Q: The oxygen-fluorine bond length in a fluorous acid molecule is $$2.10 \times 10$$^{-8}$$\ \mathrm{cm}. $$What is this bond length expressed in nanometers $$(\mathrm{nm})$$? (Express your answer in scientific notation.)

$$2.10 \times 10$$^{-1}$$\ \mathrm{nm}$$

Q: If a molecule has a bond length of $$1.54\ \mathrm{\AA}$$, what is this length in meters? (Recall $$1\ \mathrm{\AA} = 1 \times 10$$^{-10}$$\ \mathrm{m}.)$$

$$1.54 \times 10$$^{-10}$$\ \mathrm{m}$$

Q: Which of the following is the correct formula for calculating the average atomic mass of an element with two isotopes?

$$\text{Average atomic mass} = (\text{mass}_1 \times \text{abundance}_1) + (\text{mass}_2 \times \text{abundance}_2)$$

Question 1

A newly discovered element, duranium (Dr), has two isotopes: Dr-40 and Dr-42. The average atomic mass of duranium is $$41.5\ \mathrm{amu}. If $$the isotope mass and abundance for Dr-40 are $$40.05\ \mathrm{amu}$$ and $$22\%$$ respectively, what is the isotope mass of Dr-42 if its abundance is $$78\%$$? (Express your answer to two decimal places.)

Accepted Answer

$$42.05\ \mathrm{amu}$$

Question 2

The oxygen-fluorine bond length in a fluorous acid molecule is $$2.10 	imes 10$$^{-8}$$\ \mathrm{cm}. $$What is this bond length expressed in nanometers $$(\mathrm{nm})$$? (Express your answer in scientific notation.)

Accepted Answer

$$2.10 	imes 10$$^{-1}$$\ \mathrm{nm}$$

Question 3

A table has a top area of $$0.340\ \mathrm{m}^2. $$What is the area of this tabletop in square inches $$(\mathrm{in}^2)$$? (Use $$1\ \mathrm{m} = 39.37\ \mathrm{in}.)$$

Accepted Answer

$$527\ \mathrm{in}^2$$

Question 4

A marble has a mass of $$0.114\ \mathrm{pounds}$$ and a density of $$2.85\ \mathrm{g/cm}^3. $$What is the volume of this marble in cubic inches $$(\mathrm{in}^3)$$? (Use $$1\ \mathrm{lb} = 453.6\ \mathrm{g}$$ and $$1\ \mathrm{in}^3 = 16.39\ \mathrm{cm}^3.)$$

Accepted Answer

$$1.09\ \mathrm{in}^3$$

Question 5

Which of the following best describes the concept of isotopic abundance as it relates to the calculation of average atomic mass?

Accepted Answer

It is the percentage of each isotope present in a naturally occurring sample of an element.

Question 6

If a molecule has a bond length of $$1.54\ \mathrm{\AA}$$, what is this length in meters? (Recall $$1\ \mathrm{\AA} = 1 	imes 10$$^{-10}$$\ \mathrm{m}.)$$

Accepted Answer

$$1.54 	imes 10$$^{-10}$$\ \mathrm{m}$$

Question 7

A student measures the mass of a sample as $$14.0\ \mathrm{g}$$ and its volume as $$4.2\ \mathrm{cm}^3. $$What is the density of the sample in $$\mathrm{g/cm}^3$$?

Accepted Answer

$$3.33\ \mathrm{g/cm}^3$$

Question 8

Which of the following is the correct formula for calculating the average atomic mass of an element with two isotopes?

Accepted Answer

$$	ext{Average atomic mass} = (	ext{mass}_1 	imes 	ext{abundance}_1) + (	ext{mass}_2 	imes 	ext{abundance}_2)$$

Question 9

A chemist needs to convert $$5.00\ \mathrm{cm}^3 to$$ $$\mathrm{mL}. $$Which of the following is correct?

Accepted Answer

$$5.00\ \mathrm{mL}$$

Question 10

A sample of an unknown metal has a density of $$7.85\ \mathrm{g/cm}^3. If a $$cube of this metal has a side length of $$2.00\ \mathrm{cm}$$, what is its mass?

Accepted Answer

$$62.8\ \mathrm{g}$$

Question 11

Which of the following statements about density is correct?

Accepted Answer

Density is an intensive property and does not depend on the amount of substance.

Question 12

A student is asked to express $$0.00340\ \mathrm{m}^2 in$$ $$\mathrm{cm}^2. $$What is the correct answer?

Accepted Answer

$$3400\ \mathrm{cm}^2$$

Question 13

Which of the following is the correct conversion factor to use when converting from $$\mathrm{cm}^3 to$$ $$\mathrm{in}^3$$?

Accepted Answer

$$1\ \mathrm{in}^3 = 16.39\ \mathrm{cm}^3$$

Question 14

A chemist finds that a sample of duranium contains $$22\% Dr-40 $$and $$78\% Dr-42. If $$the atomic mass of Dr-40 is $$40.05\ \mathrm{amu}$$ and Dr-42 is $$42.05\ \mathrm{amu}$$, what is the average atomic mass of duranium?

Accepted Answer

$$41.50\ \mathrm{amu}$$

Question 15

Which of the following best explains why the average atomic mass of an element is rarely a whole number?

Accepted Answer

It is a weighted average of the masses of all naturally occurring isotopes.

Question 16

A student needs to convert $$2.50\ \mathrm{in}^2 to$$ $$\mathrm{cm}^2. $$Which conversion factor should be used?

Accepted Answer

$$1\ \mathrm{in}^2 = 6.45\ \mathrm{cm}^2$$

Introduction to Chemistry: Atomic Mass, Scientific Notation, and Density Calculations

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