Q: A reaction vessel contains 0.250 mol of oxygen gas. How many molecules of oxygen are present? (Avogadro's number $$= 6.022 \times 10$$^{23}$$\ \mathrm{mol}^{-1})$$

$$1.51 \times 10$$^{24}$$ molecules

Question 1

Which of the following best describes the difference between a hypothesis and a theory in the scientific method?

Accepted Answer

A hypothesis is a tentative explanation that can be tested, while a theory is a well-substantiated explanation based on a body of evidence.

Question 2

A student measures the mass of a sample as 0.00560 kg. How many significant figures does this measurement have?

Accepted Answer

3

Question 3

Which of the following is the correct SI base unit for the amount of substance?

Accepted Answer

mol

Question 4

Convert 0.0250 km to centimeters (cm).

Accepted Answer

$$2.50 	imes 10^4$ cm

Question 5

A sample of ethanol has a mass of 78.5 g and a volume of 100.0 mL. What is its density in $$\mathrm{g/cm^3$}$$?

Accepted Answer

$$0.785\ \mathrm{g/cm^3$}$$

Question 6

Which of the following correctly expresses 0.000 003 2 meters using an SI prefix?

Accepted Answer

Question 7

A temperature is measured as 25.0 $$^\circC. $$What is this temperature in Kelvin?

Accepted Answer

$$298.15\ \mathrm{K}$$

Question 8

A reaction vessel contains 0.250 mol of oxygen gas. How many molecules of oxygen are present? (Avogadro's number $$= 6.022 	imes 10$$^{23}$$\ \mathrm{mol}^{-1})$$

Accepted Answer

$$1.51 	imes 10$$^{24}$$ molecules

Question 9

A sample of copper contains two naturally occurring isotopes: $$^{63}\mathrm{Cu} ($$mass = 62.93 u, abundance = 69.2%) and $$^{65}\mathrm{Cu} ($$mass = 64.93 u, abundance = 30.8%). What is the average atomic mass of copper?

Accepted Answer

$$63.55\ \mathrm{u}$$

Question 10

A 50.0 mL sample of a liquid has a mass of 39.5 g. What is the density of the liquid in $$\mathrm{g/mL}$$, and what would be the mass of 250 mL of this liquid?

Accepted Answer

Density: $$0.790\ \mathrm{g/mL}$$; Mass: $$197.5\ \mathrm{g}$$

Question 11

A patient’s body temperature is measured as 102.2 $$^\circF. $$What is this temperature in Celsius?

Accepted Answer

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

Question 12

Which of the following statements best describes the Law of Conservation of Mass?

Accepted Answer

The total mass of substances present after a chemical reaction is the same as the total mass before the reaction.

Question 13

A 10.0 g sample of a compound contains 2.0 g of hydrogen and 8.0 g of oxygen. If the compound is decomposed, what is the total mass of products expected according to the Law of Conservation of Mass?

Accepted Answer

10.0 g

Question 14

A block of metal has a mass of 250 g and a volume of $$95.0\ \mathrm{cm^3$}. $$What is its density in $$\mathrm{g/cm^3$}$$?

Accepted Answer

$$2.63\ \mathrm{g/cm^3$}$$

Question 15

Which of the following is the correct relationship between $$\mathrm{dm^3$}$$ and L?

Accepted Answer

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

Question 16

A car is traveling at a speed of 90.0 km/h. What is its kinetic energy if its mass is 1200 kg? (1 J = 1 kg m$$^2/s$^2)$$

Accepted Answer

$$3.75 	imes 10^5$ J

Question 17

Which of the following is the correct molar mass of glucose ($$\mathrm{C_6H_{12}O_6$}$$)? (Atomic masses: C = 12.01, H = 1.008, O = 16.00)

Accepted Answer

$$180.16\ \mathrm{g/mol}$$

Question 18

A sample contains $$3.00\ \mathrm{g} of $$NaCl (molar mass = $$58.44\ \mathrm{g/mol}). $$How many moles of NaCl are present?

Accepted Answer

$$0.0514$$ mol

Question 19

A naturally occurring element has two isotopes: $$^{10}\mathrm{B} ($$mass = 10.01 u, abundance = $$x) $$and $$^{11}\mathrm{B} ($$mass = 11.01 u, abundance = $$1-x). If $$the average atomic mass is 10.81 u, what is the abundance of $$^{11}\mathrm{B}$$?

Accepted Answer

81%

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

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