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.

a. the law of proportion states the combination of 2 atoms in a specific ratio to produce multiple compounds such as the given statement of question ‘1st compound contains 88.8 % cu ’ indicates 88.8 g of cu is present along with 11.2 g oxygen in 100 g of compound whereas the statement ‘2st compound contains 79.9 % cu ’ indicates 79.9 g of cu is present along with 20.1 g oxygen in 100 g of compound

1st compound contains 88.8 g cu

for cu

m = 63 g /mol

atomic % = 88.8 /63 = 1.42

for o

m = 16 g /mol

atomic % = 11.2 /16 = 0.7

b. the emperical formula of 1st compound is

cu1.4o0.7

cu2o