Q: Naturally occurring chlorine consists of 75.77% chlorine-35 (mass = 34.97 amu) and 24.23% chlorine-37 (mass = 36.97 amu). What is the atomic mass of chlorine?

$$(0.7577 \times 34.97) + (0.2423 \times 36.97) = 35.45$$ amu

Q: How many moles of silver atoms are in a pure silver ring containing $$8.49 \times 10$$^{22}$$ silver atoms? (N_A = 6.022$$ \times $$10^{23}$$ mol$$^{-1})$$

$$\frac{8.49 \times 10$$^{22}$$}{6.022 \times 10$$^{23}$$} = 0.141$$ mol

Q: A titanium cube contains $$2.15 \times 10$$^{23}$$ atoms. The density of titanium is 4.50$ g/cm^3$. What is the edge length of the cube? (Molar mass of Ti = 47.87 g/mol, N_A = 6.022$$ \times $$10^{23}$$ mol$$^{-1})$$

First, calculate moles: $$\frac{2.15 \times 10$$^{23}$$}{6.022 \times 10$$^{23}$$} = 0.357$$ mol. Mass: $$0.357 \times 47.87 = 17.1 g. $$Volume: $$\frac{17.1}{4.50} = 3.80 cm$^3. $$Edge length: $$\sqrt[3]{3.80} = 1.56 cm.$$

Question 1

Which of the following statements best describes the difference between a scientific law and a scientific theory?

Accepted Answer

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

Question 2

Which of the following is an example of a homogeneous mixture?

Accepted Answer

Sweetened tea

Question 3

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

Accepted Answer

$$\frac{16.0}{2.0} = 8.0$$

Question 4

Which experiment provided evidence for the existence of the nucleus in the atom?

Accepted Answer

Rutherford’s gold foil experiment

Question 5

Which of the following statements is consistent with Dalton’s atomic theory?

Accepted Answer

Atoms combine in simple, whole-number ratios to form compounds.

Question 6

A chlorine isotope has 17 protons and 18 neutrons. What is its isotope symbol?

Accepted Answer

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

Question 7

Which law states that when two elements form two different compounds, the masses of one element that combine with 1 gram of the other can be expressed as a ratio of small whole numbers?

Accepted Answer

Law of multiple proportions

Question 8

A neutral atom of fluorine has an atomic number of 9. How many electrons does a fluoride ion ($$\mathrm{F}^-) $$have?

Accepted Answer

10

Question 9

Which of the following samples contains the greatest number of atoms?

Accepted Answer

1 gram of carbon

Question 10

Naturally occurring chlorine consists of 75.77% chlorine-35 (mass = 34.97 amu) and 24.23% chlorine-37 (mass = 36.97 amu). What is the atomic mass of chlorine?

Accepted Answer

$$(0.7577 	imes 34.97) + (0.2423 	imes 36.97) = 35.45$$ amu

Question 11

How many moles of silver atoms are in a pure silver ring containing $$8.49 	imes 10$$^{22}$$ silver atoms? (N_A = 6.022$$ 	imes $$10^{23}$$ mol$$^{-1})$$

Accepted Answer

$$\frac{8.49 	imes 10$$^{22}$$}{6.022 	imes 10$$^{23}$$} = 0.141$$ mol

Question 12

A titanium cube contains $$2.15 	imes 10$$^{23}$$ atoms. The density of titanium is 4.50$ g/cm^3$. What is the edge length of the cube? (Molar mass of Ti = 47.87 g/mol, N_A = 6.022$$ 	imes $$10^{23}$$ mol$$^{-1})$$

Accepted Answer

First, calculate moles: $$\frac{2.15 	imes 10$$^{23}$$}{6.022 	imes 10$$^{23}$$} = 0.357$$ mol. Mass: $$0.357 	imes 47.87 = 17.1 g. $$Volume: $$\frac{17.1}{4.50} = 3.80 cm$^3. $$Edge length: $$\sqrt[3]{3.80} = 1.56 cm.$$

Question 13

Which of the following best describes an element?

Accepted Answer

A substance that cannot be chemically broken down into simpler substances

Question 14

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 15

A sample of carbon monoxide produces 17.2 grams of oxygen and 12.9 grams of carbon. Another sample produces 10.5 grams of oxygen and 7.88 grams of carbon. Show these results are consistent with the law of definite proportions.

Accepted Answer

Both samples have an oxygen to carbon mass ratio of $$\frac{17.2}{12.9} = 1.33$$ and $$\frac{10.5}{7.88} = 1.33$$, so they are consistent.

Question 16

Which of the following statements about isotopes is correct?

Accepted Answer

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

Question 17

Which of the following is a property of gaseous matter?

Accepted Answer

Atoms or molecules are free to move relative to one another and have a lot of space between them.

Question 18

A sample of ammonia contains 10.0 g of hydrogen. If the mass ratio of nitrogen to hydrogen in ammonia is 14:3, how many grams of nitrogen does it contain?

Accepted Answer

14

Atoms: Structure, Properties, and the Foundations of Chemistry

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