This PowerPoint Will highlight the main chemical tests you MUST be familiar with before the observation exercise and then give you some examples to work through

Homework Learn tables for appearance, sodium hydroxide solution, barium chloride solution, silver nitrate solution Today Observation – coursework briefing

Aims To carry out observations to determine the identify of an unknown – assessment preparation

Check list – you need to be able to… Name the TM from the colour of its solution Name the TM from the colour of the precipitate formed with ammonia or sodium hydroxide solution Recall the colours of the precipitates of the silver halides Recall the results of testing carbonates and sulphates with barium chloride Write ionic equations

In order to identify the transition metal – you need to be VERY familiar with the colours of the TM in solution, and the appearance of precipitates formed between the Tm and sodium hydroxide solution or ammonia solution.

What would be our 1 st approach? Look at the colours of the solutions of F and G and suggest which TM they contain – this is table 1 from the data sheets

Table 1

Practice identification Can you use table 1 to identify the transition metals in these solutions?

Cr(VI) Cu(II) Fe(II) or Ni(II) Mn(VII) Click to reveal label

Ignore the ammonium in this example – this is used as the ammonium iron(II) is more stable in air than iron(II) sulphate

Click to reveal label

Manganese(VII)

Addition of sodium hydroxide

Name the Transition metal

Copper(II)

Iron(II)

Iron(III)

Chromium(III) Blue precipitate with NaOH – re dissolves to give green solution This could be Mn(VII)

Addition of barium chloride This is usually the test for a SULPHATE

Addition of silver nitrate This is the test for HALIDES

Name it

Other chemical tests What is observed when we add starch to a solution of iodine? Would you see the same result if starch is added to iodide?

Can you write an ionic equation for the formation of iodine from iodide? 2I - - 2e -  I 2 Has the iodide been oxidised or reduced?

Can you… Name the TM from the colour of its solution? Name the TM from the colour of the precipitate formed with ammonia or sodium hydroxide solution? Recall the colours of the precipitates of the silver halides? Recall the results of testing carbonates and sulphates with barium chloride? Write ionic equations?

Try these practice questions

Example 1 A solution of W was green in appearance. A green precipitate was formed when NaOH(aq) was added and the precipitate re dissolved when excess NaOH was added forming a green solution. On addition of barium nitrate solution, a white precipitate was formed. (The solution was still pale green and we had to tip the test tube to see the colour of the ppt formed) The formula of the compound is …. Cr 2 (SO 4 ) 3 Chromium(III) sulphate

Example 2 A solution of X was green in appearance. A green precipitate was formed when NaOH(aq) was added and the precipitate did not dissolve when excess NaOH was added forming a green solution. On addition of barium nitrate solution, a white precipitate was formed. (The solution was still pale green and we had to tip the test tube to see the colour of the ppt formed) The formula of the compound is …. NiSO 4 Nickel(II) sulphate

Example 3 A solution of Y was orange in appearance. A brown precipitate was formed when NaOH(aq) was added and the precipitate did not dissolve when excess NaOH was added forming a green solution. On addition of silver nitrate solution, a white precipitate was formed. When aqueous potassium iodide was added and the solution formed tested using starch, a blue-black colour was seen The formula of the compound is …. FeCl 3 Iron(III) chloride In this reaction – the Fe 3+ is reduced to Fe 2+ and iodide is oxidised to iodine

Example 4 A solution of Z was green in appearance. A green precipitate was formed when NaOH(aq) which was insoluble when excess NaOH was added but turned brown on standing. On addition of silver nitrate solution, a yellow precipitate was formed. The formula of the compound is …. FeI 2 Iron(II) iodide

Useful background reading Link Homework Learn tables for appearance, sodium hydroxide solution, barium chloride solution, silver nitrate solution

Finally click onto the science minisite minisite I will have put here links to You Tube clips that show you the reactions