Variables:
Independent variables:
- The tablets/ Sachets/ Syrup of antacids( Eno powder, Tums Tablets, Zolicid gel)
Dependent Variables:
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The moles of HCl neutralized by each antacid
- The moles of HCl neutralized by the sodium hydroxide base
- The volume of sodium hydroxide needed to neutralize the excess hydrochloric acid
Controlled Variables:
- The concentration of Hydrochloric acid ( HCl)
- The volume of Hydrochloric acid (HCl) to which each antacid is added
- Amount/ dosage of each antacid( e.g. 2 tablets, I sachet, 2 teaspoons..)
- The concentration Of aqueous sodium hydroxide base( NaOH )
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The number of drops of phenolphthalein indicator added for each trial.
Specifications for the controlled variables:
The concentration of Hydrochloric acid ( HCl)- 0.5 M standardized HCl will be used for all the trials, for all antacids.
The volume of Hydrochloric acid (HCl) added to each antacid- 25 cm3 of HCl will be used for all trials, for all antacids.
Amount/ dosage of each antacid-the maximum dosage of each antacid will be used as per the intrustion guide on the antacid packages. Therefore 2 tablets of Actal Tums per Trial, 1 sachet of Eno powder per trial and 2 tea spoons of Zolicid gel per trial.
The concentration Of aqueous sodium hydroxide base( NaOH )- 0.5M standardized NaOH will be used for all trials.
The number of drops of phenolphthalein indicator added for each trial- three drops of phenolphthalein indicator will be added in each trial, for all antacids.
Planning B:
Apparatus
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A 250 cm3 conical flask
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a 50 cm3 burette ± 0.05 cm3
- a metal clip
- a white tile
- a plastic funnel
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a 25 cm3 pipette± 0.06 cm3
- a metal clamp stand
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2 glass beakers( 250 cm3)
- A glass rod
Materials.
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Aqueous standardized Sodium hydroxide base- 0.5 M (150 cm3)
- Eno sachets ( 4.5 grams each) x3
- Tums Tablets (500mg each) x6
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Zolicid gel- 30 cm3 ( 10 cm3 x 3)
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Distilled water (150 cm3)
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Phenolphthalein indicator ( 15 cm3)
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Aqueous standardized Hydrochloric acid- 0.5 M (250 cm3)
- A pair of gloves
- Labels( 2 stickers)
Diagram 1: A representation of the titration experiment setup.
Methodology:
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Wash and Rinse a 50 cm3 burette with sodium hydroxide( 0.5M).
- Attach the burette to a clamp stand, ensuring that it is vertically positioned.
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Fill the 50 cm3 burette with aqueous sodium hydroxide(0.5M) till the 0 cm3 mark of using a plastic funnel.( Be aware of parallax errors and ensure that the base of the meniscus lies on the 0 cm3 mark )
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Measure 25.0 cm3 of hydrochloric acid and pour it in the conical flask using a 25 cm3 pipette.
(N/b: flick the pipette slowly against the conical flask to release the last drop of base)
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Dissolve 2 Actal Tums tablets in the hydrochloric acid in the 250 cm3 conical flask.
- Stir manually or use the glass rod is necessary until all the antacid had dissolved.
- Remove the funnel from the mouth of the burette, and add 2-3 drops of Phenolphthalein indicator to the mixture in the conical flask.
- Place a white tile under the conical flask.
- Add sodium hydroxide, a little at a time to the conical flask with the dissolved mixture and the indicator, from the burette.
- Stop adding sodium hydroxide as soon as the conical flask mixture just changes colour from colourless to pink.
- Note down the final volume reading of the base in the burette.
- Record your results in the observation table.
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Repeat the experiment several times until two readings with a 0.1 cm3 difference are obtained for each antacid.
- Repeat procedures 3-13 for the other antacids, namely Eno powder( Use one sachet per trial) and Zolicid Gel( use two tea spoons per trial).
Nb: When washing the conical flask after each trial, wash in the sink, and then rinse with distilled water.
Data Collection:
Table 1: Showing the volumes of Sodium hydroxide base(0.5 M) needed to neutralize excess Hydrochloric acid(25 cm3, 0.5 M), after addition of 2 Actal Tums, for three trials.
Volume of HCl(aq) used per trial= 25cm3 ± 0.05 cm3
Table 2: Showing the volumes of Sodium hydroxide base(0.5 M) needed to neutralize excess Hydrochloric acid(25 cm3, 0.5 M), after addition of an Eno sachet, for three trials.
Volume of HCl(aq) used per trial= 25cm3 ± 0.05 cm3
Table 3: Showing the volumes of Sodium hydroxide base(0.5 M) needed to neutralize excess Hydrochloric acid(25 cm3, 0.5 M), after addition of Zolicid Gel(10cm3), for three trials.
Volume of HCl(aq) used per trial= 25cm3 ± 0.05 cm3
Other Observations:
Actal Tums Tablets:
- They slowly dissolved in the hydrochloric acid to form a cloudy white suspension.
- On addition of sodium hydroxide, there was a colour change from cloudy white to milky pink.
Eno Sachets:
- There was a vigorous reaction when the white Eno powder was dissolved in hydrochloric acid.
- Effervescence was observed as soon as the Eno powder made contact with the acid.
- After about 2 minutes, a transparent lime green solution was evident and fizzing ceased.
- On addition of sodium hydroxide, there was a colour change from transparent lime green to light brown.
Zolicid Gel:
- There was a moderate reaction between hydrochloric acid and Zolicid gel, and a cream suspension was formed.
- On addition of sodium hydroxide, the phenolphthalein indicator experienced a colour change from cream to pinkish white.
Data Processing:
Actal Tums Tablets:
Average volume of NaOH required to neutralize the remaining acid in the conical flask= = 1.25 cm3
Moles of HCl neutralized by the NaOH= =0.000625 moles
Initial number of moles of HCl in 25 cm3 == 0.0125 moles
Moles of HCl neutralized by the antacid=0.0125 moles-0.000625 moles=0.011875 moles
Eno Sachets
Average volume of NaOH required to neutralize the remaining acid in the conical flask= = 25.55 cm3
Moles of HCl neutralized by the NaOH= =0.010275 moles
Initial number of moles of HCl in 25 cm3 == 0.0125 moles
Moles of HCl neutralized by the antacid=0.0125 moles-0.010275 moles =0.002225 moles
Zolicid Gel:
Average volume of NaOH required to neutralize the remaining acid in the conical flask= = 23.60 cm3
Moles of HCl neutralized by the NaOH= =0.0118 moles
Initial number of moles of HCl in 25 cm3 == 0.0125 moles
Moles of HCl neutralized by the antacid=0.0125 moles-0.0118 moles =0.0007 moles
As seen from the calculations, Actal Tums neutralize the greatest number of moles of aqueous hydrochloric acid, that is to say 0.011875 moles. On the other hand, Eno sachets neutralized the second highest number moles of hydrochloric acid, that is to say 0.002225 moles. Finally, the Zolicid gel which was supposed to be a prescribed antacid, neutralized the least number of moles of hydrochloric acid, that is to say only 0.0007 moles.
We can hence see that the Actal Tums were the most effective antacid in relation to the other two since it neutralized many more moles of hydrochloric acid compared to the other antacids. The powdered Eno sachets were the best alternative, neutralizing just a few more moles of hydrochloric acid in relation to the Zolicid Gel. Lastly, Zolicid gel was the least effective antacid since it only neutralized 0.0007 moles of hydrochloric acid.
Using the obtained results obtained for the number of moles of hydrochloric acid neutralized by the maximum dosage of each antacid, we can calculate the relative effectiveness of the antacids in relation to the least effective antacid, that is to say Zolicid gel.
Relative effectiveness of an antacid=
Therefore Relative effectiveness of Actal Tums= =16.96 i.e. 17 (nearest whole number)
Relative effective of Eno powder= = 3.18 i.e. 3 ( nearest whole number)
We can therefore say that in accordance to our results, Actal Tums is approximately 17 times more effective than Zolicid gel and Eno powder is approximately 3 times more effective than the Zolicid gel.
Calculating Errors:
Errors for the first step of the experiment( adding the Hydrochloric acid to the conical flask)
Moles HCl= Volume in litres x concentration(this was as standardized solution with no errors)
The volume of 25cm3 to which the antacid is added also has an error. The pipette has an error label of ±0.06 cm3
Pipette error= 0.06/ 25 cm3 x 100= 0.24 %
Therefore initial moles of HCl= 0.0125 moles ± 0.24%
Errors in titrating the remaining NaOH with hydrochloric acid
For Actal Tums:
Moles of HCl remaining= moles of NaOH reacted
Moles of sodium hydroxide reacted= concentration * volume(L)
Concentration has no additional error but volume from the Burette has an error of ± 0.05cm3
Error in 1.25 cm3= 0.05/1.25 X 100 =4%
Moles of sodium hydroxide( also Moles of HCl)= 0.5M * 0.00125(±4%)
Moles of sodium hydroxide=0.000625 moles ±4%
Initial moles of HCl= 0.0125 moles (± 0.24%)
Moles of HCl that reacted with 1.25cm3 NaOH=0.000625 moles( ±4%)
Moles of HCl that react with the antacid = 0.0125 moles (± 0.24%)-0.000625 moles( ±4%)
=0.011875 moles ±4.24%
For Eno sachets:
Moles of HCl remaining= moles of NaOH reacted
Moles of sodium hydroxide reacted= concentration * volume(L)
Concentration has no additional error but volume from the Burette has an error of ± 0.05cm3
Error in 20.55 cm3= 0.05/20.55 X 100 =0.24%
Moles of sodium hydroxide( also Moles of HCl)= 0.5M * 0.02055(±0.24%)
Moles of sodium hydroxide=0.010275 moles ± 0.24%
Initial moles of HCl= 0.0125 moles (± 0.24%)
Moles of HCl that reacted with 20.55cm3 NaOH=0.010275 moles ± 0.24%
Moles of HCl that react with the antacid = 0.0125 moles (± 0.24%)-0.010275 moles (± 0.24%)
=0.002225 moles ± 0.48%
For Zolicid gel:
Moles of HCl remaining= moles of NaOH reacted
Moles of sodium hydroxide reacted= concentration * volume(L)
Concentration has no additional error but volume from the Burette has an error of ± 0.05cm3
Error in 23.60 cm3= 0.05/23.60 X 100 =0.21%
Moles of sodium hydroxide( also Moles of HCl)= 0.5M * 0.0236(±0.21%)
Moles of sodium hydroxide=0.0118 moles ±0.21%
Initial moles of HCl= 0.0125 moles (± 0.24%)
Moles of HCl that reacted with 1.25cm3 NaOH=0.0118 moles ( ±0.21%)
Moles of HCl that react with the antacid = 0.0125 moles (± 0.24%)-0.0118 moles ( ±0.21%)
=0.0007 moles ±0.45%
Conclusion and Evaluation:
In my hypothesis, I had predicted that Zolicid gel would neutralize the greatest number of moles of hydrochloric acid followed by Actal Tums and then finally Eno sachets.
However after carrying out the back titration and calculating the results, it was observed that unlike my predictions, Actal Tums neutralized the greatest number of moles of hydrochloric acid(0.011875 moles ±4.24%). Also, Eno sachets neutralized the second greatest number of moles(0.002225 moles ± 0.48%), followed by Zolicid gel which ironically neutralised the least number of moles of hydrochloric acid (0.0007 moles ±0.45%).
I would therefore like to reject my hypothesis because as clearly seen from the results, the Actal Tums were almost 16 times more effective than the Zolicid gel, and the Eno tablets were about 3 times more effective in terms of the number of moles of hydrochloric acid neutralised, in comparison to the Zolicid Gel. Zolicid gel instead of being the most effective antacid, was in fact the least effective of the three antacids. This was contrary to my hypothesis and hence I completely reject my hypothesis which stated that Zolicid Gel would be the most effective neutralising agent of hydrochloric acid, followed by Actal Tums and Eno sachets respectively.
On the other hand, I would like to conclude that Actal Tums was by far the most effective antacid is neutralizing excess hydrochloric acid, as it neutralized almost 16 times more moles in relation to Zolicid gel and about 5 times more moles of hydrochloric acid in relation to Eno sachets. The purpose of this lab practical was to establish between a set of three antacids, which is more effective in relation to the number of moles of hydrochloric acid neutralized by each respective antacid. Hence I would recommend the use of Actal Tums in reducing excess acidity in the stomach. ( with the recommendation of Eno as a second option)
Errors:
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There may have been errors in correctly knowing the end-point of the reaction. The addition of sodium hydroxide to the hydrochloric acid may have been stopped just before the end-point of the neutralisation reaction. The colourless phenolphthalein may have not yet have turned pink colour and may have just formed a few streaks of pink. In this case the volume of sodium hydroxide would be less than the correct volume used to neutralise the hydrochloric acid. However if the addition of base is stopped before the end-point in the titration, then the moles of hydrochloric acid would be understated. The moles of hydrochloric acid would therefore also be lower then their correct value. Since the reacted moles of hydrochloric acid ( the ones that had reacted with the antacid) are found by subtracting the understated remaining moles of hydrochloric acid from the initial moles, the moles of hydrochloric acid reacted with the antacid would also be understated. This could have lead to an inconsistency and inaccuracy in the results.
- On the contrary, if the addition of sodium hydroxide has been stopped slightly after the end point of the equivalence point( the point of neutralisation) the moles of hydrochloric acid would have been overstated. This would occur if the phenolphthalein indicator had already experienced a colour change, and yet the addition of drops of sodium hydroxide base still continued. This could have been a large source of error especially for the Eno powder and the Zolicid gel. The Eno powder formed a transparent green solution when it was initially added to the acid. Addition of base was stopped when the solution just turned brown. However it was hard to know the exact point whereby one could define the solution as being brown. On the other hand Zolicid gel which formed a thick cream solution also may have experienced this problem , as it was hard to know when exactly the solution had become pinkish white.
- There may have been parallax errors in reading off the volume readings from the burette. These errors occur when the line of sight is not perpendicular to the readings being taken. These errors may have varied from trial to trial, and were not fixed. This inconsistency and inaccuracy may have affected the average volumes calculated and hence bringing inaccuracies in the moles of hydrochloric acid neutralised by each antacid.
- The funnel was present in the burette during titration of some trials. This may have led to a gradual increase in the volume of the burette. The Initial value noted would therefore be less than the correct initial volume. This would lead to a smaller number of remaining moles of hydrochloric acid. Therefore the reacted moles would be overstated to inaccuracies in the results.
- Although the titration clearly helped in showing us that one antacid was more effective than the other by seeing the number of moles of hydrochloric acid neutralised, this may not give a proper justification as to the performance of each antacid. The stomach is a much more complex organ whereby there are lots of specialised cells performing specific functions. In addition, there is presence of enzymes too. The temperature of the stomach is also greater than the room temperature in which this laboratory practical was carried out. All these factors, with the addition of mechanical digestion, can increase the effectiveness of one antacid over the other. So even though we can generally conclude that one antacid is better than the other, this may not necessarily be the case when we take all other variables in consideration.
- The antacids all tended to have different chemical compositions. In addition to the individual flavourings, each tablet/ gel must be composed of other different compounds. The solubility of these compounds may be different as well as the time taken for the antacid compounds to become active. So just carrying out a quick 5 minute titration may not really represent a thorough model of how the antacid really prevents stomach acidity in the stomach, and the time needed for it to take complete effect. In this respect some of the antacids have acted completely where as other may be in need of other stimuli to complete their full action.
- Phenolphthalein indicator is a weak acid and hence the number of moles initial number of moles would have been overstated. As a result of this, more sodium hydroxide would be needed to neutralise the remaining moles of acid. The number of remaining moles would be overstated, hence the calculated number of moles neutralised by the antacid would be understated. This problem could be avoided using a digital ph meter.
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The error on the volume of the Actal Tums was quite high( 4%). This could have affected the outcome of the results. Even though the Actal Tums considering its great performance may have still been the best antacid, the relative effectiveness figure could have been affected by this error. The errors were notably different, that is to say ±4.24%,± 0.48% and ±0.45%.
Improvements
- In order to correctly know the end-point of the reaction, a digital Ph meter can be used to ensure that the clip of the burette is closed, exactly when the solution in the conical flask is neutral. Similarly, a colourimeter can also be used to accurately follow the colour changes of the indicator and to accurately stop the titration at the neutral point. The addition of hydrochloric acid is stopped when the phenolphthalein indicator just turns from colourless to pink( exactly at the point of equivalence).
- Perhaps to better find out the effectiveness of the given antacids one could try to bring in to account other factors such as temperature, presence of acidic enzymes. The solid tablets could also perhaps be grinded as this would enable the antacid to be extracted relatively faster as compared to the solid form.
- The time intervals should also be taken into consideration. Perhaps the trials could also be carried out for different time periods e.g. leaving the antacids for 5 min, 10 min, 15 min before titration. This would help to show whether time really affects the results we have obtained. By doing these experiments, we would also be able to establish which antacid could provide quickest relief.
- Always ensure that your line of sight is perpendicular to the readings of volumes, you wish to take. This will ensure that your readings and calculated percentages are accurate.
- Remove the funnel from the burette as soon as the acid had been added. This will prevent any in accuracy in the volume of acid needed for titration.
References:
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in finding the weak acidic nature of phenolphthalein.
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Diagram of pipette-core.ecu.edu/chem/chemlab/equipment/epipette.htm
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Diagram of titration-www.rjclarkson.demon.co.uk/middle/salts.htm