BTEC Applied Science
Unit 2 - pH Titration
● Achieved DISTINCTION
● Includes a detailed evaluation
● Includes Part 1 (Making a Standard Solution) and Part 2 (pH Titration)
● Entire practical
~ results
~ chemical equations working out
~ detailed evaluation
...
The aim of this part was to make a standard solution of sodium carbonate and calculate its exact
concentration.
To standardise the solution, we began by weighing the empty weighing boat by using a top pan
balance. After recording the balance of the empty weighing boat, 1.42g of sodium carbonate ( Na₂CO₃)
was measured in the same boat, on a calibrated balance. Then it was transferred into a volumetric
flask of 250cm³ using a funnel. The weighing boat was then rinsed with distilled water, and all the
liquid (the rinsed funnel included) was transferred into the volumetric flask. The weighing boat was
then accurately re-weighed, to ensure that all its’ contents had been fully transferred.
After having, once again, weighed the empty weighing boat, approximately 100cm³ of distilled water
was added into the flask containing Na₂CO₃ . The stopper was plugged into the flask. Holding my
)
thumb over the stopper, the flask was shaken until the sodium carbonate was entirely dissolved.
Distilled water was then added into the volumetric flask, to bring the liquid level to just below the
graduation mark. Using a teat pipette, the last few drops of water was added into the flask, so that
the bottom of the meniscus was on the graduation mark, when viewed at eye level. Once the
stopper had been plugged back in, the flask was inverted a few times to mix the solution thoroughly
with the newly added distilled water.
Results:
Initial mass of weighing boat empty 0.9g
Mass of Sodium Carbonate Na₂CO₃ 1.42g
Mass of weighing boat after transfer 0.9g
Calculations:
Mass of Na₂CO₃ in grams 1.42g
Mr of Na₂CO₃ 106
Moles of Na₂CO₃ 0.013
Volume in dm³ 0.25dm³
Concentration of Na₂CO₃ in moldm-3 0.052moldm-3
Molecular Mass: (23*2) +12+(16*3) =106
Moles: 1.42/106=0.013
Volume (dm3): 250/1000=0.25
Concentration (moldm-3): 0.013/0.25=0.052
, Evaluation:
By ensuring the balance is calibrated, and was on zero before measuring, we cleared out a possible
systematic error that could have risen. Leaning on the bench could also alter the reading on the
balance. We should also ensure that our balance is on a flat surface, making sure that it is away from
any open windows, as it could decrease the quantity of our sodium carbonate in our weighing boat.
It was made sure that no solids were spilt. All the masses on the balance were recorded.
The boat was re-weighed after the transfer into the volumetric flask, assuring that all its’ contents
had been entirely transferred. Care was taken when transferring the solids into the flask, by using a
funnel. The funnel was used to ensure that the sodium carbonate was correctly transferred into the
flask, thereby reducing the risk of spillage. After usage, the funnel was rinsed inside and out into the
flask to ensure its’ complete transfer.
Less water than the total volume was added into the flask and was shaken to dissolve the solids.
Once all the solid had dissolved, we made the standard solution up to the line, where the bottom of
the meniscus was sitting on the line. In the calculations, no rounding was done to increase the
accuracy.
Conclusion:
The standard solution was made, and its concentration was found to be 0.052moldm -3.
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