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Warm-Up Problem!

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Warm-Up Problem! What volume of 0.175 M solution of KOH is needed to titrate 30.0 mL of 0.200 M H2SO4? * * * * * * Figure: 10-11 Title: A comparison illustrating ... – PowerPoint PPT presentation

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Title: Warm-Up Problem!


1
Warm-Up Problem!
  • What volume of 0.175 M solution of KOH is needed
    to titrate 30.0 mL of 0.200 M H2SO4?

2
Chapter 10 Gases
3
Units of Pressure
  • mm Hg or torr
  • These units are literally the difference in the
    heights measured in mm (h) of two connected
    columns of mercury.
  • Atmosphere
  • 1.00 atm 760 torr

4
Manometer
  • Used to measure the difference in pressure
    between atmospheric pressure and that of a gas in
    a vessel.

5
Boyles Law
  • The volume of a fixed quantity of gas at
    constant temperature is inversely proportional to
    the pressure.

P1V1 P2V2
6
Charless Law
  • The volume of a fixed amount of gas at constant
    pressure is directly proportional to its absolute
    temperature.

V1 V2
T1 T2
A plot of V versus T will be a straight line.
7
Avogadros Law
  • The volume of a gas at constant temperature and
    pressure is directly proportional to the number
    of moles of the gas.

Relates V and moles
8
1 mol gas 22.4 L gas, D ? MW
9
Ideal Gas Equation
  • V ? 1/P (Boyles law)
  • V ? T (Charless law)
  • V ? n (Avogadros law)

PV nRT
10
Warm-Up!
  • A sample of gas occupies a volume of 1248 ft3 at
    0.988 atm and 28 C.
  • Calculate the pressure of the gas if its volume
    is decreased to 978 ft3 while its temperature is
    held constant.

11
Calculating Density and Molecular Weight!
rearrange to solve for MW
(x M)
(m/vd)
12
Cumulative Problem!
  • An organic compound had the following analysis
    C, 55.8 by mass H, 7.03 O, 37.2. A 1.500 g
    sample was vaporized and was found to occupy 530
    cm3 at 100oC and 740 torr. What is the molecular
    formula of the compound?

13
AP Question 1972
  • A 5.00 gram sample of a dry mixture of potassium
    hydroxide, potassium carbonate, and potassium
    chloride is reacted with 0.100 liter of 2.0 molar
    HCl solution.
  • (a) A 249 milliliter sample of dry CO2 gas,
    measured at 22C and 740 torr, is obtained from
    the reaction. What is the percentage of potassium
    carbonate in the mixture?
  • (b) The excess HCl is found by titration to be
    chemically equivalent to 86.6 milliliters of 1.50
    molar NaOH. Calculate the percentages of
    potassium hydroxide and of potassium chloride in
    the original mixture.

14
Warm Up!
  • A Scuba divers tank contains 0.29 kg of oxygen
    compressed into a volume of 2.3 L.
  • Calculate the pressure inside the tank at 9 C.
  • What volume would this oxygen occupy at 26 C and
    0.95 atm.

15
Agenda for Today
  • Go back to 1972
  • Partial Pressure discussion
  • Partial Pressure Practice Problems!

16
KOH HCl ? KCl H2O K2CO3 2HCl ? 2KCl H2O
CO2 KCl HCl ? no reaction
  • Find K2CO3 in original 5 g total solid
  • Use PVnRT to find moles of CO2
  • .249 L .974 atm 0.01 moles CO2
  • .0821Latm/molK(295K)
  • 0.01 moles CO2 x 1molK2CO3 0.01 mol K2CO3
  • 1 mol CO2
  • 0.01 mol K2CO3x 138g/mol 1.38 g
  • Find percent mass 1.38g K2CO3/5 g total solid
    27.6

2. Find moles of original HCl ? 0.1L x 2 mol/L
0.2 mols HCl total
3. Find moles of HCl ? 0.1 moles K2CO3 x 2 mol
HCl 0.02 moles HCl reacted with K2CO3
1 mol K2CO3
4. Use NaOH titration to find unreacted
HCl 0.0866L NaOH x 1.5 mol 0.13 moles NaOH
0.13 moles HCl (b/c 11) L
5. Find moles of HCl that reacted with KOH from
steps 2, 3, and 4 0.2 moles total 0.02 moles
reacted with K2CO3 - 0.13 moles excess 0.05
moles HCl
6. Find grams of KOH 0.05moles HCl x 1 mol KOH x
56.1 g KOH 2.81g KOH 1 mol HCl
1 mol KOH
7. Find mass KOH ? 2.81g KOH 56.2 5g
total
8. Find KCl ? 100 - 56.2 - 27.6 16.1 KCl
17
Daltons Law of Partial Pressures
  • The total pressure of a mixture of gases equals
    the sum of the pressures that each would exert if
    it were present alone.

Ptotal P1 P2 P3
18
Partial Pressure Practice (say that 3 times fast)
  • What is the total pressure exerted by a mixture
    of 2.00 g of hydrogen and 8.00 g of nitrogen at
    273 K in a 10.0-L vessel?

19
Partial Pressure Mole Fraction x Ptot
  • Whats a mole fraction?
  • The relationship between the moles of each gas to
    the total moles of the gas mixture
  • n1/ntotal c1
  • Use the mole fraction and total pressure to find
    partial pressures!
  • P1 c1 (Ptotal)
  • What is the mole fraction of oxygen in air?
  • Air 78 nitrogen, 21 oxygen, 1 water vapor,
    0.9 argon, and .04 carbon dioxide

20
Partial Pressures
  • A mixture of 9.00 g of oxygen, 18 g of argon, and
    25 g of carbon dioxide exert a pressure of 2.45
    atm. What is the partial pressure of Argon in the
    mixture?
  • What is the partial pressure of oxygen in air?
    (Atmospheric pressure 760 torr)

21
AP Multiple Choice Warm Up!!
  • A student pipetted five 25.00-milliliter samples
    of hydrochloric acid and transferred each sample
    to an Erlenmeyer flask, diluted it with distilled
    water, and added a few drops of phenolphthalein
    to each. Each sample was then titrated with a
    sodium hydroxide solution to the appearance of
    the first permanent faint pink color. The
    following results were obtained.
  • Volumes of NaOH Solution
  • First Sample..................35.22
    mL Second Sample..............36.14 mL Third
    Sample.................36.13 mL Fourth
    Sample..............36.15 mL Fifth
    Sample..................36.12 mL
  • Which of the following is the most probable
    explanation for the variation in the student's
    results?
  • (A) The burette was not rinsed with NaOH
    solution.
  • (B) The student misread a 5 for a 6 on the
    burette when the first sample was titrated. (C) A
    different amount of water was added to the first
    sample. (D) The pipette was not rinsed with the
    HCl solution. (E) The student added too little
    indicator to the first sample.

22
Collecting Gases over Water
  • Ptotal Pgas PH2O
  • 2KClO3(s) ? 2KCl(s) 3O2(g)
  • The volume of gas collected is 0.250 L at 26C
    and 765 torr total pressure. (a) How many moles
    of O2 are collected? (b) How many grams of KClO3
    were decomposed? (The pressure of water vapor at
    26C 25 torr .)

23
Kinetic Molecular Theory
  • Gases consist of large numbers of molecules that
    are in continuous, random motion.
  • The combined volume of all the molecules of the
    gas is negligible relative to the total volume in
    which the gas is contained.
  • Attractive and repulsive forces between gas
    molecules are negligible.
  • The collisions between molecules are perfectly
    elastic.
  • The average kinetic energy of the molecules is
    proportional to the absolute temperature.

24
  • Pressure is caused by collisions of molecules
    with the walls of the container!
  • Magnitude of pressure is related to how often and
    how forcefully the particles strike the walls.
  • Temperature of a gas is a measure of the average
    kinetic energy of its molecules!
  • Motion increases with increasing temperature.
  • Why does pressure increase with increasing
    temperature?

25
KE 1/2mu2
v
r1 M2 r2 M1
v
t1 M1 t2 M2
26
Effusion Problem
  • At a particular T and P, neon gas effuses at a
    rate of 16 mol/s.
  • (a.) What is the rate at which Ar effuses under
    the same conditions?
  • (b.) Under a different set of conditions, 3.0 mol
    of Ar effuse in 49.0 seconds. How long will it
    take an equal amount of helium to effuse?

27
Deviation from Ideal Behavior
Real gases at high pressure are like the mall at
christmas. Too many people in a small
space, people are on top of one another! Compared
to the space in the checkout line, the people in
front of you and behind you have significant
volume. Ugh If molecules are crowded in a
container, as pressure increases
attractive forces take over. Also the volume of
the gas particles are significant compared
to the volume of the container. NOT IDEAL!
28
Deviation from Ideal Behavior
At low temperature there is not enough energy to
overcome attractive forces and the gas is forced
to condense into a liquid. Ice is NOT an ideal
gas
The van der Waals Equation corrects for
non-ideal behavior
29
Non-Ideal Practice
  • Arrange the following gases in order of
    increasing deviation from ideality
  • H2O, CH4, Ne
  • WHY???

30
Warm-Up
  • 1) Sulfuryl chloride, SO2Cl2, is a highly
    reactive gaseous compound. When heated, it
    decomposes as follows.
  • SO2Cl2(g) ltgt SO2(g) Cl2(g)
  • This decomposition is endothermic. A sample of
    3.509 grams of SO2Cl2 is placed in an evacuated
    1.00-liter bulb and the temperature is raised to
    375 K.
  • (a) What would be the pressure in atmospheres in
    the bulb if no dissociation of the SO2Cl2(g)
    occurred?
  • (b) When the system has come to equilibrium at
    375 K, the total pressure in the bulb is found to
    be 1.43 atmospheres. Calculate the partial
    pressures of SO2, Cl2, and SO2Cl2 at equilibrium
    at 375 K.

31
  • a) Gas pressure atmospheric pressure h
  • b) Gas pressure atmospheric pressure h

32
Non Ideal Sample AP ?
  • The van der Waals equation of state for one mole
    of a real gas is as follows
  • (P a/V2)(V - b) RT
  • For any given gas, the values of the constants a
    and b can be determined experimentally. Indicate
    which physical properties of a molecule determine
    the magnitudes of the constants a and b. Which of
    the two molecules, H2 or H2S, has the higher
    value for a and which has the higher value for b?
    Explain.
  • One of the van der Waals constants can be
    correlated with the boiling point of a substance.
    Specify which constant and how it is related to
    the boiling point.

33
Tips for Gas Law Success
  • Everything relates back to PVnRTthink about the
    relationships in terms of ideal gas equation.
  • T HAS to be in Kelvin for relationships to work.
  • Rate ?1/time High rate low time and smaller
    MW have higher rate!
  • In barometer, diameter doesnt matter!
  • When in doubt write out chemical eqn and think
    about stoichiometry.
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