METHOD
- Weigh mass of boat set scales to 0 then add 2.65g of anhydrous sodium carbonate to the boat using a spatula
- Put sodium carbonate in to beaker rinse boat using distilled water
- Put 150cm³ of distilled was to the same beaker
- Stir well with glass rod till solution goes clear and sodium carbonate is completely dissolved
- Transfer the dissolved sodium carbonate to a volumetric flask. Wash out any remains on the funnel using distilled water to ensure accuracy of sodium carbonate solution
- Add distilled water to the volumetric flask until the solution is close to the graduation mark. Then use as a pipette to make sure the bottom of the meniscus touches the graduation mark. This ensures the sodium carbonate solution concentration is kept accurate. Shake well one more time.
- Set up the burette with clamp on the floor put paper on the reading so it can be read easily. Fill it with sulphuric acid to the top (0) using funnel and pipette to get it accurate as you get close to the zero. Place beaker underneath to avoid spillages.
- Use pipette filler and pipette to transfer 25cm³ of sodium carbonate solution from the 250cm³ volumetric flask to the conical flask. Again wash out pipette using distilled water. Do not hold the pipette above the liquid as it sucks air back up.
- Add 3 drops of methyl orange solution to the conical flask. Place conical flask under the burette. Set this on the table. I am using 3 drops as this gives a darker red/ orange colour and the colour change can be detected easier.
- Add the sulphuric Acid solution from burette to the conical flask by turning the stopcock on the burette vertical note the initial final reading before the end point.
- Keep the flow rapid till the colour changes to a lighter red, but before this turn the stopcock slightly horizontal as the acid comes out drop by drop.
- Read off the value on the burette find out the volume of sulphuric acid needed to react with sodium carbonate.
- Carry out the titrations Until you have recorded three results within 0.1cm³
CONTROL VARIABLES
Ensure the same sodium carbonate solution and sulphuric acid batch is used for all titration to ensure a fair test and the results will be accurate and reliable.
Try to carry out the titrations on the same day to ensure there isn’t a temperature change and that they are done in one uniform temperature. If the temperature is increased, the liquid will expand making the test inaccurate.
RISK ASSESMENT
- Wear safety goggles to prevent acid from entering the eye
- Stools must be tucked underneath the table ensure bags are out of the way to prevent people from tripping
- Long hair should be tied back
- Ensure you are standing throughout the experiment so you are able to quickly move out of the way in case of spillages etc. Also to accurately record readings at eye level
- Use a funnel when pouring acid to prevent splashes and leakages
- Watch hands if the come in contact with any of the chemicals
- Wipe away immediately any spillages
- Don’t fiddle with the experiment too much as this may affect the temp thus the results.
- Inform the teacher if any glassware id broken
- Ensure there is no running in the lab as this can cause hazards
Bibliography
Chem ideas
Chem storylines
Elements of life activity sheet 2.1
Results
Calculations
Concentration of sodium carbonate solution:
No. Of moles
Concentration=
Volume
- 2.65g of anhydrous sodium carbonate
RFM of Na2 CO3 = 2×23+12+3×16
=106
Moles of Na2 CO3 = 2.65/106
= 0.025 moles (3 vs.)
- Combined with 0.25dm³ of water therefore concentration of solution =
Conc. of sodium carbonate/conc. of water=
0.025
=0.1 moldm³ (3.s.f.)
0.25
Concentration of 28.43 ml of H2SO4:
Na3CO3 (aq) + H2SO4 (aq) Na2SO4 (aq) + Co2 (g)
1 mole of Na2CO3 neutralises 1 mole of H2 SO4
Therefore the ratio of sulphuric acid to sodium carbonate is 1:1
25cm² of sodium carbonate is needed to neutralise 28.43cm² of sulphuric acid
Moles = concentration of solution × volume of solution (dm³)
0.1mol dm³ × (28.43/1000)-0.02843dm³=0.002843 moles of H2SO4 in 25cm³ of sodium carbonate solution
Conc. Of H2 SO4 =0.002843 moles
0.025dm³
= 0.11 moldm³
Conclusion
The results obtained from my titration suggests that the concentration of the sulphuric acid is 0.11 moldm³ whilst this value may not be accurate it appears to agree with the statement that the acid is thought to have a conc. between 0.05-0.15 moldm³. This is strong evidence that the investigation results are quite satisfactory as they are in the expected range. The accuracy of my results is discussed in my evaluation.
Evaluation
My measurements were quite precise and reliable when I weighed out the anhydrous sodium carbonate using the digital balance; I used a spatula to measure exactly 2.65g. Also to ensure the distilled water was exactly on the graduation mark I used a pipette to ensure the meniscus sat exactly on the graduation mark. The pipette filler was extremely accurate and precise it is designed to release exactly 25cm³. Also I repeated my experiment 5times and three of my results are within 0.1ml of each other. The concentration of sodium carbonate was accurate because I used distilled water to wash all the sodium carbonate off the weighing boat and funnel in to the volumetric flask.
However the most inaccurate part of the experiment was deciding when the colour change of the indicator had occurred. This was hard because although the colour change was fairly rapid, it was not always instantly obvious. It was important to keep a specific colour in mind, and stop the titration when the colour was reached. Fortunately I kept the colour change point constant, although this could have been a cause of any anomalies. To improve the investigation a pH metre can be used instead of using a pH indicator to see when neutralisation occurs. This would eliminate the most significant source of error, which is largely due to human error.
I could have further improved the experiment by checking the pipette filler for air gaps. Also using a magnetic stirrer would have ensured all the sodium carbonate was completely dissolved. I could have used more accurate scale –analytical balance which measure to 0.0001g so it has a high degree of precision
Percentage error
I am going to work out the percentage error using the following equation:
(True value- experimental value) × 100
True value
In order to minimise measurements errors larger quantities of all solution could be used although concentration would remain the same. For example
250 cm³ graduated flask 0.2 × 100 = 0.08%
250
1 dm³ flask 0.2 ×100 = 0.02%
1000
