Question

A salt crystal has a mass of 0.15 mg. How many NaCl formula units does it contain?

Answer 1

0.15mg = 0.00015g

Na =22g/mol

Cl= 35g/mol

35g/mol + 22g/mol = 57g/mol

0.00015g * 1 mol/ 57 g =2.63 * 10⁻⁶

0.00015g * 1 mol/ 57 g * NA/1mol = 2.63 * 10⁻⁶ NA

2.63 * 10⁻⁶ * 6.02 * 10²³ = 15.8326 * 10¹⁷

Answer 2

2.56×10^-6 moles

Step-by-step explanation:

Number of formula units is the same as the number if moles of NaCl present.

Number of moles= mass/ molar mass

Molar mass of NaCl= (23+35.5)= 58.5gmol-1

Given mass of NaCl= 0.15×10^-3g

Number of moles= 0.15×10^-3/58.5

Number of moles = 2.56×10^-6 moles