Q: A radioactive isotope has a half-life of 4 days. If you start with 80 mg, how much will remain after 12 days?

$$80 \text{ mg} \times \left(\frac{1}{2}\$$right)^{3}$$ = 10 \text{ mg}$$

Q: How many moles of $$\mathrm{NaCl}$$ are present in $$117 \text{ g} of$$ $$\mathrm{NaCl}$$? (Molar mass of $$\mathrm{NaCl} = 58.5 \text{ g/mol})$$

$$\frac{117 \text{ g}}{58.5 \text{ g/mol}} = 2.0 \text{ mol}$$

Q: A sample contains $$3.01 \times 10$$^{23}$$ molecules of $$\mathrm{CO}_2$$. How many moles of $$\mathrm{CO}_2$$ are present?

$$\frac{3.01 \times 10$$^{23}$$}{6.02 \times 10$$^{23}$$} = 0.5 \text{ mol}$$

Question 1

Which of the following statements best describes the difference between nuclear fission and nuclear fusion?

Accepted Answer

Nuclear fission splits a heavy nucleus into lighter nuclei, while nuclear fusion combines two light nuclei to form a heavier nucleus.

Question 2

A radioactive isotope has a half-life of 4 days. If you start with 80 mg, how much will remain after 12 days?

Accepted Answer

$$80 	ext{ mg} 	imes \left(\frac{1}{2}\$$right)^{3}$$ = 10 	ext{ mg}$$

Question 3

Which type of radiation has the highest penetrating power and requires the most shielding?

Accepted Answer

Gamma rays

Question 4

Which of the following best explains why atoms form chemical bonds?

Accepted Answer

Atoms form bonds to achieve a full outer shell of electrons, following the octet rule.

Question 5

Which of the following is the correct formula for the compound formed between magnesium and nitrogen?

Accepted Answer

$$\mathrm{Mg}_2\mathrm{N}_3$$

Question 6

Which of the following molecules is nonpolar, given the following electronegativity values: H (2.1), C (2.5), O (3.5)?

Accepted Answer

$$\mathrm{CO}_2 ($$carbon dioxide)

Question 7

Which of the following best describes a dipole moment in a molecule?

Accepted Answer

A separation of charge due to a difference in electronegativity between two bonded atoms.

Question 8

How many moles of $$\mathrm{NaCl}$$ are present in $$117 	ext{ g} of$$ $$\mathrm{NaCl}$$? (Molar mass of $$\mathrm{NaCl} = 58.5 	ext{ g/mol})$$

Accepted Answer

$$\frac{117 	ext{ g}}{58.5 	ext{ g/mol}} = 2.0 	ext{ mol}$$

Question 9

Which of the following best describes the role of a catalyst in a chemical reaction?

Accepted Answer

A catalyst increases the rate of a reaction by lowering the activation energy.

Question 10

Which of the following is a correct balanced nuclear equation for the beta decay of $$^{14}\mathrm{C}$$?

Accepted Answer

$$^{14}_{6}\mathrm{C} \$$rightarrow ^{14}$$_{7}\mathrm{N} $$+ ^{0}$$_{-1}\beta$$

Question 11

Which of the following best explains why water ($$\mathrm{H}_2\mathrm{O}) $$has a higher boiling point than methane ($$\mathrm{CH}_4$$)?

Accepted Answer

Water molecules form hydrogen bonds, which are stronger than the dispersion forces in methane.

Question 12

A sample contains $$3.01 	imes 10$$^{23}$$ molecules of $$\mathrm{CO}_2$$. How many moles of $$\mathrm{CO}_2$$ are present?

Accepted Answer

$$\frac{3.01 	imes 10$$^{23}$$}{6.02 	imes 10$$^{23}$$} = 0.5 	ext{ mol}$$

Question 13

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

Accepted Answer

$$2\mathrm{Na} + \mathrm{Cl}_2 \rightarrow 2\mathrm{NaCl}$$

Question 14

Which of the following statements about the law of conservation of mass is correct?

Accepted Answer

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

Question 15

Which of the following best describes the difference between an ionic and a covalent bond?

Accepted Answer

An ionic bond involves the transfer of electrons from one atom to another, while a covalent bond involves the sharing of electrons.

Question 16

Which of the following is the correct Lewis structure for methane ($$\mathrm{CH}_4$$)?

Accepted Answer

A central C atom with four single bonds to four H atoms, each H having no lone pairs.

Question 17

Which of the following is the correct name for $$\mathrm{N}_2\mathrm{O}_5$$?

Accepted Answer

Dinitrogen pentoxide

Question 18

A patient is given a radioisotope with a half-life of 6 hours. If the initial dose is 32 mg, how much remains after 18 hours?

Accepted Answer

$$32 	ext{ mg} 	imes \left(\frac{1}{2}\$$right)^{3}$$ = 4 	ext{ mg}$$

Question 19

Which of the following is a correct statement about Avogadro’s number?

Accepted Answer

One mole of any substance contains $$6.02 	imes 10$$^{23}$$ particles.

Question 20

Which of the following best describes the shape and bond angle of a molecule with four electron groups around the central atom according to VSEPR theory?

Accepted Answer

Tetrahedral, $$109.5^\circ$$

CHEM 1300 Exam 2 Study Guide: Nuclear Chemistry, Ionic & Molecular Compounds, and Chemical Quantities & Reactions

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