Question

What is the equivalent weight of \[N{{a}_{2}}{{S}_{2}}{{O}_{3}}.5{{H}_{2}}O\]?
A) 240g
B) 246g
C) 248g
D) 250g

Answer 1

Hint:The equivalent weight of the solution is defined as the molecular weight of the solute present in it divided by the valency of the solute. It helps to determine the mass of the substance which tends to react with the one atom of hydrogen in the acid base analysis such as titration. The unit used for equivalent weight is atomic mass unit or amu.

Complete answer:
The formula using for calculating the equivalent weight is the following:
Equivalent weight = \[\dfrac{molecular weight}{n-factor}\]
We can get an idea by reading the term equivalent that it is the mass of 1 equivalent of the compound. It is also known as the gram equivalent. It is referred to as the mass of a given substance which tends to combine with the fixed mass of a fixed quantity of another substance. But for the element the equivalent weight of an element is the mass which combines what is placed is one gram of hydrogen. It is also the gram molecular weight which is divided by the number of those electrons which have been lost or gained by each molecule. If the\[N{{a}_{2}}{{S}_{2}}{{O}_{3}}\] is reacted with iodine we will get the following products. So the reaction for them is:
\[2N{{a}_{2}}{{S}_{2}}{{O}_{3}}+{{I}_{2}}\to N{{a}_{2}}{{S}_{4}}{{O}_{6}}+2NaI\]
Here we see that for two moles of sodium thiosulphate require two moles of iodine atoms that means the transfer of electrons in this is of two electrons. So now for 1 mole of sodium thiosulphate there will be the transfer for 1 electron.
The molecular weight of \[N{{a}_{2}}{{S}_{2}}{{O}_{3}}.5{{H}_{2}}O\]=\[23\times 2+32\times 2+16\times 3+5(18)=248g/mol\]
n- factor= 1
now substituting the value in the formula we get,
 equivalent weight= \[\dfrac{248}{1}=248g/mol\]

Hence,the correct option is C.

Note:Sodium thiosulphate is a chemical compound which is a white crystalline substance and is odourless in nature. It has a neutral charge and is stable at standard conditions. It undergoes decomposition when it is exposed to dilute acids. It is a monocline in structure and a water soluble compound.