Answer to Question #290495 in Chemistry for thaiana

Question

1. When 9.0 g of hydrogen gas, H₂, reacts with oxygen gas, O₂, 73.0 g of water is produced.    

2H2 + O2 --> 2H2O 

a) What is the theoretical yield of water? 

b) What is the percentage yield?

2. Powdered zinc metal reacts with sulphur (S₈) when heated to produce zinc sulphide.

8Zn + S₈ --> 8ZnS

a) What mass of product can be produced with 25 g of zinc?

b) What is the actual yield if the percentage yield was 80%?

3. The thermite reaction has been used to weld railroad rails, make bombs, and ignite solid rocket fuel. The equation of the reaction is:

Fe₂O₃ + 2Al --> 2Fe + Al₂O₃

a) What is the theoretical yield of iron if 100.0 g of Fe₂O₃ is used?

b) What is the percentage yield if 52.3 g of iron is actually produced?

Answer 1

1. When 9.0 g of hydrogen gas, H₂, reacts with oxygen gas, O₂, 73.0 g of water is produced.    

2H₂ + O₂ → 2H₂O 

a) What is the theoretical yield of water? 

b) What is the percentage yield?

Solution (1):

Calculate the moles of hydrogen gas (H₂):

The molar mass of H₂ is 2.016 g/mol

Hence,

Moles of H₂ = (9.0 g H₂) × (1 mol H₂ / 2.016 g H₂) = 4.4643 mol H₂

Balanced chemical equation:

2H₂ + O₂ → 2H₂O

According to stoichiometry:

2 mol of H₂ produces 2 mol of H₂O

Thus, 4.4643 mol of H₂ produces:

(4.4643 mol H₂) × (2 mol H₂O / 2 mol H₂) = 4.4643 mol H₂O

Calculate the theoretical yield of water (H₂O):

The molar mass of H₂O is 18.0153 g/mol

Hence,

Mass of H₂O = (4.4643 mol H₂O) × (18.0153 g H₂O / 1 mol H₂O) = 80.426 g H₂O = 80.43 g H₂O

The theoretical yield of water (H₂O) is 80.43 grams

Calculate the percentage yield:

%yield = (actual yield / theoretical yield) × 100%

%yield = (73.0 g / 80.43 g) × 100% = 90.76%

The percentage yield is 90.76%

Answer (1):

a) The theoretical yield of water is 80.43 grams

b) The percentage yield is 90.76%

2. Powdered zinc metal reacts with sulphur (S₈) when heated to produce zinc sulphide.

8Zn + S₈ → 8ZnS

a) What mass of product can be produced with 25 g of zinc?

b) What is the actual yield if the percentage yield was 80%?

Solution (2):

Calculate the moles of zinc (Zn):

The molar mass of Zn is 65.38 g/mol

Hence,

Moles of Zn = (25 g Zn) × (1 mol Zn / 65.38 g Zn) = 0.3824 mol Zn

Balanced chemical equation:

8Zn + S₈ → 8ZnS

According to stoichiometry:

8 mol of Zn produces 8 mol of ZnS

Thus, 0.3824 mol of Zn produces:

(0.3824 mol Zn) × (8 mol ZnS / 8 mol Zn) = 0.3824 mol ZnS

Calculate the mass of product (ZnS):

The molar mass of ZnS is 97.474 g/mol

Hence,

Mass of ZnS = (0.3824 mol ZnS) × (97.474 g ZnS / 1 mol ZnS) = 37.27 g ZnS

The theoretical mass of product (ZnS) is 37.27 grams

Calculate the actual yield:

%yield of product = 80%

%yield = (actual yield / theoretical yield) × 100%

Hence,

actual yield of product (ZnS) = theoretical yield × (%yield / 100%)

actual yield of product (ZnS) = (37.27 g) × (80% / 100%) = 29.82 g

The actual yield of product (ZnS) is 29.82 grams

Answer (2):

a) The mass of product is 37.27 grams

b) The actual yield of product is 29.82 grams

3. The thermite reaction has been used to weld railroad rails, make bombs, and ignite solid rocket fuel. The equation of the reaction is:

Fe₂O₃ + 2Al → 2Fe + Al₂O₃

a) What is the theoretical yield of iron if 100.0 g of Fe₂O₃ is used?

b) What is the percentage yield if 52.3 g of iron is actually produced?

Solution (3):

Calculate the moles of Fe₂O₃:

The molar mass of Fe₂O₃ is 159.69 g/mol

Hence,

Moles of Fe₂O₃ = (100.0 g Fe₂O₃) × (1 mol Fe₂O₃ / 159.69 g Fe₂O₃) = 0.6262 mol Fe₂O₃

Balanced chemical equation:

Fe₂O₃ + 2Al → 2Fe + Al₂O₃

According to stoichiometry:

1 mol of Fe₂O₃ produces 2 mol of Fe

Thus, 0.6262 mol of Fe₂O₃ produces:

(0.6262 mol Fe₂O₃) × (2 mol Fe / 1 mol Fe₂O₃) = 1.2524 mol Fe

Calculate the theoretical yield of iron (Fe):

The molar mass of Fe is 55.845 g/mol

Hence,

Mass of Fe = (1.2524 mol Fe) × (55.845 g Fe / 1 mol Fe) = 69.94 g Fe

The theoretical yield of iron (Fe) is 69.94 grams

Calculate the percentage yield:

%yield = (actual yield / theoretical yield) × 100%

%yield = (52.3 g / 69.94 g) × 100% = 74.78%

The percentage yield is 74.78%

Answer (3):

a) The theoretical yield of iron is 69.94 grams

b) The percentage yield is 74.78%