amount/mol = (concentration of solution/ mol dm-3) X (volume of solution/dm3)
APPARATUS
- Volumetric flask
- Conical flask
-
Beaker: 50cm3 x 2
-
Pipette: 25.0cm3
- Pipette filter
- Burette
- Funnel
- Clamp and stand
- Balance
- Test tube x2
- Test tube rack
- White tile
MATERIALS
- Sulphuric acid
- Anhydrous sodium carbonate
- Indicator: methyl orange
- Distilled water
JUSTIFICATION OF MATERIALS
I will use the sulphuric acid of the unknown concentration that will be given to me.
The concentration of sodium carbonate that I am going to use will be of 0.1 mol dm-3 as the concentration of the sulphuric acid is between 0.05 and 0.15 mol dm-3. I am going to make 250 cm3 of the solution as I am going to need quite a lot of it. To work out the number of moles needed to make 250 cm3 of 0.1 mol dm-3 Na2CO3 I am going to use the following formula:
Amount/mol = (concentration of solution/ mol dm-3) X (volume of solution/dm3)
Concentration = 0.1 mol dm-3
Volume = 250 cm3
= (250/1000) dm3
= 0.25 dm3
amount = 0.1 X 0.25
= 0.025 mol
To work what the weight of the in Na2CO3 grams, I am going to use the following formula:
Mass in grams / molar mass = amount in moles of atoms
molar mass of Na2CO3 (in g mol-1): (2X23) + 12 + (3X16)
= 106g mol-1
number of moles: 0.025 mol
weight (in g) = 106 X 0.025
= 2.65 g
In my experiment I am using sulphuric acid which is a strong acid and sodium carbonate which is a weak alkali. From the worksheets I have been given, I worked out that for a titration between a strong acid and a weak alkali, methyl orange is used as an indicator.
I am going to use distilled water to make all my solutions and wash the apparatus. This is because the chlorine in the normal water may affect the experiment.
PLAN
-
First I will weigh 2.65gm of sodium carbonate using a balance. I will transfer the sodium carbonate to a 250 cm3 of volumetric flask using a funnel. While pouring the powder I will make sure that I do not put all of it at one go, as this might block the funnel. Then add some distilled water to dissolve it. I will keep adding the water until it reaches the 2503 cm mark. I will then take 25 cm3 of the solutions, using a 25cm3 pipette, into a 100 cm3 conical flask.
- After making the solution, I will put both the sodium carbonate and the sulphuric acid in to two different test tubes. I will add 3 drops of methyl orange into each of the test tube. The acid will turn into pink and the alkali will turn in to fluorescent orange. I will put both the test tubes in to the tube rack. This will help me to decide the end of point of the neutralisation.
- I will wash the burette using distilled water and afterwards with acid. Then I shall clamp it using boss head with iron stand. I will fill up the burette with sulphuric acid and record the reading as the initial reading.
- I will then put some drops of methyl orange into the conical flask containing sodium carbonate and make the colour same as the one I made before. Then put the conical flask underneath the burette and on top of a white tile. This is so that I can see the exact colour. Then I will open the tap of the burette slowly. open the tap slowly.
- As soon as I see any colour change, I will stop the tap and swirl. If the colour goes away, I will add some more acid until a slight colour change takes place.
- To decide the end point, that is when the acid has neutralised the alkali completely, with the colour in the test tube containing acid and alkali. The end point will be somewhere in the middle of the two colours.
- I will then take the final reading. To work out the volume of sulphuric acid needed to neutralise the sodium carbonate(alkali), I will subtract the initial reading for the final reading.
- I will repeat my experiment at 4- 5times, or until I get at least three readings which are between 0.1cm.
RISK ASSESSMENT
- Risks: It is very corrosive
Concentration with more than 15 causes burns
Reacts vigorously with water
- Safety procedure: Wear lab coats at all time
Wash hands if any acid is spilled
Wear goggles to protect the eyes
- Risks: irritating to eyes and skin
Irritates the respiratory system
- Safety procedure: Do not breath the gas
- Wear goggles to protect the eyes
- Methyl orange:
May evoke toxic fumes in fire
Maybe harmful by ingestion
Irritates eye
Makes stain
- Safety procedure: Handle with care
Do not breath
RESULTS
Mass of solid: 2.65g
ANALYSING THE RESULTS
After doing my experiment, I have got 6 sets of result. However 4 of my results are between 0.1. so I am going to take the average of the 4, and use it to work out the concentration.
Average titre: (20.5 + 20.4 + 20.6 + 20.5) / 4
20.5 cm3
From my background research i have worked out that the ratio between sodium carbonate and the sulphuric acid is 1:1. This means that the number of moles in sodium carbonate is same as sulphuric acid.
Working out the number of mole in Na2CO3:
General formula,
amount/mol = (concentration of solution/ mol dm-3) X (volume of solution/dm3)
Volume used in the experiment: 25 cm3
= (25 / 1000) dm3
= 0.025
Concentration: 0.1 mol dm-3
Number of moles: 0.025 X 0.1
= 0.0025 mol
working out the concentration of sulphuric acid:
amount = 0.0025 mol
volume = 20.5 cm3
= (20.5 / 1000) dm3
= 0.0205 dm3
concentration = 0.0025 / 0.0205
= 0.12 mol dm-3
i conclude that the concentration of the unknown sulphuric acid was 0.12 mol dm-3.
