Question

Potassium combines with two isotopes of chlorine ${(}^{35}Cland{}^{37}Cl)$ respectively to form two samples of $KCl$. Their formation follows the law of:

• A. constant proportions
• B. multiple proportions
• C. reciprocal proportions
• D. none of these

Answer 1

The correct option is A constant proportions

According to the Law of Definite Proportions, a chemical compound will always have exactly the same proportion of elements by mass.

This means that the elements that make up a compound will always have the same per cent composition by mass, regardless of the actual mass of the sample.

In this case, potassium chloride has a molar mass of 74.551 g/mol. The two elements that form potassium chloride are potassium, which has a molar mass of 39.0983 g/mol, and chlorine, which has a molar mass of 35.4527 g/mol.

This tells you that every mole of potassium chloride weighs 74.551 g, out of which 39.0983 g is potassium and 35.4527 g is chlorine.

Therefore, chlorine and potassium will always be in a ratio by mass of

$\frac{35.4527g}{39.0983g}$=0.90681

so the constant proportion is the right answer