Pupil sheet · Relative masses
Relative masses — final check
Name ______________________ Date ____________
Work alone, with the lesson closed. Answer every question; there are no hints.
1. describe / calculate
(a) Describe what is meant by the relative atomic mass, Ar, of an element. (b) In a sample of potassium, 93 % of the atoms are potassium-39 and 7 % are potassium-41. Calculate the relative atomic mass of potassium. Give your answer to one decimal place.
(a) Relative atomic mass
(b) Potassium
2. calculate
Calculate the relative formula mass of potassium carbonate, K2CO3, and of ammonium phosphate, (NH4)3PO4. (Ar: H 1, C 12, N 14, O 16, P 31, K 39.)
Mr of K2CO3: ______________ unit ________
Mr of (NH4)3PO4: ______________ unit ________
3. calculate
Ammonia is made from nitrogen and hydrogen: N2 + 3H2 → 2NH3. (Ar: H 1, N 14.) (a) Calculate the mass of ammonia made from 7 g of nitrogen. (b) Calculate the mass of hydrogen that reacts with 7 g of nitrogen. (c) Calculate the mass of nitrogen needed to make 17 g of ammonia.
(a) Ammonia from 7 g of N2: ______________ unit ________
(b) Hydrogen that reacts with 7 g of N2: ______________ unit ________
(c) Nitrogen needed for 17 g of NH3: ______________ unit ________
4. calculate
Epsom salts are hydrated magnesium sulfate, MgSO4·7H2O. (Ar: H 1, O 16, Mg 24, S 32.) (a) Calculate the relative formula mass of MgSO4·7H2O. (b) A sample of 24.6 g is heated to constant mass and all its water leaves. Calculate the mass of anhydrous magnesium sulfate left. (c) Calculate the mass of water lost. Give your answers to (b) and (c) to 3 significant figures.
(a) Mr of MgSO4·7H2O: ______________ unit ________
(b) Magnesium sulfate left: ______________ unit ________
(c) Water lost: ______________ unit ________