Q: Calculate the percent yield if 5.0 g of product is obtained from a reaction with a theoretical yield of 8.0 g.

$$\frac{5.0}{8.0} \times 100\% = 62.5\%$$

Q: A calorimeter contains 100.0 g of water at 25.0$$^\circC. If 500 J of $$heat is added, what is the final temperature? (Specific heat of water = 4.18 J/g$$\cdotK)$$

$$T_f = 25.0^\circ\mathrm{C} + \frac{500}{100.0 \times 4.18} = 26.2^\circ\mathrm{C}$$

Q: Which of the following is the correct formula for calculating molarity?

$$M = \frac{\text{moles of solute}}{\text{liters of solution}}$$

Question 1

Which of the following best describes the process of balancing a chemical equation?

Accepted Answer

Adjusting the coefficients of reactants and products so that the number of atoms of each element is equal on both sides of the equation.

Question 2

A student mixes aqueous solutions of Na$$_2SO$_4$$ and BaCl$$_2. $$What is the net ionic equation for the formation of the precipitate?

Accepted Answer

$$\mathrm{Ba$$^{2+}$$(aq) + SO_4$^{2-}(aq) \rightarrow $$BaSO_4$$(s)}$$

Question 3

Which compound is most likely to be insoluble in water?

Accepted Answer

AgCl

Question 4

When hydrochloric acid reacts with sodium hydroxide, which type of reaction occurs?

Accepted Answer

Acid-base neutralization

Question 5

Which of the following is the correct oxidation half-reaction for the oxidation of Fe$$^{2+} to Fe$^{3+}$$?

Accepted Answer

$$\mathrm{Fe$$^{2+}$$ \rightarrow Fe$$^{3+}$$ + e^-}$$

Question 6

A student needs to determine the limiting reactant in the reaction: $$2H_2 + O_2$ \rightarrow 2H_2O. If 4 $$mol of H$$_2$$ and 2 mol of O$$_2$$ are mixed, which is the limiting reactant?

Accepted Answer

Neither; excess O$$_2$$ remains.

Question 7

Which of the following best describes a redox reaction?

Accepted Answer

A reaction in which electrons are transferred from one species to another.

Question 8

Calculate the percent yield if 5.0 g of product is obtained from a reaction with a theoretical yield of 8.0 g.

Accepted Answer

$$\frac{5.0}{8.0} 	imes 100\% = 62.5\%$$

Question 9

Which of the following is the correct formula for calculating the energy change when a substance is heated?

Accepted Answer

$$q = m c \Delta T$$

Question 10

A calorimeter contains 100.0 g of water at 25.0$$^\circC. If 500 J of $$heat is added, what is the final temperature? (Specific heat of water = 4.18 J/g$$\cdotK)$$

Accepted Answer

$$T_f = 25.0^\circ\mathrm{C} + \frac{500}{100.0 	imes 4.18} = 26.2^\circ\mathrm{C}$$

Question 11

Which of the following is the correct net ionic equation for the reaction between HCl and NaOH?

Accepted Answer

$$\mathrm{H^+(aq) + OH^-(aq) \rightarrow H_2O(l)}$$

Question 12

A student is asked to identify the oxidizing agent in the reaction: $$2Fe^{2+}$$ + $$Cl_2$$ \rightarrow $$2Fe^{3+} + 2Cl$$^-$$. Which is the oxidizing agent?

Accepted Answer

Cl$$_2$$

Question 13

Which of the following best describes the enthalpy change ($$\Delta H) $$for an exothermic reaction?

Accepted Answer

$$\Delta H is $$negative because heat is released to the surroundings.

Question 14

Which of the following is the correct formula for calculating molarity?

Accepted Answer

$$M = \frac{	ext{moles of solute}}{	ext{liters of solution}}$$

Question 15

A student titrates 25.0 mL of HCl with 0.100 M NaOH. If the endpoint is reached after adding 30.0 mL of NaOH, what is the concentration of HCl?

Accepted Answer

$$M_{HCl} = \frac{0.100 	imes 30.0}{25.0} = 0.120\ \mathrm{M}$$

Question 16

Which of the following is the correct formula for calculating the energy change using Hess's Law?

Accepted Answer

$$\Delta H_{rxn} = \sum \Delta H_{products} - \sum \Delta H_{reactants}$$

Question 17

Which of the following is a correct statement about the conservation of energy in chemical reactions?

Accepted Answer

The total energy of the system and surroundings remains constant during a chemical reaction.

Question 18

A sample of methane (CH$$_4) is $$combusted in excess oxygen. Which of the following is the balanced chemical equation for this reaction?

Accepted Answer

$$\mathrm{CH_4$ + 2O_2 \rightarrow CO_2$ + 2H_2O}$$

Question 19

Which of the following best describes the role of a reducing agent in a redox reaction?

Accepted Answer

It donates electrons and is itself oxidized.

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