How to Calculate Moles from Mass in Chemistry

How can we calculate the number of moles from a given mass in chemistry?

Given data: How many moles of H2O are equivalent to 18 g of H2O?
(H = 1.01 g/mol, O = 16.00 g/mol)

Answer:

The answer is 1 mole.

Explanation:

In order to determine the number of moles of H2O from the given mass, we must first calculate the molecular mass of H2O. The molecular mass of H2O is calculated by adding the atomic masses of hydrogen (H) and oxygen (O):

Molecular mass of H2O = 2(1.01) + 16.00 = 18.02 g/mol

Next, we use the formula:

n = m/M

where:

n is the number of moles

m is the mass (given as 18 g)

M is the molecular mass (calculated as 18.02 g/mol)

Plugging in the values, we get:

n = 18 g / 18.02 g/mol = 0.999 moles

However, since moles must be a whole number, the answer is rounded to 1 mole.

Therefore, 18 g of H2O is equivalent to 1 mole of H2O.