Question

A 42.7 gram sample of potassium nitrate contains how many grams of potassium?

Answer 1

Moles KNO3 = 42.7 g / 101.037 g/mol= 0.422  

Moles K = 0.422  

mass K = 0.422 mol x 39.1 g/mol=16.5 g

Answer 2

Given:

A 42.7-gram sample of potassium nitrate.

To Find:

The number of grams of potassium.

Solution:

To find the number of grams of potassium we will follow the following steps:

As we know,

Potassium nitrate = KNO3

The weight of 1 mole of potassium is 39 grams.

KNO3 has 1 atom of potassium and the molecular weight of KNO3 = 39 + 14 + 16×3 = 1gramsram.

Number of moles in 42.7 grams of potassium nitrate =

$\frac{42.7}{101} = 0.422 \: moles$

1 mole of potassium nitrate contains 1 mole of potassium.

So,

0.422 moles of potassium nitrate will contain 0.422 moles of potassium.

Weight of 0.422 moles of potassium = 0.422 ×39 = 16.4 grams.

Henceforth, a 42.7-gram sample of potassium nitrate contains 16.4 grams of potassium.