PROBLEM: Mary had a headache one afternoon and went to her local pharmacy. She decided to use aspirin. Two brands of aspirin were suggested to her. She decided to purchase the more expensive brand even though both brands had the same amount and mass of tablets in each bottle and both brands claimed that the tablets were 100% aspirin. Prepare a suitable hypothesis for this observation and plan and design an experiment to test this hypothesis.
HYPOTHESIS: The more expensive brand of aspirin contained a higher percentage of the
active ingredient, (2-ethanoylhydroxybenzoic acid)
AIM: To determine the percentage of the active ingredient in two commercial brands of
APPARATUS + MATERIALS: 5 tablets of each aspirin brand, mortar, pestle,
conical flask, volumetric flask, pipette, pipette filler, burette, stirring rod, Bunsen burner, white tile, retort stand, balance, distilled water, .05M H2SO4, 1 M NaOH, phenolphthalein indicator, Potassium acid phthalate (KHP) solution
METHOD 1: Standardisation of NaOH:
1) Pipette 25cm³ of 1M NaOH into a volumetric flask and dilute with distilled water to the 1 Litre mark.
2) Fill burette with NaOH solution and ensure burette is zeroed.
3) Weigh another conical flask on balance and record value.
4) Measure .8g KHP into this conical flask.
5) Using a measuring cylinder, measure 100ml of distilled water and pour into volumetric flask.
6) Swirl flask until completely dissolved.
7) Add 3 drops of phenolphthalein indicator to solution.
8) Titrate the KHP solution against the NaOH solution to be standardized. Titrate until
faint pink colour appears (pink colour will only last about 30secs)
9) Repeat titration several times until precise values are obtained.
10) Calculate average molarity of NaOH. (within 1% of each other)
1) Using a mortar and pestle, crush 5 tablets of the cheaper brand...