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Both plates were then weigh separately and were recorded as initial mass of anode and cathode in the table below. 4. Both weighed plate were clipped using crocodile clips and the batteries were placed in the battery socket. After that, both plates were immersed in copper (II) solution and the stop watch was started to allow the apparatus to run for 30 minutes.
5. the reading of ammeter was recorded. Then, both plates were taken out from the solution, and were dipped into propanone, before blow to dry for both plates using hair drier. 6. The dried plates were then weighed and were recorded as final mass accordingly.
The mass lost (at anode) and gained (at cathode) were calculated. Observation : | Copper (anode)| Copper (cathode)| Initial mass / g| Xinitial| Yinitial| Final mass / g| Xfinal| Yfinal| Difference / g| X| Y| Time taken : 30 minutesCurrent used : p ADiscussion :The current used : Q = It ; Q = (p)(30 x 60) = a CMol of e- used = Q / F @ a / 96500 ; mol of e- = d molAt anode, since Cu > Cu2+ + 2 e- ; 1 mol of Cu = 2 mol of e-Mass of copper dissolved = d mol / 2 x 63.
5 g = f g % of purity of Cu = mass gained at cathode / mass of Cu dissolve= Y / f x 100%[Note that your mass of Cu gained must be less than Cu dissolved]| | |
Stpm Chemistry Experiment 2
Experiment 8 : Suggested salts for KA1 is MgS2O3 or MgSO3 or CuSO3 or Pb(CH3COO)2 or Ca(CH3COO)2 | Observation| Deduction| (b) Add dilute hydrochloric acid to a small amount of solid KA 1, then warm gently.
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| If S2O32- : Yellow precipitate; brimstone [pungent] smell gas/ gas decolourise KMnO4/H+| S2O32- may present| | If SO32- : brimstone smell gas/ gas decolourise KMnO4/H+| SO32- may present| | If CH3COO- : Gas smell of vinegar is released when heated| CH3COO- ” present| (c) Dissolve solid KA 1 in distilled water and filter. Use separate portions of the filtrate for tests (i) to (vi). i) Add aqueous NaOH, then in excess. | i. White precipitate insoluble in excess NaOH| Mg2+ , Ca2+ may present| | ii. White precipitate soluble in excess NaOH| Pb2+,Zn2+,Al3+ may present| | Blue precipitate insoluble in excess NaOH| Cu2+ may present| (ii) Add aqueous NH3, then in excess followed by aqueous NH4Cl| White precipitate insoluble in excess NH3 (if (i) is fulfilled)| Mg2+ confirm present| | White precipitate insoluble in excess NH3 (if (ii) is fulfilled)| Pb2+ , Al3+ present| | No precipitate formed when NH3 is added| Ca2+ confirm present| | Blue precipitate insoluble in excess
NaOH| Cu2+ confirm present| (iii) Add aqueous iron(III) chloride, then warm. | 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 formed| Zn2+,Al3+ may present| (iii) Add aqueous potassium chromate(VI). (Since mixture has no Pb2+, so its either white or orange)| Orange precipitate is formed. Ppt dissolve in mineral acid| Al3+ may present| | White precipitate is formed| Zn2+ may present| (iv) Add aqueous sodium ethanoate, then warm. | No changes observed initially but turn cloudy when heated| Al3+ confirm present| | No changes occur| Zn2+ confirm present| (v) Add aqueous sodium carbonate, then warm. | White ppt is formed. Pungent smell gives off when heated| NH4+ confirm present| Experiment 9 KA 1 is solid CuCO3 or MgCO3 or CaCO3 or MnCO3 or NiCO3 or BaCl2 or MgCl2 or CaCl2.
Test (plan must be written)| Observation| Deduction| 1. About 2 g of KA1 is put in a test tube and heated strongly. | KA1 is white solid (Ded : transition metal ion is absent) ; green solid (Ded : Ni2+, Fe2+, CuCO3 may present); buff colour solid (Ded : Mn2+ may present)| | Colourless gas evolved which turn lime water chalky| CO32- may present| 2. Salt is dissolved using distilled water (If salt cannot dissolved in water, then) | (Only chloride salt dissolved in water) Colourless solution is formed| | 2.
Salt is dissolved using mineral acid| Colourless gas evolved which turn lime water chalky| CO32- confirm present| 3. Solution is then divided into 5 portion| | | i. Add little NaOH then until excess| White precipitate soluble in excess NaOH (Ded : Pb2+,Zn2+,Al3+ may present) ; White precipitate insoluble in excess NaOH (Ded : Ba2+,,Mg2+ may present) ; blue ppt insoluble in excess (Cu2+ may present) ; green ppt insoluble in excess (Ni2+ may present) ; buff ppt insoluble in excess (Mn2+ may present)| ii.
Add little NH3 then until excess(Once when cation is almost confirmed, you can always perform 2 confirmatory tests)| For Pb2+,Zn2+,Al3+| For Ba2+, Mg2+| For Cu2+| For Ni2+| For Mn2+| White ppt soluble in excess NH3| White ppt insoluble in excess NH3| White ppt insoluble in excess NH3| No changes formed| Blue p soluble in excess NH3 form blue soln| Green ppt insoluble in excess| Buff ppt insoluble in excess| Zn2+ may present| Al3+ Pb2+ may present| Mg2+ may present| Ba2+ may present| Cu2+ may present| Ni2+ may present| Mn2+ may present| | v.
Add 2-3 drops of conc. H2SO4 into solution| White fume is given off| White fume is HCl, so Cl- may present| vi. Add 5 mL of Pb(NO3)2 into solution| White precipitate is formed instantly| Cl- confirm present| (Since salt only contain Cl- & CO32-. If CO32- not present, so Cl- is present, so do 2 confirmatory tests for Cl-) KA 2 is a mixture of anions I- and NO3- or a mixture of Br- and NO3- Test (plan must be written)| Observation| Deduction| 1. KA2 is heated gently then strongly heated. | Brown pungent gas released which turned damp blue litmus paper red.
Gas also ignite the glowing wooden splinter| NO2 and O2 gas releasedNO3- may present| 2. KA2 is then added with a few drop of conc. H2SO4| Mixture of brown and reddish brown gas were observed(or)| NO2 and Br2 gas releasedBr- ; NO3- may present| | Brown gas were observed. Upon heating, mixture of brown and purplish gas were witnessed together with a bad egg pungent smell| NO2 and I2 gas releasedI- ; NO3- may present| 3. KA2 is dissolved using distilled water and was separate into 5 portion for further testing. | [Don’t write this!!
Since you can more or less tell what ion presence is either Br- or I-, so try to do 2 test for each ion]| Test of NO3-i. Add 2 mL of conc. FeSO4 into KA2, followed by 2 drop of conc H2SO4. | A brown ring is formed in the middle of solution mixture| NO3- may present| ii. Add 2 g of Devarda alloy to KA2 solution| A colourless pungent gas is formed| NO3- confirm present| Test of I- / Br-iii. Add 2 mL of AgNO3 into KA2| A milky [ Pale yellow] precipitate is formed. Precipitate is dissolved in conc. NH3| Br- may present| | A yellow precipitate is formed| I- may present| iv.
Add 2 mL of Pb(NO3)2 into KA2| A milky [ Pale yellow] precipitate is formed. | Br- confirm present| | A yellow precipitate is formed| I- confirm present| Experiment 10Observation (a) Mass of container + KA 3/g | | Mass of empty container/g | | Mass of KA 3/g | SA| Observation (b) Mass of crucible + precipitate/g | | Mass of empty crucible/g | | Mass of precipitate/g | SB| | Question :(c)i. [to ensure a homogeneous solution for the formation of complex ion and allow collision between reactants to ensure complete reaction ] increase the rate of reaction between aluminium and ligandii. o washed away the impurities as well as to [prevent precipitate from dissolving] lower the rate of reaction(d) the mass of complex is constant [ by repeating the process of drying, cooling and weighing until the mass of precipitate is constant](e) mass in 1 mol of Al(C9H6NO)3 = 27. 0 + 3[9(12. 0) + 6(1. 0) + 14. 0 + 16. 0] = 459. 0 g(f) % Al = 27. 0 / 459. 0 x 100% = 5. 88%(g) mass of Al in sample prepared = ( 5. 88 / 100 ) x SB = C g % of Al in sample = (C / SA) x 100% = answer %|
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