Q: Pitchblende, an oxide ore of uranium, contains only U and O. If a sample of pitchblende has a total mass of $$102\ \mathrm{kg}$$ and the mass fraction of U is $$0.8479$$, what is the mass of U in the sample?

$$102\ \mathrm{kg} \times 0.8479 = 86.5\ \mathrm{kg}$$

Question 1

Which statement best describes the Law of Conservation of Mass as demonstrated by Lavoisier's experiment with glucose and oxygen?

Accepted Answer

The total mass of reactants equals the total mass of products in a chemical reaction.

Question 2

A 20.0 g sample of calcium carbonate ($$\mathrm{$$CaCO_3$$}) $$contains 8.0 g Ca, 2.4 g C, and 9.6 g O. What is the mass fraction of oxygen in the sample?

Accepted Answer

$$\dfrac{9.6\ \mathrm{g}}{20.0\ \mathrm{g}} = 0.48$$

Question 3

Pitchblende, an oxide ore of uranium, contains only U and O. If a sample of pitchblende has a total mass of $$102\ \mathrm{kg}$$ and the mass fraction of U is $$0.8479$$, what is the mass of U in the sample?

Accepted Answer

$$102\ \mathrm{kg} 	imes 0.8479 = 86.5\ \mathrm{kg}$$

Question 4

Which law states that a compound always contains the exact same proportions of elements by mass regardless of its source?

Accepted Answer

Law of Definite Proportions

Question 5

Given the following data for compounds of nitrogen and oxygen: Compound A ($$1.750\ \mathrm{g} N $$per $$1\ \mathrm{g} O$$), Compound B ($$0.8750\ \mathrm{g} N $$per $$1\ \mathrm{g} O$$), Compound C ($$0.4375\ \mathrm{g} N $$per $$1\ \mathrm{g} O$$), which law do these ratios illustrate?

Accepted Answer

Law of Multiple Proportions

Question 6

According to Dalton's Atomic Theory, which statement is FALSE?

Accepted Answer

Atoms can be converted into atoms of another element by chemical reaction.

Question 7

Which experiment provided evidence for the existence of negatively charged sub-atomic particles?

Accepted Answer

Thomson's Cathode Ray Tube experiment

Question 8

What was the main conclusion from Rutherford’s Gold Foil experiment?

Accepted Answer

Atoms contain a dense, positively charged nucleus.

Question 9

Which subatomic particle is found outside the nucleus and has a negative charge?

Accepted Answer

Electron

Question 10

An atom has a mass number $$A = 23$$ and atomic number $$Z = 11. $$How many neutrons does it have?

Accepted Answer

$$23 - 11 = 12$$ neutrons

Question 11

Which statement about isotopes is correct?

Accepted Answer

Isotopes have the same number of protons but different numbers of neutrons.

Question 12

What is the charge of an ion formed when a neutral atom loses two electrons?

Accepted Answer

$$2^+$$

Question 13

Which group of elements in the periodic table tends to lose electrons to achieve the electron configuration of a noble gas?

Accepted Answer

Alkali metals

Question 14

If an atom has 17 protons, 18 neutrons, and 17 electrons, what is its atomic number and mass number?

Accepted Answer

Atomic number $$= 17$$, Mass number $$= 35$$

Question 15

Which experiment determined the absolute charge of an electron?

Accepted Answer

Millikan's Oil Drop experiment

Question 16

A neutral atom of sodium ($$\mathrm{Na}) $$has 11 protons. How many electrons does it have?

Accepted Answer

11 electrons

Question 17

Which of the following best explains why the nucleus accounts for most of the atom’s mass but very little of its volume?

Accepted Answer

The nucleus is very dense and contains protons and neutrons, which are much heavier than electrons.

Question 18

Which statement about chemical reactions is consistent with Dalton’s Atomic Theory?

Accepted Answer

Atoms are reorganized, but the atoms themselves are not changed.

Question 19

Which of the following is NOT a principal subatomic particle found in atoms?

Accepted Answer

Alpha particle

Question 20

Which scientist is credited with the discovery of the electron?

Accepted Answer

J.J. Thomson

chapter 2 p1

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