Q: A sugar crystal contains approximately $$1.7 \times 10$$^{17}$$ molecules of sucrose ($$\mathrm{$$C_{12}H$$_{22}$$O_{11}}). $$What is the mass of this crystal in milligrams? (Molar mass of sucrose = $$342.30\ \mathrm{g/mol}$$, Avogadro's number $$= 6.022 \times 10$$^{23}$$\ \mathrm{$$mol^{-1}$$}$)

$$9.7 \times 10$$^{-2}$$\ \mathrm{mg}$$

Q: A drop of water has a volume of $$7 \times 10$$^{-2}$$\ \mathrm{mL}. $$How many water molecules does it contain? (Density of water $$= 1.0\ \mathrm{g/cm^3$}$$, Molar mass of $$\mathrm{H_2O} = 18.02\ \mathrm{g/mol}$$, Avogadro's number $$= 6.022 \times 10$$^{23}$$\ \mathrm{$$mol^{-1}$$})$$

$$2.3 \times 10$$^{21}$$ molecules

Question 1

A sugar crystal contains approximately $$1.7 	imes 10$$^{17}$$ molecules of sucrose ($$\mathrm{$$C_{12}H$$_{22}$$O_{11}}). $$What is the mass of this crystal in milligrams? (Molar mass of sucrose = $$342.30\ \mathrm{g/mol}$$, Avogadro's number $$= 6.022 	imes 10$$^{23}$$\ \mathrm{$$mol^{-1}$$}$)

Accepted Answer

$$9.7 	imes 10$$^{-2}$$\ \mathrm{mg}$$

Question 2

A drop of water has a volume of $$7 	imes 10$$^{-2}$$\ \mathrm{mL}. $$How many water molecules does it contain? (Density of water $$= 1.0\ \mathrm{g/cm^3$}$$, Molar mass of $$\mathrm{H_2O} = 18.02\ \mathrm{g/mol}$$, Avogadro's number $$= 6.022 	imes 10$$^{23}$$\ \mathrm{$$mol^{-1}$$})$$

Accepted Answer

$$2.3 	imes 10$$^{21}$$ molecules

Question 3

Which of the following best describes the difference between a homogeneous and a heterogeneous mixture?

Accepted Answer

A homogeneous mixture has a uniform composition throughout, while a heterogeneous mixture has visibly different parts or phases.

Question 4

Which of the following changes is a chemical change?

Accepted Answer

Sugar burns when heated on a skillet.

Question 5

What is the difference between $$Z ($$atomic number) and $$A ($$mass number) for an atom?

Accepted Answer

$$Z is $$the number of protons; $$A is $$the total number of protons and neutrons.

Question 6

Given the empirical formula $$\mathrm{CH_2O}$$ and a molar mass of $$60.05\ \mathrm{g/mol}$$ for acetic acid, what is its molecular formula?

Accepted Answer

$$\mathrm{C_2H_4O_2}$$

Question 7

A sample of baking soda contains $$9.122\ \mathrm{g} Na$$, $$0.4000\ \mathrm{g} H$$, $$4.766\ \mathrm{g} C$$, and $$19.04\ \mathrm{g} O. $$What is the empirical formula of baking soda?

Accepted Answer

$$\mathrm{$$NaHCO_3$$}$$

Question 8

Which of the following is a balanced equation for the combustion of propane ($$\mathrm{C_3H_8}$$)?

Accepted Answer

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

Question 9

In a balanced chemical equation, what do the stoichiometric coefficients represent?

Accepted Answer

The relative number of moles of each reactant and product involved in the reaction.

Question 10

How many moles of $$\mathrm{O_2$}$$ are required to completely react with $$0.50$$ mol of propane ($$\mathrm{C_3H_8}) in $$its combustion, and how many moles of $$\mathrm{CO_2$}$$ are produced?

Accepted Answer

$$2.5$$ mol $$\mathrm{O_2$}$$ and $$1.5$$ mol $$\mathrm{CO_2$}$$

Question 11

If $$44\ \mathrm{g} of $$propane ($$\mathrm{C_3H_8}$$, molar mass $$= 44.10\ \mathrm{g/mol}) is $$combusted, how many grams of $$\mathrm{O_2$}$$ are required and how many grams of $$\mathrm{H_2O}$$ are produced? (Molar mass $$\mathrm{O_2$} = 32.00\ \mathrm{g/mol}$$, $$\mathrm{H_2O} = 18.02\ \mathrm{g/mol})$$

Accepted Answer

$$176\ \mathrm{g}$$ $$\mathrm{O_2$}$$ and $$72.1\ \mathrm{g}$$ $$\mathrm{H_2O}$$

Question 12

You have $$100$$ bolts, $$150$$ nuts, and $$150$$ washers. If each set requires $$2$$ washers, $$1$$ bolt, and $$1$$ nut, how many complete sets can you assemble and which component is limiting?

Accepted Answer

50 sets; washers are limiting

Question 13

In the reaction $$2\mathrm{H_2$} + \mathrm{O_2$} \rightarrow 2\mathrm{H_2O}$$, if you react $$6$$ moles of $$\mathrm{H_2$}$$ with $$4$$ moles of $$\mathrm{O_2$}$$, which is the limiting reactant and how many moles of water are produced?

Accepted Answer

$$\mathrm{H_2$} is $$limiting; $$6$$ moles of water produced

Question 14

If you have $$17.3\ \mathrm{g} of $$hydrogen ($$\mathrm{H_2$}) $$and $$8.91\ \mathrm{g} of $$oxygen ($$\mathrm{O_2$}$$), which is the limiting reactant in the formation of water, and how many grams of water can be produced? (Molar mass $$\mathrm{H_2$} = 2.02\ \mathrm{g/mol}$$, $$\mathrm{O_2$} = 32.00\ \mathrm{g/mol}$$, $$\mathrm{H_2O} = 18.02\ \mathrm{g/mol})$$

Accepted Answer

Oxygen is limiting; $$10.0\ \mathrm{g} of $$water produced

Question 15

Cisplatin ($$\mathrm{Pt(NH_3$)_2Cl_2}) is $$synthesized from platinum. If $$1\ \mathrm{kg} of $$platinum is the limiting reactant, how many grams of cisplatin can be produced? (Molar mass $$\mathrm{Pt} = 195.08\ \mathrm{g/mol}$$, $$\mathrm{Pt(NH_3$)_2Cl_2} = 300.05\ \mathrm{g/mol})$$

Accepted Answer

$$1.54\ \mathrm{kg}$$

Question 16

Hydrogen cyanide is produced by the reaction $$2\mathrm{CH_4$} + 2\mathrm{NH_3$} + 3\mathrm{O_2$} \rightarrow 2\mathrm{HCN} + 6\mathrm{H_2O}. If $$you start with $$100\ \mathrm{kg} of $$each reactant, which is the limiting reactant?

Accepted Answer

$$\mathrm{O_2$}$$

Question 17

A student is asked to balance the following equation: $$\mathrm{N_2H_4(l)} \rightarrow \mathrm{NH_3$(g)} + \mathrm{N_2$(g)}. $$What are the correct stoichiometric coefficients for the balanced equation?

Accepted Answer

$$2\ \mathrm{N_2H_4(l)} \rightarrow 4\ \mathrm{NH_3$(g)} + 1\ \mathrm{N_2$(g)}$$

General Chemistry I: Mole, Molar Mass, Balancing Equations, and Limiting Reactants – Guided Study

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