1. To determine the neutralizing ability of antacids in different brands. 2. To compare the effectiveness of commercial antacids and their side effects. Reasons for Choice of Topic In nowadays, many HK people are suffering from upset stomach due to heavy workload, nervous tension due to the stress of daily life and poor eating habit, which is eating too much high-fat foods too quickly. They usually use antacid therapy to relieve the symptoms. From our previous knowledge, we know that antacids contain weak bases to neutralize the excess antacid in the stomach.

We Will Write A Custom Essay Sample On
ANY TOPIC SPECIFICALLY
FOR YOU

For Only $13.90/page


order now

Every day we are bombarded by commercials dealing with acid indigestion. Each in turn declares they neutralize more acid and provide strongest relief and are fastest acting. Hence, we are interested in which brand of antacid is the most effective medicine and its side effects. Introduction Stomach contents are highly acidic due to the action of cells in the stomach walls that secrete hydrochloric acid. The acid environment suppresses growth of bacteria and aids in the digestion process. The acid hydrolyzes proteins and helps to activate the enzyme pepsin, which further breaks down food proteins.

The primary component of gastric juice is hydrochloric acid and the pH is very close to 1. This is the pH of a 0. 1 M HCl solution. Under normal conditions, the inner lining of the stomach is not damaged by the hydrochloric acid because this lining, the mucosa, is being replaced at a very rapid rate. The stomach often responds to overeating or under stress with a greatly increased secretion of acid. This excess acid can lower the pH, which is normally in the range from 0. 9 to 1. 5, to the point where discomfort (acid indigestion) is experienced.

Upset stomach, indigestion, and gastroesophageal reflux disease (GERD) may occur when the excess acid travels to more delicate tissues, causing a burning, painful sensation which is so-called heartburn. Apart from short-term discomfort and in the long term, gastric and duodenal ulcers may occur as the excess acid denatures proteins composing the stomach wall. An antacid is taken to neutralize this excess acid. Antacids are over-the-counter medications which are used to decrease the concentration of hydrochloric acid in the stomach. They are available in solid or liquid form and many formulations.

Antacids can contain any one or a combination of the following active ingredients: aluminum hydroxide Al(OH)3, calcium carbonate (commonly known as chalk) CaCO3, magnesium hydroxide Mg(OH) 2 and sodium bicarbonate (commonly known as baking soda)NaHCO3. Antacid tablets neutralize the HCl in the stomach according to one of the following reactions, depending on the active ingredient. Acid + Base –> Salt + Water NaHCO3 + HCl –>NaCl + H2O + CO2 Al(OH) 3 + 3HCl –>AlCl3 + 3H2O Mg(OH) 2 + 2HCl–> MgCl2 + 2H2O Theory The chemical reaction of antacids: Antacids react with excess stomach acid by neutralization.

It is a chemical reaction, (also called a water forming reaction since a water molecule is formed during the process) in which an acid and a base or alkali (soluble base) react to produce salt and water (H2O). i. e. HCl + NaOH –>? H2O + NaCl During the process, hydrogen ions H+ (a bare proton) from the acid (proton donor) or a hydronium ion H3O+ and hydroxide ions OH- or oxide ions O2- from the base (proton acceptor) react together to form a water molecule H2O. In the process, a salt is also formed when the anion from acid and the cation from base react together.

Neutralization reactions are generally classified as exothermic since heat is released into the surroundings. Acids are proton donors which convert into conjugated bases. They are generally pure substances which contain hydrogen ions (H+) or cause them to be produced in solutions. Hydrochloric acid (HCl) and sulfuric acid (H2SO4) are common examples. In water, these break apart into ions: HCl i?? H+(aq) + Cl-(aq) OR H2SO4 i?? H+(aq) + HSO4-(aq) Bases are proton acceptors which convert into conjugated acids. They are generally substances which contain hydroxide ion (OH-) or produce it in solution.

Alkalis are the soluble bases, i. e. a base which contains a metal from column 1 or 2 of the periodic table. To produce hydroxide ions in water, the alkali breaks apart into ions as below: NaOH i?? Na+(aq) + OH-(aq) Examples of bases include sodium hydroxide (NaOH), potassium hydroxide (KOH), magnesium hydroxide (Mg(OH)2), and calcium hydroxide (Ca(OH)2). In this project, antacids are bases. Explanation of action of neutralization of antacids : The Lewis definition of acid-base reactions is a donation mechanism, which conversely attributes the donation of electron pairs from bases and the acceptance by acids.

Ag+ + 2 :NH3 i?? [H3N:Ag:NH3]+ (A silver cation reacts as an acid with ammonia which acts as an electron-pair donor, forming an ammonia-silver adduct) In reactions between Lewis acids and bases, there is the formation of an adduct when the highest occupied molecular orbital (HOMO) of a molecule, such as NH3 with available lone electron pair(s) donates lone pairs of electrons to the electron-deficient molecule’s lowest unoccupied molecular orbital (LUMO)through a co-ordinate covalent bond; in such a reaction, the HOMO-interacting molecule acts as a base, and the LUMO-interacting molecule acts as an acid.

In highly-polar molecules, such as boron trifluoride (BF3), the most electronegative element pulls electrons towards its own orbitals, providing a more positive charge on the less-electronegative element and a difference in its electronic structure due to the axial or equatorial orbiting positions of its electrons, causing repulsive effects from lone pair-bonding pair (Lp-Bp) interactions between bonded atoms in excess of those already provided by bonding pair-bonding pair (Bp-Bp) interactions. Determination of concentrations of substances in neutralization: The experimental method about neutralization is the acid-base titration.

An acid-base titration is a method in chemistry that allows quantitative analysis of the concentration of an unknown acid or base solution. It makes use of the neutralization reaction that occurs between acids and bases, and that we know how acids and bases will react if we know their formula. Before starting the titration a suitable pH indicator must be chosen. In this project, phenothelain is chosen. The endpoint of the reaction, the point at which all the reactants have reacted, will have a pH dependent on the relative strengths of the acid and base used. The pH of the endpoint can be estimated using the following rules:

A strong acid will react with a strong base to form a neutral (pH=7) solution. * A strong acid will react with a weak base to form an acidic (pH<7) solution. * A weak acid will react with a strong base to form a basic (pH>7) solution. Phenophthalein is used to determine the end point of the titration which indicates complete neutralization. In the presence of, an acid solution is colourless, a basic solution is very dark pink, and a neutral solution is very pale pink. At this point the solution is very slightly basic, with a negligible amount of excess NaOH.

By keeping track of exactly how much NaOH is needed to complete the neutralization process, the amount of HCl originally neutralized by the antacid can be calculated. The difference between the number of moles of HCl initially added to the antacid and the number of moles of HCl neutralized by the NaOH during the titration is the number of moles neutralized by the antacid. Several antacids will be tested and the relative strengths of each will be compared. Nature of phenolphthalein: Phenolphthalein is a chemical compound with the formula C20H14O4.

It is insoluble in water, and is usually dissolved in alcohols for use in experiments. It is itself a weak acid, which can lose H+ ions in solution. The phenolphthalein molecule is colorless. However, the phenolphthalein ion is pink. When a base is added to the phenolphthalein, the molecule ? ions equilibrium shifts to the right, leading to more ionization as H+ ions are removed. This is predicted by Le Chatelier’s principle. Hypothesis Our hypothesis is the greater proportion of the active ingredient with stronger base in an antacid tablet will have the greater neutralizing power.

And thus, it will be more effective to cure upset stomach. Information of three types of antacid tablets 1. WEISEN-U Composition OUTER LAYER (yellowish green) INNER CORE (white to yellowish white) Biodiastase 2000… 25mg Methylmethionine Sulfonium Chloride… 25mg Dried Aluminum Hydroxide Gel… 192mg Magnesium Hydroxide… 159mg Double layer structure isolates the ingredients and let them exert their effects individually Each WEISEN-U tablet consists of 2 tablets, an outer yellowish green tablet containing antacids and an enclosed inner core tablet containing Methylmethionine Sulfonium Chloride.

Outer layer (Dried Aluminum Hydroxide Gel) will neutralize the excessive acid and give instant relief. Inner layer (methylemethionine Sulfonium Chloride )dissolves, releasing the anti-ulcer agent which calms the vagus nerve, and so prevents more acid from being produced. This restores the damaged gastric mucosa and provides lasting effect. Dosage The usual adult dose is one tablet to be taken three times a day after meals. To prevent a relapse, treatment should be continued 2 to 3 weeks after the symptoms have disappeared. Caution Store in a cool and dry place.

Protected from light and moisture. Packing WEISEN-U Dual-Action tablets are packed in bottles of 30. Diseases treated Gastric ulcer, duodenal ulcer, pain of gastric ulcer, pain of duodenal ulcer, hyperacidity, stomach pain, indigestion, anorexia, heartburn, heaviness in the chest. 2. ACTAL Composition Na polyhydroxyaluminium monocarbonate hexitol complex (equiv to Al(OH)3 216 mg) Dosage Allow two tablets to dissolve on the tongue as required, up to 8 times daily. Do not exceed 16 tablets in 24 hours. Administration Should be taken on an empty stomach (Take 1/2-1 hr after meals. ). Caution.

Actal can cause constipation when taken in large amounts. Actal can interfere with the special coating of some tablets and affect the absorption of some medicines such as tetracycline, rifampicin, warfarin, iron or digoxin Not suitable for children under 12 years of age. Store below 25 Celsius in a dry place. Adverse Drug Reactions Constipation (prolonged use). Interactions May impair absorption of tetracyclines. Packing 360mg x 20’s Effectieness Provides rapid relief from indigestion, or dysepsia due to over acidity. 3. Unknown Composition Aluminium/ magnesium hydroxide simethicone.

 

6. The dissolved antacid was cooled to room temperature (25? ) by immersing it in tap water 7. The dissolved antacid was transferred to a 250ml volumetric flask. 8. The flask was filled to the mark with water. 9. The flask was capped and inverted several times to mix well. 10. A pipette was used to transfer 25ml of dilute HCl solution to the conical flask that HCl was in excess. 11. The dissolved antacid was added to the conical flask 12. The flask was swirled until the liquid became slightly cloudy. 13. A burette was cleaned, rinsed and filled with NaOH solution 14.

A small amount of NaOH solution was released to leave the tip entirely filled. 15. The initial NaOH volume reading was recorded from the burette. 16. A white tile was placed under the flask. 17. 3-4 drops of phenothalein was added to the flask 18. NaOH solution was added from the burette with continuous swirling until the colour of the liquid changed from colourless to pale pink. 19. The final NaOH volume reading was recorded from the burette. 20. The experiment was recorded by using antacids in different brands. Precaution 1. Avoid touching the antacid with your fingers.

2. Be careful not to lose any solid when crushing the antacid tablet. 3. Avoid touching hot surfaces when working near the hot plate and be cautious when transporting heated solutions. 4. The hot plate should not be left unattended 5. Dilute HCl and NaOH were corrosive and can damage your eyes and cause skin irritation. Use eye protection at all times and immediately wash spills from your skin and clothing. 6. The burette must be rinsed out with NaOH before use to prevent dilution of the solution. 7. It should be made sure that there were no air bubbles in the burette tips.

8. Burette readings should be recorded to the nearest 0. 05 cm3. 9. Sodium hydroxide should be removed from the burette as soon as possible after the titration. It was because NaOH is corrosive and it reacted with carbon dioxide in the air to form sodium carbonate which was a white solid and clogged the tip of the burette easily. Clean Up: 1. Upon completion of the experiment, all chemicals can be safely disposed of in the sinks. 2. Glassware should be washed. 3. The burettes should be inverted and mounted in the burette clamp with the stopcock open allowing them to drain.

Observation Upon heating, the powders dissolved quickly and easily with a small amount of stirring. The solution’s color would change to reflect the color of the tablet inserted. The Weisen U Brand tablets had the greatest difficulty dissolving, doing so at a slow pace. –> –> –>–>–> Calculations: Brand name of antacid used: ACTAL Active ingredient: aluminium hydroxide Al(OH)3 (s) Mass of a tablet: 0. 69g Mass of antacid used: 0. 61 g Volume of HCl added: 25ml Molarity of HCl: 0. 1M No. of moles of HCl added to antacid: 0. 0025 mol Results Table: Burette solution NaOH

Indicator Phenolphthalein Trial 1 2 3 Burette readings Initial 0 0 14 Final 19. 5 19. 5 33 Volume used (titre)/ cm3 19. 5 19. 5 19 Mean titre / cm3 19. 3 No. of moles of NaOH required to neutralize excess HCl: No. of moles of NaOH = Molarity i?? volume = 0. 1 i?? (19. 3 / 1000 ) = 0. 00193 mol HCl(aq +NaOH(aq –> NaCl(aq) + H2O (l) No. of moles of HCl neutralized by NaOH : 0. 00193 mol No. of moles of HCl neutralized by the 25ml antacid solution: 0. 0025 – 0. 00193 = 0. 00057 mol No. of moles of HCl neutralized by the 250ml antacid solution: 0. 00057 i?? 10 = 0. 0057 mol.

No. of moles of HCl per gram antacid: 0. 0057 i?? 0. 61 = 0. 00934 mol g-1 No. of moles of HCl neutralized by 1 tablet: 0. 69g i?? 0. 00934 mol g-1 = 0. 00645 mol Vol of HCl neutralized by 1 tablet = 0. 00645/0. 1= 0. 0645dm3 = 64. 5cm3 Vol/ mass = 64. 5/0. 61= 106cm3/g 3HCl (aq) + Al(OH)3 (s) –> AlCl3 (aq) +3 H2O (l) No. of moles of Al(OH)3: 0. 00645 i?? 3 = 0. 00215 mol Molar mass of Al(OH) 3 : 27 + 3 i?? (16+1) = 78 gmol -1 (According to the manufacturer, each tablet contains 216 mg of aluminium hydroxide) percentage yield: 0. 00215 i?? 78 i?? 1000 i?? 100% 216 =77. 6 %.

Brand name of antacid used: Weisen U Active ingredient: aluminium hydroxide Al(OH)3 (s) 192mg magnesium hydroxide Mg(OH)2 (s) 159mg Mass of a tablet: 0. 59 g Mass of antacid used: 0. 50 g Volume of HCl added: 25ml Molarity of HCl: 0. 1M No. of moles of HCl added to antacid: 0. 0025 mol Results Table: Burette solution NaOH Indicator phenolphthalein Trial 1 2 3 Burette readings Initial 0 20. 5 25. 9 Final 20. 5 41. 7 46. 8 Volume used (titre)/ cm3 20. 5 21. 2 20. 9 Mean titre / cm3

20. 9 No. of moles of NaOH required to neutralize excess HCl: No. of moles of NaOH = Molarity i?? volume = 0. 1 i?? (20. 9 / 1000 ) = 0. 00209 mol HCl(aq +NaOH(aq –> NaCl(aq) + H2O (l) No. of moles of HCl neutralized by NaOH : 0. 00209 mol No. of moles of HCl neutralized by the 25ml antacid solution: 0. 0025 – 0. 00209 = 0. 00041 mol No. of moles of HCl neutralized by the 250ml antacid solution: 0. 00041 i?? 10 = 0. 0041 mol No. of moles of HCl per gram antacid: 0. 0041 i?? 0. 50 = 0. 00820 mol g-1 No. of moles of HCl neutralized by 1 tablet: 0. 59g i?? 0. 00820 mol g-1 = 0.

 

Burette readings Initial 0. 4 19. 0 17. 2 Final 19. 0 39. 0 38. 1 Volume used (titre)/ cm3 18. 6 20. 0 20. 9 Mean titre / cm3 20. 5 No. of moles of NaOH required to neutralize excess HCl: No. of moles of NaOH = Molarity i?? volume = 0. 1 i?? (20. 5 / 1000 ) = 0. 00205 mol HCl(aq +NaOH(aq –> NaCl(aq) + H2O (l) No. of moles of HCl neutralized by NaOH : 0. 00205 mol No. of moles of HCl neutralized by the 25ml antacid solution: 0. 0025 – 0. 00205 = 0. 00045 mol No. of moles of HCl neutralized by the 250ml antacid solution: 0. 00045 i?? 10 = 0. 0045 mol No. of moles of HCl per gram antacid: 0. 0045 i?? 0.

65 = 0. 00692 mol g-1 No. of moles of HCl neutralized by 1 tablet: 0. 71g i?? 0. 00692 mol g-1 = 0. 00491 mol Vol of HCl neutralized by 1 tablet = 0. 00491/0. 1= 0. 0491dm3 = 49. 1cm3 Vol/ mass = 49. 1/0. 71= 69. 2 cm3/g Results: Brand name Vol. of HCl neutralized/ mass (cm3/g) Effectiveness (1: highest; 3: lowest) ACTAL 106cm3/g 1 Weisen U 82. 0cm3/g 2 Unknown 69. 2 cm3/g 3 Results The most effective antacid brand was ACTAL and the least effective antacid brand was the unknown antacid. . Discussion Sources of error 1. Some ingredients in the anti-acid may affect the pH value of the mixture and the result.

2. Loss of active ingredient during transferring. 3. The meniscus didn’t sit at the graduated mark of the burette or pipette. 4. The coatings of anti-acid may not dissolve in acid or dissolve slowly. 5. The other ingredients may affect the solubility of the bases inside the anti-acid 6. The reaction may not be complete. 7. Error in taking burette reading (0. 05 cm3). 8. The end point may not equal to the equivalence point. 9. The antacid was coloured and the solution was cloudy and it was difficult to observe the colour change and hence the end point may be overshoot. 10.

During the heating process, some of the liquid may evaporate. Improvements 1. Sufficient time should be given for the reaction of acid and base. 2. pH metre should be used to detect the end point. 1. Why do we use back titration instead of acid/base titration? Acid/ base titration is very difficult because the active ingredient is only sparingly soluble in water. Comparison between H2 blockers and antacid: Histamine-2 receptor antagonists/ H2 blockers Antacids Lowers the stomach acid production Neutralizes acid in the stomach raising the pH level to between 3 and 4 Provides longer-lasting relief.

Provides relief more quickly Do not neutralize any stomach acid already present in the stomach. Less expensive Takes H2 blockers if one suffers from heartburn two or more times per week Takes antacid if one suffers from heartburn Antacids and H2 blockers should not be taken within 2 hours of each another, because the antacid will slow down the effect of the acid reducers. 2. What is the side effect of taking in too much antacid? Generally, this may result acid rebound where the stomach begins to over secrete acid in order to make up for the quantity that is being neutralized.

Overdose of antacid containing aluminium hydroxide will weaken bones by depleting the body of phosphorus and calcium. Taking in too much magnesium hydroxide will initiate serious muscle cramping and lead to diarrhea or constipation. If too much sodium bicarbonate is absorbed by the intestinal tract, blood pH will be changed and this may cause alkalosis in high doses Alkalosis is characterized by headaches, stomach pain, nausea, and vomiting. Also, fatal metabolic imbalance may occur, taking too much calcium carbonate will weaken bones and initiate serious muscle cramping. 3. Do milk and cheese provide the same effect as antacid?

One of the oldest remedies for heartburn was drinking milk or eating cheese. While this provided an almost immediate relief, possibly due to coating of the stomach lining, the relief was an illusion. Milk and cheese are high protein foods. Protein is digested by protease enzymes. The enzyme pepsin, which requires a highly acidic environment, begins this digestion in the stomach. The stomach dutifully pumps out vast quantities of acid to help in this digestion. While milk or cheese might provide a temporary buffering effect, the stomach immediately pumps out excess acid, thereby reigniting the heartburn.

4. Comparison between different active ingredients: Active ingredients Aluminium hydroxide Magnesium hydroxide Magnesium hydroxide & aluminium hydrocide Sodium bicarbonate Calcium carbonate Advantages provides long- lasting relief Long-acting quick, long-lasting relief less risk of constipation well absorbed most readily available and neutralizes acids quickly fast and neutralizes acids for a relatively long time help boost calcium intake Disadvantages Insoluble and less readily absorbed dissolves slowly in the stomach cause constipation Insoluble and less readily absorbed.

Pproduce CO2 gas in the stomach loses its effectiveness quickly produce CO2 gas in the stomach has an unpleasant taste. 5. What are the uses of the other ingredients in antacid? Extra ingredients include flavors, a sweetener (artificial or natural), usually a dye (for color), a fragrance, and a binder. The flavors, sweetener and fragrance are designed to make the antacid more palatable. Binders are clay- like minerals and are used to bind the ingredients into a solid tablet that is sturdy enough to survive handling. They absorb water and prevent the antacid from degrading.

6. Which one is more effective in treating upset stomach, liquid antacid or tablet antacid? Liquid antacids may relieve symptoms faster than antacid tablets and therefore are more effective than antacid tablets 7. If the antacid tablet did not dissolve completely in the 0. 1 M HCl solution, how can you explain this? Because antacid usually contains fillers and other inert ingredients that cannot dissolve in water. For example, sweetener, like inulin is a food additive added the basic taste of sweetness to an antacid but it may not be completely soluble in water.

Also, antifoaming agents added to antacids are intended to curb effusion or effervescence in preparation or serving but may not be soluble in water, too. 8. Do the different fillers used to lengthen the tablet shelf-life, provide flavor and hold the tablet together make any difference on the ability of the antacid to neutralize stomach acid? No. Because the neutralizing ability of the antacid only depends on its active ingredients. 9. What is the danger of taking in antacid with milk? Since milk contains lactic acid (2-hydroxypropanoic acid), it may neutralize the base in the antacid to form salt with lactate ion (CH3CH(OH)COO-).

As a result, there may be loss of active ingredient on antacid and it will reduce the effectiveness of the medicine. 10. Why is solid weak acid added to the antacids? It is used to prevent the acid rebound effect in the stomach. When too much stomach acid is neutralized, the acid-secreting cells of the stomach may produce more acid that makes indigestion become more serious. To avoid this danger, solid weak acid, like citric acid is added to the antacid to compensate the loss of stomach acid and restore the concentration of stomach acid back to the normal level.

11. Which one of the antacid that you tested appeared to be the most effective? ACTAL is the most effective among other antacids. 12. The neutralizing strength is not the only factor for determining which antacid provides the most relief for acid indigestion. What other factors should be considered? Other factors, like recommended dosage, inert ingredients and ways to take in tablets orally may affect the effectiveness of the antacid. For dosage, number of time to take in antacids daily and the taking time should be considered.

For example, some antacids require to be taken before meal as food digestion may affect the absorption of the drugs and lower the effectiveness. On the other hand, some antacids should be served one hour after meal in order to prolong the drug’s effectiveness. Therefore, the taking time depends on the nature of the antacid. And for inert ingredients, some people may have allergy to them. Lastly for ways to take in tablets, whether the tablet should be chewed well before swallowing since fragments have a larger surface area that leads to the increase of reaction rate between the base of the antacid and the stomach acid.

As a result, effectiveness can be enhanced. 13. Who should take antacids? The adverse drug reactions associated with NSAIDs, aspirin and bisphosphonates are gastrointestinal ulcer and stomach bleeding, especially in higher doses. Therefore, patients, particularly, the elderly should also take antacid therapy to relieve GI upset and to strengthen the gastric mucosa. In general, stomachache, nausea, etc, gastrointestinal adverse drug reactions are simply temporary side effects of drugs and will not pose any risk of gastrointestinal ulcer or stomach bleeding.

Hence, there is no need to take antacids in these cases. Take antibiotic as an example, the symptoms of gastrointestinal upset will probably disappear after seven-day medication. Some medicines, like Digoxin which treat cardiovascular diseases, pills which enrich blood and tetracycline which treats inflammation caused by bacteria, the decomposition or absorption will be affected and the effectiveness of drugs will be greatly reduced if antacids are taken at the same time.

Hence, patients should not feel panic when stomach upset appears and take antacids recklessly. On the other hand, this may also cover up the truth which causes stomachache since this is a non-specific symptom of many different kinds of diseases. For example, patients with gastric ulcer take antacid therapy for temporary relieve of symptoms, like abdominal pain, nausea, and lots of vomiting. When medication cease, symptoms may relapse and in serious cases, bleeding or anemia may occur and this may pose the risk of death due to delay of treatment.

To conclude, if one finds that stomach upset continues after one-week antacid therapy, one should seek doctor’s advice. 14. Apart from taking antacid, what else should be aware of? It is very important to have a healthy diet to get the most benefit from this medication and to prevent serious side effects. Avoid eating fatty food or spicy food, alcohol. Conclusion: Antacids are common and effective tablets in treating the excess acids in the stomach.

From our investigation, the most effective antacid brand is ACTAL and the least effective one was the unknown brand. Thus we recommend the ACTAL tablets in treating the stomach problem.

Reference: http://www. reachoutmichigan. org/funexperiments/quick/csustan/antacid. htm http://icn2. umeche. maine. edu/genchemlabs/Antacid/antacid2. htm http://www. chem. latech. edu/~deddy/chem104/104Antacid. htm http://www. nku. edu/~cinsam/intsci/sci110/worksheets/antacid_tablets. html http://cnx. org/content/m15804/latest/.