Report

Name: _____________________________
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Exp 5. Report Form: Analysis of Milk of Magnesia
A. Raw Data NOTE: Include All Pictures Taken, Imported into a single Word file (with labels), with your submission.
Mass of 15-mL conical tube, empty (before Titration 1) _______________
Mass of 15-mL conical + sample of Milk of Magnesia for Titration 1 _______________
Volume of sample of Milk of Magnesia for Titration 1 [This is not 40 mL! See Step 13!] _______________
Initial HCl(aq) buret Reading, Titration 1 _______________
Final HCl(aq) buret Reading, Titration 1 _______________
Was this titration clearly (or likely) overshot? Y or N
Mass of 15-mL conical tube, empty (before Titration 2) _______________
Mass of 15-mL conical + sample of Milk of Magnesia for Titration 2 _______________
Volume of sample of Milk of Magnesia for Titration 2 _______________
Initial HCl(aq) buret Reading, Titration 2 _______________
Final HCl(aq) buret Reading, Titration 2 _______________
Was this titration clearly (or likely) overshot? Y or N
Mass of 15-mL conical tube, empty (before Titration 3) _______________
Mass of 15-mL conical + sample of Milk of Magnesia for Titration 3 _______________
Volume of sample of Milk of Magnesia for Titration 3 _______________
Initial HCl(aq) buret Reading, Titration 3 _______________
Final HCl(aq) buret Reading, Titration 3 _______________
Was this titration clearly (or likely) overshot? Y or N
Assumed Information:
Molarity of HCl(aq)solution _______________
Calculated Quantities and Results (use “best” two titrations): Titration ____ Titration ____
Volume (in mL) of HCl(aq) used _______________ _______________
Moles of hydrochloric acid (HCl) used _______________ _______________
Moles Mg(OH)2 in sample of Milk of Magnesia _______________ _______________
Mass (in g) of Mg(OH)2 in sample of Milk of Magnesia _______________ _______________
(MM of Mg(OH)2 = 58.3197 g/mol)
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Mass (in mg) of Mg(OH)2 in sample of Milk of Magnesia _______________ _______________
Mass (in mg) of Mg(OH)2 per mL of Milk of Magnesia _______________ _______________
Average mg Mg(OH)2 per mL of Milk of Magnesia _______________
Mass % of Mg(OH)2 in sample of Milk of Magnesia _______________ _______________
Average Mass % of Mg(OH)2 in Milk of Magnesia _______________
Density of sample of Milk of Magnesia (g/mL) _______________ _______________
Average Density of Milk of Magnesia (g/mL) _______________
Analysis
1. Does the density value you obtained for Milk of Magnesia seem reasonable to you? Why or why not? In what way(s)
was it surprising to you? Hint: What is the major component of Milk of Magnesia?! It’s the first “inactive ingredient” listed on the label!
2. Does the mass percent value of Mg(OH)2 in Milk of Magnesia you obtained seem generally reasonable to you? Why
or why not? (NOTE: Unlike in Q1 above, I am not expecting you to have a specific idea of what this value might be.
But consider the ideas raised in Q1 above—namely, is most of your sample Mg(OH)2 or water?)
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3. (a) Look at the image of the label of the Milk of Magnesia bottle (see Reagents section). What is the active ingredient,
and how many mg of it are present in 15 mL of product? (BE CAREFUL: active ingredient is not “magnesium”!)
(b) Using your average value for the number of mg of Mg(OH)2 per mL of Milk of Magnesia determined above (from
your titration data), calculate the number of mg of Mg(OH)2 that your determination predicts would be in 15
mL of product. Consider this your “best estimate”. Also calculate the upper and lower values of mg Mg(OH)2 in
15 mL of product from your experiment by using each individual trial’s value of mg/mL (rather than the average).
(This range of values reflects your uncertainty [and thus also the precision] of this determination. The closer your two values are to one
another, the greater is the precision and the smaller is the uncertainty.)
Calculated value for mg of Mg(OH)2 in 15 mL of milk of magnesia…
…using Your Average Value (of mg Mg(OH)2 per mL product):
…using Your Lower Value (of mg Mg(OH)2 per mL product):
…using Your Higher Value (of mg Mg(OH)2 per mL product):
(c) Given the approximate precision in your result (reflected in the range of values you got in 3(b) above), how well
would you say your prediction in 3(b) matches the value on the label (noted in 3(a))? Does the label value fall
within the range of uncertainty of your determination? Discuss. (This reflects the accuracy of your determination.)
4. In an experiment similar to this one, the amount of an active ingredient in a commercial product was found by Student
A to be 24 mg/g (of product) in one trial of the experiment and 25 mg/g in a second trial. Student B did experiments
on the same product and got values of 23 mg/g and 29 mg/g in her two trials. The value listed on the label was 27
mg/g of product. Assume that the label value is “correct” (i.e., the actual value). Now answer the following:
(a) Which student’s determination had greater accuracy? Justify your answer with reasoning.
(b) Which student’s determination had greater precision? Justify your answer with reasoning.
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Note: The following question does NOT utilize your data at all. It is all “theory” (and comparison to label info).
5. (a) Assuming there are “exactly” 1200 mg of Mg(OH)2 in each 15 mL of milk of magnesia, calculate the number of
mg of magnesium (Mg) there would be in each 15 mL of milk of magnesia. Although it is unclear if it is
warranted, assume 3 significant figures for this calculation (all values)
Hint: First calculate the mass % of Mg in Mg(OH)2 (by using only the chemical formula and molar masses of elements from the
Periodic Table). Then use that* as a conversion factor to get from mg Mg(OH)2 to mg Mg. *Note that this particular mass
percent is “g of Mg per 100 g Mg(OH)2”, which is the same as “mg of Mg per 100 mg Mg(OH)2”
(b) Compare the answer you got in 5(a) to the value for this quantity found on the label. + Are they consistent with
one another? Are you surprised? What is interesting/”coincidental” about the answer you got in 5(a)? (I was kind
of surprised…)?