Chapter 2– Acids Bases and Salt Solutions
Question - 1 : - You are given three test tubes. The three test tubes contain distilled water, acidic solution and the basic solution respectively.
Answer - 1 : - There is only red litmus paper available in order to identify what is there in each test tube. How will you find out what is in each of the test tubes?
We can identify the content in each of the test tubes using red litmus paper. This can be done by noticing the colour change of the red litmus paper.
• If the red litmus paper changes to blue colour the solution is a basic solution (or alkaline).
• If the red litmus paper stays red, then the solution is an acid.
• If the red litmus paper changes to purple, then it indicates that the solution is near neutral (distilled water in this case)
Question - 2 : - Why should curd and sour substances not be kept in brass and copper vessels?
Answer - 2 : - Curd and sour food substances contain acids; these acidic substances combine with metal. This reaction turns food to poison which damage people’s health.
Question - 3 : - Which gas is usually liberated when an acid reacts with a metal? I
Answer - 3 : - llustrate with an example. How will you test for the presence of this gas?
Answer
When an acid reacts with any metal, salt and hydrogen gas are formed.
Metal + Acid → Salt + Hydrogen gas
Question - 4 : - Metal compound A reacts with dilute hydrochloric acid to produce effervescence.
Answer - 4 : - The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride.
Answer
As metal compound released is Calcium Chloride the gas evolved here is CO2. Hence metal A should be Calcium Carbonate. Hence the reaction between Calcium Carbonate and HCl is
CaCO3 (s) + 2HCl (Aq) → CaCl2( Aq) + CO2 (g) + H2O (l)
Answer - 5 : -
Release of H+ ion in water will make a compound acidic or non-acidic. Acids are the substance which upon dissociating with water results in production of Hydrogen ions. Some compounds show acidic character as they dissociate in the aqueous solution which results in the production of hydrogen ions (acids like HCl, HNO3).
Compounds similar to glucose or alcohol do contain hydrogen element but they do not show signs of acidic nature. The fact that the hydrogen in them will not separate as like the hydrogen in the acids. They will not separate to become hydrogen ions, on dissolving in the water.
Hence dissociation of hydrogen gas will decide the acidic or non-acidic nature of a compound.
Question - 6 : - Why does an aqueous solution of an acid conduct electricity?
Answer - 6 : - Charged particles are responsible for the conductance of electricity in an acid. These charged particles called as ions are the reason behind conductance of electricity in acid.
Question - 7 : - Why does dry HCl gas not change the colour of the dry litmus paper?
Answer - 7 : - HCL does not give out Hydrogen ions, therefore HCL does not show any acidic behaviour and colour of the litmus paper remain the same on reacting with HCl gas.
Question - 8 : - While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?
Answer - 8 : - While diluting an acid, it is recommended that the acid should be added to water and not water to the acid because if water is added to concentrated acid, it release huge amount of heat which may result in explosion and can cause acid burns o face, clothes and body parts. Hence it is safe to add acid to water but not water to acid.
Question - 9 : - How is the concentration of hydronium ions (H3O+) affected when a solution of an acid is diluted?
Answer - 9 : - When acid is added to water there will be a fixed amount of hydronium present in the fixed volume of solution. If we dilute the solution hydronium ion per volume of solution decrease, this in-turn decreases Hydronium concentration in the solution.
Question - 10 : - How is the concentration of hydroxide ions (OH–) affected when excess base is dissolved in a solution of sodium hydroxide?
Answer - 10 : - When base is dissolved in sodium hydroxide solution its hydroxide ions increase but it will reach saturation at some point. After saturation point hydroxide ion concentration is not affected even after adding base further.