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Chem Lab Report

By tiffanylika07 Jul 24, 2013 762 Words
S.4Chemistry 2nd Term Project
Be a Chemical Analyst-Analysis on ethnoic acid.
This experiment aims at determining the percentage by mass of ethanoic acid(CH3COOH) in a commercial vinegar using titration method.

Chemical reaction involved:
CH3COOH(aq) + NaOH(aq)→ NaCH3COO(aq) + H2O(l)

An electronic balance, a 10.0cm3 pipette, a 25.0cm3 pipette, a pipette filler, a 250.0cm3 volumetric flask, a burette, stand and clamp, a conical flask, a white tile, 3 large beakers, a small beaker, a dropper, a boiling tube, a rinsing bottle

0.1M NaOH(aq),phenolphthalein indicator, commercial vinegar (5% acidity), distilled water

Part1: The density of the commercial vinegar was found.
A small breaker was put on an electronic balance and the reading of the balance was set to zero gram.
10.0cm3 of the commercial vinegar was pipetted into a small beaker.
The vinegar was weighed with an electronic balance.
And the density of the vinegar was known as 1gcm-3.

Part2: The commercial vinegar was diluted 10 times.
A 25.0cm3 pipette was washed with distilled water and then with the commercial vinegar.
25.0cm3 of the commercial vinegar was pipetted into a 250.0cm3 volumetric flask
Distilled water was added to the volumetric flask and made up to right before the graduation mark.
A dropper was used to add distilled water into the volumetric flask, then the solution was made up to the graduation mark and the vinegar was diluted 10 times.

Part:3 The diluted vinegar was titrated against standard NaOH(aq).
25.0cm3 of dilute commercial vinegar solution was transferred from the 250.0cm3 volumetric flask into a conical flask with the washed 25.0cm3 pipette.
A few drops of phenolphthalein was added into the diluted vinegar as indicator.
A burette was washed with distilled water and then the standard NaOH(aq).And then was filled with standard NaOH(aq).
The conical flask was placed under the burette and with a white tile under it.
Standard NaOH(aq) was added into the conical flask until the colour change from colourless to pink, then titration was completed.

At the end point of titration, the reaction mixture changes from colourless to pink.

Volume of NaohTitration Number
Initial burette reading(cm3)11.622.158.359.3
Final burette reading(cm3)38.2549.134.936.0

Equation: CH3COOH(aq) + NaOH(aq)→ NaCH3COO(aq) + H2O(l)
Symbol: M=molarity, mol= number of mol
(a) What is the molarity of the diluted vinegar?
The reasonable average volume of NaOH used
Let M2 be the molarity of CH3COOH
Mole ratio of CH3COOH:NaOH is 1:1
(b)What is the molarity of the commercial vinegar?

(c)What is the percentage by mass of CH3COOH in the commercial vinegar?Is the experimental value higher or lower than the labeled value? The percentage by mass of CH3COOH
=60X1.0652/10cm3 ×0.01 × 100%
The experimental value is higher than the labeled value.

(a)What are the sources of error in the experiment?
There are errors made by human during dilution or weighting.
Loss of materials during transferring.
The commercial vinegar was also consists of other acids, like citric acid and tartaric acid. Those acid may also reacts with the standard NaOH(aq).

(b)What are the skills and knowledge learned through this analysis?Comment on the importance of quantitative analysis such as titration in our daily life. Through this analysis, we have learnt:
how to calculate the percentage by mass of a substance through calculation.
the skill of using a dropper to add liquid drop by drop in order to make it up to the graduation mark during dilution.
the skill of controlling the speed of water flow through the burette during titration.
the skill of determining the colour change during titration.

As we can see in the results, the percentage we calculated is higher than the labeled value. So which means there room for improvement. Here are some ways to improve the accuracy of the quantitative analysis:

Titration should be carried more times to minimize the difference between each titration.
The solution should be made up to the graduation mark very accurately in order to reduce errors.
We should stir the conical flask quicker to make the vinegar and the NaOH(aq) become evenly distributed.

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