Sulphuric acid, is a strong acid and Sodium Carbonate is a weak base therefore it is now clear that a methyl orange indicator will be used to identify the neutralisation of the Sulphuric acid.
Apparatus
Methyl Orange Indicator
Sulphuric Acid (solution)
Sodium Carbonate (powdered)
Burette 50cm3
Retort stand, clamp and boss
White tile
Weighing boat
Graduated glass pipette 10cm3
Pipette Filler
250 cm3 Conical Flask
Glass rod
Funnel
Spatula
Two Decimal Place Balance
250 cm3 Standard Flask
Method
The first procedure of this investigation will be to make the standard solution of the 0.1 molar concentration of Sodium Carbonate. This process has to be accomplished with care and accuracy.
The correct mass of solid Sodium Carbonate will have to be used to make the 0.1 molar solution in this investigation 2.65 grams of Sodium Carbonate will be used.
Accuracy
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The set of titre results that are gained from the titration will have to be within 0.1 cm3 of at least three results.
Procedures for standard solution
- Before attaining the correct amount of Sodium Carbonate, it is important to calculate the mass of the weighing boat that is going to be used. This will be done by using a standard two decimal place scale. The mass of the boat will be recorded.
- Now it is important to tear the scale with the weighing boat placed on top, so that the correct amount of Sodium Carbonate can be obtained.
- Once the scale is teared, using a spatula the correct amount of Sodium Carbonate will be added to the weighing boat.
- Once correct mass obtained the Sodium Carbonate will be placed in the 250ml beaker.
- It is necessary to measure the weighing boat again, to see the correct amount of Sodium Carbonate that is added to the beaker.
Method for standard solution
- Using a glass rod and distilled water, the Sodium Carbonate has to be dissolved within the beaker.
- Whilst dissolving, a funnel has to be placed on top of the standard flask.
- Once the Sodium Carbonate is fully dissolved the solution will be poured into the standard flask. It is very important not to spill any of the standard solution.
- Using the distilled water, the glass rod and the inside of the beaker will be washed. Once thoroughly washed this solution will once again go into the standard flask.
- Two or more thorough washes of the glass rod and the beaker will have to be made, and the solution will always be poured into the standard flask.
- The inside of the funnel will have to be washed so that all the solution is within the standard flask.
- It is important to follow these procedures so that the investigation will be at its most accurate. All the Sodium Carbonate solution will have to end up in the standard flask to make this investigation as accurate as possible.
- It is very important that the solution does not go over the 250ml neck mark on the standard flask.
- If the solution does go over, the investigation will be incorrect therefore the standard solution will have to be done again.
Titration Method
- The Sodium Carbonate will be placed in the burette as it is the solution with the known concentration.
- The Sulphuric acid is the solution with the unknown concentration therefore it will be placed in the beaker.
- The standard clamp mechanism has to be used by using the retort stand, clamp and the bosses. The burette will be placed in the clamp, it is essential to make sure that the burette is stable.
- Every time the same amount of Sulphuric acid solution will be placed in the beaker and
- The standard solution which is the Sodium Carbonate will be placed in the burette.
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10cm3 of Sulphuric acid will be placed in the conical flask on top of a white tile, which allow you to see the methyl orange colour change.
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To the Sulphuric acid, add 5 drops of methyl orange indicator. The Sulphuric acid will turn a methyl orange. This is used to indicate the neutralisation of the acid by the base.
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Before starting to titrate record the value of your Sodium Carbonate in the burette, in cm3. This will be your initial reading.
- Slowly turn the stop cock of the burette allowing small amounts of the standard solution of Sodium Carbonate in to the conical flask.
- It is very important to swirl the conical flask, to allow the base to react fully with the acid.
- Once a pale yellow colour is noticeable, it is necessary to add the base solution very slowly to the acid, so that the reaction will not go over the end point.
- When a pale yellow colour is reached, the end point to the neutralisation is reached therefore stop adding the base to the acid.
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Record the value of the Sodium Carbonate in cm3 required for the neutralistaion of the Sulphuric Acid. This will be your final reading.
- The difference between the initial reading and the final reading will be the titre of this titration.
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These procedures will have to be followed until the accurate results with 0.1 cm3 accuracy.
Safety Procedures
Safety is very important in this investigation. Therefore there are procedures that have to be followed in order to make this investigation safe and prevent any harm.
Procedures are as following:
- Handle all glass test tubes, pipettes with great care as they can be easily broken and cause injury or cuts.
- Goggles must be worn at all times as the acid or the base can case damage to the eyes.
- It is very important not to swallow any solution in this investigation. As all solutions can cause serious damage to the body.
- Lab coat should be worn at all times during the experiment. The acid is corrosive thus causing damage to the skin as well as your clothes.
- The burette should be within eye level, allowing you to see the exact level of sodium carbonate in the burette.
Calculations
- Write the balanced chemical equation for the reaction
- Extract all the relevant information from the question
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Check that data for consistency, for example, concentrations are usually given in M or mol L-1 but volumes are often given in mL. You will need to convert the mL to L for consistency. The easiest way to do this is to multiply the volume in mL x 10-3
- Calculate the moles of reactant (n) for which you have both the volume(V) and concentration(M) : n = M x V
- From the balanced chemical equation find the mole ratio known reactant : unknown reactant
- Use the mole ratio to calculate the moles of the unknown reactant
- From the volume(V) of unknown reactant and its previously calculated moles(n), calculate its concentration(M): M = n ÷ V
Analysing Evidence
Results of Mass
Results of Titration
Concentration of Sodium Carbonate
The standard solution that was used to neutralise the Sulphuric acid was made from the solid, anhydrous Sodium Carbonate that was provided. Sodium Carbonate has the molecular formula of 2C3.
Referring back to the original titration, 2.65 grams of Sodium Carbonate was used. The decision to use this mass of 2C3 was gained from certain calculations that were made. The calculation was as following:
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Step 1 – Identify the mass of Sodium Carbonate used
2.65g of 2C3(aq) is used
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Step 2 – Calculate the moles for the Sodium Carbonate used
Use this formula: Moles = Mass
Mr
[Na: 23, C:12, O:16]
Mr = 2(23.0) + (12) + 3(16)
Mr = 106
Therefore:
Moles = 2.65
106
Moles = 0.025
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Step 3 – Calculate the concentration of Sodium Carbonate in 1dm3
Use this formula to calculate: Concentration = Moles × 1000
Volume
Note: The concentration has to be multiplied by a thousand to get the figures into decimetre cubed (dm3)
Therefore:
Concentration = 0.025 × 1000
250cm3
Concentration of Sodium Carbonate = 0.100 mol dm-3
Concentration of Sulphuric Acid
From the titration results above the mean titre has to be calculated. Once the main titre has been gained, the concentration of the Sulphuric acid can be calculated.
Mean titre = 10.1 + 10.2 + 10.0
3
Mean titre = 10.1 cm3
24(aq) + 2(aq) → 24(aq) + 2O(l) + CO2(g)
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Step 1: Calculate the moles of reactant (n) for which you have both the volume(V) and concentration(C)
Use the formula: n = C x V
Therefore: Moles of 2 = 0.100 × 10.1
Moles = 1.01 × 10-03
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Step 2: Extract all the relevant information from the question
Moles of 2 = 1.01 × 10-03 moles
Volume = 10.1 cm3
Concentration = 0.100 mol dm-3
From the equation above we know that there is 1:1 ratio, therefore the mole of Sodium Carbonate and the Sulphuric Acid used will be the same therefore:
Moles of 24 = 1.01 × 10-03 moles
Volume = 10cm3
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Step 3: From the volume (V) of unknown reactant and its previously calculated moles (n), calculate its concentration
Use the formula: C1V1n2 = C2V2n1
C1 – Concentration of the known solution
V1 – Volume of the known concentration
n2 – Moles of the unknown concentration
C2 – Concentration of unknown solution
V2 – Volume of the unknown concentration
n1 – Moles of the unknown concentration (gained from the mole ratio of equation)
Therefore: 0.100mol dm-3 × 10.1cm3 × 1.01×10-03moles = C2 × 10.0 × 1.01×10-03
1.0201×10-03 = C2 × 0.0101
C2 = 1.0201×10-03
0.0101
C2 = 0.101 mol dm-3
Therefore the Concentration of the Sulphuric Acid is: 0.101 mol dm-3 3sf Evaluation
Evaluation
The aim of the investigation was, ‘To find out the accurate concentration, of Sulphuric acid sample that is given, which is thought to have a concentration between 0.05 and 0.015 mol dm-3’. The aim was successfully met with high precision and efficiency. The concentration of the acid was gained from the calculations that were made in the analysis of the investigation. From looking at my results, I can not identify any anomalous results this suggests that my method met the suitability of the investigation.
My measurements were quite precise and reliable. When the sodium carbonate was weighed using the electronic balance, a spatula was used to add or remove sodium carbonate, to ensure it was exactly 2.65g. When using the graduated volumetric flask, it is difficult to pour in distilled water and get it exactly on the graduation mark.
One main area of concern which would make the experiment less accurate is the factor of measurements.
Errors or uncertainties related to the precision of the equipment used need to be identified to therefore indicate if the titration result was accurate.
The equipment used in the experiment for measuring, was the burette, balance and pipette. By calculating the percentage error of each piece of equipment will give a maximum and minimum value, which could have been obtained from the experiment.
By calculating the percentage error of the different equipment used, we are able to see how much error there has been in the experiment. By using the general formula of: Percentage Error = Error × 100
Measurement
Burettes 50cm3 grade B +/- 0.1cm3
Therefore: % Error = (0.1/10.1) × 100
% Error = +/- 0.99
During the experiment, an initial and final reading of the burette was taken; therefore this figure needs to be doubled.
0.99 x 2 = +/- 1.98%
Volumetric Pipettes 10cm3 grade B +/- 0.04 cm3
Therefore: % Error = (0.04/10) × 100
% Error = +/- 0.4%
- Balance (two decimal place) +/- 0.005gm
Therefore: % Error = (0.005/2.65) × 100
%Error = +/- 0.19%
By adding all errors, an overall percentage error for the experiment can be obtained.
Overall percentage error = (0.4) + (1.98) + (0.19) = +/-2.57%
Therefore to obtain the maximum and minimum value that could have been obtained from the titration is as following:
Maximum = [(10.1/100) × 2.57%] + 10.1
= 0.25957 + 10.1
= 10.4 cm3 to 3sf Evaluation
Minimum = 10.1 - [(10.1/100) × 2.57%]
= 10.1 – 0.25957
= 9.84 cm3 to 3sf Evaluation
From the values above, we are able to see how much error that there could have been in the titration of the investigation. Although it was only by 2.57%, this could have had a net effect on the Concentration of the Sulphuric Acid.
Reducing Errors
Referring back to the percentage errors, the main source of error came from the burette. Therefore to gain more accurate results a burette with a smaller volume can be used. This will reduce the percentage error, which will have a net effect in the final data. Reducing the size of the burette will have no negative effect in the volumes, as the average titre was 10.1 cm3. Possibly reducing the burette size to 20cm3 will be a great benefit to gain accurate results.
The volumetric pipettes are very hard to replace, as a 10cm3 graduated pipettes were used. The only smaller available size was the 1cm3 graduated pipette, this has a smaller percentage error, however it has to be used a number of times to gain 10cm3 of the standard solution.
The balance had the smallest percentage error and this can be reduced even further by possibly using a three decimal place scale. This will reduce the percentage error further, which will be a benefit to reduce the net percentage error.
Reducing these errors will result in more accurate titrations and gaining more accurate results. Therefore if repeated the experiment will be more successful. However the current result gained from the investigation is correct as it was compared to a reference value. In conclusion this titration investigation was successful.