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Volumetric analysis 2018 B3

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Physical Science Experiment
Grade 12
Acids and Bases
Titration/volumetric analysis
Name
:.......................................
School
:.......................................
Date
:.......................................
Acid Base titration of oxalic acid sodium hydroxide to determine the concentration of a sodium
hydroxide solution.
To determine the concentration of a supplied sodium hydroxide solution using a standard of
oxalic acid.
Investigative question:
Formulate an investigative question for this investigation.
(2)
……………………………………………………………………………………………………………………………………………........
……………………………………………………………………………………………………………………………………………………
……………………………………………………………………………………………………………………………………………………
Hypothesis:
Formulate a hypothesis for this investigation:
(2)
……………………………………………………………………………………………………………………………………………………
……………………………………………………………………………………………………………………………………………………
……………………………………………………………………………………………………………………………………………………
Variables:
Dependent…………………………………………………………… (1)
Independent :………………………………………………………..( 1)
Control :…………………………………………………………………( 1)
Apparatus
250 or 500 ml Volumetric
Filter paper
flasks
50ml Burette.
spatula
25ml Pipette.
Medicine dropper
Erlenmeyer flasks
Mass meter
Beaker
Retort stand
White tile
clamp
Chemicals
Oxalic Acid
Sodium hydroxide
phenolphthalein
Distilled water
Wash bottle
Safety Precautions:
The acid, base and indicator should not come into contact with the skin or eyes. In case of such
incident immediately flush contaminated area with running tap water. Safety goggles and
gloves are recommended.
Method:
Part 1:
Preparing a Standard solution of oxalic acid
Acid Base titration of oxalic acid sodium hydroxide to determine the concentration of a sodium
hydroxide solution.
To determine the concentration of a supplied sodium hydroxide solution using a standard of
oxalic acid.
Investigative question:
Formulate an investigative question for this investigation.
(2)
……………………………………………………………………………………………………………………………………………........
……………………………………………………………………………………………………………………………………………………
……………………………………………………………………………………………………………………………………………………
Hypothesis:
Formulate a hypothesis for this investigation:
(2)
……………………………………………………………………………………………………………………………………………………
……………………………………………………………………………………………………………………………………………………
……………………………………………………………………………………………………………………………………………………
Variables:
Dependent……………………………………………………………(1)
Independent:………………………………………………………..(1)
Control:…………………………………………………………………(1)
Apparatus
250 or 500 ml Volumetric
Filter paper
flasks
50ml Burette.
spatula
25ml Pipette.
Medicine dropper
Erlenmeyer flasks
Mass meter
Beaker
Retort stand
White tile
clamp
Chemicals
Oxalic Acid
Sodium hydroxide
phenolphthalein
Distilled water
Wash bottle
Safety Precautions:
The acid, base and indicator should not come into contact with the skin or eyes. In case of such
incident immediately flush contaminated area with running tap water. Safety goggles and
gloves are recommended.
Method:
Part 1:
Preparing a Standard solution of oxalic acid
1. The chemical formula of oxalic acid is (COOH)2.2H2O. Calculate the formula mass of
oxalic acid.
(2)
…………………………………………………………………………………………………………………………………………
…………………………………………………………………………………………………………………………………………
…………………………………………………………………………………………………………………………………………
2. What mass do you need to make 500ml of 0,1M solution of oxalic acid?
(3)
…………………………………………………………………………………………………………………………………………
…………………………………………………………………………………………………………………………………………
…………………………………………………………………………………………………………………………………………
3. What mass do you require to make 250 ml of 0.1 M solution of oxalic acid.
(1)
…………………………………………………………………………………………………………………………………………
…………………………………………………………………………………………………………………………………………
…………………………………………………………………………………………………………………………………………
4. Measure out this mass of oxalic acid accurately to one decimal place using a filter
paper. Tare the balance to correct the mass of the filter paper.
5. Carefully pour the measured amount of oxalic acid into the 250 ml volumetric flask.
6. Add some water to the volumetric flask until half full. Close the flask with a stopper and
shake the content to dissolve oxalic acid. Continue adding water with the wash bottle,
very slowly at end, until the bottom of the meniscus of the liquid lines up with the mark
on the neck/stem of the flask. Replace the stopper and give a final shake to ensure even
mixing. Label the flask.
7. This is your standard solution. What is the meaning of this statement?
…………………………………………………………………………………………………………………………………………
…………………………………………………………………………………………………………………………………………
Part 2
Finding the concentration of a solution of sodium hydroxide by titrating it against a standard
solution of oxalic acid.
1. Fit the burette into the clamp on the retort stand.
2. Use the funnel to pour the sodium hydroxide solution into the burette.
3. Place a beaker under the tap of the burette and open the tap just long enough to remove
the air in the bottom of the burette. Fill the burette to the zero mark.
4. Pipette 25 ml of the standard oxalic acid solution into the Erlenmeyer /conical flask.
5. Add 2or3 drops of phenolphthalein in to the conical flask and swirl it gently to evenly
distribute the indicator.
6. Place the flask under the tap of the burette and then [place the white tile underneath the
flask to enhance visibility of any colour change during titration.
7. Slowly open the tap and allow sodium hydroxide solution from the burette into the
conical flask. Control the tap with your left hand and use your right hand to swirl the flask.
8. When you get near the end point, add the solution from the burette drop by drop, until
the solution turns pale pink and holds this colour for approximately 10 – 15 seconds.
9. Close the tap and record the volume of sodium hydroxide used in the table provided
below.
10. Refill the burette to zero mark and repeat this procedure from 2 – 9 two more times so
that you have a total of three readings. Take the average of these reading which will be
considered as the volume of NaOH (aq) needed to neutralize 25 ml of (COOH)2.2H2O.
Results:
Titration ( Runs)
Volume of oxalic acid
Volume of Sodium Hydroxide
1
25
59
2
3
Average
(4)
Interpretation of results:
1. Write down a balanced equation for the reaction between oxalic acid and sodium
hydroxide.
……………………………………………………………………………………………………………………………………(3)
2. How many moles of sodium hydroxide will react with one mole of oxalic acid?
……………………………………………………………………………………………………………………………………(1)
3. Calculate the number of moles of oxalic acid in the Erlenmeyer flask.
(3)
…………………………………………………………………………………………………………………………………….
…………………………………………………………………………………………………………………………………….
…………………………………………………………………………………………………………………………………….
4. Calculate the number of moles of sodium hydroxide used to neutralize 25 ml of oxalic
acid in the flask.
(3)
…………………………………………………………………………………………………………………………………….
…………………………………………………………………………………………………………………………………….
…………………………………………………………………………………………………………………………………….
5. Calculate the concentration of sodium hydroxide solution.
(3)
……………………………………………………………………………………………………………………………………
……………………………………………………………………………………………………………………………………
……………………………………………………………………………………………………………………………………………….
6. How does the experimental value of sodium hydroxide solution compare to the estimated value
of 0.2 mol.dm-3?
(3)
……………………………………………………………………………………………………………………………………………….
……………………………………………………………………………………………………………………………………………….
……………………………………………………………………………………………………………………………………………….
7. List two factors that could give rise to experimental error.
(2)
……………………………………………………………………………………………………………………………………………….
……………………………………………………………………………………………………………………………………………….
8. Briefly explain why phenolphthalein is the chosen indicator?
(2)
……………………………………………………………………………………………………………………………………………….
9. What colour is phenolphthalein in and acid medium?
(1)
……………………………………………………………………………………………………………………………………………….
10. What colour does this indicator display when titration reaches the end point?
(1)
……………………………………………………………………………………………………………………………………………….
11. Conclusion:
……………………………………………………………………………………………………………………………………………….
……………………………………………………………………………………………………………………………………………….
………………………………………………………………………………………………………………………………………………
(Total marks=40)
8.
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