Q: Millikan’s oil drop experiment determined the charge of a single electron. If the measured charge on a drop was $$ -3.20 \times 10$$^{-19}$$ C$$, what is the number of electrons on the drop?

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

Question 1

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

Accepted Answer

The total mass of substances involved in a chemical reaction remains constant because matter is neither created nor destroyed.

Question 2

A sample of water is decomposed 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

$$ \frac{16.0\ \mathrm{g}}{2.0\ \mathrm{g}} = 8.0:1 $$

Question 3

Which experiment provided the first direct evidence for the existence of electrons?

Accepted Answer

J. J. Thomson's cathode ray tube experiment

Question 4

According to Dalton's atomic theory, which statement is INCORRECT?

Accepted Answer

Atoms of a given element can have different masses.

Question 5

A compound contains 2.56 g of oxygen and 0.96 g of carbon. What is the mass ratio of oxygen to carbon, and does this support the law of definite proportions?

Accepted Answer

$$ \frac{2.56}{0.96} = 2.67:1 $$, which supports the law of definite proportions.

Question 6

Which of the following best illustrates the law of multiple proportions?

Accepted Answer

Two compounds, CO and CO$$_2$$, have mass ratios of oxygen to carbon of 1.33:1 and 2.67:1, respectively, and $$ \frac{2.67}{1.33} = 2  is a $$small whole number.

Question 7

Millikan’s oil drop experiment determined the charge of a single electron. If the measured charge on a drop was $$ -3.20 	imes 10$$^{-19}$$  C$$, what is the number of electrons on the drop?

Accepted Answer

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

Question 8

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

Accepted Answer

Atoms of a given element can be subdivided into protons, neutrons, and electrons.

Question 9

A student decomposes two samples of carbon monoxide. The first sample produces 17.2 g of oxygen and 12.9 g of carbon. The second sample produces 10.5 g of oxygen and 7.88 g of carbon. Are these results consistent with the law of definite proportions?

Accepted Answer

Yes, because $$ \frac{17.2}{12.9} = 1.33 $$ and $$ \frac{10.5}{7.88} = 1.33 $$, so the mass ratio is constant.

Question 10

Which of the following best describes the result of J. J. Thomson’s cathode ray experiment?

Accepted Answer

It showed that atoms contain negatively charged particles called electrons.

Question 11

If a compound contains 2.67 g of oxygen for every 1.00 g of carbon (as in carbon dioxide), and another compound contains 1.33 g of oxygen for every 1.00 g of carbon (as in carbon monoxide), what is the ratio of oxygen in the two compounds, and what law does this illustrate?

Accepted Answer

$$ \frac{2.67}{1.33} = 2.0 $$, illustrating the law of multiple proportions.

Question 12

Which of the following is a correct statement about the structure of the atom according to the plum-pudding model?

Accepted Answer

Negatively charged electrons are embedded within a positively charged sphere.

Question 13

Which of the following best explains why the law of definite proportions is important in chemistry?

Accepted Answer

It shows that a chemical compound always contains the same elements in the same proportion by mass, regardless of the source or method of preparation.

Question 14

If the charge-to-mass ratio of an electron is $$ -1.76 	imes 10$$^{8}$$  C/g$$, and the charge of an electron is $$ -1.60 	imes 10$$^{-19}$$  C$$, what is the mass of an electron?

Accepted Answer

$$ \frac{1.60 	imes 10$$^{-19}$$\ \mathrm{C}}{1.76 	imes 10$$^{8}$$\ \mathrm{C/g}} = 9.09 	imes 10$$^{-28}$$\ \mathrm{g} $$

Question 15

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

Accepted Answer

When burning wood in a closed container, the total mass of the container and its contents remains unchanged after combustion.

Question 16

Which of the following best describes the difference between the law of definite proportions and the law of multiple proportions?

Accepted Answer

The law of definite proportions states that a compound always contains the same elements in the same ratio by mass, while the law of multiple proportions deals with the ratios of masses of one element that combine with a fixed mass of another element in different compounds.

Atoms and Elements: Foundations of Atomic Theory

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