chloride is an example of such salt.

What is water of crystallization? Write the common name and the chemical formula of commercially important compound which has ten water molecules as water crystallization. How is this compound obtaining? Write the chemical equation also: List any two uses of this compound. [CBSE 2012]

Water of crystallization is the fixed number of water molecules present in one formula unit of the compound.
The compound having ten water molecules as water of crystallization in Na2CO3.10H2O. obtained.
2NaHCO3 → Na2CO3 + H2O + CO2
Na2CO3 + 10H2O → Na2CO3.10H2O

Uses of Washing soda:
(i) It is used in removing permanent hardness of water.
(ii) It is used in this manufacture of glass, soap and paper.

(a) Three acidic solution A, B and C have pH = 0,3 and 5 respectively. (i) Which solution has concentration of H+ ions? (ii) Which solution has highest concentration of H+ ions? (b) How concentrated sulphuric acids can be diluted? Describe the process [CBSE 2016]

(a) Smaller the pH value, higher the concentration of H+ ions
(i) Solution A has the higher concentration of H+ ions.
(ii) Solution C has the lower concentration of H+ ions.

(b) Take the water in the beaker. Add to it small amount of concentrated sulphuric acid with shaking with the help of a glass stirrer. Cool the beaker in water taken in the trough if it became hot. Continue adding sulphuric acid in a similar manner till the whole of sulphuric acid became diluted.

The pH of a salt used to make tasty and crispy pakora is 14. Identify the salt and write a chemical equation for its formation. List its two uses. [CBSE 2018]

The salt is baking soda (sodium hydrogen carbonate.
NaCl + H2O + CO2 + NH3 → NH4Cl + NaHCO3
Uses:
(i) It is used in soda acid fire extinguisher.
(ii) It is an ingredient of antacid. It neutralize excess acid in the stomach and provide relief.

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