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PPT – Warm-Up Problem! PowerPoint presentation | free to download - id: 660f4d-NTgyZ

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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?

Chapter 10 Gases

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

Manometer

- Used to measure the difference in pressure

between atmospheric pressure and that of a gas in

a vessel.

Boyles Law

- The volume of a fixed quantity of gas at

constant temperature is inversely proportional to

the pressure.

P1V1 P2V2

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.

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

1 mol gas 22.4 L gas, D ? MW

Ideal Gas Equation

- V ? 1/P (Boyles law)
- V ? T (Charless law)
- V ? n (Avogadros law)

PV nRT

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.

Calculating Density and Molecular Weight!

rearrange to solve for MW

(x M)

(m/vd)

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?

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.

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.

Agenda for Today

- Go back to 1972
- Partial Pressure discussion
- Partial Pressure Practice Problems!

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

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

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?

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

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)

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.

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 .)

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.

- 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?

KE 1/2mu2

v

r1 M2 r2 M1

v

t1 M1 t2 M2

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?

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!

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

Non-Ideal Practice

- Arrange the following gases in order of

increasing deviation from ideality - H2O, CH4, Ne
- WHY???

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.

- a) Gas pressure atmospheric pressure h
- b) Gas pressure atmospheric pressure h

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.

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.