Question

CaSO4.XH2O looses 6.2% of water upon heating.
The value of x will be
(1) 2
(2) 3
(3) 4
(4) 1/2​

Answer 1

Answer:(4) $\frac{1}{2}$  

Explanation:

Decomposition of hydrated calcium sulphate is given by:

$CaSO_4.xH_2O\rightarrow CaSO_4+xH_2O$

Molar mass of $CaSO_4$ = 136.14 g/mol

According to stoichiometry:

(136.14+18x) g of $CaSO_4.xH_2O$ decomposes to give 18x g of $H_2O$

To calculate the mass percent of element in a given compound, we use the formula:

$\text{Mass percent of water}=\frac{18x}{(136.14+18x)}\times 100$

$\text{Mass percent of water}=6.2\%$

Thus we can equate the two equations:

$\frac{18x}{(136.14+18x)}\times 100=6.2$

$x=\frac{1}{2}$  

Thus the value of x is $\frac{1}{2}$  

Answer 2

Answer:

$\frac{1}{2}$

Explanation:

We are given that $CaSO_4.xh_2O$ looses 6.2% of water upon heating.

We have to find the value of x.

We know that  molecular weight of water=18 g.

Atomic mass of Ca=40 g

Atomic mass of S=32 g

Atomic mass of O=16 g

Mass of $CaSO_4=40+32+16(4)=40+32+64=136 g$

$\frac{molecular\;wt\;of\;water\times x}{mass\;of\;CaSO_4}=6.2$%

$\frac{18x}{136}=\frac{6.2}{100}$

$x=\frac{62\times 136}{18\times 1000}=0.46\sim 0.5$

$x=\frac{5}{10}=\frac{1}{2}$

Hence, the value of x=$\frac{1}{2}$