Question

(a) A solution has a $p^H$ of 7. Explain how you would :

(i) increase ist $p^H$; (ii) decrease its $p^H$;

(b) If a solution changes the colour of litmus from red to blue, what can you say about its $p^H$?

(c) What can you say about the $p^H$ of a solution, that liberates carbon dioxide from sodium carbonate ?

Answer 1

(a) pH 7 means that the solution is neutral
So
(i) adding a base will increase the pH.

(ii) we can decrease it pH by adding acid.

(b) litmus paper is either red or blue. The blue paper changes colour to red, indicating acidity somewhere between the pH range of 4.5 to 8.3 (however, note 8.3 is alkaline). Red litmus paper can indicate alkalinity with a color change to blue. In general, litmus paper is red below pH of 4.5 and blue above a pH of 8.3.

(c) The pH of the solution which liberates $C{O}_2$ from $N{a}_{2}C{O}_3$ should be less than 7 as the acid can do this. The Balanced chemical equation is:

$N{a}_{2}C{O}_3+2HCl-⟶2NaCl+H_{2}O+C{O}_2$

As salt and water are formed, it is a neutralization reaction.