OCR A Jun 2009 Paper 1 Q1

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Answer all the questions. The Group 2 element magnesium was first isolated by Sir Humphry Davy in 1808. (a) Magnesium has three stable isotopes, which are 24Mg, 25Mg and 26Mg. (i) Complete the table below to show the atomic structures of 24Mg and 25Mg. protons neutrons electrons 24Mg 25Mg (ii) A sample of magnesium contained 24Mg: 78.60%; 25Mg: 10.11%; 26Mg: 11.29%. Calculate the relative atomic mass of this sample of Mg. Give your answer to four significant figures. [2] (iii) Define the term relative atomic mass. answer =[2][3]OCR 2009<br />
 (b) The reaction between magnesium and sulfuric acid is a redox reaction. Mg(s) + H2SO4(aq) MgSO4(aq) + H2 (g) (i) Use oxidation numbers to identify which element has been oxidised. Explain your answer. element oxidisedexplanation[2] (ii) Describe what you would see when magnesium reacts with an excess of sulfuric acid.[2] (c) Epsom salts can be used as bath salts to help relieve aches and pains. Epsom salts are crystals of hydrated magnesium sulfate, MgSO4xH2O. A sample of Epsom salts was heated to remove the water. 1.57 g of water was removed leaving behind 1.51 g of anhydrous MgSO4. (i) Calculate the amount, in mol, of anhydrous MgSO4 formed. (ii) Calculate the amount, in mol, of H2O removed. amount =mol [2] (iii) Calculate the value of x in MgSO4xH2O. amount =mol [1]OCR 2009 x =[1] [Total: 15] Turn over<br />

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