Antacid Tables. How effective is that antacid tablet? We are going to use a technique called titration to find out how effective the tabs are.

Transcription

1 Antacid Tables How effective is that antacid tablet? We are going to use a technique called titration to find out how effective the tabs are. There are 4 stations. Each station has one type of antacid. You will divide yourselves in to 4 groups and each group will do the titration

2 Set up Each group will record their observations. You need to get a complete set of data from all 4 stations for your practical.

3 Record you results on a table Brand Volume HCL Used (ml) Volume NaOH used (ml) Vl of HCL Absorbed (ml)

4 Titration An operation, used in volumetric analysis, in which a measured amount of one solution is added to a known quantity of another solution until the reaction between the two is complete. If the concentration of one solution is known, that of the other can be calculated

5 Step 1 Add exactly 50 ml of HCL (stomach acid) to a flask Crush 4 tabs of antacid and add them to the solution of HCL in the flask Swirl the flask and completely dissolve the tabs in the solution

6 Step 3 Titration set-up One Buret has HCL Read off the top of the Buret how much is in it in ml. Turn the tap and drain off 50ml

7 Step 1: The reactions Compound Chemical Formula Chemical Reaction Aluminium hydroxide Al(OH)3 Al(OH)3(s) + 3 HCl(aq) -----> AlCl3(aq) + 3 H2O(l) Calcium carbonate CaCO3 CaCO3(s) + 2 HCL(aq) -----> CaCl2(aq) + H2O(l) + CO2(g) Magnesium carbonate MgCO3 MgCO3(s) + 2 HCl(aq) -----> MgCl2(aq) + H2O(l) + CO2(g) Magnesium hydroxide Mg(OH)2 Mg(OH)2(s) + 2 HCl(aq) -----> MgCl2(aq) + 2 H2O(l) Sodium bicarbonate NaHCO3 NaHCO3(aq) + HCL(aq) -----> NaCl(aq) + H2O(l) + CO2(g) Calcium Carbonate is the most common compound you will find in antacid tabs

8 Step 2 Add 5 drops of phenolphthalein to the flask. This is an indicator that will turn pink in the presence of a base

9 Titration You are going to add NaOH solution to the HCL in the flask. NaOH is a base. You are going to react a base with an acid. NaOH + HCl NaCl + H2O? Once all the HCL has been reacted with the NaOH the mixture will turn pink. Video 1 Video 2

10 Step 3 Titration set-up The other Buret has NaOH. Record from the top of the buret how much is in the Buret. Open the tap and drain off the NaOH. Swirl the flask around and mix the reactants. After a while the mix will turn pink as you saw in the video. If you stop filling and it starts to turn milky add a little more NaOH until it stays a nice light pink. Read off from the bottom of the buret And calculate how much you have used.

11 Summary So we mixed up about 50 ml of HCL with some crushed up antacid. We did this to simulate what happens when you take an antacid to neutralise stomach acid. The question is, how effective is the ant acid?

12 Quick-eze Lets consider the reaction with good old quick-eze. One tab contains the following Calcium Carbonate 780mg Magnesium Carbonate 130mg Sodium Trisilicate 130mg The major chemical is Calcium Carbonate Calcium carbonate - CaCO3(s) + 2 HCL(aq) -----> CaCl2(aq) + H2O(l) + CO2(g) The other chemicals are used to deal with side effects like constipation and diarrhea

13 Conservation of mass We had 50ml of HCL. We mixed an amount of antacid tab. The antacid tab reacted with the HCL and the product of this reaction was water and carbon dioxide gas. Was all the HCL changed in to water and CO2? If there was HCL left over. If we know how much is left over we can calculate how much was absorbed!

14 Restate the problem Effectiveness of antacid HCL + Tab Tab reacts with HCL Some HCL is left over We know how much HCL we started out with HCL start HCL let over = How much absorbed 50ml 10ml = 40ml absorbed To do this we need to find out much HCL is left

15 Conservation of Mass You cannot get more out of the reaction that you put in. Only so many CaCO3 molecules were available to react with HCL. If there are less molecules of CaCO3 than HCL you get HCL molecules left over. Simple. So how much is left over?

16 The first reaction (Calcium carbonate) CaCO3(s) + 2 HCL(aq) -----> CaCl2(aq) + CO2(g) + H2O(l) Left over HCL HCL + 50ml of Co2 Quick eze HCL H20 CaCl2 Reactants Products Q How much HCL is left?

17 Second reaction The Titration 0 ml NaOH Pour in an amount of NaOH base to React with the HCL -10 ml The remaining HCL reacts with the NaOH and the products water and salt. The chemicals in the flask turn light pink. When this happens we know that all the HCL has been used HCL Co2 H2O CaCl2 NaOH HCL Co2 H20 CaCl2 H20 & NaCL Co2 H2O CaCl2

18 Summary Lets say we measured out 10ml of NaOH to turn the remaining HCL to water and salt. So there must have been 10ml of HCL left in the flask that had not been converted by the antacid! We started with say 50ml. There was 10ml left over The tab reacted 40ml of HCL acid Boom Boom!!

19 Almost There! Basic Acidic When the flask turned pink we had just enough NaOH to mix with the remaining HCL At that point the PH was neither acid or base but almost neutral. If you put in to much NaOH the flask turned a deep pink! You had more base than acid.

20 Conclusion We looked at three different antacid tabs. The entire point of the experiment was to compare how much HCL the antacid tabs neutralised. To find that out we used the titration reaction and added NaOH to find out how much HCL was left Once we know that we can calculate how much was absorbed by the Tabs

21 Conclusion We mix say 50ml of HCL with a Tab We used Titration to find out how much HCL was left over We subtract the amount of HCL we started with from how much HCL was left over We know how much HCL was absorbed We compare the results for each group and see if the different Tab absorbed different amounts of HCL This tells us how effective each Tab type was

22 Simulated Results Brand Volume HCL Used (ml) Volume NaOH used (ml) Quick eze Milanta Tums Gaviscon Vl of HCL Absorbed (ml) If you don't have a complete set of results, use these