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NaClFind LEf

Module 3

Practical: TitrationQuestions2002-7

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F Scullion. JustChemy.Com

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Introduction

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Titration Graphs. Strong Alkali + Strong Acid Weak Alkali + Strong Acic

Strong Alkali + Weak Acid Weak Alkali + Weak Acid

pH pH

pH pH

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IndicatorTable

Indicator pH Range pKa Acid Form Base Form

methyl violet 0.0- 1.6 0.8 yellow blue

thymol blue 1.2- 2.8 1.6 red yellow

methyl yellow 2.9- 4.0 3.3 red yellow

methyl orange 3.1- 4.4 4.2 red yellow

bromocresol green

3.8- 5.4 4.7 yellow blue

methyl red 4.2- 6.2 5.0 red yellow

chlorophenol red 4.8- 6.4 6.0 yellow red

bromothymol blue

6.0- 7.6 7.1 yellow blue

phenol red 6.4- 8.0 7.1 yellow red

cresol purple 7.4- 9.0 8.3 yellow purple

thymol blue 8.0- 9.6 8.9 yellow blue

phenolphthalein 8.0- 9.8 9.7 colorless red

thymolphthalein 9.3-10.5 9.9 colorless blue

alizarin yellow R 10.1-12.0 11.0  yellow red

indigo carmine 11.4-13.0 12.2 blue yellow

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Phenolphthalein in alkali

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Calculate the concentration of thepotassium hydroxide solution (i) in mol/dm3 (mol per litre) (relative atomic masses: H=1; O=16;

K=39)

KOH + HNO3 = KNO3 + H2O

M mol/dm3 ? 0.1V 25.0 22.5Mol 1 1

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2004 Practical 1

2004 Practical 1

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1 mole of KIO3 make 3 mole of I2

This 3 mol of I2 requires (3x2) = 6 mol Na2S2O3

So 1 mole of KIO3 = 6 mole Na2S2O3

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Thio

Iodine – Thiosulphate Titration

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2004/P2

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2005/P1

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Weak Acid + Strong Alkali

Phenolphthalein changes colour in range 8 - 10

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2005/P2

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Sodium carbonate

Methyl Orange turns colour in range 3 – 4.5

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Red to Yellow

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2006/P1

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1 mole of KIO3 make 3 mole of I2

This 3 mol of I2 requires (3x2) = 6 mol Na2S2O3

So 1 mole of KIO3 = 6 mole Na2S2O3

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Thio

Iodine – Thiosulphate Titration

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2006/P2

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2007/P1

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Strong Acid + Strong Alkali

Phenolphthalein changes colour in pH range 8 - 10

Methyl Orange changes colour in pH range 3 - 4.5

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2007/P2

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That’s it. Thanks for listening.

Do consider using the other three parts in this Series: -

Observation & Deduction Planning Structured Questions

Good luck with your Practical Examination.

F Scullion, JustChemy.Com