NCERT Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts

Ans : If the colour of red litmus paper gets changed to blue, then it is a base and if there is no colour change, then it is either acidic or neutral. Thus, basic solution can be easily identified. 
Let us mark the three test tubes as A, B, and C. A drop of the solution in A is put on the red litmus paper. Same is repeated with solution B and C. If either of them changes colour to blue, then it is basic. Therefore, out of three, one is eliminated. Out of the remaining two, anyone can be acidic or neutral. Now a drop of basic solution is mixed with a drop of each of the remaining two solutions separately and then the nature of the drops of the mixtures is checked. If the colour of red litmus turns blue, then the second solution is neutral and if there is no change in colour, then the second solution is acidic. This is because acidic and basic solutions neutralize each other. 
Hence, we can distinguish between the three types of solutions. 

Ans : Curd and other sour substances contain acids. Therefore, when they are kept in brass and copper vessels, the metal reacts with the acid to liberate hydrogen gas and harmful products, thereby spoiling the food. 

Ans : Hydrogen gas is usually liberated when an acid reacts with a metal.  
 
Take few pieces of zinc granules and add 5 ml of dilute \( \mathrm { H } _ { 2 } \mathrm { SO } _ { 4 }  \). 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. 
\( 2 \mathrm { H } _ { 2 } \mathrm { SO } _ { 4 } + \mathrm { Zn } \longrightarrow \mathrm { Zn } \left( \mathrm { SO } _ { 4 } \right) _ { 2 } + 2 \mathrm { H } _ { 2 } \uparrow\)
we can test the evolved hydrogen gas by its burning with a pop sound when a candle is brought near the soap bubbles. 

Ans : Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride.
\( \mathrm { CaCO } _ { 3 ( s ) } + 2 \mathrm { HCl } _ { ( \mathrm { aq } ) }\) -> \( \mathrm { CaCl } _ { 2 ( \mathrm { aq } ) }\)+\( \mathrm { CO } _ { 2 ( g ) }\)+\( \mathrm { H } _ { 2 } \mathrm { O } _ { ( l ) }\) 

Ans : The dissociation of HCI or  \( \mathrm { HNO } _ { \mathrm { 3 } }\) to form hydrogen ions always occurs in the presence of water. Hydrogen ions (H+) combine with \(\mathrm { H } _ { 2 } \mathrm { O } \) to form hydronium ions \({ 3 } \mathrm { O } ^ { + }\). 
The reaction is as follows: 
\( \mathrm { HCl } _ { ( \mathrm { aq } ) } \longrightarrow \mathrm { H } ^ { + } + \mathrm { Cl } ^ { - }\)
\( \mathrm { H } ^ { + } + \mathrm { H } _ { 2 } \mathrm { O } \longrightarrow \mathrm { H } _ { 3 } \mathrm { O } ^ { + }\)