Q: Millikan’s oil drop experiment determined the charge of a single electron. If an oil drop has a charge of $$-3.20 \times 10$$^{-19}$$ C, how many excess electrons does it contain?

$$\frac{-3.20 \times 10$$^{-19}$$\ \text{C}}{-1.60 \times 10$$^{-19}$$\ \text{C/electron}} = 2$$

Question 1

Which statement best describes the Law of Conservation of Mass?

Accepted Answer

Mass is neither created nor destroyed; it can only change forms during chemical or physical changes.

Question 2

A sample of water decomposes to produce 16.0 g of oxygen and 2.0 g of hydrogen. What is the mass ratio of oxygen to hydrogen in water?

Accepted Answer

$$\frac{16.0}{2.0} = 8:1$$

Question 3

Which of the following is NOT a postulate of Dalton’s atomic theory?

Accepted Answer

Atoms of one element can change into atoms of another element during a chemical reaction.

Question 4

Two samples of carbon monoxide decompose to produce the following: Sample 1 yields 17.2 g oxygen and 12.9 g carbon; Sample 2 yields 10.5 g oxygen and 7.88 g carbon. Are these results consistent with the law of definite proportions?

Accepted Answer

Yes, because the mass ratio of oxygen to carbon is the same in both samples.

Question 5

Which experiment led to the discovery of the electron?

Accepted Answer

J.J. Thomson’s cathode ray experiment

Question 6

Millikan’s oil drop experiment determined the charge of a single electron. If an oil drop has a charge of $$-3.20 	imes 10$$^{-19}$$ C, how many excess electrons does it contain?

Accepted Answer

$$\frac{-3.20 	imes 10$$^{-19}$$\ 	ext{C}}{-1.60 	imes 10$$^{-19}$$\ 	ext{C/electron}} = 2$$

Question 7

Which statement best distinguishes the law of definite proportions from the law of multiple proportions?

Accepted Answer

The law of definite proportions applies to two or more samples of the same compound, while the law of multiple proportions applies to two different compounds containing the same elements.

Question 8

In Rutherford’s gold foil experiment, what observation led to the conclusion that atoms have a small, dense nucleus?

Accepted Answer

Some alpha particles were deflected at large angles, and a few even bounced back.

Question 9

Which subatomic particle has a mass nearly equal to that of a proton but no electrical charge?

Accepted Answer

Neutron

Question 10

A compound contains 2.28 g oxygen for every 1.00 g nitrogen (nitrogen dioxide), and another contains 0.570 g oxygen for every 1.00 g nitrogen (dinitrogen monoxide). Show these results are consistent with the law of multiple proportions.

Accepted Answer

The ratio $$\frac{2.28}{0.570} = 4 is a $$small whole number, consistent with the law.

Question 11

Which model of the atom proposed that electrons were embedded in a positively charged sphere?

Accepted Answer

J.J. Thomson’s plum-pudding model

Question 12

If a log burns completely in a campfire and the mass of the ash is much less than the original log, what happens to the matter that composed the log?

Accepted Answer

The matter reacts to form gases that are released into the air.

Question 13

Which of the following statements about subatomic particles is correct?

Accepted Answer

Protons and neutrons have nearly identical masses, while electrons are much lighter.

Question 14

Which law states that all samples of a given compound have the same proportions of their constituent elements?

Accepted Answer

Law of definite proportions

Question 15

Given the charge-to-mass ratio for an electron is $$-1.76 	imes 10^8$ C/g and the charge of an electron is -1.60$$ 	imes $$10^{-19} C$$, calculate the mass of an electron.

Accepted Answer

$$\frac{-1.60 	imes 10$$^{-19}$$\ 	ext{C}}{-1.76 	imes 10^8$\ 	ext{C/g}} = 9.10 	imes 10$$^{-28}$$\ 	ext{g}$$

Question 16

Which of the following best explains why the mass of the atom is concentrated in the nucleus?

Accepted Answer

Protons and neutrons, which have most of the atom’s mass, are located in the nucleus.

Question 17

Which of the following is a real-world example of the law of conservation of mass?

Accepted Answer

When ice melts to water, the total mass remains the same.

Atoms: Early Atomic Theory, Laws, and the Structure of Matter

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