This is a brief study guide to help you answer and review components of experiments #2 of the General Chemistry Laboratory course for undergraduate students at UCI. Originally made as review flashcards on Quizlet. Includes main objective, special procedures, and calculations.
Experiment #2
Study online at https://quizlet.com/_5pynb6
1. Main Objective First we find the vp of pure ethanol and then we find
the vapor pressure of the ethanol at varying temper-
atures. Then we find the vp's of varying solutions.
2. Special Procedures -Rubber-Stopper assembly: put stopper in 125 Er-
lenmeyer flask. Parafilm. Close (turn sideways). Put
ethanol in syringe.
-Get normal air pressure readings and temp before
injecting ethanol
-Increase temp using hot water
3. Vapor Pressure at -VP(ethanol)= P(total) - P(air)
Room Temp -Where p(total)= pressure you record of ethanol
and p(air)= what you recorded for air in the very
beginning
4. Vapor pressure other -Have to adjust P(air) b/c you cant assume it will be
than room temp. the same
-P1/T1=P2/T2
Where P1= p(air), T1= temp (air), P2=?, and T2=
temp for that data point
-P2 is then the new P(air) and you plug it into
VP(ethanol)= P(total)-P(air)
Where P(total) is what you initially recorded for that
temp
5. Clausius-Clapeyron ln P =(-”Hvap / R)(1/T) + C
plot (R = 8.3145 J/mol·K & C = constant)
6. Calculate deltaH -slope x R (8.314 J/molK)(1 J/1000 kJ)
7. Percent Error (true-exp/true)x100
8. In the Sapling prelab The value of ”Hf that was found using Spartan was
for this experiment you -51.59962 kJ/mol. The experimental value found for
used Spartan to cal- H
” vap was 44.1 kJ/mol. They are close in magnitude,
culate the enthalpy but their signs are different. This is because H
” f is the
of formation (”Hf) of enthalpy change when one mole of a substance is
the hydrogen bond be- formed from its elements in the standard state and
tween two ethanol mol- under the same conditions. Because ”Hf is the en-
1/2
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