Q: Which of the following is the correct formula for calculating the number of moles from a given mass and molar mass?

$$\text{moles} = \frac{\text{mass (g)}}{\text{molar mass (g/mol)}}$$

Question 1

Which of the following best describes a combustion reaction, as seen in an automobile engine burning octane (a component of gasoline)?

Accepted Answer

A reaction in which a hydrocarbon reacts with oxygen to produce carbon dioxide and water, releasing energy.

Question 2

Balance the following equation for the combustion of butane: $$\mathrm{C_4H_{10} + O_2$ \rightarrow CO_2$ + H_2O}. $$What are the correct coefficients?

Accepted Answer

$$2\ \mathrm{C_4H_{10}} + 13\ \mathrm{O_2$} \rightarrow 8\ \mathrm{CO_2$} + 10\ \mathrm{H_2O}$$

Question 3

Which of the following is the correct balanced equation for the decomposition of water as shown in the electrolysis experiment?

Accepted Answer

$$2\ \mathrm{H_2O(l)} \rightarrow 2\ \mathrm{H_2$(g)} + 1\ \mathrm{O_2$(g)}$$

Question 4

Classify the following reaction: $$\mathrm{2\ Na(s) + 2\ H_2O(aq) \rightarrow 2\ NaOH(aq) + H_2$(g)}$$

Accepted Answer

Single-displacement reaction

Question 5

Which equation represents a double-displacement reaction?

Accepted Answer

$$\mathrm{Na_2SO_4(aq) + $$BaBr_2$$(aq) \rightarrow $$BaSO_4$$(s) + 2\ NaBr(aq)}$$

Question 6

A silver ring contains $$1.1 	imes 10$$^{22}$$ silver atoms. How many moles of silver are in the ring? (Avogadro's number = 6.02$$ 	imes $$10^{23})$$

Accepted Answer

$$1.8 	imes 10$$^{-2}$$ moles

Question 7

Which of the following is the correct balanced equation for the reaction of aluminum with chlorine gas?

Accepted Answer

$$2\ \mathrm{Al} + 3\ \mathrm{Cl_2$} \rightarrow 2\ \mathrm{$$AlCl_3$$}$$

Question 8

How many molecules of HCl will form from 30 molecules of $$\mathrm{H_2$} in $$the reaction $$\mathrm{H_2$ + Cl_2$ \rightarrow 2\ HCl}$$?

Accepted Answer

60 molecules

Question 9

Which of the following best describes the Law of Conservation of Mass as it applies to chemical reactions?

Accepted Answer

The total mass of reactants equals the total mass of products in a chemical reaction.

Question 10

Which of the following is the correct formula for calculating the number of moles from a given mass and molar mass?

Accepted Answer

$$	ext{moles} = \frac{	ext{mass (g)}}{	ext{molar mass (g/mol)}}$$

Question 11

Which of the following reactions is a synthesis reaction?

Accepted Answer

$$\mathrm{Sn + 2\ Br_2$ \rightarrow $$SnBr_4$$}$$

Question 12

What is the molar mass of water ($$\mathrm{H_2O}$$)?

Accepted Answer

$$18.02\ \mathrm{g/mol}$$

Question 13

Which of the following best describes a double-displacement reaction?

Accepted Answer

Two ionic compounds exchange ions to form two new compounds.

Question 14

If you have 57.8 g of sulfur ($$\mathrm{S}$$), how many moles of sulfur do you have? (Molar mass of S = 32.06 g/mol)

Accepted Answer

$$1.80$$ moles

Question 15

Which of the following is the correct balanced equation for the reaction of solid magnesium with oxygen gas?

Accepted Answer

$$2\ \mathrm{Mg(s)} + O_2$(g) \rightarrow 2\ \mathrm{MgO(s)}$$

Question 16

Which of the following is the correct formula for Avogadro's number?

Accepted Answer

$$6.02 	imes 10$$^{23}$$

Question 17

Which of the following reactions is a decomposition reaction?

Accepted Answer

$$2\ \mathrm{H_2O(l)} \rightarrow 2\ \mathrm{H_2$(g)} + O_2$(g)$$

Question 18

In the reaction $$\mathrm{2\ Al + 3\ Cl_2$ \rightarrow 2\ $$AlCl_3$$}$$, how many molecules of $$\mathrm{Cl_2$}$$ are needed to react with 10 aluminum atoms?

Accepted Answer

15 molecules

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