Exp 4 to 6 Flashcards
The liquid, with ___, is vaporized at ____ in a ____ with ____
mass, m
a certain temperature, T
glass vessel
volume, V
Vaporization is carried out at ___. Hence, P is ___
atmospheric pressure
more or less equal to 1 atm
How to compute for molar mass using Dumas method?
MM= mRT/PV
MM = (m4 - m3) RT/PVo
R=0.08206 L atm/ mol K
Describe the Dumas method
- Empty mass of Dumas Bulb
- Fill with water
- Mass with water
- Density of water at that temperature
- Convert to volume of Dumas bulb
- Emptied and dried, mass of dried
- Small amount of sample
- Submerged in water bath
- Vaporize the sample
- Recondense the sample
- Mass of recondensed vapor
Dumas vessel can be substituted with?
Erlenmeyer flask of suitable size covered with aluminum foil that is punctured using a needle
Limitation of Dumas method
Simple but relies on ideal behavior. Deviations from ideality will cause inaccurate determination of molar mass.
Volume of Dumas flask formula, Vo
Vo = (m1 - m0)/density
What will happen to calculated molar mass if…
a. liquid is not completely vaporized
b. outside of flask is not dried properly
c. the flask is warm when weighed
a. higher MM
b. higher MM
c. lower MM
What is enthalpy change of solution?
amount of heat associated with dissolution of a substance in a solvent at constant pressure resulting in infinite dilution
enthalpy change of solution formula
-∆H sol = ∆H water + ∆Hcal
∆H sol = -[m water c water (Tf -Ti water) + Cp (Tf - Ti cal)]
When enthalpy of reactants is larger than products, the resulting heat transfer is?
exothermic (-∆H)
Occurs when products have higher enthalpies than reactants
endothermic reaction (+∆H)
Specific heat capacity of water
4.814 J/g°C
Why heat of capacity of solution is assumed to be equal with heat capacity of water?
The concentration of solute has a relatively low concentration
Heat capacity formula
Cp = [-mhot Cwater (Tf-Ti hot) + mcool Cwater (Tf-Ti cool)]/(Tf - Ti cool)
Freezing point depression is a ___ property
colligative property
Lowering of freezing point or melting point of a liquid when solute is dissolved in it
Freezing point depression
How to compute for the molar mass using freezing point depression?
MM = [(mass compound, g)/(mass solvent, kg)] x (kf/∆Tf)
For a pure solvent, the cooling curve will exhibit a ___ at its freezing point
plateau
For a solution, the temperature will ___ as the solvent freezes out of solution
continue to decrease
The freezing point temperature of a solution is determined from ___
the break in its cooling curve
What is the effect of the following in calculated MM?
a. impure compound
b. impure solvent
c. mixture is not mixed thoroughly
a. decrease in Tf, increase in MM
b. decrease in Tf, increase in MM
c. inconsistent temperature
