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WAEC 2016/2017 Chemistry Praticals Answers Posted Here [13/04/2016]


CURRENT EXAMINATION:

WAEC Chemistry Praticals Answers ;
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CHEMISTRY PRACTICALS QUESTIONS
KEEP REFRESHING!!!
( NOTE THAT of this
^ MEANS Raise to power
/ means ÷ divide
* means multiplication sign .
+ means plus
= means equal to )


1) Burette readings (initial and final) must be given to two decimal place volume of pipette used must also be recorded.All calculations must be experimental procedure is required.All calculations must be done in your answers book.
See How To Carry Out Titration (NECO, WAEC Chemistry Practical)
A is a solution containing 4.50g of an acid H2C204 per dm^3
B contains 3.6g of KMnO4 per dm^3 of solution
a) put A into the burette and titrate it against 20.0cm^3 or 25.00Cm^3 portions of B using methyl orange as indicator.
Repeat the tritration to obtain consistent titres.
TABULATE
your burette readings and calculate the average volume of acid A used
b) From your result and the information provided above calculate

CHEMISTRY PRACTICAL ANSWERS
1a )
Solution A = 4.50 gdm ^ -3 of H2 C 2 O4
Solution B = 3.16 gdm ^ -3 of KMnO 4
volume of pipette = 25 .00 cm ^ 3
colour change = orange to pink
Equation of the reaction =
4H 2C 2 O4+2 KMnO 4- ---> 8CO 2+ K 2O+MnO3 +4 H2 O
TABULATE
Burette reading / cm ^ 3 -
|
Rough | |1st | |2nd | |3 rd|
final burette reading -
|23 .55 | |46 . 05| | 22. 50 | | 45 .00 |
Initial burette reading -
|00 .00 | |23 . 55| | 00. 00 | | 22 .50 |
Volume of acid used -
|23 .55 | |22 . 50| | 22. 50 | | 22 .50 |
Average Volume of acide used
= 22. 50 + 22 .50 + 22 .50 / 3
= 67. 50 / 3
=22 .50 cm ^ 3
1bi )
Concentration of B in moldm ^ -3 = mass concentration/ molar mass .
Where molar mass of KMnO 4 = 39 + 55 +
( 4 * 16 ) = 158 g / mol
:concentration in moldm ^ -3 = 316 / 158 =
0. 02mldm ^ -3
1bii )
Concentration of A in moldm ^ -3
CaVa/ CbVb = na / nb
Where
Ca = concentration of Acide in moldm ^ -3
Cb = concentration of base in moldm ^ -3
Va = volume of acid in Cm^ 3
Vb = volume of base in Cm ^ 3
na= number of mole of acid in the balance equation
nb = number of mole of base in the balance equation
Making Ca subject of formular
Ca = Cb * Vb * na/ Va * nb = 0 .02 * 25 * 2/ 22 . 50 * 1
Ca = 0 .04 Moldm ^ -3
1biii)
No of H ^ + in A
ldm^ 3 of A = 0 .04 Moldm ^ -3 of H2 C 2O4
H2 C 2O4 dissolved completely in water to give
; H2 C 2O4 ---- --> 2H ^ + C 2 O4^ 2 -
1mole of H2 C 2O4 = 2H ^ +
0. 04moles = 0. 04 * 2 = 0. 05 H^ +
but 1mole of H ^ + = 6 .02 * 10 ^ 23
0. 08mole of H ^ + = X
X = 0. 08 * 6.02 * 10 ^ 23 = 4 .8 * 10 ^ 22 H^ +
1biv)
No of K ^ + in B
1mole of substance = 6 .02 * 10 ^ 23
but ; KMnO 4 - ----> K ^ + MnO4 ^ -
1mole of KMnO 4 = K ^ +
0. 02mole of KMnO 4 = 0. 02 * 1 = 0. 02 k^+
but 1mole = 6. 02 * 10^ 23
0. 02mole = 0. 02 * 6.02 * 10 ^ 23
= 1.2 * 10 ^ 22 K ^ +
1bv )
PH of A
PH of A = Log10 [Moldm ^ 3 of H^ + ]
but H 2C 2O4 -- ---> 2H ^ + + C 204 ^ -
1mole of H2 C 2O4 = 2Ca
0. 04mole = Log 10 [2 Ca]
= -Log10 [ 2 * 0. 04 ]
= -[2 * 4 * 10 ^ -2 ]
= -[0 .9031 + (-2 Log 10 )]
= -[0 .9031 + (-2 * 1)]
= -[-0 .9031-2 )
= -[-1 .0969]
=1 .1
1biv)
POH of B
PH + POH = 14
POH = 14 - PH
POH = 14 - 1. 1
POH = 12 .9
2)
TABULATE.
Ca =NaCl and ZnCO3
| TEST |
a ) C + water + Filtration.
i) C + NaOH in drops , in excess .
ii ) C + (aq) NH 3 in drops and in excess .
iii ) C + dil HCl in drops , and excess .
iv ) C + dil HCl + Bacl 2(aq)
v ) C + dil HNO 3 + AgNO3
vi ) C + dil HNO 3 + AgNO3 ^ + excess NH 3
vii) C + few drops of (aq ) NH 3
| OBSERVATION |
a ) Dissolves partially to give in black residue and a colourless filterate on filteration
i)white gelatinous precipitate formed , soluble in excess NH 3 solution
ii ) white gelatinous precipitate formed , soluble in excess
iii ) efferrescence due to CO 2 inssuring gas turns moist blue litimus paper red and turns lime water milky
iv )white precipitate soluble in dilute HCl
v )white preciptate in soluble in dilute HNO 3 acid solution
vi )white precipitate dissolved soluble in excess NH 3
vii)No visible reaction
| INFERENCE |
a ) C is a mixture of soluble and insoluble salts
i)Zn ^ 2 +, Pb ^ 2+ or Al ^ 3+ present
ii ) Zn +2 + confirmed
iii )Gas is CO 2 from CO 3^ 2 - or HCO3^ -
iv ) CO 3 ^ 2- confirmed
v )CL^ - present
vi ) Cl ^ - confirmed
vii) Na ^ + present
================================
(3a) The differences in Boiling point of a liquid is
(I) they are used to separate the mixture of
color
(II) with close different boiling point
(3b) (i) To make the accurate result of the
solution
(II) To avoid the error of decimal
3c)
C1=2.5moldm³
V2=500cm³
Ç2=0.2moldm³
V1=?
C1V1=C2V2
V1=C2V2/C1
V1=0.2*500/2.5
V1=40.0cm³CALL MR CHINEKS ON 08107431933 TO SUBSCRIBE FOR WAEC Chemistry Practicals Answers

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i need chemistry practical question for gce weac 2016

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