Acid Base and Salt solved Question Answer for class 10th

Question (1): Define the terms: Acid, alkali and salt.

 Answer:  An acid is a compound, which releases hydronium ions (H₃O⁺) as the only positive ions in solution. An alkali is a compound, which releases hydroxyl ions (OH^-) as the only negative ions in solution. A salt is one of the products of neutralization between an acid and a base; water being the only other product. OR A salt gives positive ions other than H⁺ ion and negative ions other than OH^- ion in solution. 

 

 

Question (2): Identify the number of replaceable hydrogen ions (H⁺) in the following acids: HCl, CH₃COOH, H₂SO₄, H₃PO₄.

Answer:  HCl = 1    CH₃COOH = 1       H₂SO₄ = 2     H₃PO₄ = 3. 

 

Question (3): What is a neutralization reaction?

Answer:  Neutralization is essentially a chemical reaction between H₃O⁺ ions of an acid with OH^- ions of the base, to give undissociated molecules of water.

 

Question (4): What are strong and weak acids? Give one example of each?

Answer:  A strong acid is one, which is almost completely dissociated in solution. Examples: Dilute nitric acid, dilute sulphuric acid and dilute hydrochloric acid. A weak acid is one, which is only partially ionized in solution (degree of dissociation is >30%). Examples: Acetic acid, carbonic acid and sulphurous acid.

 

Question (5): Why is acetic acid called a weak acid though there are 4 'H' atoms in the molecule?

Answer:  Acetic acid is called a monobasic acid because only one of the 4 'H' atoms of the acid is released as H⁺ ion in solution.

 

 

Question (6): How does a strong acid differ from a concentrated acid?

Answer:  The strength of an acid depends upon its dissociation power whereas concentration depends on water content in the acid.

 

 

Question (7): Name a salt of a strong acid HNO₃ and a weak base like NH₄OH. Represent the reaction that takes place.

Answer:  The salt that results due to the above reaction is Ammonium nitrate (NH₄NO₃). The reaction is represented as:  HNO₃         +             NH₄OH         --------à     NH₄NO₃    
                                          

Question (8):  1) Name a strong base and a weak base. 2) Name a hydrated salt.

Answer: 

1) A strong base is sodium hydroxide (NaOH) and a weak base is ammonium hydroxide (NH₄OH).
2) A hydrated salt is copper sulphate crystals (CuSO₄.5H₂O).

 

 

Question (9): Name the following:
1) Two non-hydrated crystalline salts  2) Two neutral salts  3) Two basic salts  4) Two acid salts

Answer:   1) Two non-hydrated crystalline salts are: sodium chloride (NaCl) and potassium nitrate (KnO₃)
2) Two neutral salts are: sodium chloride (NaCl) and sodium sulphate (Na₂SO₄)
3) Two basic salts are: basic copper carbonate (CuCO₃.Cu(OH)₂) and basic lead carbonate (PbCO₃.Pb(OH)₂)
4) Two acid salts are: sodium bicarbonate (NaHCO₃) and sodium phosphate (NaH₂PO₄)

 

 

Question (10): Name the salts of sulphuric acid.

Answer:  The salts of sulphuric acid are bisulphate and sulphate. Examples: NaHSO₄, KHSO₄ and Na₂SO₄.

 

 

 Question (11): Define the term "pH"; what does" pH" stand for?

Answer:  The term "pH" is defined as the negative logarithm of H⁺ ion concentration of a given solution; the concentration being expressed as moles per litre. Mathematically pH = - log [H⁺] 'pH' stands for: Power of hydrogen ion concentration, 'p' for power and 'H' for H⁺ ion concentration.

 

 

Question (12): What is 'pH' scale? Explain briefly.

Answer:  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. Some important benchmark values in the pH scale are: pH = 7 indicates neutral solutions e.g., aqueous solutions. pH > 7 to 14 indicates alkaline solutions and pH < 7 to 0 indicate acidic solutions

 

 

Question (13): What is the 'pH' of pure water and that of rain water? Explain the difference.

Answer:  The pH of pure water is seven. Rain water is slightly acidic because as rain drop fall, the carbon dioxide in the air dissolves with drops to form very weak carbonic acid. Accordingly, rain water has a pH that is slightly below 7.

 

 

Question (14): What is the pH of solution 'A' which liberates CO₂ gas with a carbonate salt? Give the reason?

Answer:  The pH of solution 'A' is lesser than 7. Carbonates salts react with acids (A) to liberate CO₂ gas.

 

 

Question (15): What is the pH of solution 'B' which liberates NH₃ gas with an ammonium salt? Give reason?

Answer:  The pH of solution 'B' is lesser than 7 because 'B' is an alkali as it liberates NH₃ gas. Question (16): How do you increase or decrease the pH of pure water? Answer:  By adding a few drops of alkali to pure water, it's pH increases; and by adding a few drops of an acid decreases the pH of pure water.

 

 

Question (17): What are indicators?

Answer:  Indicators are chemicals that show whether the given solution is acidic or basic, by the sudden change of color.

 

 

Question (18): Name the common acid-base indicators used in the laboratory with their color change.

Answer:  The three common indicators used in the laboratory are:

Indicator	Final colour
	Acid	Alkali
Litmus	Red	Blue
Methyl orange	Pink	Yellow
Phenolphthalein	Colourless	Deep pink

 

 

Question (19): What is a universal indicator? What is its advantage?

Answer:  A universal indicator is a mixed indicator of organic chemicals which not only shows whether the given solution is acidic or basic, but also shows the approximate pH values by giving a wide particular colour for a specific value of pH.

 

 

Question (20): What is the action of litmus on ferric chloride solution and why?

Answer:  An aqueous solution of FeCl₃ salt undergoes hydrolysis and releases H⁺ ions from the stronger acid HCl formed. Hence, the resulting solution is acidic and turns blue litmus turns red.

          Fecl₃    +   3 H₂O          -----------------------------à     Fe (OH)₃    + 3 H Cl

                                                          HCl -------------------------à   H⁺                 + Cl ^-