Q. Find the percentage a mass of magnesium in magnesium oxide MgO given the relative atomic mass of magnesium is twenty-four and that of oxygen is sixteen.


Q. Calculate the percentage mass of sulphur in sulphuric acid given the formula of sulphuric acid H2SO4 and the relative atomic masses of H = 1, O = 16 and S = 32


Q. Calculate the percentage by mass of manganese in potassium manganate (VII) (potassium permanganate), given the relative atomic masses of potassium = 39 manganese = 55 and oxygen = 16.


Part of the art of answering chemistry questions, or indeed any science question, is making sure you've actually established what the question wants. Examiners can construct questions in such a way that you need to study it quite carefully to establish what it is exactly asking you well before you set about calculating it. Many students have the knowledge but respond with the wrong answers because they have clearly misunderstood the question.


Q. A mixture of iron oxide and sodium chloride solids contains 36% sodium ions by mass. Given that the only compound containing sodium is the sodium chloride, calculate the mass of sodium chloride in 120 g of the mixture.


Q. A mixture contains 40% magnesium by mass. The only compound in the mixture that contains magnesium is magnesium oxide MgO. Calculate the mass of magnesium oxide in 45 g of the mixture.


Q.A mixture of lead nitrate (solid) and potassium chloride (solid) contains 6% nitrogen atoms by mass. Given that the only substance in the mixture containing nitrogen is lead nitrate, calculate the mass in grams of lead nitrate contained in 225 g of the mixture.


Go To >> Solutions <<

Back To >> Atomic and Formula Mass <<