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practical skills procedures
- Module
- Unit 2
- Institution
- PEARSON (PEARSON)
2.1 assignment- Undertake titration and colorimetry to determine the concentration of solution. grade: Distinction
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UNIT 2 LEARNING AIM A. UNDERTAKE TITRATION AND COLORIMRTY TO DETERMINE THECONCENTRATION OF SOLUTIONS.
Resubmission is highlighted with yellow.
In this assignment we did 3 different practicals. We had to identify unknown concentration of NAOH.
The first part is to prepare a standard solution of Na 2CO3 , the second part is standardized HCl solution
using Na2CO3 , the third part is to titrate unknown NAOH with standardize HCL using an appropriate
indicator and calibrate the pH meter. Then we did a colometry experiment.
Calibration for all the equipment.
Weigh balance.
- Turn on the weigh balance by pressing the “on” bottom
- Ensure that the reading shows as 0.00.
- Place the weigh boat on the balance and zero it out.
Pipette/ graduated pipette/ burette.
- Prepare the pipette for calibration.
- Pre-rinse the tip with distilled water.
- Aspirate the calibration volume.
- Put the beaker into a weigh balance and set it a zero to measure the liquid
- Dispense the liquid into the beaker
- Measure the liquid into a weigh balance
- 1cm3= 1g
Colorimeter
- Turn on the colorimeter.
- Fill a cuvette with distilled water and place it into the cap of the colorimeter.
- Press the bottom.
- 100% absorbance or 0.00 absorbance should be seen in the screen. (in case of no tis means the
water is contaminated or the machine does not measure properly).
Ph meter
- Collect pH calibration buffer solution of 4.00, 7.00 and 10.00
- Switch on the machine and allow it to stabilise and set the temperature control.
- Remove the protective cap and rinse the electrode with distilled water.
- Place it into 7.00 buffer solution and adjust the pH meter accordingly.
- Repeat it with the other two solution and make sure to rinse in between with distilled water.
IDENTIFY UNKOWN CONCENTRATION OF NAOH.
Part 1- prepare standard solution of Na2CO3
Most laboratories have an electronic balance and top-pan balances which is useful to calibrate in the
exact weight. The balance is a rough balance with two decimal places. Degree of precision depends on
many factors like the surface, draughts, room temperature, vibration, magnetism and static electricity.
,In our experiment we use a single-pan balance, this is one has two decimal places which gives you the
exact number of the mass. Calibrating a balance is quick and easy. Using a balance is an easy machine in
the laboratory. First you switch on the balance and wait until it is shown as 0.00g if doesn’t you must
place a calibration which consists of setting the balance to zero. Before weighing the material use a
weight boat. Put the weight boat on the balance and set it on zero to measure the mass only without
the weight boat. Then fill the weight boat with your substance until you get the exact mass that you
need. To keep the balance without any errors, check for drift which is a variation in the reading of the
balance and adjust the weights.
To prepare a standard solution you need to calculate the mass of Na2CO3 .10H20, to make 0.05 mol/dm3
in a 250 cm3 flask. The formula that we need to calculate the mass is c= n/v and moles= mass/ Mr.
First, we calculate the Mr of Na2CO3 .10H20.
Mr of Na2CO3 .10H20 = (2x23) + 12 + (3x16) + (10(1x2) + 16 = 286
Second, we need to calculate the number of moles to find the mass of Na 2CO3 .10H20. We must use this
formula: c = n/v, to use it we must rearrange because we don’t have the number of moles, n= c x v.
n = c x v n = 0.25 x 0.05
Finally, we must rearrange the formula to calculate the number of moles into mass= moles x Mr
Mass= moles x Mr mass= 0.0125 x 286= 1.43g
Result
Concentration 0.05 M
Volume 0.25dm3
Moles 0.0125
Mass 3.575g
Risk assessment.
Hazard Risk What could happen Solution
Sodium carbonate Medium Toxic and corrosive Wear goggles and
gloves
Glass beaker Medium It can break because it Use it carefully and do
is made of glass not place it on the edge
of the table
Weigh balance Low Electroshock Use it carefully and do
not place it on the edge
of the table.
Method.
1. Add weighing boat to balance. Set the balance to zero after you put your weighing boat.
Carefully weigh out the required mass of substance (3.57g).
2. Carefully transfer the sodium carbonate to a large beaker, rinse the weighing boat with distilled
water 2 or 3 times to ensure that all the substance is in the beaker, accurately and precisely
record the measurements to determinate the exact mass transferred.
, 3. Add 150 cm3 of distilled water to the beaker about half of the beaker, stir and completely
dissolve the sodium carbonate.
4. Carefully and accurately transfer all the solution to a 250 cm3 volumetric flask with a funnel.
Rinse the beaker with distilled water to ensure that any substance is not left in the beaker
almost 2 or 3 times, make up the solution to 250 cm3 with more distilled water. Make sure that
you don’t spill any solution because if you do then you lost some of the mass of sodium
carbonate and you need to do it again.
Part 2- standardize HCl solution using Na2CO3.
Volumetric glassware are the common items to measure the volume of a substance and they are
necessary for chemical analysis. The volumetric glassware are:
Name Size Uses Limitations
5.0- 50 ml Used to add small When handle it can be
volumes like drop by fragile
Pipette (non-
drop, it takes the
graduated)
solution volume when
accuracy.
Between 1ml- 1/10th ml It takes specific random To use a gradated
Pipette (graduated) volumes from solution pipette and get
accurate volume, you
need before a practise
with pipette fillers
25- 50ml It allows to see the The tip can become
meniscus of the clogged, or it could be
solution and get a fill with air bubbles.
specific volume
Burette
50-500ml Used to mix and swirl No limitation of using it
volumes of solution to
reduce the risk of
spillage.
Conical flask
10-250 cm3 Used to mix and swirl Glass can expand cause
and make up the the chemical reaction.
volume and it give a
high degree of
accuracy.
Volumetric flask
10-1000ml Measure non-accurate No limitation but hot
volumes normally is alkali can damage it
used as a waste.
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