
A solution of$N{{a}_{2}}{{S}_{2}}{{O}_{3}}$ is standardised iodometrically by using ${{K}_{2}}C{{r}_{2}}{{O}_{7}}$. The equivalent weight of ${{K}_{2}}C{{r}_{2}}{{O}_{7}}$ in this method is:
A) mol.wt/2
B) mol.wt/6
C) mol.wt/3
D) equal to mol.wt.
Answer
474.3k+ views
Hint: The answer here is based on the concept of calculating equivalent weight based on the definition and the formula which is given by $Eq.Wt.=\dfrac{M}{n-factor}$ and by finding n- factor according to reaction gives you the required answer.
Complete step – by – step solution:
We have come across the chapters in physical chemistry that is based on several measurement techniques like conductometry, potentiometry, iodometry etc.
- Now, let us see what does iodometry means and how is equivalent weight calculated in this technique.
- Iodometry or which is also known as iodimetric titration is a method of volumetric analysis where the appearance or disappearance of iodine indicates the end point and it is the redox reaction.
The reaction is as follows,
$26{{H}^{+}}+3{{S}_{2}}Ol3+4C{{r}_{2}}{{O}_{7}}^{2-}\to 6S{{O}_{4}}^{2-}+8C{{r}^{3+}}+13{{H}_{2}}O$
Here, in ${{K}_{2}}C{{r}_{2}}{{O}_{7}}(C{{r}_{2}}{{O}_{7}}^{2-})$, chromium is in +6 oxidation state and in the product it changes to +3 state.
Thus, there is net change of +3 in oxidation state.
Now, the net change in oxidation per formula is from $4C{{r}_{2}}{{O}_{7}}^{2-}$ to $8C{{r}^{3+}}$ is 2
Thus, net change for oxidation = $2\times 3=+6$
Thus, n-factor = +6
Now according to the formula of equivalent weight, $Eq.Wt.=\dfrac{M}{n-factor}$ where M is the molecular weight.
Substituting values, we have$Eq.Wt.=\dfrac{M}{6}$
Therefore, the correct answer is option B) mol.wt./6
Note: There are chances to be confused between iodometry and iodimetry. Here, iodometry involves indirect titration of the iodine that is liberated by the reaction with that of analyte and iodimetry involves direct titration using iodine itself as the titrant.
Complete step – by – step solution:
We have come across the chapters in physical chemistry that is based on several measurement techniques like conductometry, potentiometry, iodometry etc.
- Now, let us see what does iodometry means and how is equivalent weight calculated in this technique.
- Iodometry or which is also known as iodimetric titration is a method of volumetric analysis where the appearance or disappearance of iodine indicates the end point and it is the redox reaction.
The reaction is as follows,
$26{{H}^{+}}+3{{S}_{2}}Ol3+4C{{r}_{2}}{{O}_{7}}^{2-}\to 6S{{O}_{4}}^{2-}+8C{{r}^{3+}}+13{{H}_{2}}O$
Here, in ${{K}_{2}}C{{r}_{2}}{{O}_{7}}(C{{r}_{2}}{{O}_{7}}^{2-})$, chromium is in +6 oxidation state and in the product it changes to +3 state.
Thus, there is net change of +3 in oxidation state.
Now, the net change in oxidation per formula is from $4C{{r}_{2}}{{O}_{7}}^{2-}$ to $8C{{r}^{3+}}$ is 2
Thus, net change for oxidation = $2\times 3=+6$
Thus, n-factor = +6
Now according to the formula of equivalent weight, $Eq.Wt.=\dfrac{M}{n-factor}$ where M is the molecular weight.
Substituting values, we have$Eq.Wt.=\dfrac{M}{6}$
Therefore, the correct answer is option B) mol.wt./6
Note: There are chances to be confused between iodometry and iodimetry. Here, iodometry involves indirect titration of the iodine that is liberated by the reaction with that of analyte and iodimetry involves direct titration using iodine itself as the titrant.
Recently Updated Pages
The correct geometry and hybridization for XeF4 are class 11 chemistry CBSE

Water softening by Clarks process uses ACalcium bicarbonate class 11 chemistry CBSE

With reference to graphite and diamond which of the class 11 chemistry CBSE

A certain household has consumed 250 units of energy class 11 physics CBSE

The lightest metal known is A beryllium B lithium C class 11 chemistry CBSE

What is the formula mass of the iodine molecule class 11 chemistry CBSE

Trending doubts
State the laws of reflection of light

One Metric ton is equal to kg A 10000 B 1000 C 100 class 11 physics CBSE

Difference Between Prokaryotic Cells and Eukaryotic Cells

How do I convert ms to kmh Give an example class 11 physics CBSE

Give an example of a solid solution in which the solute class 11 chemistry CBSE

Describe the effects of the Second World War class 11 social science CBSE
