Q: How many atoms are in $$2.0$$ moles of helium?

$$1.20 \times 10$$^{24}$$ atoms

Q: How many molecules are in $$0.50$$ mol of $$\mathrm{H_2O}$$?

$$3.01 \times 10$$^{23}$$ molecules

Question 1

Which statement best describes the law of constant composition?

Accepted Answer

A compound always contains the same proportion of its elements by mass.

Question 2

How many oxygen atoms are present in one formula unit of $$\mathrm{Mg(NO_3$)_2}$$?

Accepted Answer

6

Question 3

Which of the following compounds is ionic?

Accepted Answer

$$\mathrm{NaCl}$$

Question 4

What is the correct formula for aluminum oxide?

Accepted Answer

$$\mathrm{Al_2O_3}$$

Question 5

What is the systematic name for $$\mathrm{$$FeCl_2$$}$$?

Accepted Answer

Iron(II) chloride

Question 6

A compound is found to be 40% C, 6.7% H, and 53.3% O by mass. What is its empirical formula?

Accepted Answer

$$\mathrm{CH_2O}$$

Question 7

If the empirical formula of a compound is $$\mathrm{CH_2O}$$ and its molar mass is $$180\ \mathrm{g/mol}$$, what is its molecular formula?

Accepted Answer

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

Question 8

How many atoms are in $$2.0$$ moles of helium?

Accepted Answer

$$1.20 	imes 10$$^{24}$$ atoms

Question 9

Convert $$24\ \mathrm{g} of $$carbon to moles. (Atomic mass of C = $$12.0\ \mathrm{g/mol})$$

Accepted Answer

$$2.0$$ mol

Question 10

How many molecules are in $$0.50$$ mol of $$\mathrm{H_2O}$$?

Accepted Answer

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

Question 11

Determine the percent by mass of carbon in $$\mathrm{CO_2$}. ($$Atomic masses: C = $$12.0$$, O = $$16.0)$$

Accepted Answer

27.3%

Question 12

Which of the following is evidence of a chemical reaction?

Accepted Answer

Formation of bubbles

Question 13

When $$3.0$$ mol of $$\mathrm{N_2$}$$ react with $$5.0$$ mol of $$\mathrm{H_2$}$$ according to $$\mathrm{N_2$ + 3H_2 \rightarrow 2NH_3}$$, which is the limiting reactant?

Accepted Answer

$$\mathrm{H_2$}$$

Question 14

Using the limiting reactant above, how many moles of $$\mathrm{NH_3$}$$ are produced?

Accepted Answer

3.33 mol

Question 15

If the theoretical yield is $$3.33$$ mol but only $$2.50$$ mol are produced, what is the percent yield?

Accepted Answer

75%

Question 16

Write the balanced equation for the combustion of propane ($$\mathrm{C_3H_8}).$$

Accepted Answer

$$\mathrm{C_3H_8 + 5O_2 \rightarrow 3CO_2 + 4H_2O}$$

Question 17

How many grams of $$\mathrm{CO_2$}$$ are produced from $$50.0\ \mathrm{g} of$$ $$\mathrm{CH_4$} in $$the reaction $$\mathrm{CH_4$ + 2O_2 \rightarrow CO_2$ + 2H_2O}$$? (Molar masses: $$\mathrm{CH_4$}$$ = $$16.0\ \mathrm{g/mol}$$, $$\mathrm{CO_2$}$$ = $$44.0\ \mathrm{g/mol})$$

Accepted Answer

137.5 g

Question 18

Which element is oxidized and which is reduced in the reaction $$2\mathrm{Mg} + \mathrm{O_2$} \rightarrow 2\mathrm{MgO}$$?

Accepted Answer

Mg is oxidized, O is reduced

Question 19

What is the net ionic equation for the reaction between $$\mathrm{$$AgNO_3$$(aq)}$$ and $$\mathrm{NaCl(aq)}$$?

Accepted Answer

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

Molecules, Compounds, Chemical Composition, and Reactions: Study Guide

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