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(1)
Tabulate;
Burette readings;
|Rough |1st |2nd|3rd|
Final readings in cm³;
|22.00|20.10 |20.20|20.30|
Initial reading in cm³;
|0.00|0.00|0.00 |0.00|
Volume of A (acid) used cm³;
|22.00|20.10|20.20| 20.30|
The average titre
= 20.10+20.20+20.30/3
=60.60/3
= 20.20cm³
;Va 20.20cm³
(1bi)
Concentration of A in mol/dm³, Ca = ?
Concentration of A (g/dm³) = 4.40g/dm³.
.m.m of A, H²SO⁴ =(1*2)+(32*1)+(16*4)
=2+32+64
=98g/mol
Using concentration (mol/dm³) = Concentration (g/dm³)/m.m
Concentration (mol/dm³)
=4.40/98
=0.045mol/dm³
;: Concentration of A(mol/dm³) = 0.045mol/dm³
(1bii)
Concentration of B(mol/dm³) =???
Ca=0.045, Va=20.20, Vb=25.00, na=1, nb=1, cb=?
Using; CaVa/CbVb = na/nb
Cb=CaVanb/Vbna =0.045*20.20*1/25.00*1
Cb=0.036mol/dm³
(1biii)
Conc. of B(g/dm³) that reacted =??
molar mass of B, Na₂CO₃ = (23*2)+(12*1)+(16*3) = 106g/mol
Conc. of B(mol/dm³) = 0.036mol/dm3
Conc. (mol/dm³) = Conc. (g/dm³)/molar mass
(0.036/1) = Conc. (g/dm³)/106
Conc. (g/dm³) = 0.036*106 = 3.82g/dm³
Conc. of B(g/dm³) = 3.82/dm³
(1biv)
mass of the impurity in 1.0dm³ of B=??
Conc. of impurity (g/dm³) = 7.50 – 3.82 = 3.68g/dm³
:. Mass of impurity= Conc. (g/dm³) x vol. (dm³)
= 3.68×1 = 3.68g
(1bv)
Vol. of CO₂ produced in 1.0dm³ of B = ??
Mole of B= Conc. x Vol. (dm³)
Mole of B = 0.036*1
Mole of B =0.036mol
By proportion,
1mol of Na₂.10₃ = 1mol of CO₂
0.036mol of Na₂.10₃ = xmol of CO₂
mole of CO₂ produced = 1*0.036 = 0.036mol
:. Volume = mole * 22.4
Volume = 0.036 * 22.4 = 0.81dm³
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(2)
[FILL THE TABLE WITH THE INFORMATION BELOW]
(ai)
-TEST: C+5 cm³ of distilled water and shake thoroughly. Divide the solution into two portions
-OBSERVATION: It dissolves completely to give a colourless solution
-INFERENCE: C is a soluble salt
(aii)
-TEST: To the first portion, add NaOH solution in drops.
-OBSERVATION: A white gelatinous precipitate is formed
-INFERENCE: Al³⁺ and Zn²⁺ present
(aiii)
-TEST: Then add NaOH in excess
-OBSERVATION: The precipitate dissolve to give a colourless solution
-INFERENCE: Zn²⁺ present
(aiv)
-TEST: To the second portion, add NH₃ solution in drops
-OBSERVATION: A white precipitate is formed
-INFERENCE: Al³⁺ and Zn²⁺ present
(av)
-TEST: then in excess
-OBSERVATION: The white precipitate dissolves in excess NH₃
-INFERENCE: Zn²⁺ is confirmed
(bi)
-TEST: 2cm³ of solution D + soda lime, heat, test with litmus paper.
-OBSERVATION: Ammonia gas (NH₃) is evolved, turning red litmus paper blue.
-INFERENCE: Presence of NH₄⁺ ions.
(bii)
-TEST: Solution D + NaOH solution + CuSO₄ solution
-OBSERVATION: A blue precipitate formed
-INFERENCE: Presence of peptide bonds (proteins or peptides).
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(3ai)
(I) The funnel is removed from the burette before taking the initial reading to prevent any excess liquid in the funnel from draining into the burette and affecting the accuracy of the reading.
(II) The burette is first rinsed with distilled water before filling it with acid to remove any impurities or residues that may affect the accuracy of the titration.
(III) The tip of the pipette is dipped well below the surface of the alkali before sucking up to ensure that the pipette is filled with the alkali solution and not air, which would affect the accuracy of the measurement.
(3aii)
(i) Dissolve the rock salt in distilled water to create a solution.
(ii) Filter the solution to remove any insoluble impurities.
(iii) Boil the solution to remove any volatile impurities.
(iv) Allow the solution to cool and crystallize.
(v) Collect the crystals of sodium chloride by filtration.
(vi) Wash the crystals with distilled water to remove any impurities.
(vii) Dry the crystals to obtain pure sodium chloride.
(3bi)
(i) Evaporating dish
(ii) Bunsen burner
(3bii)
Solubility in water: This property ensures that when the gas is dissolved in water, it creates a pressure difference that drives the fountain effect in the experiment.
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