3. How many moles are in 75g of Na20?

1.2 moles

Explanation:

Given that,

Amount of moles of Na2O (n) = ?

Mass of Na2O in grams = 75g

For molar mass of Na2O, use the atomic masses:

Sodium, Na = 23g;

Oxygen, O = 16g

Na2O = (23g x 2) + 16g

= 46g + 16g

= 62g/mol

Since, amount of moles = mass in grams / molar mass

n = 75g / 62g/mol

n = 1.2 moles

Thus, there are 1.2 moles are in 75g of Na20