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Unit 2A: Undertake titration and colorimetry to determine the concentration of solutions
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Part A of Unit 2, Undertake titration and colorimetry to determine the concentration of solutions (Distinction Level)
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Unit 2ATitration and colourimetry
For the first experiment I had to find the concentration of an unknown sodium hydroxide
sample. I had to find the concentration of the hydrochloric acid (HCl) by titrating the acid in
opposition to a standard solution of sodium carbonate (Na 2CO3). To do this I first prepared a
standard solution of sodium carbonate. The equipment I had to use for this listed below. I
had a choice whether to use a volumetric flask or a measuring cylinder, I chose a volumetric
flask. This is because the volumetric flask proved to be much more accurate than the
measuring cylinder which is important in this experiment as the results need to be reliable.
It allowed me to shake the flask to make sure the sodium carbonate inside was mixed, the
measuring cylinder did not allow me to do this. A weighing boat was used to weigh the
sodium carbonate because if it were weighed using filter paper some of the
carbonate would be stuck onto the paper and would not be put into the volumetric flask.
The sodium carbonate in the weighing boat was put in a beaker then water (approximately
50cm3) was added to the beaker to dissolve it. After that, it was dissolved it was put into the
volumetric flask and the beaker and weighing boat rinsed with distilled water and poured
into the volumetric flask to make sure all sodium carbonate was in the volumetric flask. A
glass funnel was used to empty the remaining Na2CO3 into the volumetric flask. The glass
funnel was also rinsed for the same reason.
The equipment used:
1. Volumetric pipette (with pump filler)
2. Volumetric flask (250cm3)
3. Measuring cylinder (100cm3)
4. Glass Burette
5. Beaker
6. Small Beaker (150cm3)
7. Conical flask (250cm3)
8. Balance
9. Plastic weighing boat
The substances used:
1. Phenolphthalein Indicator
2. Methyl Orange Indicator
3. Hydrochloric Acid
4. Anhydrous Sodium Carbonate
5. Distilled Water
6. Sodium hydroxide
Making a standard solution of sodium carbonate
All the equipment used were calibrated accordingly. To avoid contamination the beaker was
left in a drying cabinet to prevent the sodium carbonate from sticking to it when put in.
, I started by calibrating the apparatus I was going to use. I rinsed the burette, glass pipette
and beaker with distilled water, I tried to make sure I wipe any droplets of the distilled
water to minimise the amount left that could affect the experiment. I also rinsed the beaker
and conical flask with distilled water but made sure to dry them to make sure the solid
sodium carbonate does not dilute to any droplets. I calibrated the balance using known
masses of 0.1g, 10g and 100g to make sure it correctly measures correctly. The balance that
I was using at first was not working properly, it would not display the correct mass for each
mass, the reading would be 5-10 grams off, so I had to use another one as it was unreliable.
After I finished calibrating all the apparatus, I started the titration. I used the balance to
measure 1.42g of solid sodium carbonate in a beaker, this was measured in a plastic
weighing boat, which was put on a balanced that was reset to zero before the sodium
carbonate was added. I then added approximately 50cm3 of distilled water to the beaker
and used the glass rod to stir until the solid sodium carbonate fully dissolved into the
distilled water, then I had to pour the solution into a 250cm3 volumetric flask, using a funnel,
making sure the meniscus was touching the 250cm3 mark on the volumetric flask. After this
was done the glass rod was rinsed with distilled water to clean it and the beaker was rinsed
to make sure there was no solution left. The volumetric flask lid was put on the volumetric
flask and the flask was shaken so the solution is fully mixed. The moles for the Na 2CO3
(sodium carbonate) in the solution was calculated so the solution can be used to standardise
the HCl (hydrochloric acid).
Formula mass for Na2CO3 – (23x2) + 12 + (16x3) = 106
Mass dissolved in the solution is 1.42g
1.42 ÷ 106 = 0.01339 moles
Titration for the standardisation of hydrochloric acid
I filled the pipette to the 25ml line, making sure the bottom of the meniscus rested on the
25ml line. Then I added a few drops of phenolphthalein indicator, filled the burette with
50ml of hydrochloric acid, also making sure I wore goggles to protect my eyes (before that I
made sure the burette did not have any drops of distilled water that could affect the
experiment), then used the burette to pour drops of hydrochloric acid to solution while
swirling the conical flask until it neutralised. The solution neutralised at 31.5ml hydrochloric
acid. Then I repeated the experiment three times with more accuracy knowing that the
titration point would be around 30 to 35ml to create an average. I measured 25ml of sodium
carbonate and put it in a conical flask using the 25ml pipette. this time I used a different
indicator, methyl orange. I added a few drops of the indicator into the sodium carbonate.
The solution turned yellow indicating it is an alkali and recorded how much HCl was in the
burette, which was 50ml, then I poured the HCl into the sodium carbonate while swirling the
conical flask to make sure they mixed properly. I kept doing this until the solution turned
pink, I recorded the volumes of all my attempts then I averaged them out to come to a more
accurate result. I did this to decrease the margin of error.
1st Attempt 2nd Attempt 3rd Attempt Final Attempt
3
Starting volume in cm 0.00 0.00 0.00 0.00
Concluding volume in cm3 31.5 30.0 31.0 30.5
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