Atomic Structure and Properties

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AP Chemistry › Atomic Structure and Properties

Questions 1 - 10
1

Which answer choice shows the correct chemical formula for barium sulfate?

Explanation

We should first remember the difference between sulfate, sulfite, and sulfide. Sulfate is , sulfite is ` and sulfide is .

The only answer choices that could be right must have in them. We then need to see that barium usually has a charge of , as the periodic table shows us, and so we need a charge of to cancel that out. The answer is .

2

What is the percent of carbon by mass in acetone CH3C(O)CH3?

62%

50%

75%

10%

25%

Explanation

To calculate the percent mass of a particular element within a substance I like to use a formulaic approach.

First multiply the number of moles of the atom of interest (C) by its molar mass.

3moles* 12 g/mol= 36g

Then divide by the overall molar mass of the molecule, obtain this by adding the atomic weights of each atom present in the molecule:

36g/58g= 62%

3

Which answer choice shows the correct chemical formula for barium sulfate?

Explanation

We should first remember the difference between sulfate, sulfite, and sulfide. Sulfate is , sulfite is ` and sulfide is .

The only answer choices that could be right must have in them. We then need to see that barium usually has a charge of , as the periodic table shows us, and so we need a charge of to cancel that out. The answer is .

4

What is the percent of carbon by mass in acetone CH3C(O)CH3?

62%

50%

75%

10%

25%

Explanation

To calculate the percent mass of a particular element within a substance I like to use a formulaic approach.

First multiply the number of moles of the atom of interest (C) by its molar mass.

3moles* 12 g/mol= 36g

Then divide by the overall molar mass of the molecule, obtain this by adding the atomic weights of each atom present in the molecule:

36g/58g= 62%

5

Which of the following isotopes has the greatest number of neutrons?

Carbon-14

Nitrogen-13

Oxygen-15

Fluorine-16

Boron-10

Explanation

Carbon-14 has 8 neutrons

Nitrogen-13 has 6 neutrons

Oxygen-15 has 7 neutrons

Fluorine-16 has 7 neutrons

Boron-10 has 5 neutrons

6

Which of the following isotopes has the greatest number of neutrons?

Carbon-14

Nitrogen-13

Oxygen-15

Fluorine-16

Boron-10

Explanation

Carbon-14 has 8 neutrons

Nitrogen-13 has 6 neutrons

Oxygen-15 has 7 neutrons

Fluorine-16 has 7 neutrons

Boron-10 has 5 neutrons

7

What is the percent composition of potassium in K2Cr2O7?

26.5%

35.4%

50%

22%

Explanation

The molecular weight of K2Cr2O7 is 2(39 g/mol) + 2(52 g/mol) + 7(16 g/mol) = 294 g/mol.

Out of this total weight, the percent composition of K is: (2(39 g/mol)/294 g) = 26.5%

8

What is the percent composition of potassium in K2Cr2O7?

26.5%

35.4%

50%

22%

Explanation

The molecular weight of K2Cr2O7 is 2(39 g/mol) + 2(52 g/mol) + 7(16 g/mol) = 294 g/mol.

Out of this total weight, the percent composition of K is: (2(39 g/mol)/294 g) = 26.5%

9

Which of the following does not have the empirical formula CH?

C6H6

Ethyne

C3H4

C100H100

Explanation

An empirical formula represents a molecule with the simplest ratio. C6H6, ethyene (C2H2) and C100H100 can all be reduced to CH, however, C3H4 cannot because it does not have C and H atoms in a 1 : 1 ratio.

10

What is the mass of 5.34\times10^{15} particles of C_2H_6?

2.66\times 10^{-7}g\hspace{1 mm}C_2H_6

6.02\times 10^{-7}g\hspace{1 mm}C_2H_6

2.66\times 10^{-15}\hspace{1 mm}g\hspace{1 mm}C_2H_6

1.78\times 10^{-7}\hspace{1 mm}g\hspace{1 mm}C_2H_6

1.78\times 10^{-15}\hspace{1 mm}g\hspace{1 mm}C_2H_6

Explanation

5.34\times10^{15}\hspace{1 mm}particles\hspace{1 mm}C_2H_6\times \frac{1\hspace{1 mm}mole\hspace{1 mm}C_2H_6}{6.022\times 10^{23}\hspace{1 mm}particles\hspace{1 mm} C_2H_6}\times \frac{30.0\hspace{1 mm}g\hspace{1 mm}C_2H_60=}{1\hspace{1 mm}mole\hspace{1 mm}C_2H_6}=2.66\times 10^{-7}g\hspace{1 mm}C_2H_6

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