Stpm Sem 2 Chemistry Experiment 2013

1775 Words Aug 13th, 2013 8 Pages
Experiment 6 :Observation | KA2 | KA3 | Weight of test-tube + solid / g | | | Weight of empty test-tube / g | X1 | X2 | Weight of solid / g | | | Initial temperature of acid / °C | | | Final temperature of mixture / °C | θ1 | θ2 | Temperature change / °C | | |
Discussion :[In the experiment sheet, the is an error where questions in (c)(i) should be "the heat change involved the reactions involving KA2 and KA3] (c). i : q1 = mcθ1 ; q = (30.00)(4.18)( θ1) = q1 q2 = mcθ2 ; q = (30.00)(4.18)( θ2) = q2ii. mol of KA2 = mass / RMM ; mol of KA2 = x1 / 84 = a1 mol of KA3 = mass / RMM ; mol of KA3 = x2 / 106 = a2iii. HKA2 = q1 / a1 = - P kJ / mol HKA3 = q2 / a2 = +Q kJ / mol(d)KA2 + KA1 : Na2CO3(s) + 2 HCl
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| Red solution; brown precipitate when heated. | SO32- ; CH3COO- may present | | Purplish solution decolourise. | S2O32- may present | (iv) Add aqueous silver nitrate, followed by HNO3 | White precipitate, soluble in HNO3 / NH3 (aq), or SO32− in excess; turn black precipitate when heated. | SO32- may present | | White precipitate turn to yellow and then brown and finally black; white precipitate soluble in excess S2O32−. | S2O32- may present | | White precipitate in concentrated solution, soluble in HNO3 or NH3(aq). | | (v) Add aqueous disodium hydrogen phosphate. (No reaction for Ca2+) | White precipitate insoluble in excess | Pb2+ may present | | Blue precipitate is formed | Cu2+ confirm present | | White precipitate, soluble in mineral acid | Mg2+ confirm present | (vi) Add aqueous potassium chromate(VI) followed | (Confirmatory test for Pb2+) yellow precipitate is formed | Pb2+ confirm present | | No change occur (or form white ppt) | Pb2+ is absent |

KA 2 is a mixture of Al3+ and NH4+ or a mixture of solids Zn2+ and NH4+ | Observation | Deduction | (d) Dissolve all of solid KA 2 in distilled water and filter. Use separate portions of the filtrate for tests (i) to (v). (i) Add aqueous NaOH, then in excess, and warm. | White precipitate dissolved in excess NaOHWhen warmed, a pungent smell was given off | Pb2+,Zn2+,Al3+ may presentNH4+ may present | (ii) Add aqueous potassium iodide | White precipitate is

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