Q: Calculate the average atomic mass of an element with two isotopes: 70.0% $$^{63}Cu (62.93 $$amu) and 30.0% $$^{65}Cu (64.93 $$amu).

$$(0.700 \times 62.93) + (0.300 \times 64.93) = 63.55\ \mathrm{amu}$$

Question 1

Which of the following statements best describes the law of definite proportions?

Accepted Answer

A compound always contains the same elements in the same proportion by mass.

Question 2

A sample of magnesium reacts completely with oxygen to form 40.3 g of magnesium oxide. If the reaction started with 24.3 g of magnesium, what mass of oxygen reacted? (Law of conservation of mass)

Accepted Answer

$$40.3\ \mathrm{g} - 24.3\ \mathrm{g} = 16.0\ \mathrm{g}$$

Question 3

Which of the following is a transition metal?

Accepted Answer

Fe

Question 4

Which of the following best describes an isotope?

Accepted Answer

Atoms of the same element with different numbers of neutrons.

Question 5

A chlorine atom has 17 protons and 18 neutrons. What is its isotope symbol?

Accepted Answer

$$^{35}_{17}\mathrm{Cl}$$

Question 6

Which experiment provided evidence for the existence of the electron?

Accepted Answer

Thomson's cathode ray tube experiment

Question 7

Which of the following is a correct statement about Rutherford's gold foil experiment?

Accepted Answer

It demonstrated that atoms have a small, dense, positively charged nucleus.

Question 8

Calculate the average atomic mass of an element with two isotopes: 70.0% $$^{63}Cu (62.93 $$amu) and 30.0% $$^{65}Cu (64.93 $$amu).

Accepted Answer

$$(0.700 	imes 62.93) + (0.300 	imes 64.93) = 63.55\ \mathrm{amu}$$

Question 9

Which of the following best describes a covalent bond?

Accepted Answer

A bond formed by the sharing of electrons between two nonmetals.

Question 10

Which of the following compounds is an example of a molecular (covalent) compound?

Accepted Answer

$$\mathrm{CO}_2$$

Question 11

How many moles are in 18.0 g of water ($$\mathrm{H}_2\mathrm{O}$$)? (Molar mass of $$\mathrm{H}_2\mathrm{O} = 18.0\ \mathrm{g/mol})$$

Accepted Answer

$$\frac{18.0\ \mathrm{g}}{18.0\ \mathrm{g/mol}} = 1.00\ \mathrm{mol}$$

Question 12

Which of the following is a correct electron configuration for a neutral sodium atom ($$Z=11$$)?

Accepted Answer

$$1s^2$$\ $$2s^2$$\ $$2p^6$$\ $$3s^1$$

Question 13

Which of the following is a property of metals?

Accepted Answer

They are good conductors of electricity.

Question 14

Which of the following best describes Avogadro's number?

Accepted Answer

The number of particles in one mole, $$6.022 	imes 10$$^{23}$$.

Question 15

Which of the following is a correct name for $$\mathrm{Na}_2\mathrm{SO}_4$$?

Accepted Answer

Sodium sulfate

Question 16

Which of the following is a correct formula for dinitrogen pentoxide?

Accepted Answer

$$\mathrm{N}_2\mathrm{O}_5$$

Question 17

Which of the following best describes a mixture?

Accepted Answer

A physical combination of two or more substances that retain their own properties.

Question 18

Which of the following is a main group element?

Accepted Answer

Oxygen

Question 19

Which of the following best explains the difference between a physical and a chemical property?

Accepted Answer

A physical property can be observed without changing the substance's identity, while a chemical property describes how a substance reacts to form new substances.

General Chemistry: Elements, Atomic Structure, and Chemical Compounds – Study Notes

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