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Part II: Data Sheet for 2nd Week |
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| Below is the top half of the data sheet for the second week of the Antacids lab completed for our antacid using our data. Make sure to put the name of the antacids you are using into the columns in line 1. X-acid is not one of the antacids you will be testing but we forgot which one we used and made up a name instead. As you complete the data sheet make sure you keep your data for each antacid in the appropriate column. Also, make sure to record your data very carefully in each blank, taking care not to forget significant figures.
Lines 2 and 3 contain masses for the antacid dose and antacid powder sample as measured on the previous page. Lines 4 and 5 record the initial and final readings of our acid buret when acid was added. Final minus the initial volume readings gives the volume of acid solution added to the flask and recorded in line 6. The moles of HCl added are calculated using the equation located between lines 6 and 7. The "average [HCl]" in the equation is simply the average concentration for your acid solution you determined in last week's experiment. The answer on line 7 should contain at least 3 significant figures. Our answer on the data sheet contains 4 significant figures, for example. Recorded on lines 8 and 9 are the base buret initial and final readings before and after the titration. Line 10 is the volume used to titrate the solution obtained by subtracting the final base reading from the initial base reading. Located between lines 10 and 11 is the equation for the calculation of the moles of NaOH added. The "average [NaOH]" in the equation is simply the average concentration of base you determined in last week's experiment. Line 11 contains the answer for the number of moles required, notice that it also has 4 significant figures. Once again, your answer should have at least 3 significant figures. |
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| Lines 12 - 14 of the data are combined because they are part of a three step process to calculate the number of grams of acid neutralized by 1 dose of antacid. While we have intentionally made errors in our measurements so that the results of our calculations are not quite correct, they are similar in magnitude to the results you should be getting. We have included the price of the antacid per 1 dose because it is needed for a later calculation. There is not a blank on the data sheet for this so we put it above the name of the antacid used. This value will be given to you in class for each particular antacid.
Notice that since the acid (HCl) and base (NaOH) react in a 1:1 molar ratio the moles of base used equal the moles of acid remaining after partial neutralization by the antacid. Hence the number of moles of acid neutralized by the antacid sample is the moles of acid added minus the moles of base used, as indicated in the equation between lines 11 and 12 on the data sheet. This quantity, the moles of acid neutralized by the antacid sample, is a simple measure of how effective the antacid is . In other words, the more effective the antacid the more acid it should neutralize. But we will go on to calculate some more careful measures of effectiveness after first calculating the moles of stomach acid neutralized by one dose of the antacid (line 13) and the number of grams of acid neutralized by one dose of the antacid (line 14). |
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| We have enough information now to calculate two kinds of efficiency: relative efficiency and cost efficiency. The relative efficiency measure, how many grams of acid are neutralized per gram of antacid. This tells you which antacid will neutralize the most acid regardless of cost. The cost efficiency measures how many grams of acid are neutralized per penny. If you were interested in neutralizing the most stomach acid possible regardless of cost you would pick the antacid with the highest relative efficiency. If, however, you wanted to neutralize the most acid as cheaply as possible, you would pick the antacid with the highest cost efficiency. | ||||
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| Last of all, identify the chemical formula of the active antacid ingredient in each antacid and the molar ratio of and to active antacid ingredient.
The chemical formula can be found listed in Table 2 of the lab handout or the label of the antacid bottle. Often two or more ingredients are present, as is the case with the Mg(OH)2 and Al(OH)3 listed here in line 17. Notice that we could just as well have listed OH- as the active ingredient since that is the single species in both compounds that acts as a base. The molar ratio of acid to active antacid ingredient can be determined from the balanced acid-base reaction chemical equations. In our case, since OH- is the active ingredient and one HCl reacts with one OH- ion, the molar ratio of acid molecule to active antacid ingredient is 1:1. |
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