2018 Waec Gce Chemistry Practical Answers
(2)
A is HCl(aq)
B is ZnSO4(aq)
C is NaOH(aq)
D is Pb(NO3)2(aq)
Reasons:
Row 1: Hcl is used to distinguish pb²+ from Zn²+ ions since both behave alike with NaOH. It gives a white precipitate with pb²+ ions but not with Zn²+. The first row obviously shows that. Also there is usually no visible reaction when Hcl(A) and NaOH are mixed (c)
Row 2: When A and B mixes, the products Zncl2 and H2SO4 are soluble hence no visible reaction is seen. Between B and D, a white precipitate is seen because PbSO4 is insoluble. Between B and C, Zn²+ ions yield a while gelatinous precipitate with NaOH
(1ai)
Tabulate:
Burette reading |1 |2 |3 |
final reading |24.80|34.50|20.65|
initial reading |0.00 |10.50|6.55 |
vol of acid used|24.80|24.00|24.10|
(1aii) Average volume of A used
Va = 24.00 + 24.10/2
= 24.05cm^3
(1bi)
Concentration of A in moldm^-3
A contains 0.79g of KMnO4 per 250cm³ of solution.
Hence since 250cm³ = 0.79g
100cm³ = Xg
X = 1000×0.79/250 = 3.16g
Hence Conc in g/dm³ of A = 3.16gdm^-³
But molar conc = mass conc(gdm^-³)/molar mass(g/mol)
Hence molar Conc.Of A= 3.16gdm^-3/molar mass ofA
But molar mass of A = KMnO4
= 39 + 55 + 4(16) = 39 + 55 + 64
= 158g/mol
Hence Conc in moldm^-³ of A = 3.16gdm^-3/158g/mol
= 0.020moldm^-3
(1bii)
To get concentration of B in moldm^-³, we use the relation
CAVA/CBVB = na /nb
Where,
CA = 0.02moldm^-³
VA = 24.05cm^-³
na = 1
CB = ?
VB = 25.0cm³
nb = 5
0.02×24.05/CB×25 = 1/5
CB = 5 × 0.02×24.05/25
= 2.405/25
=0.0962
CB = 0.096moldm^-³
(3ai)
Sodium is stored under paraffin oil to prevent its oxidation by atmospheric gases
(3aii)
Desiccator lid must be greased with a thin layer of grease, to ensure an airtight seal.
(3aiii)
Because it is hygroscopic
(3bi)
Add an acid eg HCL and this gives a neutralization reaction and the indicator react with the acids. Heat the solution to obtain the NaCL(s)
(3bii)
Dip a rod in aqueous Ammonia and dip in a beaker containing the acids, only HCl produces dense white fumes of ammonium chloride
(3ci)
(i)Beaker
(ii)glass rod
(iii)volumetric flask
(3cii)
On adding the dilute HCL to Na3SO3 a gas with a chocking smell evolves
2018 Waec Gce Chemistry Practical Questions and answers is available, Get verified Chemistry Practical questions and answers midnight before the exam day. 2018 Waec Gce Chemistry Practical exam Expo is available at 9Jatechs.
Subjects for Friday, 14th September, 2018
Chemistry 3 (Alternative to Practical Work) >> 9.30am – 11.00am
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Number 1 and 2
(2)
A is HCl(aq)
B is ZnSO4(aq)
C is NaOH(aq)
D is Pb(NO3)2(aq)
Reasons:
Row 1: Hcl is used to distinguish pb²+ from Zn²+ ions since both behave alike with NaOH. It gives a white precipitate with pb²+ ions but not with Zn²+. The first row obviously shows that. Also there is usually no visible reaction when Hcl(A) and NaOH are mixed (c)
Row 2: When A and B mixes, the products Zncl2 and H2SO4 are soluble hence no visible reaction is seen. Between B and D, a white precipitate is seen because PbSO4 is insoluble. Between B and C, Zn²+ ions yield a while gelatinous precipitate with NaOH
(1ai)
Tabulate:
Burette reading |1 |2 |3 |
final reading |24.80|34.50|20.65|
initial reading |0.00 |10.50|6.55 |
vol of acid used|24.80|24.00|24.10|
(1aii) Average volume of A used
Va = 24.00 + 24.10/2
= 24.05cm^3
(1bi)
Concentration of A in moldm^-3
A contains 0.79g of KMnO4 per 250cm³ of solution.
Hence since 250cm³ = 0.79g
100cm³ = Xg
X = 1000×0.79/250 = 3.16g
Hence Conc in g/dm³ of A = 3.16gdm^-³
But molar conc = mass conc(gdm^-³)/molar mass(g/mol)
Hence molar Conc.Of A= 3.16gdm^-3/molar mass ofA
But molar mass of A = KMnO4
= 39 + 55 + 4(16) = 39 + 55 + 64
= 158g/mol
Hence Conc in moldm^-³ of A = 3.16gdm^-3/158g/mol
= 0.020moldm^-3
(1bii)
To get concentration of B in moldm^-³, we use the relation
CAVA/CBVB = na /nb
Where,
CA = 0.02moldm^-³
VA = 24.05cm^-³
na = 1
CB = ?
VB = 25.0cm³
nb = 5
0.02×24.05/CB×25 = 1/5
CB = 5 × 0.02×24.05/25
= 2.405/25
=0.0962
CB = 0.096moldm^-³
(3ai)
Sodium is stored under paraffin oil to prevent its oxidation by atmospheric gases
(3aii)
Desiccator lid must be greased with a thin layer of grease, to ensure an airtight seal.
(3aiii)
Because it is hygroscopic
(3bi)
Add an acid eg HCL and this gives a neutralization reaction and the indicator react with the acids. Heat the solution to obtain the NaCL(s)
(3bii)
Dip a rod in aqueous Ammonia and dip in a beaker containing the acids, only HCl produces dense white fumes of ammonium chloride
(3ci)
(i)Beaker
(ii)glass rod
(iii)volumetric flask
(3cii)
On adding the dilute HCL to Na3SO3 a gas with a chocking smell evolves
2018 Waec Gce Chemistry Practical Questions and answers is available, Get verified Chemistry Practical questions and answers midnight before the exam day. 2018 Waec Gce Chemistry Practical exam Expo is available at 9Jatechs.
Subjects for Friday, 14th September, 2018
Chemistry 3 (Alternative to Practical Work) >> 9.30am – 11.00am
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Mathematics Objective and Theory examProcedure on How To Subscribe for 2018 Waec Gce Chemistry Practical Questions and Answers
We only Run our Waec Gce Packages on Whatsappbecause it is the fastest means of sending messages and photos online.
Answers delivery via whatsapp for Chemistry Practical Questions and Answers Cost N500 MTN recharge card.
First Procedure on how to Subscribe
To subscribe for Chemistry Practical Questions and Answers send the card pin, Subject name( Chemistry Practical Questions and Answers) and your phone number Via SMS or Via WhatsApp To 08065889844
Note: 9Jatechs 2018 Waec Gce Chemistry Practical Questions and Answers is N500 MTN Card
Note: please do not call our number, simply send message on whatsapp or using SMS
For More Info Whatsapp 08065889844
Get verified 2018 Waec Gce Chemistry Practical Questions and Answers at Midnight, Read the above article to see every procedures on how to Subscribe for 2018 Waec Gce Chemistry Practical Questions and Answers. 2018 Waec Gce Chemistry Practical Questions and Answers is available, To get verified Questions and Answers for Chemistry Practical at midnight before the actual exam day, just read the article below to see every due process.
Also see the 2018 Waec Gce Biology Practical Questions and Answers.
We give reliable and verified Questions and Answers for all exams, get Chemistry Practical Questions and Answers from 9Jatechs to free your self from SSCE exam bondage , Get verified 2018 Waec Gce Chemistry Practical Questions and Answers at Midnight, Read the above article to see every procedures on how to Subscribe for 2018 Waec Gce Chemistry Practical Questions and Answers. 2018 Waec Gce Chemistry Practical Questions and Answers is available, To get verified Questions and Answers for Chemistry Practical at midnight before the actual exam day, just read the article below to see every due process.