Question

A sample of $CaC{O}_3$ has Ca (40%), C (12%), O (48%) by mass. If the law of constant proportions is true then find the mass of Ca in 5 g of $CaC{O}_3$ obtained from another source.

Answer 1

Law of constant proportions states that a given chemical molecule will always contain the same elements in same proportions, irrespective of the source.

Since, it is given that a sample of $CaC{O}_3$ has $40$% $Ca$ in it.

$\therefore$ The percentage of $Ca$ in $5g$ of sample would be the same as in $100g$ of $CaC{O}_3$

$\therefore$ $5g$ sample $CaC{O}_3$ will have $40$% $Ca$ i.e; $\frac{40}{100}\times 5=2g$