Q: Which of the following is a correct statement about the mole?

A mole contains $$6.022 \times 10$$^{23}$$ particles of a substance.

Q: If 0.50 moles of $$\mathrm{Na_2SO_4}$$ are dissolved in water, how many sodium ions are present in solution?

$$6.02 \times 10$$^{23}$$ \times 2 = 1.20 \times 10$$^{24}$$

Question 1

A chemist combines solid magnesium with aqueous hydrochloric acid at room temperature, producing aqueous magnesium chloride and hydrogen gas. Which of the following is the correctly balanced chemical equation for this reaction?

Accepted Answer

$$\mathrm{Mg(s) + 2HCl(aq) \rightarrow $$MgCl_2$$(aq) + H_2$(g)}$$

Question 2

Which of the following statements about balancing chemical equations is CORRECT?

Accepted Answer

Coefficients can be changed to balance the equation, but subscripts in chemical formulas must not be altered.

Question 3

Consider the reaction: $$\mathrm{2KClO_3(s) \rightarrow 2KCl(s) + 3O_2(g)}. $$What type of reaction pattern does this represent?

Accepted Answer

Decomposition

Question 4

Which of the following is the correct net ionic equation for the reaction between aqueous solutions of silver nitrate and sodium chloride?

Accepted Answer

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

Question 5

Assign oxidation numbers to each element in $$\mathrm{H_2SO_4}. $$What is the oxidation number of sulfur?

Accepted Answer

+6

Question 6

Which of the following reactions is a redox reaction?

Accepted Answer

$$\mathrm{Zn(s) + 2HCl(aq) \rightarrow $$ZnCl_2$$(aq) + H_2$(g)}$$

Question 7

A student mixes solutions of potassium sulfate and barium nitrate. Which compound will precipitate, based on solubility rules?

Accepted Answer

$$\mathrm{$$BaSO_4$$}$$

Question 8

Calculate the molar mass of $$\mathrm{C_2H_6O} ($$ethanol). (Atomic masses: C = 12.0, H = 1.0, O = 16.0)

Accepted Answer

$$46.0\ \mathrm{g/mol}$$

Question 9

How many molecules are present in 0.25 moles of $$\mathrm{CO_2$}$$?

Accepted Answer

$$1.51 	imes 10$$^{23}$$

Question 10

A reaction has a theoretical yield of 10.0 g, but only 7.5 g of product is actually obtained. What is the percent yield?

Accepted Answer

$$75\%$$

Question 11

Given the balanced equation: $$\mathrm{2Al(s) + 3Cl_2(g) \rightarrow 2AlCl_3(s)}$$, how many moles of $$\mathrm{Cl_2$}$$ are needed to react completely with 4.0 moles of $$\mathrm{Al}$$?

Accepted Answer

6.0 moles

Question 12

Which of the following best describes the role of the oxidizing agent in a redox reaction?

Accepted Answer

It is reduced by gaining electrons.

Question 13

A chemist reacts 5.0 g of $$\mathrm{H_2$}$$ with 40.0 g of $$\mathrm{O_2$} to $$produce water according to $$\mathrm{2H_2 + O_2$ \rightarrow 2H_2O}. $$Which reactant is limiting?

Accepted Answer

$$\mathrm{H_2$}$$

Question 14

Which of the following is a correct statement about the mole?

Accepted Answer

A mole contains $$6.022 	imes 10$$^{23}$$ particles of a substance.

Question 15

Which of the following is an example of an acid/base neutralization reaction?

Accepted Answer

$$\mathrm{HCl(aq) + NaOH(aq) \rightarrow NaCl(aq) + H_2O(l)}$$

Question 16

If 0.50 moles of $$\mathrm{Na_2SO_4}$$ are dissolved in water, how many sodium ions are present in solution?

Accepted Answer

$$6.02 	imes 10$$^{23}$$ 	imes 2 = 1.20 	imes 10$$^{24}$$

Question 17

Which of the following best describes a double displacement reaction?

Accepted Answer

Two compounds exchange ions to form two new compounds.

Question 18

A student is asked to calculate the mass of $$\mathrm{$$CuSO_4$$}$$ needed to prepare 0.250 moles of solution. (Molar mass = 159.6 g/mol) What mass should the student use?

Accepted Answer

$$39.9\ \mathrm{g}$$

Question 19

Which of the following is NOT a correct guideline for balancing chemical equations?

Accepted Answer

Change the subscripts in chemical formulas to balance the atoms.

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