General Chemistry Imu Exp 1

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Introduction

Background
Indicators are used in acid-base titrations to determine end points as both acid and base are colourless in nature. However, indicators chosen must be suitable according to the type of reactions such as: - Strong acid-weak base titration

- Weak acid-strong base titration
- Strong acid-strong base titration
- Weak acid-weak base titration
Only the first two mentioned above will be investigated in this experiment.

Aims/Objectives
1. To understand to importance of selecting suitable indicators for detecting the end-points of acid-base titrations. 2. To obtain titration curves for:
a. Strong acid-weak base titration
b. Weak acid-strong base titration

Learning Outcome
1. Able to choose a suitable indicator for detecting the end points of different types of acid-base titrations. 2. Able to draw and hence determine the end-point on the titration curves.

Materials and Methods
The experiment is carried out according to the procedures described in Experiment (1): Investigation of the suitability of indicators and instrumental detection of equivalence points in acid-base titration under the General Chemistry module

Results
Part 1: Suitability of Indicators
A. Strong acid-weak base titration
Acid: HCl (aq)
Base: NH4OH (aq)
Reaction: HC1(aq) + NH4OH(aq) → NH4Cl(aq) + H2O(l)
Indicator: Phenolphthalein
| |1 |2 | |Final burette reading/ [pic] |29.90 |29.70 | |Initial burette reading/ [pic] |0.00 |0.00 | |Titre value/ [pic] |29.90 |29.70 |

Mean titre value = [pic]
= 29.80 [pic]

1
Indicator: Methyl orange

| |1 |2 | |Final burette reading/ [pic] |27.00 |27.00 | |Initial burette reading/ [pic] |0.00 |0.20 | |Titre value/ [pic] |27.00 |26.80 |

Mean titre value = [pic]
= 26.90 [pic]

B. Weak acid-strong base titration
Acid: CH3COOH(aq)
Base: NaOH(aq)
Reaction: CH3COOH(aq) + NaOH(aq) [pic] CH3COONa(aq) + H2O(l) Indicator: Phenolphthalein

| |1 |2 | |Final burette reading/ [pic] |25.50 |25.80 | |Initial burette reading/ [pic] |0.00 |0.20 | |Titre value/ [pic] |25.50 |25.60 |

Mean titre value = [pic]
= 25.55 [pic]

Indicator: Methyl orange

| |1 |2 | |Final burette reading/ [pic] |4.60 |4.90 | |Initial burette reading/ [pic] |4.20 |4.60 | |Titre value/ [pic] |0.40 |0.30 |

Mean titre value = [pic]
= 0.35...
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