10 (A410U10-1) Examiner only 11. A student is provided with a set of unknown ionic solids. She is told that the compounds could be any four of the following. lead(II) carbonate lead(II) iodide lead(II) nitrate sodium carbonate sodium iodide potassium carbonate calcium nitrate magnesium hydroxide magnesium sulfate (a) All of the samples provided were white. State which one of the compounds from the list above could not be amongst the samples. Give a reason for your answer. [1] (b) She planned to test each of the samples by following the steps below. © WJEC CBAC Ltd. add a small amount of solid to distilled water and shake hydroxide or oxide ions are present in the original sample; a solution of metal chloride is formed test samples of the solution separately with each of the following solutions • silver nitrate • barium chloride • a small amount of dilute sodium hydroxide • an excess of dilute sodium hydroxide • bromine water carbonate ions are present in the original sample; a solution of metal chloride is formed add a small amount of solid to hydrochloric acid solid does not dissolve effervescence no effervescence solid dissolves (i) Explain why the method as written would not conclusively identify all the unknown samples that contain carbonate ions. [1] (A410U10-1) Turn over. A 410 U101 11 11 Examiner only (ii) Her teacher says that hydrochloric acid is not the correct reagent to use in this method. Give two reasons why hydrochloric acid is not appropriate and suggest an alternative reagent that would avoid these problems. [3] (iii) Another student starts her method with a flame test. State which s-block cations she could identify by this method, giving the colours expected for each. [2] (iv) As time was short the teacher suggested the following simplified method. • Look at the colour of the sample • Carry out a flame test to identify s-block cations • Try to dissolve the sample in water • Add acid to the samples and look for effervescence This method allowed seven of the nine compounds to be identified. lead(II) carbonate lead(II) iodide lead(II) nitrate sodium carbonate sodium iodide potassium carbonate calcium nitrate magnesium hydroxide magnesium sulfate Name the two compounds that could not be distinguished and suggest a test that would tell them apart. Give reagent(s) and observations for both compounds. [4] © WJEC CBAC Ltd. 11