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Chemistry 212 Lab Final Exam
1. Which solution would have the lower freezing point?: Higher molality = lower
freezing point
2. DeltaTf=Kf*molal: Molal = (moles solute)/(kg solvent)
3. Calculate molar mass from change in temp: Find molality from DeltaT=Kf*mo-
lal Use molal to get moles solute molar mass = grams/mole solute
4. Calculate % aspirin in tablet from absorbance vs concentration graph: y=ab-
sorbance x=concentration/molarity Find x from y=mx+b Get moles from molarity by multiplying by volume Multiply moles by molecular weight of aspirin to get grams of aspirin.Divide grams of aspirin by tablet mass and * 100
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5. Sunscreen question: A=-log(%T/100%)
Thickness ratio from both sunscreens SPF 10 A =-3log(1/10) = 3 SPF 100 A=-2log(1/100) = 2 Higher absorbance (A) is better protection
- Absorbance of solution?
Concentration of solution increased x3
Concentration of solution decreased x3: A=-log(80%/100%)
A=-3log(80%/100%)... A=2.91.... T=10^(-A). ... T=10^-(2.91) A=-(1/3)log(80/100)...A=0.0323. .. T=10^-(0.0323)
- When performing the reaction of I- with H2O2 you accidentally added more
Na2S2O3 to the solution. How would that affect the reaction time?: Increase
time but wouldn't affect rate
8. Which trial should take the most amount of time?: Multiply concentrations of
each trial.Smallest rate = greatest time
- Concentrations of KI and H2O2 increased x3
Concentrations deceased x3: =reaction time/concentration
=reaction time * concentration
10. Increase concentration of Na2S2O3 on reaction rate: unchanged
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