Question

Which of the following will turn blue litmus red?
(A) Vinegar
(B) Lime water
(C) Baking soda solution
(D) Washing soda solution

Answer 1

Hint: Blue litmus solution is a natural indicator that turns red in the presence of an acidic solution and remains unchanged in a neutral as well as acidic solution. Acids can be mineral acids or weak organic acids that are easily obtained from natural sources.

Complete Step By Step Answer:
An indicator is a substance that shows visible changes in colour upon getting exposed to an acidic or basic solution and therefore helps in distinguishing between an acid and a base.
Litmus is naturally occurring and derived from a plant called ‘lichens’. It is available in two forms in laboratories, one is the solution form and the other is in the form of litmus strips. Both these forms have two types i.e. red litmus and blue litmus.
Acids turn blue litmus red and bases turn red litmus blue. If the color of both the litmus solution remains unchanged then it is a neutral solution.
Vinegar is a source of acetic acid ( formula \[C{H_3}COOH\] ) which is a weak organic acid that partially dissociates in an aqueous medium. Due to its acidic character vinegar is capable of turning the blue litmus solution red.
\[ \Rightarrow \] Thus, Vinegar can turn blue litmus red and option (A) is correct.

Note:
Lime water is calcium hydroxide, baking soda is sodium bicarbonate or sodium hydrogen carbonate and washing soda is sodium carbonate. The carbonates, bicarbonates and hydroxides of alkali and alkaline earth metals are basic in nature and will therefore not affect the blue litmus solution.