Rev test 3 Qualitative analysis + SALT PREPARATION

REVISE SALT SOLUBILITY SEPERATELY

Due to budget cuts, a robot has been put in charge of labelling four bottles of solutions. The four solutions have been labelled but have been mixed up!

Outline how you can identify which solution is which.

Your method should use only chemical tests, i.e. not pH indicator or flame test results, and give a positive test for each solution. Include all reagents / tests and observations in your answer. (4)

• M1 (K_2CO_3): add dilute acid \rightarrow effervescence

• M2 (CH_3COOH): add Mg powder / CaCO_3 powder \rightarrow effervescence * OR add C_2H_5OH_{(l)} (& warm with conc. H_2SO_4 ) \rightarrow fruity smell

• M3 (Na_2SO_4): add acidified Ba^{2+}_{(aq)} \rightarrow white ppt

• M4 ($FeCl_3$): add NaOH_{(aq)} \rightarrow brown ppt

  • OR add acidified Ag^+_{(aq)} \rightarrow white ppt

Describe how you would prepare a sample of pure, dry potassium sulphate. You need to give all the reagents used and a brief summary of the method, including the apparatus. Please use bullet points. (10)

• M1: use a pipette to add 10.0 / 25.0 cm^3 of KOH_{(aq)} to a conical flask

  • (Note: stated plausible volume required)

• M2: add a few drops of indicator, e.g. phenolphthalein, to the conical flask

  • (Note: named indicator required)

• M3: fill a burette with H_2SO_{4(aq)}

• M4: record initial burette reading

• M5: add acid to flask, swirling continuously

• M6: add acid slowly near end point

  • (Note: both points needed for M5/M6)

• M7: use a white tile beneath conical flask

• M8: stop when indicator changes colour, e.g. pink $\rightarrow$ colourless for phenolphthalein

  • (Note: correct colour change for indicator needed)

• M9: record final burette reading

• M10: repeat until two titre volumes are concordant, i.e. agree to within 0.1 cm^3

• M11: repeat without indicator adding av. (average) titre of H_2SO_4

• M12: evaporate resulting solution to half-bulk / crystallisation point

• M13: leave to cool and crystallise

• M14: dry crystals between filter papers

• Any 10 (marks)

Describe the method used to prepare a sample of pure, dry lead(II) sulfate. (4)

• M1: mix solutions of Pb(NO_3)_{2(aq)} and Na_2SO_{4(aq)}

• M2: filter to obtain residue

• M3: wash with cold deionised water

• M4: dry between filter papers

• ACCEPT: alternative soluble lead compounds / sulfate compounds

• ACCEPT: alternative methods of drying

Give balanced symbol equations for zinc oxide solid + hydrochloric acid (3)

ZnO(s) + 2HCl(aq) \rightarrow ZnCl_2(aq) + H_2O(l)

potassium hydrogencarbonate solid + sulphuric acid

2KHCO_3(s) + H_2SO_4(aq) \rightarrow K_2SO_4(aq) + 2H_2O(l) + 2CO_2(g)

ethanoic acid + calcium

Ca(s) + 2CH_3COOH(aq) \rightarrow Ca(CH_3COO)_2(aq) + H_2(g)

ionic equation for sodium hydroxide and nitric acid

H^+(aq) + OH^-(aq) \rightarrow H_2O(l)

Nitric acid reacts with ammonia. State and explain in terms of proton transfer which is the acid and which is the base. (2 marks)

• HNO_3: acid / proton donor

• NH_3: base / proton acceptor