Q: A titanium cube contains $$2.86 \times 10$$^{23}$$ atoms. The density of titanium is 4.50$$\ \mathrm{$$g/cm^3$$}$$. What is the edge length of the cube? (Molar mass of Ti = 47.87$$\ \mathrm{g/mol}$$, Avogadro’s number = 6.022$$ \times $$10^{23})$$

First, calculate moles: $$\frac{2.86 \times 10$$^{23}$$}{6.022 \times 10$$^{23}$$} = 0.475\ \mathrm{mol}$$; mass: $$0.475\ \mathrm{mol} \times 47.87\ \mathrm{g/mol} = 22.7\ \mathrm{g}$$; volume: $$\frac{22.7\ \mathrm{g}}{4.50\ \mathrm{g/cm^3$}} = 5.04\ \mathrm{cm^3$}$$; edge length: $$\sqrt[3]{5.04} = 1.71\ \mathrm{cm}$$

Q: Calculate the atomic mass of chlorine given the following data: 75.77% chlorine-35 (mass = 34.97 amu) and 24.23% chlorine-37 (mass = 36.97 amu).

$$0.7577 \times 34.97 + 0.2423 \times 36.97 = 35.45\ \mathrm{amu}$$

Question 1

Which of the following best describes the difference between a compound and a mixture?

Accepted Answer

A compound is made of two or more elements in fixed, definite proportions, while a mixture is composed of two or more substances in variable proportions.

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 in water, and what law does this illustrate?

Accepted Answer

The mass ratio is $$8:1$$, illustrating the law of definite proportions.

Question 3

Which of the following statements about the scientific method is correct?

Accepted Answer

A hypothesis is a tentative explanation that can be tested and is falsifiable.

Question 4

Which of the following is a heterogeneous mixture?

Accepted Answer

A mixture of sand and salt

Question 5

A log burns in a campfire, leaving behind ash with much less mass than the original log. According to the law of conservation of mass, what happened to the missing mass?

Accepted Answer

The matter that composed the log reacted to form gases that were released into the air.

Question 6

Which experiment led to the discovery of the electron?

Accepted Answer

J.J. Thomson’s cathode ray experiment

Question 7

A neutral atom of chlorine has 17 protons and 18 neutrons. What is the isotope symbol for this atom?

Accepted Answer

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

Question 8

Which of the following best explains the difference between a law and a theory?

Accepted Answer

A law summarizes a series of related observations, while a theory gives the underlying reasons for them.

Question 9

How many electrons are in the $$\mathrm{O}^{2-}$$ ion?

Accepted Answer

10

Question 10

A titanium cube contains $$2.86 	imes 10$$^{23}$$ atoms. The density of titanium is 4.50$$\ \mathrm{$$g/cm^3$$}$$. What is the edge length of the cube? (Molar mass of Ti = 47.87$$\ \mathrm{g/mol}$$, Avogadro’s number = 6.022$$ 	imes $$10^{23})$$

Accepted Answer

First, calculate moles: $$\frac{2.86 	imes 10$$^{23}$$}{6.022 	imes 10$$^{23}$$} = 0.475\ \mathrm{mol}$$; mass: $$0.475\ \mathrm{mol} 	imes 47.87\ \mathrm{g/mol} = 22.7\ \mathrm{g}$$; volume: $$\frac{22.7\ \mathrm{g}}{4.50\ \mathrm{g/cm^3$}} = 5.04\ \mathrm{cm^3$}$$; edge length: $$\sqrt[3]{5.04} = 1.71\ \mathrm{cm}$$

Question 11

Which sample contains the most atoms: 1 g of copper, 1 g of carbon, or 1 g of uranium?

Accepted Answer

1 g of carbon

Question 12

Which of the following is true about isotopes?

Accepted Answer

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

Question 13

Calculate the atomic mass of chlorine given the following data: 75.77% chlorine-35 (mass = 34.97 amu) and 24.23% chlorine-37 (mass = 36.97 amu).

Accepted Answer

$$0.7577 	imes 34.97 + 0.2423 	imes 36.97 = 35.45\ \mathrm{amu}$$

Question 14

Which of the following statements about the nuclear model of the atom is correct?

Accepted Answer

Most of the atom’s mass and all of its positive charge are contained in a small core called the nucleus.

Question 15

Which law is illustrated when two elements form more than one compound and the masses of one element that combine with a fixed mass of the other are in a ratio of small whole numbers?

Accepted Answer

Law of multiple proportions

Question 16

A neutral atom of potassium-39 ($$^{39}_{19}\mathrm{K}) $$has how many protons, neutrons, and electrons?

Accepted Answer

19 protons, 20 neutrons, 19 electrons

Question 17

Which of the following is the correct conversion factor to calculate the number of atoms in a given number of moles?

Accepted Answer

$$1\ \mathrm{mol} = 6.022 	imes 10$$^{23}$$ atoms

Question 18

Which experiment provided evidence for the existence of a small, dense, positively charged nucleus in the atom?

Accepted Answer

Rutherford’s gold foil experiment

Question 19

A sample contains $$2.80 	imes 10$$^{22}$$ silver atoms. How many moles of silver atoms does it contain? (6.022$$ 	imes $$10^{23}$$ atoms/mol)

Accepted Answer

$$\frac{2.80 	imes 10$$^{22}$$}{6.022 	imes 10$$^{23}$$} = 0.0465$$ mol

Atoms: Structure, Properties, and Laws of Matter

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