Q: How many molecules are present in $$0.250$$ moles of carbon dioxide ($$\mathrm{CO_2$}$$)? (Avogadro's number $$= 6.022 \times 10$$^{23}$$ molecules/mol)

$$1.51 \times 10$$^{23}$$ molecules

Question 1

A sample of magnesium metal with a mass of 12.0 g is reacted completely with hydrochloric acid. How many moles of magnesium are present in the sample? (Molar mass of Mg = 24.3 g/mol)

Accepted Answer

$$0.494$$ moles

Question 2

How many molecules are present in $$0.250$$ moles of carbon dioxide ($$\mathrm{CO_2$}$$)? (Avogadro's number $$= 6.022 	imes 10$$^{23}$$ molecules/mol)

Accepted Answer

$$1.51 	imes 10$$^{23}$$ molecules

Question 3

A compound contains $$40.0\%$$ carbon, $$6.7\%$$ hydrogen, and $$53.3\%$$ oxygen by mass. What is the empirical formula of the compound?

Accepted Answer

$$\mathrm{CH_2O}$$

Question 4

A compound has an empirical formula of $$\mathrm{CH_2O}$$ and a molar mass of $$180 g/$$mol. What is its molecular formula?

Accepted Answer

$$\mathrm{C_6H_{12}O_6$}$$

Question 5

How many grams of sodium chloride ($$\mathrm{NaCl}$$, molar mass $$= 58.44 g/$$mol) are needed to prepare $$0.500 L of a$$ $$1.00 M $$solution?

Accepted Answer

$$29.2 g$$

Question 6

Which of the following is a strong electrolyte when dissolved in water?

Accepted Answer

Potassium chloride ($$\mathrm{KCl})$$

Question 7

Which of the following is the correct net ionic equation for the reaction between aqueous solutions of silver nitrate ($$\mathrm{$$AgNO_3$$}) $$and sodium chloride ($$\mathrm{NaCl}$$)?

Accepted Answer

$$\mathrm{Ag^+ (aq) + Cl^- (aq) \rightarrow AgCl (s)}$$

Question 8

Which of the following best describes the oxidation number of sulfur in $$\mathrm{SO_2$}$$?

Accepted Answer

$$+4$$

Question 9

A $$25.0 mL $$sample of $$0.200 M $$hydrochloric acid ($$\mathrm{HCl}) is $$neutralized by sodium hydroxide ($$\mathrm{NaOH}). $$What volume (in mL) of $$0.100 M$$ $$\mathrm{NaOH} is $$required for complete neutralization?

Accepted Answer

$$50.0 mL$$

Question 10

Which of the following statements about precipitation reactions is correct?

Accepted Answer

A solid forms when two aqueous solutions are mixed and an insoluble product is produced.

Question 11

What is the molarity of a solution prepared by dissolving $$10.0 g of$$ $$\mathrm{NaOH} ($$molar mass $$= 40.00 g/$$mol) in enough water to make $$250 mL of $$solution?

Accepted Answer

$$1.00 M$$

Question 12

Which of the following is the correct oxidation number for nitrogen in $$\mathrm{NO_3$^-}$$?

Accepted Answer

$$+5$$

Question 13

A $$2.00 g $$sample of a compound containing only carbon and hydrogen is found to contain $$1.60 g of $$carbon. What is the empirical formula of the compound?

Accepted Answer

$$\mathrm{CH_4$}$$

Question 14

Which of the following is a weak electrolyte?

Accepted Answer

Acetic acid ($$\mathrm{CH_3COOH})$$

Question 15

Which of the following is the correct complete ionic equation for the reaction between aqueous solutions of barium chloride ($$\mathrm{$$BaCl_2$$}) $$and sodium sulfate ($$\mathrm{Na_2SO_4}$$)?

Accepted Answer

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

Question 16

In the reaction $$\mathrm{2Al (s) + 3Cu$$^{2+}$$ (aq) \rightarrow 2Al$$^{3+}$$ (aq) + 3Cu (s)}$$, which species is oxidized?

Accepted Answer

$$\mathrm{Al (s)}$$

Question 17

A $$0.500 g $$sample of a compound contains $$0.200 g of $$hydrogen and $$0.300 g of $$oxygen. What is the empirical formula of the compound?

Accepted Answer

$$\mathrm{H_2O}$$

Question 18

Which of the following best describes a non-electrolyte?

Accepted Answer

A substance that dissolves in water but does not conduct electricity.

Question 19

A $$100.0 mL $$sample of $$0.250 M$$ $$\mathrm{K_2SO_4} is $$diluted to a final volume of $$500.0 mL. $$What is the new molarity?

Accepted Answer

$$0.0500 M$$

Question 20

Which of the following is the correct net ionic equation for the neutralization of hydrochloric acid ($$\mathrm{HCl}) $$with sodium hydroxide ($$\mathrm{NaOH}$$)?

Accepted Answer

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

CHM 121 Exam 2 Study Guide: Chemical Reactions, Stoichiometry, and Reactions in Aqueous Solution

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