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 unchanged.

Question 2

A sample of water is decomposed into 16.0 g of oxygen and 2.0 g of hydrogen. What is the mass ratio of oxygen to hydrogen, and which law does this illustrate?

Accepted Answer

$$\frac{16.0\ g}{2.0\ g} = 8.0:1$$, illustrating the Law of Definite Proportions.

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 based on modern knowledge?

Accepted Answer

All atoms of a given element have the same mass and properties.

Question 5

A chemist analyzes two samples of carbon monoxide. The first contains 17.2 g of oxygen and 12.9 g of carbon. The second contains 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 $$\frac{10.5}{7.88} = 1.33$$, showing a constant ratio.

Question 6

Which of the following best illustrates the Law of Multiple Proportions?

Accepted Answer

The ratio of oxygen to carbon in CO$$_2 is$$ $$2.67:1$$ and in CO is $$1.33:1$$, and $$\frac{2.67}{1.33} = 2.$$

Question 7

Millikan’s oil drop experiment determined the charge of the electron. If the measured charge on a drop was always a whole-number multiple of $$-1.60 	imes 10$$^{-19}$$ C, what does this imply?

Accepted Answer

The charge of the electron is quantized and fundamental.

Question 8

Which statement about atoms is supported by modern atomic theory?

Accepted Answer

Atoms of the same element can have different masses due to isotopes.

Question 9

A sample of nitrogen dioxide contains 2.28 g of oxygen per 1.00 g of nitrogen, while dinitrogen monoxide contains 0.570 g of oxygen per 1.00 g of nitrogen. What is the ratio of oxygen in NO$$_2 to N$_2O$$, and what law does this demonstrate?

Accepted Answer

$$\frac{2.28}{0.570} = 4.00$$, demonstrating the Law of Multiple Proportions.

Question 10

Which of the following is a direct consequence of the Law of Definite Proportions?

Accepted Answer

All samples of a given compound have the same proportions of their constituent elements.

Question 11

J.J. Thomson’s cathode ray tube experiment led to which important discovery?

Accepted Answer

The existence of a negatively charged, low-mass particle within all atoms.

Question 12

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

Accepted Answer

$$\frac{1.60 	imes 10$$^{-19}$$\ 	ext{C}}{1.76 	imes 10^8$\ 	ext{C/g}} = 9.1 	imes 10$$^{-28}$$\ 	ext{g}$$

Question 13

Which of the following best describes the 'plum-pudding' model of the atom?

Accepted Answer

Electrons are embedded within a positively charged sphere.

Question 14

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

Accepted Answer

Atoms of a given element can have different numbers of neutrons.

Question 15

A scientist decomposes two samples of carbon dioxide. The first sample contains 25.6 g of oxygen and 9.60 g of carbon. The second contains 21.6 g of oxygen and 8.10 g of carbon. Are these results consistent with the law of definite proportions?

Accepted Answer

Yes, because $$\frac{25.6}{9.60} = 2.67$$ and $$\frac{21.6}{8.10} = 2.67$$, showing a constant ratio.

Question 16

Which of the following best explains why the law of conservation of mass is consistent with the atomic theory?

Accepted Answer

Atoms are neither created nor destroyed in chemical reactions; they are only rearranged.

Atoms and Elements: Foundations of Modern Atomic Theory

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