More Stoichemistry Problems

Question

Which of the following statements are always true? Never true? Not always true?

a. A compound wit the molecular formula C6H6 has the same simplest formula.

b. The mass percent of copper in CuO is less than in Cu2O.

c. The limiting reactant is the one present in the smallest number of grams.

d. Since C3H6O3 and C6H12O6 reduce to the same formula, they represent the same compound.

A bedroom 11 ft x 12 ft x 8.0 ft contains 35.41 kg of air at 25˚C. Express the volume of the room in liters, the amount of air in moles (molar mass of air is 29.0 g/mol) and the temperature in Kelvin.

A sample of carbon dioxide gas, CO2 (g), occupies a volume of 5.75 L at 0.890 atm. If the temperature and the number of moles remain constant, calculate the volume when the pressure

a. increased to 1.25 atm

b. decrease to 0.350 atm

A nitrogen sample at 30˚C has a volume of 1.75L. If the pressure and the amount of gas remain unchanged, determine the volume when:

a. The Celsius temperature is doubled

An open flask contains 0.200 mol of air. Atmospheric pressure is 745 mmHg and room temperature is 68˚F. How many moles are present in the flask when the pressure is 1.10 atm and the temperature is 33˚C?

On a warm day, an amusement park balloon is filled with 47.8 g He. The temperature is 33˚C and the pressure in the balloon is 2.25 atm. Calculate the volume of the balloon.

A drum use to transport crude oil has a volume of 162 L. How many water molecules, as steam, are required to fill the drum at 1.00 atm and 100˚C? What volume of liquid water (density of water is 1.0 g/cm3) is required to produce that amount of steam?

Calculate the densities of the following gases at 27˚C and 763 mmHg

a. Carbon monoxide

b. Chlorine

Answer 1

lll

Which of the following statements are always true? Never true? Not always true?

a A compound wit the molecular formula C6H6 has the same simplest formula. (.Never True, its simlpest formula, the empirical formula is CH)

b. The mass percent of copper in CuO is less than in Cu2O.(Never true, Cu has the mass of 2 coppers to 1 oxygen ,... & so has the greater % Cu)

c. The limiting reactant is the one present in the smallest number of grams.(sometimes true, its based on the number moles added vs. the moles needed in the balanced equation)

d. Since C3H6O3 and C6H12O6 reduce to the same formula, they represent the same compound.(never true, & even sometimes two different compounds can be C6H12O6)

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A bedroom 11 ft x 12 ft x 8.0 ft contains 35.41 kg of air at 25˚C. Express the volume of the room in liters, the amount of air in moles (molar mass of air is 29.0 g/mol) and the temperature in Kelvin.

11 ft x 12 ft x 8.0 ft can be changed to centimeters each (@ 2.54cm / inch), then multiplied to cubic centimeters, which are milliliters, then to litres.

but: 11 ft x 12 ft x 8.0 ft = 1056 cu ft

1056cu ft @ 28.32 liters / 1cu ft = 29905.9 litres

Your answer (3 sig figs) : 29,900 litres or 2.99e4 litres

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35,410 grams air @ 29.0 g/mol = 1221 moles of air

your answer (3 sig figs) : 1220 moles of air

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25 Celsius + 273 =

your answer: 298 Kelvin

======================================...

A sample of carbon dioxide gas, CO2 (g), occupies a volume of 5.75 L at 0.890 atm. If the temperature and the number of moles remain constant, calculate the volume when the pressure

a. increased to 1.25 atm

P1V1T2 = P2V2T1 which @ constant temperature simplifies to:

P1V1=P21V2

(0.890)(5.75) = (1,25)(V2)

V2 = 4.09 litres

b. decrease to 0.350 atm

P1V1=P21V2

(0.890)(5.75) = (0.350)(V2)

V2 = 14.6 litres

==============================

A nitrogen sample at 30˚C ,(aka 303 Kelvin),has a volume of 1.75L. If the pressure and the amount of gas remain unchanged, determine the volume when:

a. The Celsius temperature is doubled to 60 Celsius, (aka 333Kelvin)

P1V1T2 = P2V2T1 which, at constant pressure, simplifies to:

V1T2= V2T1

(1.75L)(333Kelvin) = (V2)(303K)

V2 = 1.92 litres

====================

An open flask contains 0.200 mol of air. Atmospheric pressure is 745 mmHg and room temperature is 68˚F. How many moles are present in the flask when the pressure is 1.10 atm and the temperature is 33˚C?

find the volume of the flask:

PV=nRT

(745Torr)(V) = 0.200(62.36Torrr-Litres/mol-K)(341K)

V = 5.7086 litres

now find the moles in that volume at the new conditions:

PV=nRT

(1.10 atm)(5.7086 L) = n (0.08206 L-atm/mol-K)(306K)

n= 0.250 moles

===========================

On a warm day, an amusement park balloon is filled with 47.8 g He. The temperature is 33˚C and the pressure in the balloon is 2.25 atm. Calculate the volume of the balloon.

find moles using molar mass of Helium:

47.8 grams He @ 4.0026 g/mol = 11.942 moles He

find volume, using

PV=nRT

(2.25 atm) (V) = 11.942 moles (0.08206 L-atm/mol-K) (310K)

V= 135.02 litres

Your answer (3 sig figs): 135 litres

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A drum use to transport crude oil has a volume of 162 L. How many water molecules, as steam, are required to fill the drum at 1.00 atm and 100˚C? What volume of liquid water (density of water is 1.0 g/cm3) is required to produce that amount of steam?

find moles of :

PV=nRT

(1.00atm)(162L) = n (0.08206L-atm/mol-K)(373K)

n= 5.2927 moles at those conditions

use Avagadro's # to get molecules:

5.2927 moles @ 6.022e23 molecules / mole = 3.187e24 molecules

your answer(3sigfigs) = 3.19e24 molecules

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What volume of liquid water ...

first find grams of water:

5.2927 moles @ 18.015 g/mol = 95.348 grams of water

now find ml's using density:

95.348 grams @ 1.0 g/ml = 95 ml

your answer(2sigfigs) : 95 ml

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Calculate the densities of the following gases at 27˚C and 763 mmHg

a. Carbon monoxide ,

first find the volume of 1 mole of CO:

PV=nRT

(763Torr)(V) = 1 mol(62.36 Torr-Litres/mol-K)(300K)

V= 24.52 litres

now find the density of that mole of CO, (whose molar mass is 28.01 g/mol):

28.01 grams / 24.52 litres =

your answer: 1.14 grams /Litre

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b. Chlorine ( Cl2 's molar mass is 70.9 grams/mole)

same steps:

70.9 grams / 24.52 litres =

your answer: 2.89 grams / litre