Question 1

Which of the following best describes a double replacement reaction?

Accepted Answer

Two compounds exchange ions to form two new compounds.

Question 2

Given the unbalanced equation: $$\ce{C_2H_6} + \ce{O_2$} \rightarrow \ce{CO_2$} + \ce{H_2O}$$, what is the correct set of coefficients to balance the equation?

Accepted Answer

$$2, 7, 4, 6$$

Question 3

Which compound is insoluble in water according to the solubility rules?

Accepted Answer

$$\ce{AgCl}$$

Question 4

A student mixes $$\ce{Zn}$$ with $$\ce{$$CuSO_4$$}$$ solution. According to the activity series, what will happen?

Accepted Answer

Zinc will replace copper, forming $$\ce{$$ZnSO_4$$}$$ and $$\ce{Cu}.$$

Question 5

How many molecules are in $$0.25$$ moles of $$\ce{H_2O}$$? (Use Avogadro’s number $$6.022 	imes 10$$^{23}$$)

Accepted Answer

$$3.01 	imes 10$$^{23}$$

Question 6

What is the percent composition by mass of oxygen in $$\ce{H_2SO_4}$$? (Atomic masses: H = 1, S = 32, O = 16)

Accepted Answer

$$65.0\%$$

Question 7

A hydrated salt has the formula $$\ce{$$CuSO_4$$ \cdot 5H_2O}. $$What percent of the mass is due to water? (Atomic masses: Cu = 63.5, S = 32, O = 16, H = 1)

Accepted Answer

$$36.1\%$$

Question 8

Which of the following is a decomposition reaction?

Accepted Answer

$$\ce{2H_2O \rightarrow 2H_2 + O_2$}$$

Question 9

If $$22.4 L of$$ $$\ce{CO_2$}$$ gas is measured at STP, how many moles of $$\ce{CO_2$}$$ are present?

Accepted Answer

$$1$$ mole

Question 10

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

Accepted Answer

$$\ce{CH_2O}$$

Question 11

Which equation represents a neutralization reaction?

Accepted Answer

$$\ce{HCl + NaOH \rightarrow NaCl + H_2O}$$

Question 12

What is the molar mass of $$\ce{Na_2SO_4}$$? (Na = 23, S = 32, O = 16)

Accepted Answer

$$142 g/$$mol

Question 13

A sample of $$\ce{O_2$}$$ gas has a mass of $$32 g. $$How many molecules are present? (Molar mass $$= 32 g/$$mol, Avogadro’s number $$= 6.022 	imes 10$$^{23}$$)

Accepted Answer

$$6.022 	imes 10$$^{23}$$

Question 14

Which of the following is NOT a diatomic molecule?

Accepted Answer

$$\ce{CO}$$

Question 15

A $$10 g $$sample of $$\ce{NaCl} is $$dissolved in water. What is the number of formula units present? (Molar mass $$= 58.5 g/$$mol, Avogadro’s number $$= 6.022 	imes 10$$^{23}$$)

Accepted Answer

$$1.03 	imes 10$$^{23}$$

Question 16

Which of the following best describes the use of the activity series in predicting chemical reactions?

Accepted Answer

It determines if an element can replace another in a single replacement reaction.

Question 17

A $$5 g $$sample of $$\ce{Mg}$$ reacts with $$\ce{HCl} to $$produce $$\ce{$$MgCl_2$$}$$ and $$\ce{H_2$}. $$How many moles of $$\ce{Mg}$$ are present? (Mg = 24 g/mol)

Accepted Answer

$$0.208$$ moles

Question 18

Which of the following compounds is a common hydrate?

Accepted Answer

$$\ce{$$CaSO_4$$ \cdot 2H_2O}$$

Question 19

A gas has a density of $$1.25 g/L at $$STP. What is its molar mass? (Molar volume at STP $$= 22.4 L/$$mol)

Accepted Answer

$$28 g/$$mol

Question 20

A student is given a compound with a molar mass of $$180 g/$$mol and an empirical formula of $$\ce{CH_2O}. $$What is the molecular formula?

Accepted Answer

$$\ce{C_6H_{12}O_6$}$$

Study Guide: Chemical Reactions and The Mole Concept (Chapters 7 & 8)

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