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Modeling Chemistry Unit 9 Packet Page | 1

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Unit 9 Packet – Stoichiometry 2

Packet Contents Sheet (This Page)

Unit 9 Objectives

Worksheet 1- Gases Again

Worksheet 2

Gas Stoichiometry Practice/ Ideal Gas Law Practice

Worksheet 3- Molar Concentration (2 pages)

Molarity Practice Problems

Notes on H

Worksheet 4

Unit 9 Study Guide

DO NOT, under any circumstances, throw this away!

This packet MUST be saved for the final exam.


Unit 9 – Stoichiometry II - Objectives Students can derive and use the Ideal Gas Law to determine an unknown pressure, quantity,

volume, or temperature. They will be able to use balanced chemical equations and quantity of a

reactant or product to calculate moles, mass, and chemical potential energy. Students will also

be able to calculate and use partial pressures within a mixture.

Scale Score Comment

Score 4 Without any major errors, students can independently:

Students can apply laboratory data to derive and use the Ideal Gas Law to

determine an unknown pressure, quantity, volume, or temperature. They

will be able to use balanced chemical equations and quantity of a reactant or

product to calculate moles, mass, and chemical potential energy. Students

will also be able to calculate and use partial pressures within a mixture.

Score 3 Without any major errors, students can independently:

Students can derive and use the Ideal Gas Law to determine an unknown

pressure, quantity, volume, or temperature. They will be able to use

balanced chemical equations and quantity of a reactant or product to

calculate moles, mass, and chemical potential energy. Students will also be

able to calculate and use partial pressures within a mixture.

Score 2 With one or two major errors, students can independently:

Students can understand how to use the Ideal Gas Law to determine an

unknown pressure, quantity, volume, or temperature. They will be able to

understand the relationship between balanced chemical equations and

calculations of moles, mass, and chemical potential energy. Students will

also be able to calculate and use partial pressures within a mixture.

Score 1 With help from the teacher, students can:






Score 0 Even with the teachers help, students show no understanding or ability to:







Name

Date Pd

Chemistry – Unit 9 Worksheet 1 – Gases Again

1. A can of spray paint contains nitrogen gas as the propellant. The pressure of the

gas is 3.5 atm when the temperature is 20˚C. The can is left in the sun, and the

temperature of the gas increases to 50˚C. What is the pressure in the can?

2. A 90.0 mL volume of helium was collected under a pressure of 740. mmHg. At

what volume would the pressure of this gas be 700. mm Hg? Assume

temperature is constant.

3. A small bubble rises from the bottom of a lake, where the temperature is 8˚C and

the pressure is 6.4 atm, to the water’s surface, where the temperature is 25˚C

and pressure is 1.0 atm. Calculate the final volume (in mL) of the bubble if its

initial volume was 2.1 mL.

4. Three gases are mixed in a 1.00 L container. The partial pressure of CO2 is 250.

mm Hg, N2 is 375 mm Hg, and He is 125 mm Hg. What is the pressure of the

mixture of gases?

5. What are the percentages, by moles, of the gases in the above mixture?


6. Our atmosphere is a mixture of gases (roughly 79% N2, 20% O2 and 1% Ar).

What is the partial pressure (in mm Hg) of each gas at standard pressure?

7. A mixture of He and O2 gases is used by deep-sea divers. If the pressure of the

gas a diver inhales is 8.0 atm, what percent of the mixture should be O2, if the

partial pressure of O2 is to be the same as what the diver would ordinarily

breathe at sea level?

8. When you found the density of carbon dioxide gas, you collected the gas by

displacing water in a bottle. The gas you collected was a mixture of CO2 and

H2O vapor. If, on the day of the lab, the room pressure were 730 mm Hg and

the partial pressure of water vapor were 21 mm Hg, what would be the partial

pressure of the carbon dioxide gas? What fraction of the mixture was CO2?

9. Suppose that when you reacted the zinc with the hydrochloric acid, you collected

the hydrogen gas by water displacement. If the pressure in the room were 735

mm, and the partial pressure of the water were 22mm Hg, what would be the

partial pressure of the hydrogen gas? If the volume at this pressure were 25.0

mL, what would be the volume of the hydrogen gas alone at standard pressure?


Name

Date Pd

Chemistry – Unit 9 Worksheet 2

1. What volume does 16.0 g of O2 occupy at STP?

2. A mixture contains 5.00 g each of O2, N2, CO2, and Ne gas. Calculate the

volume of this mixture at STP

3. A 250 mL flask of hydrogen gas is collected at 763 mm and 35˚C by

displacement of water from the flask. The vapor pressure of water at 35˚C is

42.2 mmHg. How many moles of hydrogen gas are in the flask?

4. When calcium carbonate is heated strongly, carbon dioxide gas is evolved.

CaCO3(s) –––> CaO(s) + CO2 (g)

If 4.74 g of calcium carbonate is heated, what volume of CO2 (g) would be

produced when collected at STP?


5. Zinc metal reacts vigorously with chlorine gas to form zinc chloride. What

volume of chlorine gas at 25˚C and 1.00 atm is required to react completely with

1.13 g of zinc?

6. Consider the following reaction:

P4(s) + 6 H2 (g) ––> 4 PH3 (g)

What mass of P4 will completely react with 2.50 L of hydrogen gas, at 0˚C and

1.50 atm pressure?

7. If water is added to magnesium nitride, ammonia gas is produced when the

mixture is heated.

Mg3N2(s) + 3H2O(l) ––> 3 MgO + 2NH3(g)

If 10.3 g of magnesium nitride is treated with water, what volume of ammonia

gas would be collected at 20˚C and 0.989 atm?

8. Nitrogen gas and hydrogen gas combine to produce ammonia gas (NH3). What

volume of hydrogen gas at 25˚C and 735 mm is required for the complete

reaction of 10.0g of nitrogen?


Name

Date Pd

Gas Stoichiometry Practice

For all of these problems, assume that the reactions are being performed at STP.

1. Calcium carbonate decomposes at high temperatures to form carbon dioxide

and calcium dioxide:

CaCO3(s) CO2(g) + CaO(s)

How many grams of calcium carbonate will I need to form 3.45 liters of carbon

dioxide?

2. Ethylene burns in oxygen to form carbon dioxide and water vapor:

C2H4(g) + 3 O2(g) 2 CO2(g) + 2 H2O(g)

How many liters of water can be formed if 1.25 liters of ethylene are consumed

in this reaction?

3. When chlorine is added to acetylene, 1,1,2,2-tetrachloroethane is formed:

2Cl2(g) + C2H2(g) C2H2Cl4(l)

How many liters of chlorine will be needed to make 75.0 grams of C2H2Cl4?


Name

Date Pd

Ideal Gas Law Practice

Solve the following problems using the ideal gas law.

1. How many moles of gas does it take to occupy 120 liters at a pressure of 2.3

atmospheres and a temperature of 340 K?

2. If I have a 50 liter container that holds 45 moles of gas at a temperature of

200C, what is the pressure inside the container?

3. It is not safe to put aerosol canisters in a campfire, because the pressure

inside the canisters gets very high and they can explode. If I have a 1.0 liter

canister that holds 2 moles of gas, and the campfire temperature is 1400C,

what is the pressure inside the canister?

4. How many moles of gas are in a 30 liter scuba canister if the temperature of

the canister is 300 K and the pressure is 200 atmospheres?

5. I have a balloon that can hold 100 liters of air. If I blow up this balloon with

3 moles of oxygen gas at a pressure of 1 atmosphere, what is the temperature

of the balloon?


Name

Date Pd

Unit 9 Worksheet 3: Molar Concentration

Part A: Describing Molar Concentration

1. Sodium chloride was dissolved in water to produce a 1.5M solution.

Explain what this concentration tells us about the NaCl solution.

How might a chemist use this ratio?

2. A 45.3 g sample of potassium nitrate is dissolved in enough water to make

225 mL of solution. Determine the molar concentration of the potassium

nitrate.

3. Find the molarity of a solution made from 275 g of CuSO4 dissolved in enough

water to make 4.25 L.

4. An alcoholic iodine solution (“tincture” of iodine) is prepared by dissolving 5.15 g

of iodine crystals in enough alcohol to make a volume of 225 mL. Calculate the

molarity of iodine in the solution.

5. What final volume would be needed in order to prepare a 0.25 M NaCl solution

from 5.2 g of NaCl (s)?


6. Draw a particle diagram of each of these ionic substances in solution. Then

calculate the molarity of each ion present in each of the following solutions.

a. 0.25 M AlCl3

b. 0.375 M Na2CrO4

c.0.0020 Ca(OH)2

d. 0.103 M Na3PO4

7. How many grams of silver nitrate are needed to prepare 250 mL of standard

0.100 M silver nitrate solution?

8. If 10.0 g of AgNO3 is available, find the volume needed to prepare a 0.25 M

AgNO3 solution.

9. Concentrated hydrochloric acid is made by pumping hydrogen chloride gas into

distilled water. If concentrated HCl contains 439 g of HCl per liter, what is the

molarity?


Part B: Molar Concentration and Stoichiometry

10. How many moles of lead(II) hydroxide (solid) can be formed when 0.0225L of

0.135 M Pb(NO3)2 solution reacts with excess sodium hydroxide? (Hint: Use a

BCA table).

11. Barium nitrate reacts with aqueous sodium sulfate to produce solid barium

sulfate and aqueous sodium nitrate. Abigail places 20.00 mL of 0.500 M

barium nitrate in a flask. She has a 0.225M sodium sulfate solution available.

What volume of this solution must she add to her flask of barium nitrate so she

has no excess reactant left over? (Use a BCA table to answer).

12. Calcium chloride (aq) reacts with sodium carbonate (aq) to from solid calcium

carbonate and aqueous sodium chloride. Determine the volume of a 2.00 M

Calcium chloride solution would be needed to exactly react with 0.0650 L of 1.50

M Na2CO3. (Use BCA!)


Name

Date Pd

Molarity Practice Problems

1. How many grams of potassium carbonate are needed to make 200 mL of a

2.5 M solution?

2. How many liters of a 4 M solution can be made using 100 grams of lithium

bromide?

3. What is the concentration of an aqueous solution with a volume of 450 mL

that contains 200 grams of iron (II) chloride?

4. How many grams of ammonium sulfate are needed to make a 0.25 L

solution at a concentration of 6 M?

5. What is the concentration of a solution with a volume of 2.5 liters

containing 660 grams of calcium phosphate?

6. How many grams of copper (II) fluoride are needed to make 6.7 liters of a

1.2 M solution?


7. How many liters of a 0.88 M solution can be made with 25.5 grams of

lithium fluoride?

8. What is the concentration of a solution with a volume of 660 mL that

contains 33.4 grams of aluminum acetate?

9. How many liters of a 0.75 M solution can be made with 75 grams of lead

(II) oxide?

10. How many grams of manganese (IV) oxide are needed to make 5.6 liters

of a 2.1 M solution?

11. What is the concentrarion of a solution with a volume of 9 mL that

contains 2 grams of iron (III) hydroxide?

12. How many liters of a 3.4 M isopropanol solution can be made with 78

grams of isopropanol (C3H8O)?

13. What is the concentration of a solution with a volume of 3.3 mL that

contains 12 grams of ammonium sulfite?


Chemistry – Unit 9 Notes on ∆H

The Modeling approach stresses representing structure in systems or processes

several ways. We want you to be able to represent energy changes in chemical

reactions in multiple ways.

Consider the reaction in which methane burns in air to produce carbon dioxide

and water. The balanced equation for this reaction is

CH4 + 2 O2 CO2 + 2 H2O

Experiments show that when one mole of CH4 is burned, 890 kJ are released.

There are several ways we can represent this information.

1. Write the chemical equation including the energy term. Since energy is

released, we regard it as a product of the reaction.

CH4 + 2 O2 CO2 + 2 H2O + 890 kJ

We are now quantifying the treatment of chemical potential energy we began in

unit 5.

Sample question: What mass of oxygen gas is consumed when 35 kJ are

released in the reaction above?

35kJ2molesO2

890kJ

32g

1mole 2.5gO2

2. Sketching an energy bar graph for the reaction.

Note in this representation, we show that chemical potential energy of the

system decreases as the atoms are rearranged to form new molecules. The

thermal energy increases (system gets hotter) as energy is conserved.

Eventually, the system will lose energy to the cooler surroundings.

3. Write the energy term using ∆H notation.

The reaction is written: CH4 + 2 O2 CO2 + 2 H2O ∆H = –890 kJ

The negative sign indicates that the system loses chemical potential energy. It

is as if you made a withdrawal from the bank, lowering your account balance.


4. This reaction is said to be exothermic because eventually energy is transferred

from the system to the surroundings.

Next, you can show the various ways to represent an endothermic reaction.

Experimental evidence has shown that the chemical reaction:

H2 + Br2 2 HBr requires 72.8 kJ of energy to proceed. Your goal is to

represent this reaction three different ways:

1. by writing a balanced equation with the energy term in the equation.

2. by completing an energy bar graph diagram, showing how Eth and Ech change

in the system. Will energy eventually flow into or out of the system? Why?

3. by using the ∆H notation to describe the energy.


Name

Date Pd

Chemistry – Unit 9 Worksheet 4

1. How many kJ of heat will be released when 4.72 g of carbon react with excess

oxygen gas to produce carbon dioxide?

C + O2 CO2 ∆Hº = –393.5 kJ

2. How much heat should be transferred when 38.2 g of liquid bromine reacts with

excess hydrogen gas to form hydrogen bromide? Is the heat being transferred

from the system to the surroundings or from the surroundings to the system?

H2 + Br2 2 HBr ∆Hº = 72.80 kJ

3. How many kJ of heat would you expect to be transferred when 6.44 g of sulfur

react with excess oxygen gas to produce sulfur trioxide? Is this reaction

endothermic or exothermic?

2 S + 3 O2 2 SO3 ∆Hº = –791.4 kJ

4. Nitrogen gas and oxygen gas can combine to produce nitric oxide, NO. If such a

reaction absorbs 88.0 kJ of heat from the surroundings, how many grams of

nitrogen gas do you predict were consumed in the reaction?

N2 + O2 2 NO ∆Hº = 180 kJ


5. Ammonia gas combines with excess oxygen gas to produce nitric oxide and

water. If 256 kJ of energy were released in such a reaction, how many grams of

ammonia gas were reacted?

4 NH3 + 5 O2 4 NO + 6 H2O ∆Hº = – 1170 kJ

6. Carbon in the form of graphite combines with excess hydrogen gas to form

benzene, C6H6. In the following reaction 3.95 kJ of heat were transferred.

Calculate the grams of graphite reacted. Is the reaction endothermic or

exothermic?

6C (graphite) + 3 H2 C6H6 ∆Hº = 49.03 kJ

7. How much heat will be released if 30.0 g of octane (C8H18) is burned in excess

oxygen?

C8H18 + 12 1/2 O2 8 CO2 + 9 H2O ∆H = –5483.4 kJ

How much heat would be released by burning one gallon of octane? The density

of octane is 0.703g/mL. 1 gallon = 3.79 liters.

1. 155 kJ 2. 17.4 kJ 3. 79.5 kJ 4. 13.7 g

5. 14.9 g 6. 5.80 g 7. 1440 kJ, 128,000 kJ


Chemistry – Unit 9 Review

Molar volume and gas stoichiometry

1. A mixture contains 8.00 g each of O2, CO2, and SO2 at STP. Calculate the

volume of this mixture. Which of the gases would exert the greatest pressure

and why?

Molar volume =

22.4L

1mole

2. Nitrogen gas and hydrogen gas combine to produce ammonia gas (NH3). What

volume of hydrogen gas at STP would be required to react with 10.0 g of nitrogen

gas?

3. Consider the following reaction: P4(s) + 6 H2(g) 4 PH3(g)

What volume of hydrogen gas at 25C and 0.981 atm is required to react

completely with 2.51 g of P4 ?

PV nRT

R 0.0821L atm

mole K


Molar concentration 4. What mass of Na2CO3 is needed to prepare 1.25 L of a 0.75M solution?

Mass stoichiometry 5. When potassium carbonate reacts with hydrogen chloride, the products are

potassium chloride, carbon dioxide and water. What mass of hydrogen chloride

is needed to completely react with 14.8 g of potassium carbonate?

Representing reactions 6. Nitric oxide (NO) reacts with oxygen gas to produce nitrogen dioxide. In the box

at left represent a mixture containing 8 molecules of NO and 6 molecules of O2.

In the box at right represent the system after the reaction had gone to

completion. Be sure to provide a key.

––>

a. Write the balanced equation for the reaction.

b. Which is the limiting reactant?

c. How many molecules of the xs reactant remain?

do not, under any circumstances, throw this away! this ... ws...modeling chemistry unit 9 packet...

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