WAEC Chemistry(Pract.) 2015 Answers For Free (ENTER HERE)

2(iv) TEST Sample D + dilute Hcl(aq)

OBSERVATION A colourless and odourless gas evolve with a effervescence. The gas turn like water milky. The gas turn blue litmus to red.

INFERENCE The gas in CO2 from CO3^2- or HCO3-

2(iii) TEST Solution of sample C + dilute HN3 + BaCl2(aq) + HCl(aq)

OBSERVATION No visible reaction. White ppt form. White ppt insoluble in dilute Hcl.

INFERENCE SO3^2- or SO4^2- may be present. SO4^2- confirmed.

2(ii) TEST 5cm^3 of C NH4OH in drop, then in excess.

OBSERVATION white geletenous precipitate in drop. White geletenous ppt dissolve in excess.

INFERENCE: Zn^2 or Al^3 present. Zn^2 confirmed (in excess).

(OR) (2) Test | Observation | Inference

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1. Sample C water 5cm^3 of C NaoH in drop and in excess | soluble white geletenous precipitate in drop. White soluble or dissolve (in excess) | soluble salt. Zn^2 or Al^3 present.

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2. 5cm^3 of C NH4OH in drop. In excess | white geletenous precipitate in drop. White geletenous ppt dissolve (in excess) | Zn^2 or Al^3 present. Zn^2 confirmed (in excess).

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3. Solution of sample C dilute HN3 Bacl2(AQ) HCL (AQ) | No visible reaction. White ppt form. White ppt insoluble in dilute Hcl | SO3^2- or SO4^2- may be present. SO4^2- confirmed.

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4. Sample D dilute Hcl(aq) | A colourless and odourless gas evolve with a effervescence. The gas turn like water milky. The gas turn blue litmus to red | The gas in CO2 from CO3^2- or Hco3^-

(1A) Table of Values

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Burette Reading | Rough | First Reading | Second Reading | Third Reading

Final Reading (in cm^3) | 28.00 | 28.00 | 28.00 | 28.00

Initial Reading (in cm^3) | 0.00 | 0.00 | 0.00 | 0.00 | 0.000

Volume of acid used (in cm^3) | 28.00 | 28.00 | 28.00 | 28.00

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Average = 28.00 28.00 28.00/2 = 28.00cm^3

OR

Average = 28.00 28.00/2 = 28.00cm^3

1(ii) molar concentration =mass conc/molar mass mass conc=molar conc*molar mass =0.0434*106 =4.69g/dm^3

1(iii) 2.50g of Na2CO3 Na2SO4->250cm^3 Xg of Na2CO3 Na2SO4->1000cm^3 Xg=2.50*1000/250 Xg=10g % of Na2CO3=4.6/10*100 =46%

(1) TABULATE Burrette Readings(cm3),1st Reading | 2nd Reading | 3rd reading|

Final burette Reading|23.70|45.00|26.00|

Initial burette Reading|2.00|23.50|4.30|

Volume of acid used|21.50|20.70|20.90|

Average titre value = (21.70 21.50 21.70)cm^3 /3 =(64.90)/3 = 21.70cm3

(1b) A IS 0.100 mol 2.50g of Na2CO3 and Na2SO4 in 250cm^3 Na2CO3 2HNO3->2NaNO3 H2O CO2 Conc of B in mol/dm^3 Conc of Na2CO3 in the mixture Na2CO3 =106 VA=21.7cm^3 CA=0.100 VB=25cm^3 CB=? NA=2 NB=1 CAVA/CBVB=NA/NB 0.1*21.7/CB*25=2/1 CB=(0.1*21.7*1)/(25*2) =0.0434M

(3aiv) The water turn red immediately

(3av) No

(3avi) because of its solubility in water

(3b) u=>(heated) v CO2 CaCo3(s) =>(heated) Cao(s) Co2(g) v H20 => w Cao(s) H20(l) => Ca (OH)2(aq) U = CaCa(3), V = Cao, W = Ca (OH)2

(3ai) fountain experiment

(3aii) to show that HCL is extremely soluble in water

(3aiii) Ammonia gas (NH3)

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Posted by Dickson on April 15, 2015.

Categories: Education