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Reviewed BACK TITRATION - 082606

The document outlines two back titration experiments for determining the amount of calcium compounds in rock samples using hydrochloric acid and sodium hydroxide. Each experiment includes detailed procedures for titration, calculations for excess acid, and the determination of the mass and percentage composition of calcium carbonate or calcium oxide in the samples. Additionally, it emphasizes the importance of ceasing effervescence before titration for accurate results.

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68 views2 pages

Reviewed BACK TITRATION - 082606

The document outlines two back titration experiments for determining the amount of calcium compounds in rock samples using hydrochloric acid and sodium hydroxide. Each experiment includes detailed procedures for titration, calculations for excess acid, and the determination of the mass and percentage composition of calcium carbonate or calcium oxide in the samples. Additionally, it emphasizes the importance of ceasing effervescence before titration for accurate results.

Uploaded by

tettehawaitey45
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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BACK TITRATION

WASSCE 2022 – ALT B


1. Calcium trioxocarbonate (IV), CaCO3 is found in some rocks and is insoluble in
water.
As a result, it cannot be conveniently titrated in the solid form.
E is 0.100mol/dm3 of NaOH solution.
D is a solution obtained by dissolving 8.00g of a powdered sample of rock in 1dm3 of
0.200mol/dm3 HCl solution and shaken well until effervescence ceased.
(a) Put D into the burette and titrate it with 20.00cm3 or 25.00cm3 portions of E using
methyl orange as indicator. Repeat the titration to obtain concordant titre values.
Tabulate your results and calculate the average volume of the acid used.
The equations for the reaction are;

CaCO3 + 2HCl → CaCl2 + H2O + CO2


NaOH + HCl → NaCl + H2O

(b) From your results and the information provided, calculate the;

(i) excess amount of HCl in mol/dm3 of solution E;

(ii) amount of HCl per dm3 that reacted with the rock;

(iii) amount of calcium trioxocarbonate (IV) in moles in the rock;

(iv) percentage mass of calcium trioxocarbonate (IV) in 4.00g of the rock.

(c) Explain briefly why effervescence had to cease before titration.


BACK TITRATION
WASSCE 2014 ALT B
1. The quantity of Calcium Oxide CaO in a rock sample can be determined by treating a
known mass of the powdered sample of a rock with excess dilute HCl and then
titrating the unreacted acid with a standard alkali.

A is a solution obtained by reacting 4.05g of powdered rock sample with 1.00dm3 of


0.150 mol/dm3 HCl solution.

B is 0.100mol/dm3 NaOH solution.

(a) Put A into the burette. Titrate 20.00cm3 or 25.00cm3 portions of B against A using
phenolphthalein as indicator.

Repeat the exercise to obtain consistent titres. Tabulate your burette readings and
calculate the average volume of acid used.

The equations involved in the reactions are;

CaO + 2HCl → CaCl2 + H2O

HCl + NaOH → NaCl + H2O

(b) From your results and the information provided, calculate the;

(i) concentration of excess HCl in A in mol/dm3;

(ii) amount of HCl that reacted with 4.05g of the rock sample;

(iii) mass of CaO in the rock sample;

(iv) percentage composition by mass of CaO in the rock.


(Na = 23, Cl = 35.5, O = 16, Ca = 40.0, H = 1.0)

‘When you cross over, build bridges and not walls. No one stays up forever’
ORTEGA

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