JC2 Science Practical Assessment (2) hints:

Note : This JC2 SPA hint (not really a true practice) is easy and your JC’s SPA should be much more difficult. It is just used to illustrate SPA practices. The actual SPA questions and style differ markedly from this practice. You may wanna grab hold of HCI, VJC and RJC and other JCs SPA packages for great references!

Question

Carry out the following experiments with FA6 which contains up to 3 cations and 2 anions from the following list: H+, NH4

+, Mg2+, Al3+, Ca2+, Cr3+, Mn2+, Fe2+, Fe3+, Cu2+, Zn2+, Ba2+, Pb2+, CO3

2-, NO3-, NO2

-, SO42-, SO3

2-, CrO42-, Cl-, Br- and I-.

Record your observations and the deductions you make from them in the spaces provided. Your answers should include:(i) details of colour changes and precipitates formed;(ii) names of gases evolved and details of the test used to identify each one.

Test Observation Deduction

(a) Add aqueous sodium carbonate to FA6 and warm gently.

Filter the mixture. Collect the filtrate produced and retain it for test (b).

Reddish brown ppt is formed.Effervescence is observed.Colourless gas evolved forms white ppt with aq. Ca(OH)2. Another gas evolved turns moist red litmus paper blue.

Reddish brown residue and colourless filtrate are obtained.

Fe(OH)3 is pptedFe3+ is present in FA6CO2 is evolved due to hydrolysis of Fe3+

NH3 is evolvedNH4

+ is present in FA6

(b) To the filtrate from (a), add dilute hydrochloric acid.

Then add aqueous barium chloride.

No gas is evolved.

White ppt is formed insoluble in excess dil. HCl

No CO2, SO2, NO2 is evolved.CO3

2-, SO32-, NO2

- absent in FA6

BaSO4 is pptedSO4

2- is present in FA6

(c) Add aqueous sodium hydroxide to FA6 and warm gently.

Filter the mixture.

Reddish brown ppt is formed insoluble in excess aq NaOH.Effervescence is observedColourless gas evolved turns moist red litmus blue

Reddish brown ppt and colourless filtrate

Fe(OH)3 is pptedFe3+ is present in FA6NH3 is evolvedNH4

+ is present in FA6

Collect the filtrate produced and retain it for test (d).

are obtained. (No marks)

(d) To the filtrate from (c), add aqueous sodium hydroxide with a little aluminium powder and warm gently.

No gas is evolved that turns moist red litmus paper blue

No NH3 is evolvedNO3

- is absent in FA6

Test Observation Deduction

(e) Add dilute sulphuric acid followed by aqueous potassium iodide to FA6.

Dark brown solution is obtained I2 is formed from oxidation of I-

by Fe3+

ORI- is oxidised to I2

FA6 is an oxidising agent.

(f) Add zinc powder to FA6 and boil the mixture for at least two minutes.

Filter the mixture.

Pale green solution is obtained

Grey residue and pale green filtrate are obtained

Fe2+ is formed from reduction of Fe3+ by Zn

Cation(s) present in FA6 : Fe3+ , NH4+

Anion(s) present in FA6 : SO42-

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(g) You are provided with a solution labelled FA7 which contains an anion that has no reaction with dilute acids or barium chloride.

(i) State all the possible anions that could be present in FA7.

NO3-, Cl-, Br-, I-

(ii) Briefly describe two chemical tests (reagents and expected observations) that could be carried out to identify the anion present in FA7.

Test 1 : Warm FA7 with aq. NaOH and Al powder. If NO3- is present, effervescence is observed and colourless gas evolved will turn moist red litmus paper blue.

Test 2 : Add aq. AgNO3 to FA7. If Cl-/Br-/I- is present, white/cream/yellow ppt will be formed.OR Add aq. Pb(NO3)2 to FA7. If Cl-/Br- is present, white ppt will be formed. If I- is present, yellow ppt will be formed.

(iii) Carry out the chemical tests you suggest and complete the table below for the test that has given the positive observation.

Test number ____ has given the positive observation as shown:

Observation Deduction

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