Secondly, I noticed that 1g. of powder was simply too much. Even after adding a full burette (50 cm3 ) of HCl, the solution would not change colour. I decided that if I reduced the amount of powder added to the water, I would dilute the solution, thus making it take less HCl to neutralise it. If I’d reduce the amount of powder added to the water with all samples and all tablets, the results would remain the same.
Also, after weighing the powder and putting it into the water, some powder would remain in the plastic cup. Even though this is only a very small amount, the experiment would be more precise if I could get this into the water. To do this, I will measure another 10 cm3 – using an accurate pipette – which I will use to rinse the plastic cup. The water will “pick up” all bits of powder left in the plastic cup. I must add 10 cm3 on top of the 25 cm3 in every sample, to make this a fair experiment.
Final equipment list
- Stand
- X-Clamp
-
25 cm3 pipette
-
10 cm3 pipette
- pipette filler
- burette
- conical flask (x9 or more)
- funnel
- beaker for HCl
-
beaker for H2O
- 0.1M HCl
-
Purified H2O
- Methyl Orange Indicator
- Indigestion tablets
Final Method
I will go through my experiment in detail, stating reasons for my actions where appropriate. Firstly, I will get a stand with an X-clamp, clamping the burette to the stand. I will make sure that the tap on the burette is closed, before filling it with HCl. I will put the beaker with HCl under the burette and, turn on the tap in order to fill the reservoir. Obviously, I will have to close the tap again and fill the rest of the burette.
Afterwards, I will get a plastic cup and fill it with exactly 0.25g of the indigestion tablet powder. I will fill an accurate pipette with 25cm3 of H2O, and release the deionised water into a conical flask. I will then put the indigestion tablet powder into the conical flask and, will swirl it regularly. Because some of the powder will “stick” to the plastic cup, I will fill another accurate burette with 10 cm3 and, use that water to collect all the bits of powder that did not come off the plastic cup. Also, all powder that stuck to the sides of the conical flask will be cleaned with the water. In total, there will now be 35 cm3. I know that it will not form a solution but a suspension because carbonates and water do not form a solution. The best I can do is keep the powder dispersed through the whole suspension evenly at all times, by swirling it almost at all times.
After that, I will add three drops of methyl orange, the indicator. The suspension will now be yellow, as methyl orange turns alkalis yellow. The suspension is now ready and I can place the conical flask under the burette. I will now slowly release the HCl from the burette. At some point, the solution will turn orange but, after swirling, will turn yellow again, because of the dispersion of HCl throughout the conical flask. When the colour changes to red and does not change back after a considerable amount of swirling, I will consider the substance to have gone neutral. I will now note down the reading on the burette.
I think that it’s important to repeat these steps until there are three results that are in concordancy, from which I could take an average. When using titration, it is easy to make one small mistake which could alter the results completely. I have to look at the results critically and do the experiment again if there is a “freak-result”.
Scientific details
Indigestion is caused by excess hydrochloric acid, produced in the lining of the stomach. This can be treated quickly and effectively, using medicines containing chemicals called antacids. Antacids are alkalis that are used to neutralise the acid, turning it into a salt and water. These can then be digested and egested through the digestive system.
The easiest way of solving my problem would be to use titration. In the burette I would put my known substance – the titrant - 1M HCl. In the conical flask I will put my suspension, about which I want to find something out. By adding an indicator and slowly dripping the HCl (acid) into the suspension (base) and continuing until the solution has neutralised, I will know how much HCl was needed. Using the equation for the reaction that was taking place, I can extract the number of moles relatively reacting with the acid. From that, I can use the formulae n = m / mm and n = v x c to work out the mass of the active ingredients.
Obtaining Evidence
All results
0.25g powder added to 35cm3
3 drops of methyl orange
0.1M HCl
* = changing to 0.25g of tablet
I have not used the results that were crossed out because they were not in concordancy with the rest. I had to do a fourth try on those indigestion tablets. I have also not used those for calculating the average.
Good results
The following table clearly shows the results that I used for my averages. All three tries are within 0.5 cm3 of each other.
0.25g powder added to cm3
3 drops of methyl orange
0.1M HCl
* = changing to 0.25g of tablet
Analysis
From the results, without doing any calculations, we can say that ‘Rennie’ is the most effective indigestion tablet. The concentration of calcium carbonate and heavy magnesium carbonate is the greatest of the three, as it took the most HCl to neutralise. Rennie has the greatest concentration of active ingredients and will therefore cure indigestion most effectively. My calculations will confirm this.
Calculations
Amount of CaCO3 in Setlers
CaCO3 + 2HCl → CaCl2 + CO2 + H2O
nHCl = v x c = 0.0227 x 0.1 = 0.00227mol
(dm3) (M HCl)
Therefore, nCaCO3 = 0.00227 / 2 = 0.001135mol CaCO3 in powder.
(nHCl) (1mol)
Mass of CaCO3 in powder (0.25g) = n x mm = 0.001135 x 100 = 0.1135 g
Mass of CaCO3 in powder (1.0g) = 0.1135 x 4 = 0.454g = 454 mg
Mass of CaCO3 in tablet (1.22675g) = 0.1135 x 4.907 = 0.5569445 g
(times more)
= 556.9 mg CaCO3
Amount of CaCO3 in Rennie
CaCO3 + 2HCl → CaCl2 + CO2 + H2O
nHCl = v x c = 0.0282 x 0.1 = 0.00282mol
(dm3) (M HCl)
From the packet, we can read that CaCO3 and MgCO3 are present in the following percentages:
CaCO3 = 680 / 760 x 100 = 89.5%
MgCO3 = 80 / 760 x 100 = 10.5%
nHCl reacting with CaCO3 = 0.00282 / 100 x 89.5 = 0.0025239mol
Therefore, nCaCO3 = 0.0025239 / 2 = 0.0012619mol CaCO3 in powder.
(1mol)
Mass of CaCO3 in powder (0.25g) = n x mm = 0.0012619 x 100 = 0.12619 g
Mass of CaCO3 in powder (1.0g) = 0.12619 x 4 = 0.50476 g = 504.7 mg
Mass of CaCO3 in tablet (1.315g) = 0.12619 x 5.26 = 0.6637594 g
(times more)
= 663.8 mg CaCO3
Amount of MgCO3 in Rennie
nHCl reacting with MgCO3 = 0.00282 / 100 x 10.5 = 0.0002961 mol
Therefore, nMgCO3 = 0.0002961 / 2 = 0.000148mol MgCO3 in powder.
Mass of MgCO3 in powder (0.25g) = n x mm = 0.000148 x 84 = 0.012432 g
Mass of MgCO3 in powder (1.0g) = 0.012432 x 4 = 0.049728 g = 49.7 mg
Mass of MgCO3 in tablet (1.315g) = 0.012432 x 5.26 = 0.0653923 g
(times more)
= 65.4 mg MgCO3
Amount of CaCO3 in Bisodol
CaCO3 + 2HCl → CaCl2 + CO2 + H2O
nHCl = v x c = 0.0278 x 0.1 = 0.00278mol
(dm3) (M HCl)
From the packet, we can read that CaCO3 , MgCO3 and NaHCO3 are present in the following percentages:
CaCO3 = 522 / 654 x 100 = 79.8%
MgCO3 = 68 / 654 x 100 = 10.4%
NaHCO3 = 64 / 654 x 100 = 9.8%
nHCl reacting with CaCO3 = 0.00278 / 100 x 79.8 = 0.0022184mol
Therefore, nCaCO3 = 0.0022184 / 2 = 0.0011092mol CaCO3 in powder.
(1mol)
Mass of CaCO3 in powder (0.25g) = n x mm = 0.0011092 x 100 = 0.11092 g
Mass of CaCO3 in powder (1.0g) = 0.11092 x 4 = 0.44368 g = 443.7 mg
Mass of CaCO3 in tablet (1.234g) = 0.11092 x 4.936 = 0.5475011 g
(times more)
= 547.5 mg CaCO3
Amount of MgCO3 in Bisodol
nHCl reacting with MgCO3 = 0.00278 / 100 x 10.4 = 0.0002891 mol
Therefore, nMgCO3 = 0.0002891 / 2 = 0.0001445mol MgCO3 in powder.
Mass of MgCO3 in powder (0.25g) = n x mm = 0.0001445 x 84 = 0.012138 g
Mass of MgCO3 in powder (1.0g) = 0.012138 x 4 = 0.048552 g = 48.6 mg
Mass of MgCO3 in tablet (1.234g) = 0.012138 x 4.936 = 0.0599131 g
(times more)
= 59.9 mg MgCO3
Amount of NaHCO3 in Bisodol
Because NaHCO3 reacts with a different number of nHCl, I think that it’s best to start my calculations again for sodium bicarbonate, instead of working out the mass from the other results.
NaHCO3 + HCl → NaCl + CO2 + H2O
nHCl = v x c = 0.0278 x 0.1 = 0.00278mol
(dm3) (M HCl)
nHCl reacting with NaHCO3 = 0.00278 / 100 x 9.8 = 0.0002724mol
The number of moles reacting with NaHCO3 is the same as the number of moles reacting with HCl, so I do not have to divide by two.
Mass of NaHCO3 in powder (0.25g) = n x mm = 0.0002724 x 84 = 0.022882 g
Mass of NaHCO3 in powder (1.0g) = 0.02724 x 4 = 0.10896 g = 109.0 mg
Mass of NaHCO3 in tablet (1.234g) = 0.022882 x 4.936 = 0.1129455
(times more)
= 112.9 mg NaHCO3
Conclusion
I did not compare the mass of active ingredient per tablet as they all had different prescriptions. I compared the prescriptions to the masses of one tablets and it seemed like every tablet had to be taken in, in the same dosage. I will therefore compare the amount of active ingredient per gram of tablet.
Even though the initial results showed that Rennie took the most acid to neutralise, this did not mean that the concentration of active ingredient in Rennie was the greatest. According to this table, Bisodol has the greatest efficiency as it contains more mg of active ingredient per gram of powder. This is because the three molecules have different molar masses and will therefore be present in different quantities. Also, one mole sodium bicarbonate only neutralises one mole of hydrochloric acid, whereas the other two active ingredients neutralise two moles per every mole of active ingredient. I believe that it is therefore better to compare the amount of HCl that it took to neutralise – which is proportional to the amount of acid that it will neutralise – than to compare the actual mass of actual ingredients found in the tablet. I can then conclude that Rennie is the best tablet, with the greatest efficiency.
Evaluation
The first major aspect which could have influenced my results is the fact that I did not have any means of testing the amount of magnesium carbonate myself. I had to read the values on the packet to determine the ratio in which the two or three active ingredients were divided in one tablet. It was therefore pointless to compare my results to the values on the packet, as one of the most important figures were taken from the packet in the first place. The only result that I can compare to the label is the amount of calcium carbonate in Setlers, as that was the only tablet with only one active ingredient. It seems like the value on the packet – 500 mg – is rounded up, which means that we still cannot compare this value to my results.
Also, my indicator did not completely cover the neutralisation point. It changes colour at pH 4 instead of pH 7, which alters the results slightly. Some of the deionised water may have stuck to the inside of the conical flask, making the solution or suspension slightly more concentrated. Also, the carbon dioxide in the air will make the deionised water slightly acidic but, this will cause only minute differences and can therefore be disregarded.
To improve my results, it would be better to find a way in which to clearly distinguish the amount of different active ingredients present, instead of reading it from the label. Also, if I would be able to do this experiment again, I would take a mass of powder to one decimal place (e.g. 0.2g instead of 0.25g) as the scales that we used were less accurate on the second decimal place.
Obviously, it would have been better to use real stomach acid to neutralise the tablet, as it would be better to completely simulate what is going on inside the stomach. Impurities and other chemicals that would influence the results will then also be taken into consideration.
In order to obtain results sufficient to support a scientific solution, it would have been better to try more samples of each tablet, in order to create a more accurate average. It would have been even better to let a computer recognise whether the solution is neutral. Also, it would be very beneficial to have an apparatus that would keep the solution or suspension stirred at all times, in order to make sure complete distribution of the acid, alkali and indicator.
Overall, I believe that the experiment has been a success and, that I have done everything I could in order to make these results as accurate as possible. We used the greatest attention to detail throughout the experiment, were very critical and eliminated freak-results where necessary and, I think that the results confirm that.
- Oscar van den Bosch
- Chemistry 23/11/2002
