WAEC Chemistry Practical 2021. Many WAEC candidates find it difficult to answer the WAEC Practical Chemistry Alternative A and B correctly due to not understanding the questions. I will show you the best way to answer the 2021 WAEC Chemistry Practical questions and make a good grade in your Chemistry examination.
It is pertinent you understand the WAEC Chemistry Practical making scheme before attempting any questions so as to present your answers in such a way that it will look attractive to the examiner to earn you big marks.
Bear it in mind that every single procedure is awarded marks. So, ensure you do not skip any step while reporting and presenting your practical results.
The Chemistry Practical question paper will consist of two sections and general Chemistry questions namely:
- Quantitative Analysis
- Qualitative Analysis
These involve titration and test of ions. You will be expected to carry out an experiment and report your inference and observation. What you will see will not be far from the WAEC Chemistry Specimen given to your school.
Note: Your titration endpoint will be given to you by your Chemistry teacher. It is not the same for every school but within a range.
Do not use the endpoint here. It may vary from your center endpoint but you can follow the calculation procedures.
WAEC Practical Chemistry Questions and Answers (Expo)
3ai)The value will increase
(3aii)The occur as a result of the decrease in the concentration of base due to the added volume of water
(3bi)There will be no visible reaction because copper is less than Zinc in the electrochemical series
(3bii)It absorb water and become sticky because it is hygroscopic(3biii)The solution turns pink
(3c)When NaOH is added to the solution of zn³+, a white precipitate is formed which later dissolve in excess NaOH due to the formation of zinc
All your burette readings (initials and final) as well as the size of your pipette must be recorded but no account experiment procedure is required. all calculations must be done in your answer booklet.
1. A is a solution of potassium tetraoxomanganate (VII). B is a solution of iron (II) Chloride containing 4.80 g of the salt in 250cm3 of solution. (a) Put A into the burette. Pipette 20.0cm3 or 25.0 of B into a conical flask, add 20.0cm3 of H2SO4(aq)and titrate with A. repeat the titration to obtain concordant titire values. Tabulate your results and calculate the average volume of A used. The equation of the reaction is: MnO–4(aq) + 5Fe2+(aq) + 8H+(aq) > Mn2+(aq) + 5Fe3+(aq) + 4H2O(I)
(b) From your results and the information provided, calculate the (i) concentration of B in moldm-3; (ii) Concentration of A in moldm-3 (iii) number of moles of Fe2+ in the volume of B pipetted [FeCI2 = 127 gmol-1] Credit will be given for strict adherence to the illustrations for observations precisely and for accurate inferences. all tests, observations and inferences must be clearly entered in the booklet in ink at the time they are made.
2. C and D are inorganic salts. Carry out the following exercises on them. Record your observations and identify any gas(es) evolved. State the conclusions and draw fromt the result of each test. (a) Put all of C in a test tube and add about 5cm3 of distilled water. Shake thoroughly and test the resulting solution with litmus paper. Divide the solution into three portions. (i) To the first portion, add NaOH(aq) in drops, then in excess. (ii) To the second portion, add NH3(aq) in drops, then in excess. (iii) To the third portion, add AgNO3(aq) followed by HCI(aq) (b)(i) Put all of D in a test tube and add about 5cm3 of distilled water. Shake thoroughly and feel the test tube. (ii) To about 2cm3 of the solution, add HCI(aq).
3. State the observations that would be made when each of the following reactions are carried out in the laboratory (a) Addition of 2cm3 of bench H2SO4(aq) to 2cm3 of barrium chloride solution; (b) Addition of 2cm3 of dilute hydrochloric acid to 1 g of powered iron(II) sulphide (FeS); (c) Addition of 2cm3 of dilute hydrochloric acid to 1 g of iron filings and allowed to stand for sometime.
ANSWERS
1. Equation of the reaction: MnO–4(aq) + 5Fe2+(aq) + 8H+(aq) > Mn2+(aq) + 5Fe3+(aq) + 4H2O(I)
The questions above are strictly for practice not tomorrow’s Chemistry expo.
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Today’s Practical Chemistry Answers
(2020 Answers)
3ai)
oxygen
(3c)
It turns blue litmus paper red.
3d
Pure copper(II) sulfate is white. It is also known as anhydrous copper(II) sulfate because it has no water in it. When water is present in a sample of copper(II) sulfate it turns blue. … This colour change can be used to detect the presence of water (or water vapour).
3c(i)
When exposed to light, silver chloride decomposes into gray metallic silver and chlorine. The light sensitivity of the silver chloride and other silver halides, such as silver bromide and silver iodide, forms the basis of the photographic process.
3bi()
Phenolphtalein is chosen because it changes color in a pH range between 8.3 – 10. It will appear pink in basic solutions and clear in acidic solutions. ..
3c(i)
When exposed to light, silver chloride decomposes into gray metallic silver and chlorine. The light sensitivity of the silver chloride and other silver halides, such as silver bromide and silver iodide, forms the basis of the photographic process.
3cii
The ammonia combines with silver ions to produce a complex ion called the diamminesilver(I) ion, [Ag(NH3)2]+. This is a reversible reaction, but the complex is very stable, and the position of equilibrium lies well to the right.
3d
Pure copper(II) sulfate is white. It is also known as anhydrous copper(II) sulfate because it has no water in it. When water is present in a sample of copper(II) sulfate it turns blue. … This colour change can be used to detect the presence of water (or water vapour).
Remember What I told you: Use your school endpoints to avoid being a scapegoat. Your teacher will be the one to report, any endpoint reported by him will be taken as an accurate result. Shine your eyes while copying. Goodluck
(1a)
Burette reading (cm)³|1st reading|2na Reading|3rd reading|
Final |15.25|30.53|45.79|
Initial |0.00|15.25|30.53|
Volume of acids used |15.25|15.28|15.26
Average volume of acid used =15.25+15.26/2
=15.255cm³
=15.26cm³
Or =15.27cm³
(1b)
Given; mass con of A =5g/500cm³ = 5g/0.5dn³
CA=10g/dm³
A is HNO3
Therefore molar mass =1+14+(16*3)=15+48=63g/mol¹
Molarity of A = gram con/molar mass
CA=10/63=0.1587mol/dm3
(1bii)
Using CAVA/CBVB =Na/NB
With reacting equation ; HNO³ + NaOH—NaNO3+H2O
nA=1 nB=1
0.1587*15.26/CB*25.00=1/1
25CB=0.1587*15.26
CB=0.1587*15.26/25
CB=0.09687mol/dm³
(1biii)
B is NaOH
Molar mass
23+16+1=40g/mol
Conc of B in g/dm³=molarity * molar mass
= 0.09687*40
=3.8748g/dm³
(1biv)
No of moles present in 250cm³ of NaOH is =molar conc * volume
=0.09687*250/1000
=0.0242moles
Mole ratio of NaOH and NaNO3 is 1;1
No; of mole of NaNO3 which reacted is 0.0242
Mass of NaNO3 formed =molar mass * no; of moles
=85*0.0242
=2.05grams
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(2a)
TEST: C+burning splint
OBSERVATION: Sample C burst into flame .It burns with non smoky blue flame without soot. Colorless gas that turns wet blue litmus paper faint red and turns like water milky is present.
INFERENCE: C is volatile and flammable. The gas is CO2 from combustion of saturated organic compound.
(2bi)
TEST: C + distilled water + shake
OBSERVATION: Clear or colorless solution is observed
INFERENCE: C is miscible with water
(2bii)
TEST: C + Acidified K2Cr207
OBSERVATION: Orange color of K2Cr207 solution turns pale green and eventually pale blue on cooling
INFERENCE: C is a reducing agent
(2C)
TEST: D + C + 10% NaOH + Shake
OBSERVATION: D dissolves slowly in C and produces reddish brown solution. Reddish brown solution turns yellow precipitate. The precipitate has an antiseptic odour
INFERENCE: D is soluble in organic solvents
(2d)
Compound belongs to the class of secondary alkanol
=====================================
(3ai)
Zinc nitrate
(3aii)
2 Zn(NO 3 )2 —–>2 ZnO + 4 NO 2 + O 2
(3aiii)
It turns white when cold from it yellow colour when it was hot
(3b)
Pipette / measure 50.0cm3 of the stock solution into a 250
cm3 volumetric flask (containing some distilled water). Shake / swirl and add more distilled water until the mark is reached.
(3c)
Al2(SO4)3 – turns blue litmus red
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