Q: A naturally occurring element has two isotopes: 70.00% isotope A (mass = 10.00 amu) and 30.00% isotope B (mass = 11.00 amu). What is the atomic mass of the element?

$$0.7000 \times 10.00 + 0.3000 \times 11.00 = 10.30$$ amu

Q: How many atoms are present in 0.50 mol of aluminum ($$\mathrm{Al}$$)? ($$N_A = 6.022 \times 10$$^{23}$$ atoms/mol)

$$0.50 \times 6.022 \times 10$$^{23}$$ = 3.01 \times 10$$^{23}$$ atoms

Q: A sample contains $$2.80 \times 10$$^{22}$$ silver atoms. How many moles of silver does this sample contain? (N_A = 6.022$$ \times $$10^{23}$$ atoms/mol)

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

Question 1

Which of the following best describes a compound?

Accepted Answer

A substance composed of two or more elements in fixed, definite 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 which law does this illustrate?

Accepted Answer

$$\frac{16.0}{2.0} = 8.0$$; this illustrates the law of definite proportions.

Question 3

Which statement best explains 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 4

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

Accepted Answer

Rutherford's gold foil experiment

Question 5

A neutral atom of sodium has an atomic number of 11 and a mass number of 23. How many protons, neutrons, and electrons does it have?

Accepted Answer

11 protons, 12 neutrons, 11 electrons

Question 6

Which of the following is a homogeneous mixture?

Accepted Answer

Salt dissolved in water

Question 7

Which law is illustrated by the fact that 2.67 g of oxygen combine with 1 g of carbon in carbon dioxide, while 1.33 g of oxygen combine with 1 g of carbon in carbon monoxide?

Accepted Answer

Law of multiple proportions

Question 8

A naturally occurring element has two isotopes: 70.00% isotope A (mass = 10.00 amu) and 30.00% isotope B (mass = 11.00 amu). What is the atomic mass of the element?

Accepted Answer

$$0.7000 	imes 10.00 + 0.3000 	imes 11.00 = 10.30$$ amu

Question 9

Which of the following statements about subatomic particles is correct?

Accepted Answer

The mass of a neutron is slightly greater than that of a proton.

Question 10

How many atoms are present in 0.50 mol of aluminum ($$\mathrm{Al}$$)? ($$N_A = 6.022 	imes 10$$^{23}$$ atoms/mol)

Accepted Answer

$$0.50 	imes 6.022 	imes 10$$^{23}$$ = 3.01 	imes 10$$^{23}$$ atoms

Question 11

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

Accepted Answer

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

Question 12

Which of the following best describes the result of Millikan's oil drop experiment?

Accepted Answer

It determined the charge of a single electron.

Question 13

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 14

A certain element has three naturally occurring isotopes with the following masses and abundances: 90.48% with mass 19.99 amu, 0.27% with mass 20.99 amu, and 9.25% with mass 21.99 amu. What is the atomic mass of this element?

Accepted Answer

$$0.9048 	imes 19.99 + 0.0027 	imes 20.99 + 0.0925 	imes 21.99 = 20.18$$ amu

Question 15

Which of the following statements about ions is correct?

Accepted Answer

Cations are positively charged ions formed when atoms lose electrons.

Question 16

A sample of copper has a mass of 12.7 g. The molar mass of copper is 63.55 g/mol. How many atoms of copper are in the sample? ($$N_A = 6.022 	imes 10$$^{23}$$ atoms/mol)

Accepted Answer

$$\frac{12.7}{63.55} 	imes 6.022 	imes 10$$^{23}$$ = 1.20 	imes 10$$^{23}$$ atoms

Question 17

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

Accepted Answer

A heterogeneous mixture has a composition that varies from one region to another, while a homogeneous mixture has a uniform composition throughout.

Question 18

Which of the following statements about the mole is correct?

Accepted Answer

One mole of any element contains $$6.022 	imes 10$$^{23}$$ atoms.

Atoms and the Structure of Matter: General Chemistry Study Notes

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