Which of the following numerical expressions gives the number of moles in 5.0g of CaO?

5.0g*56g/mol

A

5.0g56g/mol

B

56g/mol5.0g

C

15.0g*156g/mol

The expression for the number of moles is 5.0 g / 56 g/mol

Explanation:

The mole is the amount of substance that contains as many entities as there are carbon atoms in 12 grams of a carbon-12 isotope. It is the amount of a substance that contains the same number of units as the number of atoms in 12g of carbon - 12 isotope. A mole of an ionic substance contains 6.02 * 10^23 atoms of the element. Mathematically, moles is the mass of a substance in grams divided by the relative molecular mass.

Moles = mass / relative molecular mass

In the given question, mass = 5.0 g

Molecular mass of CaO (Ca = 40, O = 16) = (40 + 16) g/mol = 56 g/mol

Moles = 5.0 g / 56 g/mol is the expression for the number of moles in 5.0 g of CaO