1. 1
   A technician is given four unlabelled white solids left over from a school laboratory and must identify the metal ion present in each using flame tests and sodium hydroxide solution.

   (a)

   A technician heats a small sample of an unknown white solid on a clean nichrome wire loop in a blue Bunsen flame. The flame turns a lilac colour throughout the test. Which ion is most likely present in the solid?

   [1 mark]

   • ASodium ion, Na+
   • BPotassium ion, K+
   • CCalcium ion, Ca2+
   • DCopper ion, Cu2+

   (b)

   A second solid from the same set is dissolved in water and a few drops of sodium hydroxide solution are added. A blue precipitate forms immediately, and no further precipitate forms when excess sodium hydroxide is added. Which ion is present in the solution?

   [1 mark]

   • AIron(II) ion, Fe2+
   • BIron(III) ion, Fe3+
   • CCopper ion, Cu2+
   • DAluminium ion, Al3+

   (c)

   A third solid gives no colour change in a flame test, but when dissolved in water and warmed gently with sodium hydroxide solution, a gas is produced that turns damp red litmus paper blue. Identify the ion responsible for this result and explain why the flame test alone would not have identified this ion.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student analyses a second colourless solution using dilute acids and precipitation tests to identify the anions present, working through the tests for halide, sulfate and carbonate ions.

   (a)

   A student is given an unknown colourless solution and adds a few drops of dilute nitric acid followed by silver nitrate solution. A cream-coloured precipitate forms. Which halide ion is present in the solution?

   [1 mark]

   • AChloride ion, Cl-
   • BSulfate ion, SO4 2-
   • CIodide ion, I-
   • DBromide ion, Br-

   (b)

   The same student adds dilute hydrochloric acid followed by barium chloride solution to a separate sample of the solution. A dense white precipitate forms that does not dissolve when more dilute hydrochloric acid is added. Which ion does this confirm?

   [1 mark]

   • ASulfate ion, SO4 2-
   • BChloride ion, Cl-
   • CCarbonate ion, CO3 2-
   • DNitrate ion, NO3-

   (c)

   A third sample of the same solution is tested by adding a few drops of dilute hydrochloric acid directly to it. Effervescence is observed and the gas produced is bubbled through limewater, which turns cloudy. Identify the ion responsible and write the word equation for the reaction between the acid and this ion.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A school laboratory technician is asked to fully identify a mystery salt using a combination of flame tests and chemical tests, and to justify the need for using more than one type of test.

   (a)

   A laboratory receives a mystery salt sample and a technician performs a flame test, observing an orange-red flame colour. State the ion identified by this result, and explain why a flame test result on its own is not always sufficient to fully identify an unknown salt.

   [3 marks]

   (b)

   The technician then dissolves a sample of the same mystery salt in water, adds sodium hydroxide solution dropwise and observes a white precipitate that dissolves when excess sodium hydroxide solution is added, forming a colourless solution. Identify the cation present, and describe how the technician could then confirm the anion present is a chloride ion, including the observation expected.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A school science department is choosing between two methods for analysing unknown ionic compounds: traditional wet chemical tests carried out by students, versus sending samples away for instrumental analysis using a flame photometer that compares emitted light with reference data and a calibration curve.

   (a)

   Traditional wet chemical tests include flame tests, sodium hydroxide tests, and acid and precipitation tests. Describe how these tests would be used to fully identify the cation and anion in an unknown ionic solid, describing at least three different tests and the observations that would distinguish between possible ions at each stage.

   [6 marks]

   (b)

   Evaluate the advantages and disadvantages of using an instrumental method such as a flame photometer, compared with the traditional wet chemical tests, for identifying and measuring the concentration of metal ions in solution. Your answer should refer to sensitivity, accuracy, speed, and any practical limitations of each approach.

   [6 marks]

   Total for question 4: 12 marks

End of questions