Q: A sample of water is measured at $$25^\circ \mathrm{C}. $$What is this temperature in Kelvin?

$$25 + 273.15 = 298.15$$ \text{ K}$

Q: A car is traveling at $$90.0 km/h. $$What is its kinetic energy if its mass is $$1200 kg$$? (1 km/h = $$0.2778 m/s)$$

$$E_k = \frac{1}{2}mv^2$ = \frac{1}{2} \times 1200 \times (25.0)^2$ = 375,000 J$$

Q: Chlorine has two naturally occurring isotopes: $$^{35}\mathrm{Cl} ($$mass = 34.969 amu, abundance = 75.78%) and $$^{37}\mathrm{Cl} ($$mass = 36.966 amu, abundance = 24.22%). What is the average atomic mass of chlorine?

$$(0.7578 \times 34.969) + (0.2422 \times 36.966) = 35.45$$ \text{ amu}$

Q: A chemist needs $$250 mL of a $$solution. What is this volume in cubic meters ($$\mathrm{m}^3$$)?

$$2.5 \times 10$$^{-4}$$ \text{ m}^3$

Q: Which of the following is the correct SI unit and prefix for a measurement of $$1 \times 10$$^{-6}$$ meters?

$$1$$ \text{ micrometer (} \mu \text{m)}$

Question 1

Which of the following statements best distinguishes a scientific theory from a hypothesis?

Accepted Answer

A hypothesis is a testable prediction, while a theory is a comprehensive explanation supported by repeated experiments.

Question 2

A laboratory experiment requires you to convert 0.025 km to centimeters. What is the correct value?

Accepted Answer

$$2.5 	imes 10^4$ 	ext{ cm}$

Question 3

A sample of water is measured at $$25^\circ \mathrm{C}. $$What is this temperature in Kelvin?

Accepted Answer

$$25 + 273.15 = 298.15$$ 	ext{ K}$

Question 4

Which of the following is the correct relationship between cubic decimeters and liters?

Accepted Answer

$$1 \ \mathrm{dm}^3 = 1 \ \mathrm{L}$$

Question 5

A block of metal has a mass of $$250.0 g $$and a volume of $$32.0 cm$^3. $$What is its density in g/cm$$^3$$?

Accepted Answer

$$7.81$$ 	ext{ g/cm}^3$

Question 6

A car is traveling at $$90.0 km/h. $$What is its kinetic energy if its mass is $$1200 kg$$? (1 km/h = $$0.2778 m/s)$$

Accepted Answer

$$E_k = \frac{1}{2}mv^2$ = \frac{1}{2} 	imes 1200 	imes (25.0)^2$ = 375,000 J$$

Question 7

Which of the following measurements contains exactly three significant figures?

Accepted Answer

$$0.0300$$

Question 8

A student measures the mass of a sample as $$12.340 g $$and the volume as $$2.1 mL. $$What is the density, reported with the correct number of significant figures?

Accepted Answer

$$5.9$$ 	ext{ g/mL}$

Question 9

Which statement best describes the Law of Conservation of Mass?

Accepted Answer

The total mass of substances remains constant during a chemical reaction.

Question 10

An atom has 17 protons, 18 neutrons, and 17 electrons. What is its atomic number, mass number, and charge?

Accepted Answer

Atomic number: 17, Mass number: 35, Charge: 0

Question 11

Chlorine has two naturally occurring isotopes: $$^{35}\mathrm{Cl} ($$mass = 34.969 amu, abundance = 75.78%) and $$^{37}\mathrm{Cl} ($$mass = 36.966 amu, abundance = 24.22%). What is the average atomic mass of chlorine?

Accepted Answer

$$(0.7578 	imes 34.969) + (0.2422 	imes 36.966) = 35.45$$ 	ext{ amu}$

Question 12

A sample contains $$3.01 	imes 10$$^{23}$$ atoms of sodium. How many moles of sodium are present?

Accepted Answer

$$0.500$$ 	ext{ mol}$

Question 13

How many grams of carbon are in $$2.00$$ mol of carbon? (Molar mass of C = $$12.01 g/$$mol)

Accepted Answer

$$24.02$$ 	ext{ g}$

Question 14

A chemist needs $$250 mL of a $$solution. What is this volume in cubic meters ($$\mathrm{m}^3$$)?

Accepted Answer

$$2.5 	imes 10$$^{-4}$$ 	ext{ m}^3$

Question 15

A sample of an unknown element contains two isotopes: $$^{63}\mathrm{X} ($$mass = 62.930 amu, abundance = $$x) $$and $$^{65}\mathrm{X} ($$mass = 64.928 amu, abundance = $$1-x). If $$the average atomic mass is $$63.55$$ amu, what is the abundance of $$^{63}\mathrm{X}$$?

Accepted Answer

$$x = 0.692 or 69.2$$\%$

Question 16

Which of the following is the correct SI unit and prefix for a measurement of $$1 	imes 10$$^{-6}$$ meters?

Accepted Answer

$$1$$ 	ext{ micrometer (} \mu 	ext{m)}$

Question 17

A patient’s body temperature is measured as $$102.2^\circ \mathrm{F}. $$What is this temperature in Celsius?

Accepted Answer

$$39.0^\circ \mathrm{C}$$

Question 18

Which of the following best explains why significant figures are important in scientific measurements?

Accepted Answer

They indicate the precision of a measurement and ensure calculations do not imply greater accuracy than the data supports.

Question 19

A student calculates the kinetic energy of a $$0.050 kg $$baseball moving at $$40.0 m/s. $$What is the kinetic energy in Joules?

Accepted Answer

$$E_k = \frac{1}{2} 	imes 0.050 	imes (40.0)^2$ = 40.0 J$$

CHM 102 Exam 1 Study Guide: Units, Measurement, and Atomic Structure

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