Question

Aqueous solution of $N{{a}_{2}}{{S}_{2}}{{O}_{3}}$ on reaction with $C{{l}_{2}}$ gives:
A. $N{{a}_{2}}{{S}_{4}}{{O}_{6}}$
B. $NaHS{{O}_{4}}$
C. $NaCl$
D. $NaOH$

Answer 1

The product formed the reaction is used for chlorination of water bodies. As per the given question, we are asked what product is formed when $N{{a}_{2}}{{S}_{2}}{{O}_{3}}$ reacts with $C{{l}_{2}}$. We should know that when $N{{a}_{2}}{{S}_{2}}{{O}_{3}}$ with $C{{l}_{2}}$, $N{{a}_{2}}{{S}_{2}}{{O}_{3}}$ gets oxidised by chlorine i.e. one electron is lost to other species during the reaction.

Complete step by step answer:
Sodium thiosulphate with chemical formula $N{{a}_{2}}{{S}_{2}}{{O}_{3}}$ when reacts with $C{{l}_{2}}$, it gets oxidised by the chlorine water. This is shown in the following balanced chemical reaction,
$N{{a}_{2}}{{S}_{2}}{{O}_{3}}+4C{{l}_{2}}+5{{H}_{2}}O\to 2NaHS{{O}_{4}}+8HCl$

As we can see, the reaction gives products $NaHS{{O}_{4}}$ and $HCl$.
Further, $N{{a}_{2}}{{S}_{2}}{{O}_{3}}$also gets oxidised when it reacts with $FeC{{l}_{3}}$, it decomposes to,
$2N{{a}_{2}}{{S}_{2}}{{O}_{3}}+2FeC{{l}_{3}}\to N{{a}_{2}}{{S}_{4}}{{O}_{6}}+2FeC{{l}_{3}}+2NaCl$

While, when $N{{a}_{2}}{{S}_{2}}{{O}_{3}}$on treatment with dilute acids it decomposes to,
$2N{{a}_{2}}{{S}_{2}}{{O}_{3}}+2HCl\to 2NaCl+S{{O}_{2}}+S+{{H}_{2}}O$

So, we can see that, when $N{{a}_{2}}{{S}_{2}}{{O}_{3}}$ reacts with chlorine water it gives $NaHS{{O}_{4}}$.

Additional Information:
Uses of sodium thiosulfate:
- It is used as a very important chemical compound in the medical treatment of cyanide poisoning cases.
- The side effects of chemotherapy and haemodialysis are treated with sodium thiosulfate.
- Sodium thiosulfate salts are used as photographic fixers due to the ability of the thiosulfate ions to react with silver halides, which make up photographic emulsions.
- In order to reduce the chlorine levels in water, it is used in the chlorination of water
So, the correct answer is “Option B”.

Note: Sodium thiosulfate is an inorganic compound with the chemical formula $N{{a}_{2}}{{S}_{2}}{{O}_{3}}.x{{H}_{2}}O$. Typically, it exists as a white or colourless pentahydrate, that is $N{{a}_{2}}{{S}_{2}}{{O}_{3}}.5{{H}_{2}}O$. It is generally used in gold mining, water treatment, analytical chemistry, development of silver-based photographic film and prints and medicines. In medical grounds, it is used for the treatment of cyanide poisoning and pityriasis.