Q: Convert $$0.000345 to $$scientific notation and indicate the correct number of significant figures.

$$3.45 \times 10$$^{-4}$$ (3 significant figures)

Question 1

Which of the following best describes a chemical, according to the definition used in chemistry?

Accepted Answer

A substance with a definite composition, such as water or carbon dioxide.

Question 2

A student measures the mass of a sample as $$2.50 g $$and its volume as $$1.25 mL. $$What is the density of the sample, rounded to the correct number of significant figures?

Accepted Answer

$$2.0 g/mL$$

Question 3

Which of the following is an example of a heterogeneous mixture?

Accepted Answer

Salad dressing with oil and vinegar

Question 4

Which of the following statements about the scientific method is correct?

Accepted Answer

It involves making observations, forming a hypothesis, conducting experiments, and drawing conclusions.

Question 5

Convert $$0.000345 to $$scientific notation and indicate the correct number of significant figures.

Accepted Answer

$$3.45 	imes 10$$^{-4}$$ (3 significant figures)

Question 6

Which of the following best describes a chemical change?

Accepted Answer

A piece of iron rusts when left outside.

Question 7

A sample of gold has a mass of $$19.3 g $$and a volume of $$1.00 cm$^3. $$What is the density of gold, and what does this value tell you about gold compared to water (density $$= 1.00 g/cm$^3$$)?

Accepted Answer

Gold is much denser than water, with a density of $$19.3 g/cm$^3.$$

Question 8

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 9

Which of the following best explains why metals tend to form cations?

Accepted Answer

Metals lose electrons to achieve a stable electron configuration, resulting in a positive charge.

Question 10

Which of the following is the correct electron configuration for a neutral atom of oxygen ($$Z=8$$)?

Accepted Answer

$$1s^2$$\ $$2s^2$$\ $$2p^4$$

Question 11

A student adds $$25.0 mL of $$water at $$22.0\ ^\circC to a $$beaker. If the specific heat capacity of water is $$4.18 J/g$\cdot$$°C and the mass of water is $$25.0 g$$, how much energy is required to raise the temperature to $$27.0\ ^\circC$$? (Round to the correct number of significant figures.)

Accepted Answer

$$523 J$$

Question 12

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

Accepted Answer

Ionic compounds are formed by the transfer of electrons, while covalent compounds are formed by the sharing of electrons.

Question 13

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

Accepted Answer

Elements in the same group have similar chemical properties.

Question 14

Which of the following best describes Hund’s rule as it applies to electron configurations?

Accepted Answer

Electrons fill degenerate orbitals singly before pairing up.

Question 15

Which of the following molecules is polar due to its molecular geometry and bond polarity?

Accepted Answer

Water ($$\mathrm{H_2O})$$

Question 16

A sample contains $$80.0\%$$ $$^{35}Cl ($$mass $$= 34.97 u) $$and $$20.0\%$$ $$^{37}Cl ($$mass $$= 36.97 u). $$What is the average atomic mass of chlorine? (Round to 2 decimal places.)

Accepted Answer

$$35.37 u$$

Question 17

Which of the following best describes the Bohr model of the atom?

Accepted Answer

Electrons move in fixed orbits around the nucleus at specific energy levels.

Question 18

Which of the following is the correct order of increasing atomic size for the elements Na, Mg, and Al?

Accepted Answer

Al \u003c Mg \u003c Na

Question 19

Which of the following statements about exothermic and endothermic processes is correct?

Accepted Answer

Exothermic processes release energy to the surroundings, while endothermic processes absorb energy from the surroundings.

Question 20

Which of the following best explains why fluorine is the most electronegative element?

Accepted Answer

Fluorine has a small atomic radius and a high effective nuclear charge, attracting electrons strongly.

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