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Waec 2023 Chemistry Practical Practice Questions by Oduok(m): 3:28pm On May 14, 2023 |
Chemistry practical has three questions. Question 1 is quantitative analysis (titration). This year we expect titration between a strong acid and weak base. The base will be a salt with water of crystalization. Question 2 is qualitative analysis. This year we expect analysis of an organic and inorganic compound. Question 3 is always general chemistry theory question. This is not expo. It is for practice purpose. Feel free to leave your questions, comments and contributions. Question 1 A is a solution containing 0.100 moldm-3 of hydrochloric acid. B is a solution containing 5.0 g per dm3 of hydrated sodium trioxocarbonate (iv), Na2CO3.xH2O. (a)Put A into the burette and titrate it against 20.00 cm3 or 25.00 cm3 portion of B using methyl orange as indicator. Record the volume of your pipette. Tabulate your burette readings and calculate the average volume of A used. Equation for the reaction: Na2CO3.xH2O(aq) + 2HCl(aq) 2NaCl(aq) + CO2(g) + (x+1)H2O(l) (b)From your results, calculate the: (i)Concentration of B in moldm-3. (ii)Molar mass of Na2CO3.xH2O. (iii)Value of x in Na2CO3.xH2O. [H = 1.0, C = 12.0, O = 16.0, Na = 23.0] ANSWER TO QUESTION 1 1.(a) Volume of pipette used = 25.00 cm3. Indicator used = Methyl orange Burette Reading 1st Titre 2nd Titre 3rd Titre Final volume of A (cm3) 8.80 17.50 26.30 Initial Volume of A (cm3) 0.00 8.80 17.50 Volume of A used (cm3) 8.80 8.70 8.80 Average volume of Acid used = (8.80 + 8.70 + 8.80) / 3 = 26.3/3 = 8.77cm3 (b) (i) Concentration of B in moldm-3: (Ca x Va)/(Cb x Vb) = A/B (0.10 x 8.77)/(Cb x 25.00) = 2/1 Cb = (0.10 x 8.77)/(25.00 x 2) = 0.877 / 50 = 0.0175 moldm-3. (ii) Molar mass of Na2CO3.xH2O = mass conc. / molar conc. = 5.0 / 0.0175 = 285.7 g/mol (iii) Value of x in Na2CO3.xH2O: 285.7 = 106 + 18x x = (285.7 - 106)/18 = 179.7 / 18 = 9.98 approximately 10 Question 2: Carry out the following exercises on specimen C and D. Record your observations and identify any gases evolved. State the conclusion you draw from the result of each test: a.(i) Add about 5cm3 of distilled water to a portion of C in a test tube. Stir thoroughly and test with litmus. (ii). Add about 2cm3 of Fehling’s solution to the resulting mixture from (a)(i) above and heat. b.(i) Heat a portion of D strongly in a test tube. (ii) Put the rest of D in a boiling tube and add about 10cm3 of distilled water. Shake the mixture. (iii) Put about 2cm3 of the mixture from b(ii) in a test tube. Add aqueous NaOH in drops and then in excess. (iv) Put about 2cm3 of the mixture from b(ii) in a test tube. Add aqueous ammonia in drops and then in excess. ANSWERS FOR QUESTION 2 S/N TEST OBSERVATION INFERENCE (a)(i) C + distilled water Soluble in distilled water C is a soluble compound + Litmus No effect on litmus C is a neutral compound (ii) Solution of C + Fehling’s solution + Heat Brick-red precipitate C is a reducing sugar (glucose) (b)(i) D + heat Yellow when hot and white when cold D is zinc oxide (ZnO) (ii) D + water Does not dissolve in water D is an insoluble compound (iii) Mixture from (b)(ii) + NaOH(aq) in drops and in excess White precipitate. Precipitate dissolves in excess Al3+, Zn2+, Pb2+ present (iv) Mixture from (b)(ii) + NH3(aq) in drops and in excess White precipitate. Precipitate dissolves in excess Zn2+ Confirmed |
Re: Waec 2023 Chemistry Practical Practice Questions by ebomat: 6:26pm On May 14, 2023 |
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Re: Waec 2023 Chemistry Practical Practice Questions by Firstorderwizard(m): 3:27pm On May 17, 2023 |
Just came across this and decided to correct something. Al3+ and Zn2+ form white gelatinous precipitate with drops of NaOH that dissolve in excess sodium hydroxide, while Pb2+ forms white chalky precipitate with drops of NaOH that dissolves in excess NaOH too. A good observer shouldn't be suspecting Pb2+ when the ppt formed is gelatinous. I left secondary school a long time ago anyway Oduok: |
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Re: Waec 2023 Chemistry Practical Practice Questions by Oduok(m): 9:11pm On May 18, 2023 |
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Re: Waec 2023 Chemistry Practical Practice Questions by Anwons(m): 6:08am On May 19, 2023 |
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Re: Waec 2023 Chemistry Practical Practice Questions by FarmTech(m): 11:08pm On May 24, 2023 |
Anwons:. Find 2 numbers whose sum give +9 and whose multiplication gives +8. They are 8 and 1. (Y+ 8 )(Y+1)=0 °•♧ Y = -8 or -1 |
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