What is the mass of 2.90 ×1022 formula units of NaOH (Molar mass = 40.0 g/mol)?

Explanation:

1. Convert Formula Units to Moles

To do this, we use Avogadro's Number: 6.02*10²³. It is the number of particles (atoms, molecules, formula units, etc.) in 1 mole of a substance. In this case, it is formula units of sodium hydroxide.

Multiply by the given number of formula units.

Flip the ratio so the formula units will cancel.

2. Convert Moles to Grams

For this, we use the molar mass. It is the grams per mole of a substance. We are given this value for sodium hydroxide: 40.0 g/mol

Multiply by the moles we calculated.

The moles cancel.

3. Round

The original measurement of formula units has 3 significant figures, so our answer must have the same. For the number we calculated that is the hundredth place.

The 6 in the thousandth place tells us to round the 2 to a 3.

There are approximately 1.93 grams of sodium hydroxide.

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