Q: Which of the following statements best describes the concept of a mole in chemistry?

A mole is the amount of substance that contains $$6.022 \times 10$$^{23}$$ elementary entities (atoms, molecules, or ions).

Q: A sample contains 2.5 moles of iron atoms. How many atoms of iron are present in the sample?

$$1.505 \times 10$$^{24}$$ atoms

Q: Which of the following is the correct calculation for the percent by mass of oxygen in water ($$\text{H}_2\text{O}$$)?

$$\frac{16.00}{18.016} \times 100$$

Q: A reaction yields 13.9 g of NaCl when the theoretical yield is 13.923 g. What is the percent yield?

$$\frac{13.9}{13.923} \times 100 = 99.83\%$$

Q: Which of the following is the correct balanced equation for the reaction between potassium hydroxide and sulfur dioxide?

$$2\text{RbOH} + \text{SO}_2 \rightarrow \text{Rb}_2\text{SO}_3 + \text{H}_2\text{O}$$

Q: Which of the following is the correct formula to calculate the percent purity of a reactant?

$$\frac{\text{cantidad pura}}{\text{cantidad total de sustancia}} \times 100$$

Q: A compound has an empirical formula of $$\text{CH}_2\text{O}$$ and a molar mass of 180 g/mol. What is its molecular formula?

$$\text{C}_6\text{H}_{12}\text{O}_6$$

Question 1

Which of the following statements best describes the concept of a mole in chemistry?

Accepted Answer

A mole is the amount of substance that contains $$6.022 	imes 10$$^{23}$$ elementary entities (atoms, molecules, or ions).

Question 2

Given the reaction: $$2 	ext{H}_2(g) + 	ext{O}_2(g) ightarrow 2 	ext{H}_2	ext{O}(l)$$, how many moles of water are produced from 5 moles of oxygen gas, assuming excess hydrogen?

Accepted Answer

10 moles

Question 3

What is the empirical formula for a compound containing 85.63% carbon and 14.37% hydrogen by mass?

Accepted Answer

$$	ext{CH}_2$$

Question 4

A sample contains 2.5 moles of iron atoms. How many atoms of iron are present in the sample?

Accepted Answer

$$1.505 	imes 10$$^{24}$$ atoms

Question 5

Which of the following is the correct calculation for the percent by mass of oxygen in water ($$	ext{H}_2	ext{O}$$)?

Accepted Answer

$$\frac{16.00}{18.016} 	imes 100$$

Question 6

A reaction yields 13.9 g of NaCl when the theoretical yield is 13.923 g. What is the percent yield?

Accepted Answer

$$\frac{13.9}{13.923} 	imes 100 = 99.83\%$$

Question 7

Which of the following best describes the limiting reactant in a chemical reaction?

Accepted Answer

The reactant that determines the amount of product formed.

Question 8

If 2.00 g of Si (molar mass = 28.09 g/mol) and 1.50 g of N$$_2 ($$molar mass = 28.02 g/mol) react according to $$3	ext{Si} + 2	ext{N}_2 ightarrow 	ext{Si}_3	ext{N}_4$$, what is the limiting reactant?

Accepted Answer

Silicon (Si)

Question 9

Which of the following is the correct balanced equation for the reaction between potassium hydroxide and sulfur dioxide?

Accepted Answer

$$2	ext{RbOH} + 	ext{SO}_2 ightarrow 	ext{Rb}_2	ext{SO}_3 + 	ext{H}_2	ext{O}$$

Question 10

A chemist wants to obtain 25 g of cyclohexene ($$	ext{C}_6	ext{H}_{10}) $$with a reaction yield of 83%. What is the minimum mass of cyclohexanol ($$	ext{C}_6	ext{H}_{11}	ext{OH}$$, molar mass = 100.2 g/mol) required?

Accepted Answer

37 g

Question 11

Which of the following is a correct application of the Law of Conservation of Mass in a chemical reaction?

Accepted Answer

The total mass of reactants equals the total mass of products.

Question 12

How many liters of $$	ext{Cl}_2$$ gas at STP (CN) are produced from 30 g of $$	ext{MnO}_2 ($$molar mass = 87 g/mol) in the reaction $$	ext{MnO}_2 + 4	ext{HCl} ightarrow 	ext{MnCl}_2 + 	ext{Cl}_2 + 2	ext{H}_2	ext{O}$$, if the reaction yield is 90%?

Accepted Answer

6.86 L

Question 13

Which of the following is the correct formula to calculate the percent purity of a reactant?

Accepted Answer

$$\frac{	ext{cantidad pura}}{	ext{cantidad total de sustancia}} 	imes 100$$

Question 14

A compound has an empirical formula of $$	ext{CH}_2	ext{O}$$ and a molar mass of 180 g/mol. What is its molecular formula?

Accepted Answer

$$	ext{C}_6	ext{H}_{12}	ext{O}_6$$

Question 15

Which of the following is NOT a reason why the actual yield of a reaction may be less than the theoretical yield?

Accepted Answer

All reactants are pure and react completely.

Question 16

Which of the following equations correctly relates the number of moles, mass, and molar mass?

Accepted Answer

$$n = \frac{m}{M}$$

Question 17

In the reaction $$	ext{CaCO}_3 + 2	ext{HCl} ightarrow 	ext{CaCl}_2 + 	ext{CO}_2 + 	ext{H}_2	ext{O}$$, how many grams of $$	ext{CO}_2$$ are produced from 10 g of $$	ext{CaCO}_3 ($$molar mass = 100 g/mol)?

Accepted Answer

4.4 g

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