Chapter 18, Problem 9STP

Interpretation Introduction

Interpretation:

The formula of hydrate of $MgS{O}_4$ is to be found out.

Concept introduction:

Percentage composition helps to calculate the mass of water attached with $MgS{O}_4$

Answer to Problem 9STP

A

Explanation of Solution

The given hydrate contains $13\%H_{2}Oand87\%MgS{O}_4$

$\begin{array}{c}MolarmassofMgS{O}_4=24+32+64\\ =120g/mol\end{array}$

$\begin{array}{c}Massofwaterattachedto MgS{O}_4=\frac{13}{87}\times 120\\ =18g/mol\end{array}$

Thus number of water molecules attached is one molecule.

So, formula is $MgS{O}_4.H_{2}O$

Conclusion

Thus, calculations show that option A is correct.