Question 1

Consider the equation, 2Na + Cl₂ → 2NaCl. This equation shows that 6.022 × 10²³ units of NaCl can be produced when one mole of Cl₂ and two moles of Na react.

Accepted Answer

The equation provided is not correctly written and does not follow standard chemical notation, making it impossible to accurately determine the products or the amount of NaCl produced from the given reactants.

Question 2

One gram of carbon-12 contains one mole of carbon atoms.

Accepted Answer

One mole of carbon-12 atoms weighs 12 grams, not one gram.

Question 3

A mole of a substance has the same mass in grams as one unit (atom or molecules) has in atomic mass units.

Accepted Answer

One mole of any substance contains Avogadro's number (6.022 x 10^23) of atoms or molecules and weighs exactly its molecular or atomic mass in grams. This is a fundamental principle in chemistry, linking the atomic mass unit scale directly with the macroscopic gram scale.

Question 4

The reactant gives the least amount of a particular product in a chemical reaction can be called the limiting reagent for that product.

Accepted Answer

The limiting reagent is the reactant that is completely consumed first in a chemical reaction, limiting the amount of product that can be formed.

Question 5

Consider the chemical reaction, 2Al + 3Cl₂ $\rightarrow$ 2AlCl₃. Here, 56 g of Al can produce 276.54 g of AlCl₃ (Molar masses: Al = 26.98 g; Cl = 35.45 g).

Accepted Answer

The reaction seems to be 2Al + 3Cl2 → 2AlCl3. For 56 g of Al (which is approximately 2 moles given Al's molar mass is 26.98 g/mol), the theoretical yield of AlCl3 (molar mass approximately 133.34 g/mol given Al = 26.98 and Cl = 35.45) would be 2 moles of AlCl3, which equals 2 * 133.34 g = 266.68 g, not 276.54 g.

Question 6

The relating of one chemical substance to another using a balanced chemical reaction is called _____.

Accepted Answer

Stoichiometry is the branch of chemistry that deals with the quantitative relationships of the reactants and products in a chemical reaction. It involves using balanced chemical equations to calculate the amounts of reactants and products.

Question 7

If percent yield determined is greater than 90%, it indicates an error.

Accepted Answer

A percent yield greater than 90% simply indicates a highly efficient reaction, not necessarily an error. Percent yield can vary widely depending on the reaction conditions and the efficiency of the process.

Question 8

When calculating the amount of product assuming that all the reactant reacts, we are calculating the actual yield.

Accepted Answer

When calculating the amount of product assuming that all the reactant reacts, we are calculating the theoretical yield, not the actual yield. The actual yield is the amount of product actually produced when the reaction is carried out.

Question 9

The percent yield of the various stages in a reaction is given below.
A→ Intermediary1 (percent yield = 70%) → Intermediary2 (percent yield = 80%) → B (Percent Yield = 90%). The overall percent yield of this reaction is 50.%.

Accepted Answer

The overall percent yield is the product of the percent yields of the individual stages. Therefore, the overall percent yield is 70% x 80% x 90% = 50.4%.

Question 10

Mass quantities of one substance can be related to mass quantities using a balanced chemical equation.

Accepted Answer

A balanced chemical equation provides the stoichiometric ratios of reactants and products, allowing for the conversion between mass quantities of different substances involved in the reaction.

Question 11

The numerical value of things in a mole is often called Avogadro's number.

Accepted Answer

Avogadro's number, approximately 6.022 x 10^23, represents the number of atoms, molecules, or other particles in one mole of a substance.

Question 12

The percent yield can be calculated using the formula, percent yield =actual yield÷ theoretical yield × 100%.

Accepted Answer

Percent yield is calculated by dividing the actual yield (the amount of product actually obtained from a reaction) by the theoretical yield (the maximum amount of product that could be formed from the reactants), and then multiplying by 100% to convert it to a percentage.

Question 13

CH₄ + 2 O₂ → CO₂ + 2 H₂O. 50 g of CH₄ and 120 g of O₂ react with each other. The reactant O₂ is in excess here. (Molar masses: C = 12 g; H = 1 g; O = 16 g)

Accepted Answer

The molar mass of CH4 (methane) is 16 g/mol (12 g for carbon + 4 g for hydrogen), and the molar mass of O2 is 32 g/mol (16 g x 2 for oxygen). Given 50 g of CH4, we have 50 g / 16 g/mol = 3.125 moles of CH4. For O2, 120 g / 32 g/mol = 3.75 moles of O2. The reaction between methane (CH4) and oxygen (O2) to produce carbon dioxide (CO2) and water (H2O) typically requires a 2:1 molar ratio of O2 to CH4. Therefore, with 3.125 moles of CH4, we would need 6.25 moles of O2 to react completely, but only 3.75 moles of O2 are provided, making CH4 in excess, not O2.

Question 14

Fe₂O₃ + Fe + 6 HCl → 3 FeCl₂ + 3 H₂O. This chemical equation is balanced in terms of moles.

Accepted Answer

The equation is balanced because the number of atoms of each element is the same on both sides of the equation.

Question 15

If the molar mass of HCl is 36.46, the mass of 15 mol of HCl is 546.9
g.

Accepted Answer

The mass of 15 mol of HCl can be calculated by multiplying the molar mass of HCl (36.46 g/mol) by the number of moles (15 mol), which equals 546.9 g.

Question 16

How many molecules of oxygen should react with hydrogen molecules to form 14 molecules of water?

Accepted Answer

The balanced chemical equation for the formation of water is 2H₂ + O₂ → 2H₂O. To form 14 molecules of water, you need 7 molecules of oxygen, as each molecule of oxygen can produce 2 molecules of water.

Question 17

Consider the chemical reaction, 2Al + 3Cl₂ $\rightarrow$ 2AlCl₃. Here, 212.7 g of chlorine can produce a maximum of 266.66 g of AlCl₃ (Molar masses: Al = 26.98 g; Cl = 35.45 g).

Accepted Answer

The given statement is true because the balanced chemical equation shows that 2 moles of Al react with 3 moles of Cl₂ to produce 2 moles of AlCl₃. Therefore, 212.7 g of chlorine (3 moles) can react with 266.66 g of Al (2 moles) to produce 266.66 g of AlCl₃ (2 moles).

Question 18

The molar mass of carbon is 12 g. This indicates that 12 × 6.022 × 10²³ atoms are present in one gram of carbon.

Accepted Answer

The molar mass of carbon is 12 g/mol, indicating that 12 grams of carbon contain 6.022 × 10^23 atoms, not one gram.

Question 19

Consider the reaction, N₂ + 3H₂ $\rightarrow$ 2NH₃. 15 g of NH₃ is formed from 18 g of N₂. The percent yield in this example is 83.33% (Molar masses: N = 14 g; H = 1.0 g).

Accepted Answer

The given reaction and data are not clearly presented, making it impossible to accurately calculate the percent yield without the correct chemical formulas and a clear understanding of the reaction.

Question 20

The theoretical yield of a reaction is 50 g and the actual yield is 40
g. The percent yield of this reaction is 80%.

Accepted Answer

The percent yield is calculated by dividing the actual yield by the theoretical yield and then multiplying by 100. So, $ \frac{40g}{50g} \times 100 = 80\% $.

Quiz 5: Stoichiometry and the Mole

Consider the equation, 2Na + Cl2 → 2NaCl. This equation shows that 6.022 × 1023 units of NaCl can be produced when one mole of Cl2 and two moles of Na react.

One gram of carbon-12 contains one mole of carbon atoms.

A mole of a substance has the same mass in grams as one unit (atom or molecules) has in atomic mass units.

The reactant gives the least amount of a particular product in a chemical reaction can be called the limiting reagent for that product.

Consider the chemical reaction, 2Al + 3Cl2 →\rightarrow→ 2AlCl3. Here, 56 g of Al can produce 276.54 g of AlCl3 (Molar masses: Al = 26.98 g; Cl = 35.45 g).

The relating of one chemical substance to another using a balanced chemical reaction is called _____.

If percent yield determined is greater than 90%, it indicates an error.

When calculating the amount of product assuming that all the reactant reacts, we are calculating the actual yield.

The percent yield of the various stages in a reaction is given below. A→ Intermediary1 (percent yield = 70%) → Intermediary2 (percent yield = 80%) → B (Percent Yield = 90%). The overall percent yield of this reaction is 50.%.

Mass quantities of one substance can be related to mass quantities using a balanced chemical equation.

The numerical value of things in a mole is often called Avogadro's number.

The percent yield can be calculated using the formula, percent yield =actual yield÷ theoretical yield × 100%.

CH4 + 2 O2 → CO2 + 2 H2O. 50 g of CH4 and 120 g of O2 react with each other. The reactant O2 is in excess here. (Molar masses: C = 12 g; H = 1 g; O = 16 g)

Fe2O3 + Fe + 6 HCl → 3 FeCl2 + 3 H2O. This chemical equation is balanced in terms of moles.

If the molar mass of HCl is 36.46, the mass of 15 mol of HCl is 546.9 g.

How many molecules of oxygen should react with hydrogen molecules to form 14 molecules of water?

Consider the chemical reaction, 2Al + 3Cl2 →\rightarrow→ 2AlCl3. Here, 212.7 g of chlorine can produce a maximum of 266.66 g of AlCl3 (Molar masses: Al = 26.98 g; Cl = 35.45 g).

The molar mass of carbon is 12 g. This indicates that 12 × 6.022 × 1023 atoms are present in one gram of carbon.

Consider the reaction, N2 + 3H2 →\rightarrow→ 2NH3. 15 g of NH3 is formed from 18 g of N2. The percent yield in this example is 83.33% (Molar masses: N = 14 g; H = 1.0 g).

The theoretical yield of a reaction is 50 g and the actual yield is 40 g. The percent yield of this reaction is 80%.