# According to the law of definite proportions any two samples of KCl have?

Jun 30, 2015

The exact same proportion of potassium and chlorine by mass.

#### Explanation:

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 percent composition by mass, regardless of the actual mass of the sample.

In your 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

$\left(35.4527 \cancel{\text{g"))/(39.0983cancel("g}}\right) = \frac{0.9068}{1}$

Simply put, you get an almost equal contribution to the mass of the compound from both elements.

Another way of looking at this is by calculating each element's percent composition.

"For Cl": (35.4527cancel("g/mol"))/(74.551cancel("g/mol")) * 100 = 47.55%

"For K": (39.0983cancel("g/mol"))/(74.551cancel("g/mol")) * 100 = 52.45%

This means that every sample of potassium chloride, regardless of its mass, will contain 47.55% chlorine and 52.45% potassium.

So, as a conclusion, any two samples of potassium chloride will contain potassium and chlorine in a 0.9068 : 1, or 52.55% to 47.55%, mass ratio.