11382 12 Calcium is present in teeth in the form of calcium phosphate. This salt does not react with water although the element calcium does react forming a gas. (a) Write the formula of calcium phosphate. [1] (b) (i) Write an equation for the reaction of calcium with water. [2] (ii) Explain why, using the same mass of strontium in place of calcium, the volume of gas produced when strontium reacts with water is less under the same conditions. [1] (iii) Suggest another difference that would be observed in the reaction with water when strontium is used in place of calcium. Explain your answer. [2] (c) The Group II metal oxides can be formed from the metal hydroxides. (i) How would you convert calcium hydroxide to calcium oxide? [1] (ii) State and explain the trend in thermal stability of the Group II hydroxides as the Group is descended. [3] 11382 [Turn over (d) What chemical property of magnesium oxide makes it suitable for indigestion remedies? [1] (e) Magnesium sulfate is an important compound in horticulture. Industrially, the sulfates of magnesium and calcium are produced by reacting dolomite rock with excess sulfuric acid. MgCO3.CaCO3  +  2H2SO4  →  MgSO4  +  CaSO4  +  2H2O  +  2CO2 (i) Other than a temperature change, suggest two observations during this reaction. [2] (ii) Compare the solubility of magnesium sulfate with calcium sulfate in water. [1] (iii) The solubility of magnesium sulfate at two temperatures is given in the table below. In a batch process, a saturated solution of magnesium sulfate at 70 °C contained 100 tonnes of water. Use the table to calculate the mass of solid magnesium sulfate obtained when this solution is cooled to 20 °C. temperature / °C solubility / g per 100 g of water 20 35.1 70 59.2 [2] 11382 (f) 2.50 g of hydrated magnesium sulfate crystals (MgSO4.xH2O) were heated to constant mass. The anhydrous solid has a mass of 1.22 g. Calculate the value of x and hence deduce the formula for the hydrated salt. [3] 11382 BLANK PAGE DO NOT WRITE ON THIS PAGE (Questions continue overleaf) [Turn over