(1a)
DRAW A TABLE WITH THE FOLLOWING
Burette reading|ROUGH|1st |2nd |3rd
Final |13.60|15.50|14.80|12.50
Initial |1.00 |3.10 |2.40 |0.00
Vol. acid used |12.60|12.60|12.40|12.50
Volume of S2O3²- =12.60+12.40+12.50/3
=37.50/3
=12.50cm³
(1bi)
Conc. in g/dm³ = molar mass * conc in mol/dm³
But molar mass of Na2S2O3
=(23*2)+(32*2)+(16*3)
=46 + 64 + 48
=158g/mol
Therefore 15.8g/dm³ = 158g/mol * conc of A in mol/dm³
Conc of A in mol/dm³ = 15.8/158
=0.1mol/dm³
(1bii)
Using CaVa/CbVb = na/nb
0.1*12.50/Cb * 25.00 = 2/1
50Cb = 1.25
Cb = 1.25/50
Cb = 0.025mol/dm³
The conc of I2 in B = 0.025mol/dm³
(1biii)
Gram conc of I2 = molar mass * molar conc
= (127*2)*0.025
=6.35g/dm³
Percentage mass of I2 in sample = 6.35/9.0 *100%
= 0.7056 * 100%
=70.56%
(1c)
There have to be a change in the colour of the mixture before it is added. The end point is known when the blue colour formed as starch is added, changes to colourless
====================
(2a)
Test: C + Water and filtered
Observation: part of C dissolves, colour less filtrate is formed
Inference: C is a mixture of a soluble salt
(2bi)
Test: 2cm^2 of filterate of salt C + AgNO3(aq) then dilute HNO3
Observation: white precipitate is formed
Inference: Cl^- present
(2bii)
Test: Solution im 2(b)(i) + excess NH3 solution
Observation: precipitate disorder in excess solution of NH3
Inference; Cl^- confirmed
(2ci)
Test: Resident + dilute HCl + shake
Observation; residue dissolved to form a blue solution
Inference; Cu^2+ present
(2cii)
Test; solution in 2(c)(i) + NH3 solution in drops and then in excess.
Observation: light pale blue precipitate is formed precipitate dissolved in excess solution of NH3 to give a deep blue solution
Inference; Cu^2+ confirmed.
=====================
(3ai)
On adding BaCl2 solutions to a portion of saturated Na2CO3 precipitate is formed,precipitate dissolves on adding excess dilute HCl
(3aii)
Q is reducing agent like SO2, H2S, CO
(3bi)
calcium oxide(Cao)
(3bii)
concentrated H2SO4
(3c)
NaOH pellet is delinquescent because it absorb moisture from the atmosphere to form solution
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DRAW A TABLE WITH THE FOLLOWING
Burette reading|ROUGH|1st |2nd |3rd
Final |13.60|15.50|14.80|12.50
Initial |1.00 |3.10 |2.40 |0.00
Vol. acid used |12.60|12.60|12.40|12.50
Volume of S2O3²- =12.60+12.40+12.50/3
=37.50/3
=12.50cm³
(1bi)
Conc. in g/dm³ = molar mass * conc in mol/dm³
But molar mass of Na2S2O3
=(23*2)+(32*2)+(16*3)
=46 + 64 + 48
=158g/mol
Therefore 15.8g/dm³ = 158g/mol * conc of A in mol/dm³
Conc of A in mol/dm³ = 15.8/158
=0.1mol/dm³
(1bii)
Using CaVa/CbVb = na/nb
0.1*12.50/Cb * 25.00 = 2/1
50Cb = 1.25
Cb = 1.25/50
Cb = 0.025mol/dm³
The conc of I2 in B = 0.025mol/dm³
(1biii)
Gram conc of I2 = molar mass * molar conc
= (127*2)*0.025
=6.35g/dm³
Percentage mass of I2 in sample = 6.35/9.0 *100%
= 0.7056 * 100%
=70.56%
(1c)
There have to be a change in the colour of the mixture before it is added. The end point is known when the blue colour formed as starch is added, changes to colourless
====================
(2a)
Test: C + Water and filtered
Observation: part of C dissolves, colour less filtrate is formed
Inference: C is a mixture of a soluble salt
(2bi)
Test: 2cm^2 of filterate of salt C + AgNO3(aq) then dilute HNO3
Observation: white precipitate is formed
Inference: Cl^- present
(2bii)
Test: Solution im 2(b)(i) + excess NH3 solution
Observation: precipitate disorder in excess solution of NH3
Inference; Cl^- confirmed
(2ci)
Test: Resident + dilute HCl + shake
Observation; residue dissolved to form a blue solution
Inference; Cu^2+ present
(2cii)
Test; solution in 2(c)(i) + NH3 solution in drops and then in excess.
Observation: light pale blue precipitate is formed precipitate dissolved in excess solution of NH3 to give a deep blue solution
Inference; Cu^2+ confirmed.
=====================
(3ai)
On adding BaCl2 solutions to a portion of saturated Na2CO3 precipitate is formed,precipitate dissolves on adding excess dilute HCl
(3aii)
Q is reducing agent like SO2, H2S, CO
(3bi)
calcium oxide(Cao)
(3bii)
concentrated H2SO4
(3c)
NaOH pellet is delinquescent because it absorb moisture from the atmosphere to form solution
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Time and Date for Chemistry practical 2019 WAEC Examination.
Monday 6th May, 2019
- Chemistry 3 (Practical) (Alternative A) – 09:30 a.m. – 11:30 a.m. (1st Set)
- Chemistry 3 (Practical) (Alternative A) – 12:00 noon – 2:00 p.m. (2nd Set)
Recommended: 2019/2020 Waec (SSCE) April/May Official Timetable
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2019 Waec Chemistry practical Answers will be deliver to all 9Jatechs Subscribers at night before the exam day, you can also get free exam Expo on our portal(i. e we are going to post answers 1hour after the exam start) just like we did during the previous Civic Education 2018 Waec Gce Exam
Procedure on How To Subscribe for 2019/2020 Waec Chemistry practical Questions and Answers.
We only Run our Waec Gce Answers delivery on Whatsapp( Waec Runs Packages) because it is the fastest means of sending messages and photos online.
Answers delivery via whatsapp for Chemistry practical Questions and Answers Cost N600 MTN recharge card.
First Procedure on how to Subscribe
To subscribe for Chemistry Practical Questions and Answers send the card pin, Subject and your phone number Via SMS or Via WhatsApp To 08065889844
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For More Info Whatsapp 08065889844
2019/2020 Waec Chemistry practical Questions and answers now available, To get all questions and answers for 2019 Waec Chemistry practical Questions and answers now available, To get all questions and answers for Chemistry practical.
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SEE ALSO : 2019/2020 Waec (SSCE) April/May Official Timetable
2019/2020 Waec Chemistry practical Questions and answers now available, To get all questions and answers for 2019 Waec Chemistry practical Questions and answers now available, To get all questions and answers for Chemistry practical.
9Jatechs deliver it answers at midnight to her subscribe. Expo for 2019 Waec CHEMISTRY PRACTICAL Questions and answers is also available on our portal (9Jatechs). 9Jatechs deliver it answers at midnight to her subscribe. Expo for 2019 Waec Chemistry practical Questions and answers is also available on our portal (9Jatechs).
ALSO SEE: 2018 Waec Gce Physical and Practical Geography Questions and Answers | Waec Gce Expo
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