Question

A white salt is readily soluble in water and gives a colourless solution with a pH of about 9. The salt would be:
A. $N{H_4}N{O_3}$
B.$C{H_3}COONa$
C.$C{H_3}COON{H_4}$
D.$CaC{O_3}$

Answer 1

To answer this question, you should recall the concept of dissolution of salt. Write the dissolution reaction for each salt and find the salt which generates an ion of stronger base resulting in a pH greater than 7.

Complete Step by step solution:
You should know about dissolution of salt. Upon dissolution of salt like${\text{NaCl}}$in water, a dissolving reaction will occur. For the crystal to dissolve the hydrogen bonds of water must be broken. The negatively charged chloride ions are attracted by the positive sodium ions and by the partially positive hydrogen atom in the polar water molecule. Similar kind of attractive forces acts on the positive sodium ion. A "tug-of-war" occurs between different attractive forces in the system. The crystal dissolution is determined by which attractive force is stronger. In the question after dissolution in water, the salt gives a basic pH, which indicates that the salt is formed by a strong base and a weak acid.
Analyzing each salt systematically:
$HN{O_3} + N{H_4}OH \to N{H_4}N{O_3}\;$ (Strong Acid + Weak Base)
$C{H_3}COOH + NaOH \to C{H_3}COONa\;$ (Weak acid + Strong Base)
$C{H_3}COOH + N{H_4}OH \to C{H_{3}}COON{H_4}$​ (Weak Acid + Weak Base)
$Ca{\left( {OH} \right)_2} + {H_2}C{O_3} \to CaC{O_3}$​ (Weak acid + Strong Base)
We can see that option B and option D result in a strong base. But we know that $CaC{O_3}\;\;$ is insoluble in water, hence the correct answer is $C{H_3}COONa$ .
Therefore, we can conclude that the correct answer to this question is option B.

Note: Dissolving a salt molecule in water does not make its atoms ionize. The atoms in solid salts are already ionized long before touching the water. Electrons in an atom can only take on specific wave states, and only one electron can occupy one wave state at a time. As a result, electrons in an atom take different states, starting from the lowest energy state and going upwards in energy until the electrons have all found distinct states.