CBSE Class 10 Science Acids Bases and Salts VBQs

The reaction between MnO₂ with HCl is depicted in the following diagram. It was observed that a gas with bleaching abilities was released.  

Question. In the above discussed reaction, what is the nature of MnO₂?   
(a) Acidic oxide
(b) Basic oxide
(c) Neutral oxide
(d) Amphoteric oxide

Answer : B

Question. Chlorine gas reacts with ..................... to form bleaching powder   
(a) dry Ca(OH)₂
(b) dil. solution of Ca(OH)₂
(c) conc. solution of Ca(OH)₂
(d) dry CaO

Answer : A

Question. What will happen if we take dry HCl gas instead of aqueous solution of HCl?   
(a) Reaction will occur faster
(b) Reaction will not occur.
(c) Reaction rate will be slow
(d) Reaction rate will remain the same

Answer : B

Question. The chemical reaction between MnO₂ and HCl is an example of:   
(a) displacement reaction
(b) combination reaction
(c) redox reaction
(d) decomposition reaction.

Answer : C

Question. Identify the correct statement from the following:   
(a) MnO₂ is getting reduced whereas HCl is getting oxidized
(b) MnO₂ is getting oxidized whereas HCl is getting reduced.
(c) MnO₂ and HCl both are getting reduced.
(d) MnO2 and HCl both are getting oxidized.

Answer : A

Frothing in Yamuna:
The primary reason behind the formation of the toxic foam is high phosphate content in the wastewater because of detergents used in dyeing industries, dhobi ghat Yamuna’s pollution level is so bad that parts of it have been labelled 'dead' as there is no oxygen in it for aquatic life to survive.  

Question. The table provides the pH value of four solutions P, Q, R and S 
  

Which of the following correctly represents the solutions in increasing order of their hydronium ion concentration?
(a) P > Q > R > S
(b) P > S > Q > R
(c) S < Q < R < P
(d) S < P < Q < R

Answer : C

Question. Predict the pH value of the water of river Yamuna if the reason for froth is high content of detergents dissolved in it.    
(a) 10-11
(b) 5-7
(c) 2-5
(d) 7

Answer : A

Question. High content of phosphate ion in river Yamuna may lead to:   
(a) decreased level of dissolved oxygen and increased growth of algae
(b) decreased level of dissolved oxygen and no effect of growth of algae
(c) increased level of dissolved oxygen and increased growth of algae
(d) decreased level of dissolved oxygen and decreased growth of algae

Answer : A

Question. If a sample of water containing detergents is provided to you, which of the following methods will you adopt to neutralize it?   
(a) Treating the water with baking soda
(b) Treating the water with vinegar
(c) Treating the water with caustic soda
(d) Treating the water with washing soda

Answer : B

Question. Which of the following statements is correct for the water with detergents dissolved in it?    
(a) low concentration of hydroxide ion (OH–) and high concentration of hydronium ion (H₃O⁺)
(b) high concentration of hydroxide ion (OH–) and low concentration of hydronium ion (H₃O⁺)
(c) high concentration of hydroxide ion (OH–) as well as hydronium ion (H₃O⁺)
(d) equal concentration of both hydroxide ion (OH–) and hydronium ion (H₃O⁺).

Answer : B

Orchids grow best if the soil has pH between 5.5 to 6.8. An orchid grower tested various soils. The chart shows the results.
Farmers who wish to increase the nitrogen content of soil can add ammonium salts as fertilizer.

Question. What is colour of phenolphthalein in ammonium hydroxide?    
(a) Colourless
(b) Orange
(c) Yellow
(d) Pink

Answer : D

Question. The pH of NH4NO₃ in aqueous solution will be    
(a) 7
(b) 10
(c) 5
(d) 11

Answer : C

Question. Approximate pH of ammonium hydroxide is    
(a) 7
(b) 10
(c) 1
(d) 4

Answer : B

Question. Why calcium hydroxide should not be added along with ammonium salts?     
(a) It makes soil extremely acidic
(b) It makes soil extremely basic
(c) It decreases nitrogen content in soil as Ca(OH)₂ reacts with NH3 to form salt  
(d) None of these.

Answer : C

Question. Which soil is best for orchid?   
(a) A
(b) B
(c) C
(d) D

Answer : B

The electrolysis is a process in which the solution or molten liquid allows electricity to pass through it. The electrolysis of acid and water conducts electricity and the bulb glows as the circuit is complete.  

Question. Which of the following statement(s) is (are) correct?   
I. Bulb will not glow if an electrolyte solution is taken in the beaker because electrolyte is not acidic.
II. Bulb will glow if HCl is taken in the beaker as it is a strong acid and furnishes ions for conduction.
III. Bulb will glow if solid NaCl is taken in the beaker.
IV. Bulb will not glow if solution of NaOH is taken in the beaker because it is basic.
(a) (I) and (III)
(b) (II) and (IV)
(c) (II) only
(d) (IV) only

Answer : C

Question. If the acid is replaced by glucose will the bulb glow.   
(a) Glucose will not dissociate into ions and the bulb will not glow.
(b) The glucose can conduct electricity, hence the bulb will glow
(c) Glucose will dissociate into ions and the bulb will glow
(d) Both (b) & (c)

Answer : A

Question. What will happen if you replace the above solution in the beaker with molten sodium chloride?   
(a) The bulb will glow as molten sodium chloride can conduct electricity
(b) Sodium chloride is a salt and salts do not conducting electricity, the bulb will not glow
(c) The bulb will melt in molten sodium chloride
(d) None of the above

Answer : A

Question. What are the possible results if alcohol is used instead of acid?    
(a) The solution of alcohol can conduct electricity, hence the bulb will glow
(b) The alcohol do not dissociate hydronium ion in the water hence the bulb will not glow
(c) The bulb will not glow as the solution of alcohol do not conduct electricity
(d) Both (b) &(c)

Answer : D

Question. Name the ions produced during the electrolysis of HCl.   
(a) The chloride ions
(b) The hydrogen ions and chloride ions.
(c) The hydrogen ions
(d) The calcium ions and sulphide ions

Answer : B

CASE STUDY BASED QUESTIONS:

1. Read the following and answer the questions :

There are many substances which are used to detect the solutions as acidic or basic. They are called Acid-Base indicators. Depending upon the property of the indicator, we have different groups of Acid-Base indicators. Some indicators show different colors in acidic or basic medium and some indicators give different odors in acidic and basic medium. These indicators are either extracted from the plants or synthesized in the laboratory or industry.

Question. Which of the following will turn red litmus blue?
(a) Amla juice
(c) Soft drink
(b) lemon juice
(d) Baking soda
Answer : D

Question.A solution turns blue litmus red, the pH of the solution is likely to be
(a) 6
(c) 8
(b) 7
(d) 9
Answer : A

Question. Which one of the following can be used as an acid-base indicator by visually impaired student?
(a) Turmeric
(c) Vanilla
(b) Hibiscus
(d) Litmus
Answer : C

Question. Select the incorrect option.
 Indicator                     Colour in acidic medium          Colour in basic medium
(a) Litmus(Purple)                           Red                           Blue
B) Phenolphthalein(Colorless)        Pink                          Colorless
(c)Red cabbage extract (Purple)    Red                           Green
(d) Methyl orange (Orange)           Red                           Yellow
Answer : B

Question. Which of the following are olfactory indicators?
(a) Onion Extract
(c) Clove Oil
(b) Vanilla Extract
(d) All are correct
Answer : 

Read the following and answer the questions :

Taj mahal, the seventh wonder of the world, is made of white stone. This white stone contains the same substance ‘A’ that is present in chalk powder and lime-stone. It is turning yellow due to polluted air. If it is cleaned by an acidic cleaner, a gas ‘B’ is released, which when passed through a solution ‘C’, forms the same substance which is present in the white stone that was used to make Taj mahal.

Question. The substance A is-
(a) Ca₃CO₂
(c) Ca(OH)₂
(b) CaCO₃
(d) CaSO₄
Answer : B

Question. Gas B is-
A..) Hydrogen
(c) Chlorine
(b) Nitrogen
(d) Carbon di oxide
Answer : D

Question. Solution C is-
(a) CaCl₂
(c) Ca(OH)₂
(b) B. CaCO₃
(d) CaSO₄
Answer : C

Question. What is the nature of the substance A?
(a) Acidic
(c) Neutral
(b) Basic
(d) None
Answer : B

Question. The polluted air around Taj mahal leads to the following problem because of which it is getting Marble cancer:
(a) Global Warming
(c) Green House Effect
(b) Acid Rain
(d) All are correct
Answer : B

Read the following and answer the questions :

A scale for measuring hydrogen ion concentration in a solution, called pH scale has been developed. The p in pH stands for ‘potenz’ in German, meaning power. On the pH scale we can measure pH from 0 to 14. pH should be thought of simply as a number which indicates the acidic or basic nature of a solution. Higher the hydronium ion concentration, lower is the Ph value.

Question. Which one of the following will have the highest hydrogen ion concentration?
(a) pH=1.1
(c) pH =3.3
(b) pH = 2.2
(d) pH =4.4
Answer : A

Question. How is the hydrogen ion concentration and pH related to each other?
(a) They are inversely proportional.
(b) They are directly proportional.
(c) They are equal.
(d) They have no relation.
Answer : B

Question. A basic solution could have a pH of-
(a)3
(c) 7
(b) 5
(d) 9
Answer : D

Question. The table provides the pH of four solutions P, Q, R and S:
Solution     pH value
P                 2
Q                9
R                5
S                11
Which of the following correctly represents the solutions in increasing order of their hydronium ion concentration?
(a) P> Q>R >S
(b) P>S >Q >R
(c) S<Q <R <P
(d) S< P < Q<R
Answer : C

Question. If the pH of any solution is 13, then the color obtained on adding universal indicator to it will be:
(a) Red
(c) Green
(b) Orange
(d) Purple
Answer : D

Read the following and answer the questions :

The Ph value of any solution is a number which simply represents the acidity and basicity of that solution. The pH value of any solution is numerically equal to the logarithm of the inverse of the hydrogen ion(H+) concentration.

Question. The pH value for distilled water would be:
(a) 5
(c) 7
(b) 6
(d) 10
Answer : C

Question. Using above picture can you predict the colour of Ph paper when dipped in limejuice:
(a) Dark Red
(c) Green
(b) Light Orange
(d) Blue
Answer : B

Question. The nature of toothpaste is:
(a) Neutral
(c) Basic
(b) Acidic
(d) Can be acidic or basic
Answer : C

Question. If a solution gives dark blue color and water is added to it, its color will become:
(a) Dark blue
(c) Light blue to green
(b) Red
(d) Purple
Answer : C

Question. Universal indicator strip gives green colur when put in our mouth before eating food. This indicates that:
(a) The pH of saliva is basic in nature
(b) The pH of saliva is near neutral
(c) Saliva is acidic in nature
(d) All are in correct
Answer : A

Read the following and answer the questions :

Water of crystallization is the fixed number of water molecules present in one formula unit of a salt. Water of crystallization or water(s) of hydration are water molecules that are present inside crystals. Water is often incorporated in the formation of crystals from aqueous solutions. A salt with associated water of crystallization is known as a hydrate.

Question. Which of the following salt does not contain water of crystallisation?
(a) Blue Vitriol
(c) Washing soda
(b) Baking Soda
(d) Gypsum
Answer : B

Question. The temperature at which Gypsum (CaSO₄. 2H₂O) into Plaster of Paris (CaSO₄.1/2 H₂O
(a) 373K
(c) 374K
(b) 273K
(d) 430K
Answer : A

Question. The formula of Plaster of Paris is CaSO₄. ½ H₂O, it is to be noted that half water molecule is shown to be attached as water of crystallization. This indicates that
(a) Only half water molecule is present in Calcium Sulphate crystal
(b) Two formula units of Calcium Sulphate share one molecule of water.
(c) Two formula units of calcium Sulphate share two molecules of water
(d) Two formula units of Calcium Sulphate share one and a half molecules of water.
Answer : B

Question. Given below are some chemicals. Select the one that have 7 molecules of water attached in hydrated form:
(a) Blue vitriol
(c) POP
(b) Green Vitriol
(d) Washing Soda
Answer : B

Question. When blue vitriol is heated its color changes from:
(a) White to Blue 
(c) White to Green
(b) Blue to White
(d) Blue to Green
Answer : B

Very short answer type questions

Question. Name an olfactory indicator?
Answer : Onion

Question. The pH of an aqueous solution decreases from 3 to 2. What will happen to the nature of the solution ?
Answer :The acidic character of the solution will further increases.

Question. What is the chemical name and chemical formula of baking soda?
Answer : Sodium Hydrogen Carbonate or Sodium bicarbonate. Its formula is NaHCO₃.

Question. Which bases are called alkalies? Give an example.
Answer : Water soluble bases are called alkalies. e.g.- NaOH

Question. Name the gas evolved when dilute HCl reacts with sodium bi carbonate? How is it recognized?
Answer : The gas evolved is CO₂. When it is passed through lime water, it becomes milky.

Question. A cloth strip dipped in onion juice is used for testing a liquid ‘X. The liquid ‘X changes its odour. Which type of an indicator is onion juice?
Answer : Olfactory indicator

Question. What is meant by water of crystallisation?
Answer : Water of crystallisation is the fixed number of water molecules chemically attached to each formula unit of a salt in its crystalline form.

Question. A milk man adds a very small amount of baking soda to fresh milk Why?
Answer : It is done to prevent the formation of lactic acid which spoils the milk

Question. What is meant by an acidic salt?
Answer : The salt formed by the reaction between a strong acid and weak base

Short answer type questions.

Question. With the help of an example explain what happens when a base reacts with a non- metallic oxide. What do you infer about the nature of non-metal oxide?
Answer : Oxides of non-metals react with bases to form salt and water. For example, the reaction between carbon dioxide and calcium hydroxide. Calcium
hydroxide, which is a base, reacts with carbon dioxide to produce salt and water.
       CO₂            +       Ca(OH)₂ → CaCO₃      +              H₂O
Carbon dioxide           Calcium hydroxide          Calcium carbonate
Hence, oxides of non-metals are acidic in nature.

Question. When zinc metal is treated with a dilute solution of a strong acid, a gas is evolved. Name the gas evolved. Write the chemical equation of the reaction involved and also write a test to detect the gas formed.
Answer : Zinc metal gives hydrogen gas when it is treated with dilute sulphuric acid.
Therefore, the gas evolved is hydrogen.
Zn     +      H₂SO₄       →     ZnSO₄       +      H₂
zine       Sulphuric acid   zine sulphate       Hydrogen
Test for hydrogen gas: When a burning candle is brought near hydrogen gas, it burns with a pop sound which confirms the presence of hydrogen gas

Question. Mohan and Priyanka were playing in the garden. Priyanka was stung by a bee and started crying and returned home. Her mother immediately observed the affected area and applied a thin coating of toothpaste as first aid, then took her to the nearest doctor.
(i) Why did Priyanka cry?
(ii) Name the chemical substance present in bee sting.
(iii) How is toothpaste effective in such an incident?
Answer : (i) Priyanka cried because the bee injected an acid while stinging which caused pain and irritation.
(ii) Formic acid or Methanoic acid (HCOOH)
(iii) Toothpaste is basic in nature so it neutralise the effect of formic acid and gives relief.

Question. (i) Explain, why is hydrochloric acid a strong acid and acetic acid, a weak acid?
(ii) Explain, why aqueous solution of an acid conducts electricity.
(iii) 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.
(a) Identify the most acidic and most basic solutions.
(b) Arrange the above four solutions in the increasing order of H₊ ion concentration.
(c) State the change in colour of pH paper on dipping in solution C and D.
Answer : (i) Hydrochloric acid (HCl) is a stronger acid than acetic acid (CH₃COOH) because it dissociates completely into H⁺ and Cl^– ions in aqueous solution. In
(ii) An aqueous solution of an acid releases ions in aqueous solutions.
These ions conduct electricity.
(iii) (a) Most acidic is A (pH = 6) and most basic is C (pH = 12).
(b) The increasing order of H+ ion concentration is: C < B < D < A.
(c) The pH paper acquires dark purple colour in solution C and green in solution D.

Question. A sample of bleaching powder was kept in an air tight container. After a month, it lost some of its chlorine content. How will you account for it?
Answer : Bleaching powder if kept even in an air tight container will slowly decompose of its own and form calcium chlorate and calcium chloride. The reaction is called auto oxidation. This will result in decrease in its Chlorine contents.
6CaOCl₂ -----→Ca(ClO₃)₂ + 5CaCl₂

Question. An old man complained of acute pain in stomach. Doctor gave him a small antacid tablet and he got immediate relief. What actually happened?
Answer : The old man was suffering from acute acidity. Antacid tablet contains NaHCO₃. It reacts with the acid HCl formed because of acidity and neutralizes its effect.

Question. The oxide of a metal M was water soluble. When a blue litmus trip was dipped in this solution, it did not undergo any change in color .Predict the nature of the oxide.
Answer : The metal oxide (MO) is of basic in nature. It dissolves in water to from metal hydroxide as follow.
MO + H₂O-----→M(OH)₂
A blue litmus does not undergo any change in color in the basic medium.

Question. A doctor applied surgical bandages on the fractured bones of a patient after making it wet. What changes are likely to occur?
Answer : Surgical bandages are made from plaster of Paris. When applied on the fractured bones after making them wet , it changes into a hard mass called Gypsum.
CaSO₄.1/2 H₂O + 3/2 H₂O-------→ CaSO₄.2H₂O

Question. Fresh milk has pH of 6. When it changes to curd, will its pH value increase or decrease? Why?
Answer : When fresh milk changes to curd, the pH of the solution is likely to decrease. Actually, lactose present in milk gets converted to lactic acid when curd is formed from milk. Therefore, the medium becomes more acidic and its pH decreases.

Long answer type questions

Question. What will you observe when-
(i) Red litmus paper introduced into a solution of sodium carbonate.
(ii) A methyl orange drop is added to dilute hydrochloric acid.
(iii) A drop of phenolphthalein is added to the solution of lime water.
(iv) Blue litmus is introduced into a solution of Ferric chloride.
Answer : (i) The color of litmus paper will change to blue. Sodium carbonate dissolves in to water to form NaOH and Carbonic acid H₂CO₃. The solution is basic in nature since NaOH is a strong base and carbonic acid is a weak acid.
Na₂CO₃ + H₂O -------→  2 NaOH + H₂CO₃
(ii) In the acidic solution, the color of methyl orange will change to reddish
(iii) Lime water contains traces of Calcium hydroxide Ca(OH)₂ . It is therefore basic in nature. The colour of phenolphthalein will become pink.
(iv) Ferric chloride solution on reaction with water will form ferric hydroxide and HCl. Since the acid is strong, the solution will be acidic. Therefore the color of blue litmus will change to
red.
FeCl₃ + H₂O ----------→ Fe(OH)₃+ 3HCl

Question. (a) Why does an aqueous solution of an acid conduct electricity?
(b) How does the concentration of hydrogen ion changes the solution of an acid is diluted with water?
(c ) Which has a higher pH value ; a concentrated or dilute HCl?
(d) What would you observe on adding dilute HCl to
(i) Sodium bicarbonate placed in a test tube.
(ii) Zinc metal in a test tube.
Answer : (a) An aqueous solution of an acid conducts electricity because in water an acid dissociates to give ions. Since current is carried by the movements of ions, a.q. solution of acid conduct electricity.
(b) Upon dilution, more of acid dissociates into ions Therefore concentration of hydrogen ion increases.
(c ) Although more H+ ions are formed upon dilution , but the number of ions per unit volume decrease. Therefore, pH will increase upon dilution.
(d) (i) CO₂ gas would evolve accompanied by brisk effervescences.
NaHCO₃ +HCl ------→ NaCl + CO₂ + H₂O
(ii) Hydrogen gas would evolve accompanied by brisk effervescences.
Zn + 2HCl ---→  ZnCl₂ + H₂

Question. Explain why:
(i) Common salt becomes sticky during the rainy season
(ii) Blue vitriol changes to white upon heating.
(iii) If bottle full of Conc. Sulphuric acid is left open in the atmosphere by accident, the acid starts flowing out of the bottle of its own.
Answer : (i) Common salt contains the impurity of MgCl₂ which is of deliquescent in nature. When exposed to atmosphere, it becomes moist. Therefore common salt becomes sticky during the rainy season.
(ii) Blue vitriol (CuSO₄.5H₂O) upon heating changes to anhydrous copper sulphate which is white in color.
(iii) Concentrated Sulphuric acid is highly hygroscopic. It absorbs moisture from air and gets diluted. Since the volume increases, the acid starts flowing out of the bottle.

Question. (a) What is the action of red litmus on (i) dry ammonia gas (ii) solution of Ammonia gas.
(b) State the observation you would make on adding ammonium hydroxide to aqueous solution of (i) Ferrous Sulphate (ii) Aluminium Chloride.
Answer : (a) (i) Red litmus has no action on dry ammonia because it does not has hydroxyl ion.
(ii) When interact with ammonia solution it turns in blue as the solution has hydroxyl ion.
(b) (i) A green ppt of ferrous hydroxide will be formed
FeSO₄ + 2 NH₄OH -----→ Fe(OH)₂ + (NH₄)₂SO₄
(ii) A white ppt is formed
AlCl₃ + 3 NH₄OH ---→  Al(OH)₃ + 3 NH₄Cl

Question. (a) Name the raw materials used in the manufacture of Sodium carbonate in Solvay process?
(b) How is sodium bi carbonate formed during Solvay process separated from a mixture of NH₄Cl and NaHCO₃?
(c) How is sodium carbonate obtained from Sodium bi Carbonate?
Answer : (a) The raw materials used are: NaCl, Lime stone or CaCO₃ and NH₃
(b) NaHCO₃ is sparingly soluble or less soluble in water and gets separated as a precipitate while NH₄Cl remains in solution. The filtrate is removed by filtration.
(c ) NaHCO₃ is converted to sodium carbonate upon heating.
2NaHCO₃ ----→  Na₂CO₃ + H₂O + CO₂