Chemistry help please?

According to this chemical reaction, which is the number of grams of Fe produced from 49.4 moles of H₂?
Fe₃O₄(cr) + 4 H₂(g) → 3 Fe(cr) + 4 H₂O (l)

No. of moles of Fe produced = (49.4 mol) × (3/4) = 37.05 mol
Mass of Fe produced = (37.05 mol) × (55.8 g/mol) = 2070 g

The answer: a. 2070

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Calculate the number of moles of Al₂O₃ that are produced when 5.1 mol of Fe is produced in the following reaction.
2Al(s) + 3FeO(s) → 3Fe(s) + Al₂O₃ (s)

No. of moles of Al₂O₃ produced = (5.1 mol) × (1/3) = 1.7 mol

The answer: b. 1.7

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For the reaction Cl₂ + 2KBr → 2KCl + Br₂, how many moles of potassium chloride are produced from 258.1 g of potassium bromide?

No. of moles of KBr reacted = (258.1 g) / (119.0 g/mol) = 2.17 mol
No. of moles of KCl produced = (2.17 mol) × (2/2) = 2.17 mol

The answer: a. 2.17

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Mercury can be obtained by reacting mercury(II) sulfide with calcium oxide. How many grams of calcium oxide are needed to produce 31.28 g of Hg?
4HgS(s) + 4CaO(s) → 4Hg(l) + 3CaS(s) + CaSO⁴

No. of moles of Hg produced = (31.28 g) / (200.6 g/mol) = 0.1559 mol
No. of moles of CaO needed = (0.1061 mol) × (4/4) = 0.1061 mol
Mass of CaO needed = (0.1559 mol) × (56.1 g/mol) = 8.75 g

The answer: a. 8.75

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What is the mass of potassium chloride when 103.3 g of potassium reacts with excess of chlorine gas?

2 K + Cl₂ → 2 KCl
No. of moles of K reacted = (103.3 g) / (39.0 g/mol) = 2.649 mol
No. of moles of KCl produced = (2.649 mol) × (2/2) = 2.649 mol
Mass of KCl produced = (2.649 mol) × (74.5 g/mol) = 197 g

The answer: a. 197

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How many grams of H₂O will be produced if 1.7 grams of Fe are produced?
Fe₃O₄ + H₂ → Fe + H₂O

The balanced equation for the reaction should be:
Fe₃O₄ + 4H₂ → 3Fe + 4H₂O
No. of moles of Fe produced = (1.7 g) / (55.8 g/mol) = 0.03047 mol
No. of moles of H₂O produced = (0.03047 mol) × (4/3) = 0.04063 mol
Mass of H₂O produced = (0.04063 mol) × (18.0 g/mol) = 0.73 g

The answer: c. 0.73 g


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For the reaction 2H₂ + O₂ → 2H₂O, how many grams of water are produced from 6.2 mol of hydrogen?

No. of moles of H₂O produced = (6.2 mol) × (2/2) = 6.2 mol
Mass of H₂O produced = (6.2 mol) × (18.0 g/mol) = 112 g

The answer: a. 112

According to this chemical reaction, which is the number of grams of Fe produced from 49.4 moles of H2?
Fe3O4 (cr) + 4 H2 (g) → 3 Fe (cr) + 4 H2O (l)

The coefficients in a balanced equation determine the ratio of the moles of reactants to the moles of products. According to the coefficients in this balanced equation, one mole of Fe3O4 reacts with four moles of H2 to three moles of Fe and four moles of water. The ratio of moles of Fe to moles of H2 is 3:4. Let’s use the following proportion.

3 ÷ 4 = n ÷ 49.4
n = ¾ * 49.4 = 37.05

The mass of one mole of iron is 55.8 grams.
Mass = 37.05 * 55.8 = 2067.39 grams
a is the correct answer. I will use the process to solve the rest of these problems.

Calculate the number of moles of Al2O3 that are produced when 5.1 mol of Fe is produced in the following reaction.
2Al(s) + 3FeO(s) --> 3Fe(s) + Al2O3(s)
Let’s use the following proportion.

3 ÷ 1 = 5.1 ÷ n
n = 1.7

For the reaction Cl2 + 2KBr → 2KCl + Br2, how many moles of potassium chloride are produced from 258.1 g of potassium bromide?

According to the coefficients in this equation, two moles of KBr will produce two moles of KCl. This means the number of moles is the same for both compounds.

Mass of one mole of potassium bromide = 39.1 + 79.9 = 119 grams
n = 258.1 ÷ 119
This is approximately 2.17. a is the correct answer.


Mercury can be obtained by reacting mercury(II) sulfide with calcium oxide. How many grams of calcium oxide are needed to produce 31.28 g of Hg?

4HgS(s) + 4CaO(s) → 4Hg(l) + 3CaS(s) + CaSO4

This is similar to the previous problem. The number of moles of mercury sulfide is equal to the number of moles of calcium oxide and two the number of moles of mercury.

For mercury, mass of one mole = 200.6 grams
n = 31.28 ÷ 200.6
This is approximately 0.156 mole.
For calcium oxide, mass of one mole = 40.1 + 16 = 56.1 grams

To determine the mass of calcium oxide, multiply the number of moles by the mass of one mole.
Mass = 56.1 * (31.28 ÷ 200.6)
This is approximately 8.75 grams.

What is the mass of potassium chloride when 103.3 g of potassium reacts with excess of chlorine gas?

K + Cl2 → KCl
To balance this equation, make 2 K and 2KCl.
2 K + Cl2 → 2 KCl

For K, n = 103.3 ÷ 39.1

This is approximately 2.64 moles. This is also the number of moles of potassium chloride.
For KCl, mass of one mole = 39.1 + 35.5 = 74.6 grams
Mass KCl = 74.6 * (103.3 ÷ 39.1)
This is approximately 197 grams. a is the correct answer.

How many grams of H2O will be produced if 1.7 grams of Fe are produced?

Fe3O4 + H2 → Fe + H2O
To balance the Fe’s, make 3 Fe. To balance the O’s, make 4 H2O.
Fe3O4 + H2 → 3 Fe + 4 H2O
To balance the H’s, make 4 H2
Fe3O4 +4 H2 → 3 Fe + 4 H2O

According to the coefficients in this equation, one mole of Fe3O4 reacts with four moles of H2 to produce three moles of Fe and four moles of H2O. The ratio of moles of Fe to moles of H2O is 3:4.

For Fe, n =1.7 ÷ 55.8
This is approximately 0.03 mole.
For H2O, n = 4/3 * (1.7 ÷ 55.8)
This is approximately 0.041 mole. The mass of one mole of H2O is 18 grams.

Mass H2O = 18 * [4/3 * (1.7 ÷ 55.8)]
This is approximately 0.73gram. c is the correct answer.

For the reaction 2H2 + O2 → 2H2O, how many grams of water are produced from 6.2 mol of hydrogen?

Since hydrogen and water have the same coefficients, the number of mole of water is equal to the number of moles of hydrogen. As I said before, the mass of one mole of water is 18 grams.

Mass of H2O = 6.2 * 18 = 111.6 grams

This rounds to 112 grams. So “a” is the correct answer. I hope this is helpful for you. I really like these multiple choice problems. I can tell if I have made a mistake, if my answer is not in the list of answers. At 69 years old, with some serious health problems, I can use all the help that I can find. I really enjoy helping people like you.