NEET UG 2002 — Chemistry Physical Chemistry

$\mathrm{NaNO}_3$NaNO3​ is salt formed by the combination of a strong acid $\mathrm{HNO}_3$HNO3​ and a strong base $\mathrm{NaOH}$NaOH and hence it is neutral with a $\mathrm{pH}$pH. $\mathrm{CH}_3 \mathrm{COOK}$CH3​COOK is formed by the combination of weak acid $\mathrm{CH}_3 \mathrm{COOH}$CH3​COOH and strong base $\mathrm{KOH}$KOH and hence $\mathrm{pH}$pH will be above 7 . $\mathrm{NH}_4 \mathrm{Cl}$NH4​Cl is formed by the formation of strong and $\mathrm{HCl}$HCl and a weak base $\mathrm{NH}_4 \mathrm{OH}$NH4​OH and hence $\mathrm{pH}$pH will be lesser than 7. $\mathrm{Na}_2 \mathrm{CO}_3$Na2​CO3​ is a salt formed by the strong base $\mathrm{NaOH}$NaOH and weak acid $\mathrm{H}_2 \mathrm{CO}_3$H2​CO3​. Hence, $\mathrm{pH}$pH of the salt will be highest. The pH scale was invented in 1909 by a Danish biochemist Soren Sorensen. It describes how many hydrogen ions (protons) are present in a solution: the higher the pH, the lower the hydrogen ion concentration, and vice versa. But the scale does not have fixed limits, so it is indeed possible to have a pH above 14 or below zero. For example, concentrated hydrochloric acid can have a pH of around -1 , while sodium hydroxide solution can have a pH as high as 15 .