Q: A sample contains 3.0 moles of copper atoms. How many atoms are present in the sample? ($$1\ \mathrm{mol} = 6.022 \times 10$$^{23}$$ atoms)

$$1.81 \times 10$$^{24}$$ atoms

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

$$\text{Average atomic mass} = \sum (\text{fractional abundance} \times \text{isotopic mass})$$

Question 1

A student measures the mass of a metal sample as 25.0 g and its volume as 9.26 cm$$^3. $$Using the correct number of significant figures, what is the density of the metal?

Accepted Answer

$$2.70\ \mathrm{g/cm^3$}$$

Question 2

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

Accepted Answer

Salad with lettuce, tomatoes, and cucumbers

Question 3

Convert 3.50 kilometers to miles using the conversion factor $$1\ \mathrm{km} = 0.6214\ \mathrm{mi}.$$

Accepted Answer

$$2.17\ \mathrm{mi}$$

Question 4

Which of the following statements best describes the difference between accuracy and precision?

Accepted Answer

Accuracy refers to how close measurements are to the true value, while precision refers to how close measurements are to each other.

Question 5

A sample of ethanol has a mass of 15.0 g. Using the density from the table ($$0.789\ \mathrm{g/cm^3$}$$), what is the volume of the sample?

Accepted Answer

$$19.0\ \mathrm{cm^3$}$$

Question 6

Which of the following is a physical change?

Accepted Answer

Melting of ice

Question 7

How many significant figures are in the measurement 0.0045600?

Accepted Answer

6

Question 8

Which of the following best describes an exothermic process?

Accepted Answer

A process that releases heat to the surroundings

Question 9

A 50.0 g sample of water is heated from $$20.0\ ^\circ\mathrm{C} to$$ $$30.0\ ^\circ\mathrm{C}. $$Using the specific heat capacity of water ($$4.184\ \mathrm{J/g\ ^\circ C}$$), how much heat ($$q) is $$absorbed?

Accepted Answer

$$2,090\ \mathrm{J}$$

Question 10

Which of the following is a correct statement about the law of conservation of mass?

Accepted Answer

The total mass of reactants equals the total mass of products in a chemical reaction.

Question 11

Which of the following elements is a noble gas?

Accepted Answer

Argon

Question 12

A sample contains 3.0 moles of copper atoms. How many atoms are present in the sample? ($$1\ \mathrm{mol} = 6.022 	imes 10$$^{23}$$ atoms)

Accepted Answer

$$1.81 	imes 10$$^{24}$$ atoms

Question 13

Which of the following is the correct symbol for an ion with 17 protons and 18 electrons?

Accepted Answer

$$\mathrm{Cl}^-$$

Question 14

Which of the following is a correct conversion for energy units?

Accepted Answer

$$1\ \mathrm{cal} = 4.184\ \mathrm{J}$$

Question 15

Which of the following best describes a compound?

Accepted Answer

A substance composed of two or more elements chemically combined in a fixed ratio

Question 16

A 10.0 g sample of gold at $$25.0\ ^\circ\mathrm{C}$$ absorbs 128 J of heat. What is the final temperature of the gold? (Specific heat of gold = $$0.128\ \mathrm{J/g\ ^\circ C})$$

Accepted Answer

$$35.0\ ^\circ\mathrm{C}$$

Question 17

Which of the following is a correct metric prefix and its exponent?

Accepted Answer

kilo-, $$10^3$$

Question 18

Which of the following best describes a physical property?

Accepted Answer

Melting point

Question 19

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

Accepted Answer

$$	ext{Average atomic mass} = \sum (	ext{fractional abundance} 	imes 	ext{isotopic mass})$$

Question 20

A 250 mL sample of water is heated from $$15.0\ ^\circ\mathrm{C} to$$ $$85.0\ ^\circ\mathrm{C}. $$How much energy (in joules) is required? (Density of water = $$1.0\ \mathrm{g/cm^3$}$$, specific heat = $$4.184\ \mathrm{J/g\ ^\circ C})$$

Accepted Answer

$$73,220\ \mathrm{J}$$

Chem 31 Exam 1 Study Guide: Measurement, Matter, and Atomic Structure

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