3RD QUARTER S.Y. 2017: Stoichiometry (A bit difficult)

NOT ANOTHER STOIC PROBLEM

1) Barium sulfate, BaSO4, is made by the following reaction:


Ba(NO3)2(aq) + Na2SO4(aq) à BaSO4(s) + 2NaNO3(aq)
An experiment was begun with 75.00g of Ba(NO3)2 and an excess of Na2SO4. After collecting and drying the product, 63.45g BaSO4 was obtained. Calculate the theoretical yield and percent yield of BaSO4.



2) Aluminum sulfate can be made by the following reaction:
2AlCl3(aq) + 3H2SO4(aq) à Al2(SO4)3(aq) + 6HCl(aq)
It is quite soluble in water, so to isolate it the solution has to be evaporated to dryness. This drives off the volatile HCl, but the residual solid has to be treated to a little over 200°C to drive off all the water. In one experiment, 25.0g of AlCl3 was mixed with 30.0g H2SO4. Eventually, 28.46g of pure Al2(SO4)3 was isolated. Calculate the percent yield.


ANSWERS:

1.) theoretical yield = 66.98g BaSO4, % yield = 94.73%
2.) % yield = 88.74%

3RD QUARTER S.Y.2017: Stoichiometry Reviewer (SORT OF EASY)

SORT OF EASY STOICHIOMETRY PROBLEMS

1)  Chlorine is used by textile manufacturers to bleach cloth.  Excess chlorine is destroyed by its reaction with sodium thiosulfate, Na₂S₂O₃:

Na₂S₂O_3(aq) + 4Cl_2(g) + 5H₂O_(aq) à 2NaHSO_4(aq) + 8HCl_(aq)

a.     How many moles of Na₂S₂O₃ are needed to react with 0.12mol of Cl₂?

b.     How many moles of HCl can form from 0.12mol of Cl₂?

c.       How many moles of H₂O are required for the reaction of 0.12mol of Cl₂?

d.     How many moles of H₂O react if 0.24mol HCl is formed?

2)  The incandescent white of a fireworks display is caused by the reaction of phosphorous with O₂ to give P₄O₁₀.

a.     Write the balanced chemical equation for the reaction.

b.     How many grams of O₂ are needed to combine with 6.85g of P?

c.       How many grams of P₄O₁₀ can be made from 8.00g of O₂?

d.     How many grams of P are needed to make 7.46g P₄O₁₀?

3)  In dilute nitric acid, HNO₃, copper metal dissolves according to the following equation:

3Cu_(s) + 8HNO_3(aq) à 3Cu(NO₃)_2(aq) + 2NO_(g) + 4H₂O_(aq)

            How many grams of HNO₃ are needed to dissolve 11.45g of Cu?

4)  The reaction of powdered aluminum and iron(II)oxide,

2Al_(s) + Fe₂O_3(s) à Al₂O_3(s) + 2Fe_(l)

produces so much heat the iron that forms is molten.  Because of this, railroads use the reaction to provide molten steel to weld steel rails together when laying track.  Suppose that in one batch of reactants 4.20mol Al was mixed with 1.75mol Fe₂O₃.

a.     Which reactant, if either, was the limiting reactant?

b.     Calculate the mass of iron (in grams) that can be formed from this mixture of reactants.

5)  Silver nitrate, AgNO₃, reacts with iron(III) chloride, FeCl₃, to give silver chloride, AgCl, and iron(III) nitrate, Fe(NO₃)₃.  A solution containing 18.0g AgNO₃ was mixed with a solution containing 32.4g FeCl₃. How many grams of which reactant remains after the reaction is over?

ANSWERS:

1)  a. 0.030mol Na₂S₂O₃            b. 0.24mol HCl            c. 0.15mol H₂O

 d. 0.15mol H₂O

2)  a. 4P + 5O₂ à P₄O₁₀            b. 8.85g O₂            c. 14.2g P₄O₁₀               d. 3.26g P

3)  30.31g HNO₃

4)  a. limiting reactant is Fe₂O₃            b. 195g Fe is formed

5)  26.7g of FeCl₃ are left over

3RD QUATRER S.Y. 2012 - 2013: Stoichiometry Reviewer (EASY)

 _{EASY STOICHIOMETRY PROBLEMS}

1)      How many moles of sodium atoms correspond to 1.56x10²¹ atoms of sodium?

2)      How many moles of Al atoms are needed to combine with 1.58 mol of O atoms to make aluminum oxide, Al₂O₃?

3)      How many moles of Al are in 2.16 mol of Al₂O₃?

4)      Aluminum sulfate, Al₂(SO₄)₃, is a compound used in sewage treatment plants. 

a.     Construct a pair of conversion factors that relate moles of aluminum to moles of sulfur for this compound

b.     Construct a pair of conversion factors that relate moles of sulfur to moles of Al₂(SO₄)₃

c.       How many moles of Al are in a sample of this compound if the sample also contains 0.900 mol S?

d.     How many moles of S are in 1.16 mol Al₂(SO₄)₃?

5)      How many moles of H₂ and N₂ can be formed by the decomposition of 0.145 mol of ammonia, NH₃?

ANSWERS:

1)      2.59x10^-3mol Na atoms  

2)      1.05mol Al                

3)      4.32mol Al

4)      a. 2mol Al/3mol S            b. 3mol S/1mol Al₂(SO₄)₃            c. 0.600mol Al     d. 3.48mol S

5)      0.0725mol N₂ and 0.218mol H₂

 

3RD QUARTER S.Y. 2012 - 2013: Mole Conversion Reviewer

Holey-Moley!

A good mole-y day to everyone. Good thing we're not dealing with this kind of mole. Look at those nails!

Moles, Molecules, and Grams Worksheet – (Answers in Red)

1)         How many molecules are there in 24 grams of FeF₃? 1.28 x 10²³ molecules

2)         How many molecules are there in 450 grams of Na₂SO₄?  1.91 x 10²⁴ molecules

3)         How many grams are there in 2.3 x 10²⁴ atoms of silver?  421 grams

4)         How many grams are there in 7.4 x 10²³ molecules of AgNO₃?  209 grams

5)         How many grams are there in 7.5 x 10²³ molecules of H₂SO₄?  122 grams

6)         How many molecules are there in 122 grams of Cu(NO­₃)₂?  3.92 x 10²³ molecules

7)         How many grams are there in 9.4 x 10²⁵ molecules of H₂?  312 grams

8)         How many molecules are there in 230 grams of CoCl₂?  1.07 x 10²⁴ molecules

9)         How many molecules are there in 2.3 grams of NH₄SO₂?  1.69 x 10²² molecules

10)      How many grams are there in 3.3 x 10²³ molecules of N₂I₆?  430 grams

3RD QUARTER S.Y. 2012-2013: GAS LAWS

GAS LAWS

1. The volume of a person's lungs is 600.0 mL at a pressure of 760 mmHg. By how much will the pressure drop when the lungs expand to 610.0 mL?

ANSWER: 12.46 mmHg ~ 12 mmHg (Pressure dropped from 760 mmHg to 747.54 mmHg)

2.  What is the volume of a sample of oxygen at 3.0 degrees Celsius and 744 torr if it occupies 13.3 L at 55 degrees Celsius and 744 torr?

ANSWER: 11.19L ~ 11L

3.  An aerosol container has a pressure of 3.0 atm at 30 degrees Celsius. What is the new pressure in the aerosol container if it is thrown into a fire with a temperature of 550 degrees Celsius? The aerosol can may explode if the pressure exceeds 7.0 atm. Would you expect the can to explode?

ANSWER: 8.15 atm ~ 8 atm

4.  A high altitude balloon is filled with 1.2 x 10^4 L (12,000 L) of helium at a temperature of 27 degrees Celsius and a pressure of 760 torr. What is the volume of this balloon at a height of 10 km, where the temperature is -25 degrees Celsius and the pressure of 63 torr?

ANSWER: 119,682.38 L ~ 120,000 L

5.  At STP, a gas has a volume of 8.00 L. What volume will the gas occupy at 50 degrees Celsius and 600 torr? 

ANSWER: 11.995 L ~ 10 L

6.  A 3.00 L flask contains 2.33 g argon gas at 312 mmHg. What is the temperature of the gas? 

ANSWER: 257.149 K ~ 257 K

7.  The composition (in mole percent) of the atmosphere is 78.1% N2, 21.0% O2 and 0.9% Ar. What is the partial pressure of each gas when the barometric pressure is 754.1 mmHg?

ANSWER: Oxygen = 158.4 mmHg; Nitrogen = 588.95 mmHg; Argon = 6.79 mmHg

8.  A volatile compound with a mass of 0.8822 grams is placed in an evacuated 0.250 L flask. The flask is heated to evaporate the compound. At 99 degrees Celsius, the pressure in the flask is 1.25 atm. What is the molar mass of the compound? 

ANSWER: 86.25 g/mol ~ 86 g/mol

9.  A certain gas diffuses at a rate of 85 cm^3/s in a diffusion apparatus in which a second gas, He, whose molecular weight is 4.0 g/mol, diffuses at the rate of 224.9 cm^3/s. Calculate the molecular weight of the gas.

ANSWER: 28 g/mol

10.  At certain temperature and pressure, 88.75 grams of chlorine gas has a volume of 5.10 L. What is the volume after 4.00 moles of chlorine gas is added?

ANSWER: 21.4 L 

HAPPY LONG TEST EVERYONE!