Question

A salt crystal has a mass of 0.16 mg .

How many NaCl formula units does it contain?

Express your answer using two significant figures.

Answer 1

Answer:- $1.6*10^1^8$ formula units.

Solution:- We have been given with 0.16 mg of NaCl and asked to calculate the number of formula units. For formula units calculations, here the first step is to convert mg to g and then g to moles on dividing grams by the formula mass of NaCl. Moles are multiplied by Avogadro number to calculate the number of formula units.

Formula mass of NaCl is 58.44 gram per mol. The calculations are shown bellow using dimensional analysis:

$0.16mg(\frac{1g}{1000mg})(\frac{1mol}{58.44g})(\frac{6.02*10^2^3formula Units}{1mol})$

= $1.6*10^1^8$ formula units of NaCl

Hence, there are $1.6*10^1^8$ formula units of NaCl present in 0.16 mg of NaCl salt crystal.