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

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

Q: Which of the following is the correct representation for the number of neutrons in an atom?

$$\text{Number of neutrons} = A - Z$$

Question 1

Which of the following best describes the Law of Conservation of Mass as demonstrated by a chemical reaction in a closed container?

Accepted Answer

The total mass of the reactants equals the total mass of the products.

Question 2

A sample of water is decomposed into 16.0 g of oxygen and 2.0 g of hydrogen. What law does this observation best illustrate?

Accepted Answer

Law of definite proportions

Question 3

Which of the following statements is NOT a postulate of Dalton’s Atomic Theory?

Accepted Answer

Atoms can be created and destroyed in chemical reactions.

Question 4

Which experiment led to the discovery of the nucleus in the atom?

Accepted Answer

Rutherford gold foil experiment

Question 5

A neutral atom of phosphorus has 15 protons. How many electrons does it have?

Accepted Answer

15 electrons

Question 6

Which of the following is a heterogeneous mixture?

Accepted Answer

Granite

Question 7

Which of the following best describes a compound?

Accepted Answer

A substance composed of two or more elements in fixed, definite proportions

Question 8

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

Accepted Answer

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

Question 9

A sample contains 3.11 g of copper (Cu). Given that the molar mass of Cu is 63.55 g/mol, how many moles of copper are present?

Accepted Answer

$$0.0489$$ moles

Question 10

Which of the following best describes the difference between graphite and diamond, both forms of carbon?

Accepted Answer

They have different arrangements of the same atoms.

Question 11

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

Accepted Answer

Tea with sugar completely dissolved

Question 12

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 13

Which of the following best describes a cation?

Accepted Answer

An atom that has lost electrons

Question 14

A scientist observes that 1.33 g of oxygen combines with 1 g of carbon to form carbon monoxide, and 2.67 g of oxygen combines with 1 g of carbon to form carbon dioxide. What law does this illustrate?

Accepted Answer

Law of multiple proportions

Question 15

Which of the following is the correct representation for the number of neutrons in an atom?

Accepted Answer

$$	ext{Number of neutrons} = A - Z$$

Question 16

Which of the following is the correct value for Avogadro’s number?

Accepted Answer

$$6.022 	imes 10$$^{23}$$

Question 17

Which of the following best describes the scientific method?

Accepted Answer

A fluid, organized plan of investigation based on observation and experimentation

Question 18

Which subatomic particle was discovered by J.J. Thomson using cathode ray tubes?

Accepted Answer

Electron

Question 19

A sample of magnesium weighs 4.25 g. How many atoms of magnesium are present? (Molar mass of Mg = 24.305 g/mol, Avogadro’s number = $$6.022 	imes 10$$^{23}$$)

Accepted Answer

$$1.05 	imes 10$$^{23}$$ atoms

Question 20

Which of the following is true about the modern view of atomic structure?

Accepted Answer

Most of the atom's mass and all of its positive charge are concentrated in a small nucleus.

Atoms: Structure, Properties, and the Foundations of Chemistry

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