WAEC Chemistry Alternative To Practical Questions and Answer PDF Download| The Alternative to practical is a practical examination that is not carried out in a laboratory rather, it is answered theoretically but it carries the came marks with those who are performing the practical.
The WAEC Chemistry Alternative to practical has three(3) questions and the total marks allocated to this paper are determined by the West African Examination Council(WAEC) every year so we cannot exactly state the marks. Before you start, ensure that you read the instructions thoroughly and also adhere to them because one misinterpretation can cause you to fail a whole question.
1.A is a solution of 0.050moldm-3 H2C2O4 (ethanedioc acid)
B is a solution of KMnO4 (potassium tetraoxomaganate (VII)), of unknown concentration.
a. Put B into the burrete. Pipette 20.0cm3 or 25.0cm3 of A into a conical flask and add about 10.0cm3 of dillute H2SO4. Heat the mixture to about 40oC-50oC and titrate it while still hot with B.
Repeat the titration to obtain consistent titre values.
Tabulate your results and calculate the average volume of B used.
The equation of the reaction is:
2MnO4–(aq) + 5C2O42-(aq) + 16H+(aq) → 2Mn2+(aq) + 8H2OI + 10CO2(g)
b. From your results and the information provided, calculate the:
(i). Concentration of MnO4– in B in moldm-3;
(ii). Concentration of KmnO4– in B in gdm-3;
(iii) Volume of CO2 evolved at s.t.p when 25.0 cm3 of H2C2O4 reacted completely.
[O = 16.0 K = 39.0 Mn = 55.0, Molar volume of gas at s.t.p = 22.4dm3mol-1]
2. C is a mixture of two salts, containing one cation and two anions.
Carry out the following exercises on C. Record your observations and identify any gas(es) evolved. State the conclusion you draw from the result of each test.
a. Put all of C in a beaker and add about 10cm3 of distilled water.
Stir well and filter, Keep the filtrate and the residue
b. To about 2cm3 of the filtrate, add few drops of AgNO3(aq) followed by HNO3(aq) . Add excess NH3(aq) to the resulting mixture.
c. (i)Put all of the residue into a clean test tube and add about 5cm3 of HNO3(aq)
ii. To about 2cm3 of the solution from 2(c)(i), add NaOH(aq) in drops and then in excess
iii. To another2cm3 of the solution from 2(c)(i), add NH3 in drops and then in excess
3. (a) What difference in physical properties enable the separation of mixtures by”:
(i) Simple distillation
(ii) Paper Chromatography
(iii) Fractional Distillation
b. Give a reason for each of the following practices during titration in the laboratory.
(i) White tile is placed under the conical flask
(ii) Burette readings are always recorded in two decimal places
(c) Calculate the volume of 2.50moldm-3 stock HCl required to prepare 500cm3 of 0.20moldm-3 HCl
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