Question

A volume of $12.5ml,0.05M\,Se{O_2}$ reacts with $25ml$ of $CrS{O_4}$ which is oxidized to $0.1M\,C{r^{3 + }}$
The oxidation state at which selenium is converted by the reaction is _______.

Answer 1

Hint: Molarity of a substance is the number of moles of solute present per liter of solution. So, the molarity is a term which is used to measure the concentration of solute in a solution.
Oxidation state of any ion or atom indicates the ability of that ion to donate or accept electrons, in terms of certain number and proper sign.

Complete step by step answer:
As we know molarity is terms used to calculate the concentration of chemical species, amount of solute present in particular solution per unit volume of solution.
Now, coming to the solution part when selenium oxide reacts with chromium sulphate reaction may written as –
$Se{O_2} + CrS{O_4} \to C{r^{3 + }} + S{e^{x + }}$ , where x is the unknown oxidation number which has to be calculated.
Now, half-cell reaction may be written as –
At anode, where oxidation occurs that is electrons are lost $S{e^{4 + }} + (a - 4){e^ - } \to S{e^{x + }}$
At cathode, where reduction occurs that is electron are gained $C{r^{2 + }} \to C{r^{3 + }} + {e^ - }$
Then, number of equivalents of A and B is given as ; equivalent of $Se{O_2}$ is equivalent of $CrS{O_4}$
Equivalent may be given as $ = n \times V$
where, $n = $ number of moles and $V = $ volume
Hence, on substituting the required values, we get
$12.5 \times 0.05 \times (a - 4) = 0.1 \times 1 \times 25$
$ \Rightarrow (a - 4) = \dfrac{{2.5}}{{0.625}} = 4$
Hence, on further solving we get the value as
$ \Rightarrow a = 0$
a is the oxidation number of selenium which we have to calculate, Thus the oxidation at which selenium is converted by the reaction is zero. The overall reaction written as,
$Se{O_2} + CrS{O_4} \to C{r^{3 + }} + S{e^0}$

Note: sum of product of molar concentration and partial molar volume equals to one
Sum of molar concentration gives the total molar concentration, ionic strength is proportional to the sum of molar concentration of salts.
The molar concentration also depends on the variation of solution due mainly to thermal expansion.
Molarity is a temperature dependent parameter. That is the volume of a solution increases with an increase in temperature due to increase in intermolecular space and vice versa, hence molarity is affected by temperature change.