Question 1

Which of the following best describes a chemical compound?

Accepted Answer

A substance composed of two or more elements chemically combined in a fixed ratio.

Question 2

Which of the following is the correct Lewis structure for the ammonium ion ($$\mathrm{NH_4$^+}$$)?

Accepted Answer

Nitrogen atom in the center with four single bonds to hydrogen atoms and a positive charge on the nitrogen.

Question 3

A student is asked to identify an unknown white powder. Which of the following would be the most appropriate first step in a systematic chemical analysis?

Accepted Answer

Observe the physical properties such as color, texture, and solubility in water.

Question 4

Which of the following statements about the periodic table is correct?

Accepted Answer

Elements in the same group have similar chemical properties because they have the same number of valence electrons.

Question 5

Which of the following is the correct balanced equation for the reaction of sodium with water?

Accepted Answer

$$2\mathrm{Na} (s) + 2\mathrm{H_2O} (l) \rightarrow 2\mathrm{NaOH} (aq) + \mathrm{H_2$} (g)$$

Question 6

A sample contains $$3.01 	imes 10$$^{23}$$ molecules of carbon dioxide. How many moles of carbon dioxide are present?

Accepted Answer

$$0.5$$ moles

Question 7

Which of the following best explains why ionic compounds tend to have high melting points?

Accepted Answer

Strong electrostatic forces between oppositely charged ions require a large amount of energy to break.

Question 8

Which of the following is an example of a chemical change?

Accepted Answer

A piece of iron rusts when left outside.

Question 9

A student mixes 50.0 mL of 1.0 M HCl with 50.0 mL of 1.0 M NaOH. What is the final concentration of NaCl in the resulting solution, assuming volumes are additive?

Accepted Answer

$$0.5 M$$

Question 10

Which of the following statements about isotopes is correct?

Accepted Answer

Isotopes of an element have the same number of protons but different numbers of neutrons.

Question 11

Which of the following best describes the octet rule?

Accepted Answer

Atoms tend to gain, lose, or share electrons to achieve eight electrons in their valence shell.

Question 12

A solution is prepared by dissolving 10.0 g of NaCl in enough water to make 500.0 mL of solution. What is the molarity of the solution? ($$\mathrm{M_{NaCl}} = 58.44\ g/mol)$$

Accepted Answer

$$0.342 M$$

Question 13

Which of the following is a correct statement about covalent bonds?

Accepted Answer

Covalent bonds involve the sharing of electron pairs between atoms.

Question 14

Which of the following is the correct electron configuration for a neutral atom of magnesium ($$\mathrm{Mg}$$, atomic number 12)?

Accepted Answer

$$1s^2$$\ $$2s^2$$\ $$2p^6$$\ $$3s^2$$

Question 15

Which of the following best explains why water is a polar molecule?

Accepted Answer

Water has a bent molecular geometry and an unequal distribution of electrons.

Question 16

A chemical reaction is carried out in a closed container. The mass of the reactants is 10.0 g. After the reaction, the mass of the products is measured to be 9.8 g. Which law is being tested, and what is the most likely explanation for the result?

Accepted Answer

Law of Conservation of Mass; some product likely escaped as a gas.

Question 17

Which of the following is the correct formula for aluminum sulfate?

Accepted Answer

$$\mathrm{Al_2$(SO_4$)_3}$$

Question 18

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 does not.

Question 19

Which of the following is the correct name for $$\mathrm{Fe_2O_3}$$?

Accepted Answer

Iron(III) oxide

Question 20

A 25.0 mL sample of a 0.200 M NaOH solution is titrated with 0.100 M HCl. What volume of HCl is required to reach the equivalence point?

Accepted Answer

$$50.0 mL$$

Introduction to Chemistry: Course Structure and Key Topics (Syllabus Overview)

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