WAEC GCE 2017 chemistry Practical Answer – Nov/Dec Expo

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100% VERIFIED CHEMISTRY PRACTICAL ANSWERS

*PLS NOTE THIS SYMBOLS*

1. ^ means Raise to power

2. * means multiplication

3. sqrt or root means Sqr root

4. / means division or divide

5. degree means degree sign that looks like small zero

6. tita means tita sign that looks like crossed-zero


(1ai)

Burette Reading(cm^3)| 1   | 2    | 3 |

Final Reading   |33.10|30.00|25.00|

Initial Reading | 9.60|7.50 |2.40 |  

Volume of F used (cm^3)|23.50|22.50|22.60.  


(1aii) 

Average volume of F used

=22.50 + 22.60 / 2

=22.55cm^3


(1bi)

GIVEN:Molar Conc of Kmn04 =0.200mol/dm^2

Volume of Kmn04 used =22.55cm^3

Molar Conc of FeSo4. 7H2O=?

Volume of FeSO4.7H2O=25cm^3

Mole ratio of Kmn04 =1

Mole ratio of FeSO4.7H2O=5


Using,

Molar Conc of KeSO4.7H2O x Volume(FeSo4.7H2O) =n(FeSO4.7H2O)/n(KmnO4)


=molar Conc x 25 / 0.0200 x 22.55 = 5/1


=Molar Conc.  x 25=0.0200 x 22.55 x 5

=Molar Conc =0.0200 x 22.55 x 5 / 25


=Molar Conc =0.0902mol/dm^3


(1bii) 

Molar mass of FeSO4.7H2O

=56+32+(4*16)+7(18)

56+32+64+126 = 278g/mol

Conc of FeSO4.7H2O in gdm-3 = 0.0900*278

=25.02gdm-3


(1biii)      

Mass of FeSO4.H2O = 33.60-25.02

=8.58gdm-3

Percentage of FeSO4.7H2O = (8.58/33.60) * 100

= 25.54%            


(1ci)

Hydrochloric acid(HCL) is a mild reducing agent and so it will consume a certain amount of Kmn04 during titration. This will give a slightly higher value of Kmn04 consumption than the actual amount needed by the analyte


(1cii)

As Kmn04 is a dark purple colour solution, it is not possible to take readings from the button of the meniscus on the burette as in usual. Hence, the top, of the meniscus is used(visibility consideration) 


(1ciii) 

No indicator is used because Kmn04 serves as an indicator


============================================




(2a)

TEST|OBSERVATION|INFERENCE


(2ai)

TEST: A+distilled water and stirred

OBSERVATION: A disolved in water

INFERENCE: A is soluble in salt


(2aii)

TEST: A(aq)+litmus paper

OBSERVATION: Turns blue litmus paper red

INFERENCE: A is an acidiic salt


(2aiii)

TEST: A(aq)+NaOH(aq)- in drops, then in excess

OBSERVATION: -White gelatinous ppt formed.

             -Precipitate soluble/dissolved

INFERENCE: Pb^2+ or Zn^2+ or Al^3+ present

           Pb^2+ or Zn^2+ or Al^3+ present


(2aiv)

TEST:A(aq)+NH3(aq)- in dropss,

     -then in excess

OBSERVATION: -White gelatinous precipitate

             -Precipitate insoluble 

INFERENCE:   -Pb^2+ or Zn^2+ or Al^3+

             -Al^3+ present

(2av)

TEST: A(aq)+FeSO4(aq)+conc H2SO4

OBSERVATION: Brown ring forms between the two solutions

INFERENCE: NO3- confirmed


(2bi)

A is aluminium trioxonitrate(v)


(2bii)

Al(NO3)3


(2c)

TEST|OBSERVATION|INFERENCE


(2ci)

TEST: K+NaHCO3(aq)

OBSERVATION: No visible reaction is observed

INFERENCE: NaHCO3(aq) does not show result for alkanols(K)


(2cii)

TEST: K+benedict solution+heat

OBSERVATION: There is no change in the colour of the benedicts solution

INFERENCE: Benedicts solution is not an indicator for alkanols(K)


(2ciii)

TEST: K+KMnO4(aq)

OBSERVATION: KMnO4(aq) solution changes from purple to colourless

INFERENCE: Alkanol is being oxidized by KMnO4


(2civ)

TEST: K+CH3COOH+conc H2SO4

OBSERVATION: pleasant fruity smell is observed

INFERENCE: Esterification reaction has occured


================================================



(3a)

(i) Putsome distilled water in a beaker

(ii) Measure 100cm^3 of 2.00mol/dm^3 of the stock solution by means of a burette and pour all the solution into the beaker containing the distilled water

(iii) Stir the solution

(iv) Transfer the solution into a 250cm^3 volumetric flask by means of a funnel

(v) Ensure that all the solution in the volumetric flask has been transferred by thoroughly rinsing the inside of the beaker with distilled water

(vi) Dilute the solution in the volumetric flask with distilled water until it reaches the 250cm^3 mark

(vii) Shake the solution carefully


(3b)

(i) CH3COONa: It forms basic solution

(ii) Al2(SO4)3: Acidic solution

(iii) KNO3: Neutral solution


(3c)

Acidified potasium tetraoxomanganate(vii) KMnO4 was placed in the burette


==COMPLETED… GOODLUCK==





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