How many moles of CaSO4 are in 8.55×1024 formula units?

Answer 1

Use dimensional analysis to convert from formula units to moles. Dimensional analysis is based on the fact that when you multiply a quantity by "1" the answer is the same as the original quantity.

You can represent "1" in many different ways: ³/₃ or ^{1 day}/_{24 h} or ^{24 h}/_{1 day} etc

This representation of "1" is called a conversion factor, and the numerator and denominator are equivalent.

Any equivalence can be used as a conversion factor.

You make the conversion factor so that the numerator is in the new units you want your answer in and the equivalent denominator in the original unit you want to mathematically cancel (get rid of).

A mole is similar to a dozen in that it represents a specific number of any item.

1 mole = 6.02x10²³ things (in this case, formula units)

This is the equivalence you need for the conversion factor in this problem.

For this problem, the equivalence you need is: 1 mole = 6.02x10²³ formula units and you will arrange it so that formula units will cancel:

8.55 x 10²⁴ formula units x ^{1 mole}/_{6.02x1023 formula units} = your answer in moles

Do the math, 8.55×10²⁴ × 1 ÷ 6.02×10²³ = to find the answer

Answer 2

1 mole = 6.02x10²³ formula units.

Do the calculation, 8.55×10²⁴ formula units x (1 mole/6.02x10²³ formula units) to find the number of moles.