A salt crystal has a mass of 0.12 mg. How many NaCl formula units does it contain?

1 Answer
Trevor Ryan. ยท Stefan V.
Dec 22, 2015

1.2xx10^(18)

Explanation:

First, find the number of moles of sodium chloride in the "0.12 mg" by using the formula moles = mass/molar mass.

therefore n=m/(Mr)=(0.12/1000"g")/((23+35.5)"g/mol")=2.051 * 10^(-6) "moles"

But, "1 mol" contains an Avagadro number of particles, ie 6.022xx10^23 particles.

Therefore by ratio and proportion, 2.051 * 10^(-6) "mol" will contain 1.2xx10^18 particles of "NaCl".

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