Question: What is the atomic mass of hydrogen?

Answer: 1

Explanation: Hydrogen contains one proton and no neutrons, so its atomic mass is \(1+0=1\)

Question: What is the atomic mass of oxygen?

Answer: 16

Explanation: Oxygen contains eight protons and eight neutrons. Therefore its atomic mass is \(8+8=16\)

Question: What is the relative formula mass of hydrogen?

Answer: 2

Explanation: Hydrogen exists as a diatomic molecule, \(H_2\). That means that its molecular mass is the mass of two hydrogen atoms, i.e.

\(1+1=2\)

Question: What is the empirical formula of glucose, \(C_6H_{12}O_6\)?

Answer: \(CH_2O\)

Explanation: There are equal numbers of oxygen and carbon atoms. There are twice as many hydrogen as carbon atoms.

Notice that all of the subscripts are divisible by 6; if you divide through by the highest common factor, you will get the empirical formula.

Question: What is the molecular formula of a molecule that has a relative formula mass of 58 and an empirical formula of \(C_2H_5\)?

Answer: \(C_4H_{10}\)

Explanation: The molecular formula of a molecule with the formula \(C_2H_5\) would be 29. This is half of 58. Therefore, if you multiply all of the subscripts by two, this will give you the desired relative formula mass.

Molecular formulae