Chapter 13 & 14 chemistry test

What is the definition of molality?

moles of solute per kg of solvent

Solution

homogeneous mixture of two or more
substances in a single phase

solutes

the substance that dissolves in a solution

solvents

the substance that does the dissolving

Henry law meaning

Sg = Kh Pg

Sg = solubility of gas (usually mol/L)
– Pg = partial pressure of the gas over the solution
– kH = Henry’s Law constant

Calculate the concentration of CO2 in a Mountain Dew drink that is
bottled with a partial pressure of CO2 of 4.0 atm over the liquid at 25 C (
Henry’s law constant at this temp is 3.1 × 10−2 mol/L atm)

0.12 mol/L or 0.12 M

What is the concentration of O2 in a
freshwater stream in equilibruim with air at
25 oC and at a pressure of 1.0 atm?
Express answer in moles of O2/liter of
seawater.
The pressure of O2 is 0.21 atm in air and the
Henry’s law constant is 1.3 x 10 -3mol/liter . atm

2.7 x 10-4 mol/liter

When the temperature is increased, the
solubilities of most gases _____, and the
solubilities of most solids _____.
A increase; increase
B increase; decrease
C decrease; increase
D decrease; decrease

C

Raoult law

Xsolvent=moles of solvent/moles of solvent + moles of solute

Psolvent = Xsolvent Pºsolvent

Psolvent is the vapor pressure of the solvent over the
solution
Pºsolvent is the vapor pressure of the pure solvent
Xsolvent is the mole fraction of the solvent

(raoult law problem)Urea, (NH2)2CO, which is widely used in fertilizers
and plastics, is quite soluble in water. If you dissolve
9.00 g of urea in 10.0 grams of water, what is the
vapor pressure of the solution at 24 °C?
Vapor pressure of water at 24oC = 22.4 mm Hg
Molar mass of urea = 60.06g = 1 mole
Molar mass of water = 18.02g = 1 mole

17.6 mm Hg

Freezing point formula

m=moles of solute/kg of solvent

Tf=KfM

T + Tsolvent= T solution

Freezing point problem answer is 80.32 C

Eugenol, a compound found in nutmeg and cloves, has the
formula C10H12O2. What is the boiling point of a solution
containing 0.144 g of this compound dissolved in 10.0 g of
benzene?
Molar mass of Eugenol = 164.2g/mole
molal boiling point elevation constant for benzene = 2.53oC/m
The boiling point of pure benzene = 80.10oC
ΔTbp = Kbpm

What is the freezing point of a solution made by adding
1840 grams of ethylene glycol, HOCH2CH2OH, to 5500
grams of water.
molar mass of ethylene glycol = 62.07g/mole
molal freezing point depression constant for water = -1.86oC/m
freezing point of pure water is 0.0oC.
ΔTfp = Kfpm
T = Tsolution -Tsolvent

-10 ºC

Polyvinyl alcohol is a water soluble polymer with an average
molar mass of 28,000. You dissolve 1.844 g of this polymer in
water to give 150. mL of solution. What is the osmotic
pressure, measured at 27 °C ( 300 K)?
PV = nRT

R = 0.08206L .atm.mole-1.K-1

0.0108 atm

In which aqueous solution is the boiling
point greater?
• 0.30 molal NaCl
• 0.20 molal AlCl3

0.20 molal AlCl3

The units of "reaction rate" are

mol L-1 s-1.

Appropriate units for a first-order rate constant are

1/s.

Appropriate units for a second-order rate constant are

1/M·s.

Appropriate units for a third-order rate constant are

1/M2·s

The reaction A + 2B → products has been found to have the rate law, rate = k[A]
[B]2. While holding the concentration of A constant, the concentration of B is
increased from x to 3x. Predict by what factor the rate of reaction increases.

3²=9

The reaction A + 2B → products has the rate law, rate = k[A][B]3. If the
concentration of B is doubled while that of A is unchanged, by what factor will the
rate of reaction increase?

2³=8

For the chemical reaction A → B + C, a plot of [A]t versus time is found to give a
straight line with a negative slope. What is the order of reaction with respect to A?

zeroth

For the chemical reaction A → B + C, a plot of 1/[A]t versus time is found to give a
straight line with a positive slope. What is the order of reaction with respect to A?

Second

For the chemical reaction A → B + C, a plot of ln[A]t versus time is found to give a
straight line with a negative slope. What is the order of reaction with respect to A?

First

For a first order reaction, the half-life is equal to

A. t1/2 = 0.693/k.
B. t1/2 = k/0.693.
C. t1/2 = 1/k[A]o.
D. t1/2 = k.
E. t1/2 = [A]o/2k.

A. t1/2 = 0.693/k.

0th order

[A] t = −𝑘𝑡 + [𝐴] 0

1st order

ln [𝐴] 𝑡 = −kt + ln [𝐴] 0

2nd order

1/[A]t=Kt + 1/[A]o

The reaction 2A B is first order in A with a rate constant of 2.8 x 10-2 s-1 at 800C.
How long will it take for A to decrease from 0.88 M to 0.14 M ?
ln[A]t = -kt + ln[A]0

66 s

A first order reaction has a rate constant of
1.35x10-4s-1 at 25 oC.
How long will it take for the concentration to
decrease from 0.45M to 0.32M.
ln[A]t = -kt + ln[A]0

2500s

Is second order in A. What is the concentration of A after 60
seconds if the rate constant is 0.50 M-1s-1 and the initial A
concentration is 0.15M.

2nd order 1
1/[A]t=kt + 1/[A]o

0.027m

osmosis pressure formula

p=nrt/v

Rate formula

Rate 1/Rate2= K[A]^x [B]^y

c/x=1 d/y=3 k=0.625s^-1 m-3