Q: A sample contains 0.75 moles of magnesium. How many atoms of magnesium are present in the sample?

$$0.75 \times 6.022 \times 10$$^{23}$$ = 4.52 \times 10$$^{23}$$ atoms

Q: An element has two naturally occurring isotopes: one with a mass of 10.0 amu and 20% abundance, and another with a mass of 11.0 amu and 80% abundance. What is the average atomic mass of this element?

$$(0.20 \times 10.0) + (0.80 \times 11.0) = 2.0 + 8.8 = 10.8$$ amu

Q: A neutron is traveling at $$2.00 \times 10^5$ m/s. What is its de Broglie wavelength? (Given h = 6.626$$ \times $$10^{-34} J s$$, $$m_{neutron} = 1.675 \times 10$$^{-27}$$ kg)

$$\lambda = \frac{6.626 \times 10$$^{-34}$$}{1.675 \times 10$$^{-27}$$ \times 2.00 \times 10^5$} = 1.98 \times 10$$^{-12}$$ m

Q: If you have 0.50 moles of sodium chloride (NaCl), how many formula units of NaCl do you have?

$$0.50 \times 6.022 \times 10$$^{23}$$ = 3.01 \times 10$$^{23}$$ formula units

Q: A radio wave has a frequency of $$1.00 \times 10^8$ s$$^{-1}$$. What is its wavelength? (Given c = 2.998$$ \times $$10^8 m/s)$$

$$\lambda = \frac{2.998 \times 10^8$}{1.00 \times 10^8$} = 3.00 m$$

Question 1

Which of the following statements best explains why the hydrogen emission spectrum consists of sharp lines rather than a continuous spectrum?

Accepted Answer

Because electrons in hydrogen can only occupy specific, quantized energy levels, so only certain energy transitions (and thus photon energies) are possible.

Question 2

A sample contains 0.75 moles of magnesium. How many atoms of magnesium are present in the sample?

Accepted Answer

$$0.75 	imes 6.022 	imes 10$$^{23}$$ = 4.52 	imes 10$$^{23}$$ atoms

Question 3

Which of the following sets contains only nonmetals?

Accepted Answer

phosphorus, nitrogen, oxygen

Question 4

An element has two naturally occurring isotopes: one with a mass of 10.0 amu and 20% abundance, and another with a mass of 11.0 amu and 80% abundance. What is the average atomic mass of this element?

Accepted Answer

$$(0.20 	imes 10.0) + (0.80 	imes 11.0) = 2.0 + 8.8 = 10.8$$ amu

Question 5

Which law is demonstrated by the fact that hydrogen and oxygen can form both water (O:H mass ratio = 8:1) and hydrogen peroxide (O:H mass ratio = 16:1)?

Accepted Answer

Law of multiple proportions

Question 6

Which experiment determined the charge of the electron?

Accepted Answer

Millikan’s Oil Drop experiment

Question 7

A neutron is traveling at $$2.00 	imes 10^5$ m/s. What is its de Broglie wavelength? (Given h = 6.626$$ 	imes $$10^{-34} J s$$, $$m_{neutron} = 1.675 	imes 10$$^{-27}$$ kg)

Accepted Answer

$$\lambda = \frac{6.626 	imes 10$$^{-34}$$}{1.675 	imes 10$$^{-27}$$ 	imes 2.00 	imes 10^5$} = 1.98 	imes 10$$^{-12}$$ m

Question 8

Which of the following electron configurations corresponds to the element aluminum (Al)?

Accepted Answer

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

Question 9

Which of the following transitions in a hydrogen atom emits the highest energy photon?

Accepted Answer

$$n=3 \rightarrow m=1$$

Question 10

Which element is most chemically similar to oxygen?

Accepted Answer

sulfur

Question 11

If you have 0.50 moles of sodium chloride (NaCl), how many formula units of NaCl do you have?

Accepted Answer

$$0.50 	imes 6.022 	imes 10$$^{23}$$ = 3.01 	imes 10$$^{23}$$ formula units

Question 12

Which of the following best explains why a 3s electron in sodium 'feels' less of the nuclear charge than a 2s electron?

Accepted Answer

The 3s electron is farther from the nucleus and is shielded by more inner electrons, reducing the effective nuclear charge it experiences.

Question 13

Which of the following pairs of atoms, both in period 4, has the larger atomic radius?

Accepted Answer

germanium (Ge)

Question 14

Which of the following is the correct label and angular momentum quantum number $$l$$ for an orbital with $$n=4$$ and $$l=2$$?

Accepted Answer

4d, $$l=2$$

Question 15

A radio wave has a frequency of $$1.00 	imes 10^8$ s$$^{-1}$$. What is its wavelength? (Given c = 2.998$$ 	imes $$10^8 m/s)$$

Accepted Answer

$$\lambda = \frac{2.998 	imes 10^8$}{1.00 	imes 10^8$} = 3.00 m$$

Question 16

Which of the following best describes the law of conservation of mass as it applies to chemical reactions?

Accepted Answer

The total mass of reactants equals the total mass of products; atoms are neither created nor destroyed.

Question 17

Which of the following electron configurations represents the element with atomic number 20?

Accepted Answer

$$[Ar] 4s^2$

Question 18

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 19

Which of the following best explains why copper-63 is more abundant than copper-65 in nature?

Accepted Answer

Copper’s average atomic mass (63.55 amu) is closer to the mass of copper-63 (62.93 amu) than copper-65 (64.93 amu), indicating copper-63 is more abundant.

General Chemistry Exam 1 Study Guidance

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