Q: Which of the following statements best describes the mole concept in chemistry?

A mole is a counting unit that defines $$6.022 \times 10$$^{23}$$ entities, such as atoms or molecules.

Q: Which conversion factor would you use to convert grams of a substance to moles?

$$\frac{1 \text{ mol}}{\text{molar mass in g}}$$

Q: A sample contains $$5.0 g of $$aluminum ($$Al). $$How many atoms of aluminum are present? (Molar mass of $$Al = 26.98 g/$$mol)

$$1.12 \times 10$$^{23}$$ atoms

Question 1

Which of the following statements best describes the mole concept in chemistry?

Accepted Answer

A mole is a counting unit that defines $$6.022 	imes 10$$^{23}$$ entities, such as atoms or molecules.

Question 2

If you have $$3.01 	imes 10$$^{24}$$ atoms of sulfur (S), how many moles of sulfur do you have?

Accepted Answer

$$3.01$$ mol S

Question 3

What is the mass in grams of $$3.01$$ mol of sulfur ($$S$$)? (Molar mass of $$S = 32.06 g/$$mol)

Accepted Answer

$$96.5 g$

Question 4

Which conversion factor would you use to convert grams of a substance to moles?

Accepted Answer

$$\frac{1 	ext{ mol}}{	ext{molar mass in g}}$$

Question 5

A sample contains $$5.0 g of $$aluminum ($$Al). $$How many atoms of aluminum are present? (Molar mass of $$Al = 26.98 g/$$mol)

Accepted Answer

$$1.12 	imes 10$$^{23}$$ atoms

Question 6

Which of the following is the correct balanced chemical equation for the reaction of hydrogen and oxygen to form water?

Accepted Answer

$$2H_2 + O_2$ \rightarrow 2H_2O$$

Question 7

What is the formula mass of $$H_2O in $$atomic mass units (amu)? (Atomic masses: $$H = 1.008$$ amu, $$O = 16.00$$ amu)

Accepted Answer

$$18.02$$ amu

Question 8

Which of the following reactions is a decomposition reaction?

Accepted Answer

$$2HgO(s) \rightarrow 2Hg(l) + O_2$(g)$$

Question 9

Which of the following is a double-replacement reaction?

Accepted Answer

$$Pb(NO_3$)_2(aq) + 2NaCl(aq) \rightarrow $$PbCl_2$$(s) + 2NaNO_3(aq)$$

Question 10

Which of the following is NOT evidence that a chemical reaction has occurred?

Accepted Answer

Dissolving sugar in water

Question 11

What is the percent yield if the theoretical yield of iron is $$30.0 g $$and the actual yield is $$25.0 g$$?

Accepted Answer

$$83.3\%$$

Question 12

Which of the following best describes a net ionic equation?

Accepted Answer

It shows only the ions and molecules directly involved in the chemical change, omitting spectator ions.

Question 13

Which of the following compounds is insoluble in water according to the solubility rules?

Accepted Answer

$$AgCl$$

Question 14

How many grams of $$NaCl$$ are produced when $$2.00$$ mol of $$Na$$ reacts with excess $$Cl_2$$? (Molar mass of $$NaCl = 58.44 g/$$mol)

Accepted Answer

$$116.88 g$

Question 15

Which of the following is the correct molar mass of $$(NH_4$)_3PO_4$$? (Atomic masses: $$N = 14.01 g/$$mol, $$H = 1.008 g/$$mol, $$P = 30.97 g/$$mol, $$O = 16.00 g/$$mol)

Accepted Answer

$$149.10 g/$$mol

Question 16

Which of the following is an example of an oxidation-reduction (redox) reaction?

Accepted Answer

$$Mg \rightarrow Mg$$^{2+}$$ + 2e$$^{-}$$

Question 17

A hydrate is best described as:

Accepted Answer

A compound containing one or more water molecules as an integral part of its structure.

Question 18

In the reaction $$2H_2 + O_2$ \rightarrow 2H_2O$$, how many moles of $$O_2$$ are required to react with $$4.2$$ moles of $$H_2$$?

Accepted Answer

$$2.1$$ mol$

Question 19

Which of the following is a correct statement of the law of conservation of mass as applied to chemical reactions?

Accepted Answer

The total mass of the products must equal the total mass of the reactants.

Calculations and the Chemical Equation: The Mole Concept, Molar Mass, and Stoichiometry

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