Mass-Mass Problems

#1 - 10

**Problem #1:** Given the following equation:

2C_{4}H_{10}+ 13O_{2}---> 8CO_{2}+ 10H_{2}O

show what the following molar ratios should be.

(a) C_{4}H_{10}/ O_{2}

(b) O_{2}/ CO_{2}

(c) O_{2}/ H_{2}O

(d) C_{4}H_{10}/ CO_{2}

(e) C_{4}H_{10}/ H_{2}O

**Solution:**

(a) 2 / 13

(b) 13 / 8

(c) 13 / 10

(d) 2 / 8 (or 1 / 4)

(e) 2 / 10 (or 1 / 5)

**Problem #2:** Given the following equation:

2KClO_{3}---> 2KCl + 3O_{2}

How many moles of O_{2} can be produced by letting 12.00 moles of KClO_{3} react?

**Solution:**

The KClO_{3}to O_{2}molar ratio is 2:3.2 mol KClO

_{3}/ 3 mol O_{2}= 12.00 mol KClO_{3}/ x = 18.00 mol.x = 18.00 mol of O

_{2}

**Problem #3:** Given the following equation:

2K + Cl_{2}---> 2KCl

(a) How many grams of KCl is produced from 2.50 g of K and excess Cl_{2}.

(b) From 1.00 g of Cl_{2} and excess K?

**Solution:**

(a)(b)

**Problem #4:** Given the following equation:

Na_{2}O + H_{2}O ---> 2NaOH

(a) How many grams of NaOH is produced from 1.20 x 10^{2} grams of Na_{2}O? (b) How many grams of Na_{2}O are required to produce 1.60 x 10^{2} grams of NaOH?

**Solution:**

(a)(b)

**Problem #5:** Given the following equation:

8Fe + S_{8}---> 8FeS

(a) What mass of iron is needed to react with 16.0 grams of sulfur?

(b) How many grams of FeS are produced?

**Solution:**

(a)(b)

**Problem #6:** Given the following equation:

2NaClO_{3}---> 2NaCl + 3O_{2}

(a) 12.00 moles of NaClO_{3} will produce how many grams of O_{2}?

(b) How many grams of NaCl are produced when 80.0 grams of O_{2} are produced?

**Solution:**

(a)(b)

**Problem #7:** Given the following equation:

Cu + 2AgNO_{3}---> Cu(NO_{3})_{2}+ 2Ag

(a) How many moles of Cu are needed to react with 3.50 moles of AgNO_{3}?

(b) If 89.5 grams of Ag were produced, how many grams of Cu reacted?

**Solution:**

(a)(b)

**Problem #8:** Molten iron and carbon monoxide are produced in a blast furnace by the reaction of iron(III) oxide and coke (pure carbon). If 25.0 kilograms of pure Fe_{2}O_{3} is used, how many kilograms of iron can be produced? The reaction is:

Fe_{2}O_{3}+ 3C ---> 2Fe + 3CO

**Solution:**

**Problem #9:** The average human requires 120.0 grams of glucose (C_{6}H_{12}O_{6}) per day. How many grams of CO_{2} (in the photosynthesis reaction) are required for this amount of glucose? The photosynthetic reaction is:

6CO_{2}+ 6H_{2}O ---> C_{6}H_{12}O_{6}+ 6O_{2}

**Solution:**

**Problem #10:** Given the reaction:

4NH_{3}(g) + 5O_{2}(g) ---> 4NO(g) + 6H_{2}O(ℓ)

When 1.20 mole of ammonia reacts, the total number of moles of products formed is:

(a) 1.20

(b) 1.50

(c) 1.80

(d) 3.00

(e) 12.0

**Solution:**

The correct answer is d.The NH

_{3}/ (NO + H_{2}O) molar ratio is 4:104 / 10 = 1.20 / x

x = 3.00 mol

**Bonus Problem:**Potassium superoxide, KO_{2}, is used to produce O_{2} in space expeditions by using CO_{2}, governed by the following equation:

4KO_{2}+ 2CO_{2}---> 2K_{2}CO_{3}+ 3O_{2}

(a) How many grams of O_{2} are produced from 100. g KO_{2}, given sufficient CO_{2}?

(b) How many grams of CO_{2} can 100. g KO_{2} consume?

**Solution to (a):**

1) Determine moles of KO_{2}:

100. g / 71.096 g/mol = 1.40655 mol

2) From the coefficients of the balanced equation, we determine that the KO_{2} to O_{2} molar ratio is 4 : 3.

3) Determine moles of O_{2} that are produced:

4 1.40655 mol ––– = –––––––––– 3 x x = 1.0549125 mol of O

_{2}

4) Determine grams of oxygen:

(1.0549125 mol) (31.9988 g/mol) = 33.8 g

Notice that carbon dioxide is also scrubbed out of the space vehicle's atmosphere by the KO_{2}. A nice two'fer.

**Solution to (b):**

1) 100. g of KO_{2} is 1.40655 mol.

2) The molar ratio between KO_{2} and CO_{2} is 2 : 1.

3) Determine moles of CO_{2}:

2 1.40655 mol ––– = –––––––––– 1 x x = 0.703275 mol of CO

_{2}consumed

4) Determine mass of CO_{2}:

(0.703275 mol) (44.009 g/mol) = 30.950 gTo three sig figs, this is 31.0 g (a common mistake would be to write 31 g, making the answer only 2 sig figs)