1.) If your Aspirin sample did not dry completely and contained water in the sam

Question

1.) If your Aspirin sample did not dry completely and contained water in the sample would it require more or less NaOH solution to reach the endpoint of the titration?

2.) The concentration of NaOH on the bottle reads 0.0751 M. The concentration is actually 0.1023M. Will the value you compute for percent purity of Aspirin sample be too high, too low, orunchanged? Explain

3.) A 0.421 g sample of aspirin prepared in the laboratory is dissolved in 95% ethanol, diluted with water, and titrated to a phenolphthalein endpoint with 17.3 mL of 0.114 M NaOH. What is the percent purity of aspirin in the sample?

Explanation / Answer

1) amount of water doesnot effect the acidic behaviour of aspirin , hence NaOH required to reach end point will be same

2) since NaOH conc is read to a lower value than original we calculate aspirin conc lower. Hence aspirin moles calculated are lower , hence percentage purity is lower.

3) NaOH moles = 0.114 x ( 17.3/1000) = 0.0019722

aspirin moles = 0.0019722 ( they react in 1:1 ratio)

asspirin mass = 0.0019722 x 180.157 = 0.355 gm

% purity = ( 100 x 0.355/0.421) = 84.4 %

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