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Unit 2 COMPLETED
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- PEARSON (PEARSON)
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BTEC Level 3 extended Diploma Applied ScienceLearning aim, A: Undertake titration and colorimetry to determine the concentration of
solutions.
Practical 1: Making a standard solution.
We will be weighing sodium carbonate (Na2CO3) and mixing it with distilled water to
determine the concentration in this practical. We intend to prepare 250 cm3 of a standard
sodium carbonate solution (0.10 mol dm3).
CALCULATIONS:
1. 0.1 x 250 ÷ 1000 = 0.025
2. 0.025 x 106 = 2.65g
3. 2.96 ÷ 105.95 = 0.0279 (moles = mass x mr)
4. 0.0279mol ÷ 0.25dm3 = 0.116 mol/dm3
Percentage Error:
Volumetric Flask: +/- 0.3 cm3
(Maximum error / quantity measured) x 100 = Percentage Error
+/- 0.3 cm = =/-3 x 10-4
(+/-3 x 10- cm3) x 100
= +/- 0.12%
Risk Assessment:
Item / Solution: Hazard: Action taken to minimise
risk:
Glass wear Sharp when broke Sweep the glass as soon as
it drops.
Water Spilling the water on the When water is spilled, you
flour. wipe it up immediately
before someone enters the
area to work or you put a
sign to let others know.
,Sodium Carbonate When this chemical is Maintain a reasonable
inhaled, it can cause distance so you do not
irritation of the respiratory inhale any toxins.
tract, coughing, shortness of
breath, and pulmonary
oedema.
Equipment:
Weight meter
Beaker (250ml)
Volumetric flask 250 cm^3
Funnel
Pipette (30ml)
Pipette pump
Spatula
Weight boat
String rod (glass)
Sodium carbonate
Distilled water bottle
Method used:
Method 1:
1. Rinse and prepare the pipette
2. Add a definite volume of the original solution into a clean volumetric flask
3. Add distilled water to the volumetric flask until the water is just below the
calibration mark.
4. Use a dropper to add the last few cm of water slowly allowing the bottom of the
meniscus to reach the mark.
5. Shake to thoroughly mix content.
, Method 2:
1. Using a clean, dry weighing boat. I Placed the weighing boat on a pan of a digital
balance and record the initial mass of the weighing boat.
2. Using a spatula, weigh out the mass of sodium carbonate that you have calculated to
be necessary, on the weighing boat.
3. Record the total mass of weighing boat plus the sodium carbonate.
4. Transfer all the contents of the weighing boat into a beaker and reweigh the
weighing boat.
5. Calculate the mass of the sodium carbonate that you have transferred.
6. Dissolve the solid in a small amount of distilled/deionised water (50-100cm^3). Using
a glass rod, stir the contents of the beaker until all the sodium carbonate dissolves.
7. Using a suitable funnel, transfer the solution from the beaker into a (250cm^3)
volumetric flask. Rinse the beaker and transfer the washings from the beaker into
the (250cm^3) volumetric flask. (Rinse the glass rod and add the washings to the
flask also).
8. Make up the volumetric flask with distilled/deionised water, until the bottom of the
meniscus is on the graduated mark.
9. Stopper the flask and invert/shake it, to mix the contents thoroughly.
10. Calculate the exact concentration in mol of the solution you have made, quoting the
value to the appropriate precision.
Evaluation: We discussed how to calibrate a pH metre and balances. I learned how to
calibrate a pH metre and balance properly and that if they are not calibrated properly,
the entire experiment can be thrown out. This compelled me to cultivate patience and
to attempt again if something went wrong. I did not always obtain conclusive results,
which was perplexing. Additionally, we discussed and learned how to prepare a
standard sodium carbonate solution. I acquired the necessary measurement skills to
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