Q: Which equation correctly expresses the percent yield of a reaction?

$$\%\text{R} = \frac{\text{cantidad real}}{\text{cantidad teórica}} \times 100$$

Question 1

A chemical plant needs to produce 5000 kg of pure HCl per day using Cl$$_2$$ with 90% purity and a reaction yield of 95%. What is the minimum mass of impure Cl$$_2$$ required daily? (Molar masses: HCl = 36.5 g/mol, Cl$$_2 = 71 g/$$mol)

Accepted Answer

$$\approx 7,700\ 	ext{kg}$$

Question 2

Which of the following best describes the 'reactivo limitante' (limiting reactant) in a chemical reaction?

Accepted Answer

The reactant that determines the maximum amount of product formed.

Question 3

A sample of 250 g of coal contains 70% pure carbon. How many moles of CO$$_2$$ are produced if all the pure carbon reacts with excess O$$_2$$? (Molar mass C = 12 g/mol, CO$$_2 = 44 g/$$mol)

Accepted Answer

$$14.6$$ moles

Question 4

In a reaction, 36 g of NH$$_3 is $$oxidized to produce 50.82 g of NO. What is the percent yield of the reaction? (Molar masses: NH$$_3 = 17 g/$$mol, NO = 30 g/mol; Balanced equation: $$4	ext{NH}_3 + 5	ext{O}_2 ightarrow 4	ext{NO} + 6	ext{H}_2	ext{O})$$

Accepted Answer

$$88.4\%$$

Question 5

A student reacts 100 g of N$$_2$$ and obtains 110 g of NH$$_3. $$What is the percent yield of the reaction? (Molar masses: N$$_2 = 28 g/$$mol, NH$$_3 = 17 g/$$mol; $$N_2 + 3H_2$$ \rightarrow 2NH_3$$)

Accepted Answer

$$93.5\%$$

Question 6

Why is it important for an industrial chemist to identify the limiting reactant before starting large-scale production of pharmaceuticals?

Accepted Answer

To maximize product yield and minimize waste.

Question 7

If 80 g of KClO$$_3 (70$$% pure) is decomposed, how many grams of KCl can be obtained? (Molar masses: KClO$$_3 = 122.5 g/$$mol, KCl = 74.5 g/mol; $$2KClO_3 \rightarrow 2KCl + 3O_2)$$

Accepted Answer

$$34.0 g$$

Question 8

A reaction uses 150 g of steel (86% Fe) and 0.125 mol of CuSO$$_4. $$Which is the limiting reactant? (Molar masses: Fe = 56 g/mol, CuSO$$_4 = 160 g/$$mol; $$Fe + $$CuSO_4$$ \rightarrow $$FeSO_4$$ + Cu)$$

Accepted Answer

CuSO$$_4$$

Question 9

In the reaction $$2C_4H_{10} + 13O_2 \rightarrow 8CO_2 + 10H_2O$$, how many grams of CO$$_2$$ are produced from 120 g of butane and 520 g of O$$_2$$? (Molar masses: C$$_4H$_{10} = 58 g/$$mol, O$$_2 = 32 g/$$mol, CO$$_2 = 44 g/$$mol)

Accepted Answer

$$352 g$$

Question 10

A sample of sodium (Na) with 95% purity is used to produce 50 g of pure NaCl with a reaction yield of 85%. How many grams of the impure sodium sample are required? (Molar masses: Na = 23 g/mol, NaCl = 58.5 g/mol; $$2Na + Cl_2$ \rightarrow 2NaCl)$$

Accepted Answer

$$35.7 g$$

Question 11

Which equation correctly expresses the percent yield of a reaction?

Accepted Answer

$$\%	ext{R} = \frac{	ext{cantidad real}}{	ext{cantidad teórica}} 	imes 100$$

Question 12

A reaction produces 85 g of Ca$$_3(PO$_4$$)$$_2$$ from 100 g of CaO and 50 g of H$$_3PO$_4. $$What is the percent yield? (Molar masses: CaO = 56 g/mol, H$$_3PO$_4 = 98 g/$$mol, Ca$$_3(PO$_4$$)$$_2 = 310 g/$$mol; $$3CaO + 2H_3PO_4 \rightarrow Ca_3$(PO_4$)_2 + 3H_2O)$$

Accepted Answer

$$54.8\%$$

Question 13

Which of the following best defines the 'pureza de un reactivo' (purity of a reactant)?

Accepted Answer

The ratio of the mass of the desired substance to the total mass of the sample, expressed as a percentage.

Question 14

In the reaction $$2PbS + 3O_2 \rightarrow 2PbO + 2SO_2$$, how many grams of PbS are needed to obtain 446 g of PbO if the yield is 85%? (Molar masses: PbS = 239 g/mol, PbO = 223 g/mol)

Accepted Answer

$$573 g$$

Question 15

A reaction uses 2945 g of aluminum carbide (Al$$_4C$_3) $$with 70% purity. If all the pure Al$$_4C$_3$$ reacts, how much methane (CH$$_4) is $$produced? (Molar masses: Al$$_4C$_3 = 144 g/$$mol, CH$$_4 = 16 g/$$mol; $$Al_4C_3 + 12H_2O \rightarrow 4Al(OH)_3 + 3CH_4)$$

Accepted Answer

$$229 g$

Question 16

Which of the following is NOT a step in calculating the amount of product formed when using an impure reactant?

Accepted Answer

Use the total mass of the impure sample for stoichiometric calculations.

Question 17

If 5 moles of H$$_2$$ react with 2 moles of O$$_2 to $$form water ($$2H_2 + O_2$ \rightarrow 2H_2O$$), which is the limiting reactant?

Accepted Answer

O$$_2$$

Question 18

A reaction starts with 32 g of CH$$_4$$ and 12 g of O$$_2. $$Which is the limiting reactant? (Molar masses: CH$$_4 = 16 g/$$mol, O$$_2 = 32 g/$$mol; $$CH_4 + 2O_2$$ \rightarrow $$CO_2 + 2H_2O$)

Accepted Answer

O$$_2$$

Rendimiento, Pureza y Reactivo Limitante en Reacciones Químicas

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