[Waec Answer] Waec 2018 Chemistry Practical Alternative B Questions And Answers Now Posted
Chemistry Practical Alternative B Questions And Answers.
CHEMISTRY ALTERNATIVE B
i) Concentration of A in mol dm-3 From the reaction equation
CA VA = 1
CB VB 2
CA = CB VB
CA = 0.0975 x 25
= P mol dm-3 Alternative Method:
Amount of acid used = 0.025 x 0.0975 = 0.00244 mol From the equation of reaction:
2 mol of B require 1 mol of A
0.00244 mol of B requires ½ x 0.00244 mol of A
= 0.00122 mol of A. i.e VA cm3 contain 0.00122 mol.
1000 cm3 contain 0.00122 x 1000/VA mol. i.e. Conc of A = 1.22/VA = P mol dm-3
(ii) Molar mass of H2Y
Molar mass of H2Y = 6.22
= Q g mol-1
Using BENEDICT’S REAGENT.
Turn on your gas to medium heat and place your beaker filled with 100 mL of water on it. Bring it to a boil.
crush the solid sample into a powder using a mortar and pestle. Add water to the powder and pour it in the test tube.
Add approximately 1 mL of Benedict’s solution to the test tube using a dropper. Slowly swirl the test tube counterclockwise to distribute the reagent evenly.
Place your test tube into the beaker until you note a color change — this process usually takes five minutes.
Examine the color change, if it is present. Benedict’s reagent has a color change gradient from blue, meaning no simple sugars are present, to green, yellow, orange, red and brown. The color sequence indicates the increasing concentration of the simple sugar, with green being the lowest and brown being the highest.
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