Q: A naturally occurring element has two isotopes: $^{6}\mathrm{Li}$ (6.015 amu, 7.5% abundance) and $^{7}\mathrm{Li}$ (7.016 amu, 92.5% abundance). What is the average atomic mass of lithium?

$(0.075 \times 6.015) + (0.925 \times 7.016) = 6.94\ \mathrm{amu}$

Q: How many atoms are present in 2.00 moles of carbon?

$2.00 \times 6.022 \times 10^{23} = 1.2044 \times 10^{24}$ atoms

Q: A sample contains $2.70 \times 10^{22}$ atoms and has a mass of 1.96 g. What is the molar mass of the element?

$\frac{1.96\ \mathrm{g}}{2.70 \times 10^{22}\ \text{atoms}} \times 6.022 \times 10^{23}\ \text{atoms/mol} = 43.7\ \mathrm{g/mol}$

Question 1

Which of the following best describes the law of definite proportions?

Accepted Answer

A chemical compound always contains exactly the same proportion of elements by mass.

Question 2

A sample of magnesium is burned in air with 2.315 g of oxygen, producing magnesium oxide. If 2.015 g of unreacted oxygen remains, how much magnesium oxide was produced?

Accepted Answer

$2.315\ \mathrm{g} - 2.015\ \mathrm{g} = 0.300\ \mathrm{g}$; but the total magnesium oxide produced is the sum of magnesium and oxygen that reacted: $	ext{mass of MgO} = 	ext{mass of Mg} + (2.315\ \mathrm{g} - 2.015\ \mathrm{g})$

Question 3

Which of the following statements is a postulate of Dalton’s atomic theory?

Accepted Answer

Atoms of different elements can combine in simple whole-number ratios to form compounds.

Question 4

A naturally occurring element has two isotopes: $^{6}\mathrm{Li}$ (6.015 amu, 7.5% abundance) and $^{7}\mathrm{Li}$ (7.016 amu, 92.5% abundance). What is the average atomic mass of lithium?

Accepted Answer

$(0.075 	imes 6.015) + (0.925 	imes 7.016) = 6.94\ \mathrm{amu}$

Question 5

Which of the following best describes a heterogeneous mixture?

Accepted Answer

A mixture in which the composition is not uniform throughout.

Question 6

How many atoms are present in 2.00 moles of carbon?

Accepted Answer

$2.00 	imes 6.022 	imes 10^{23} = 1.2044 	imes 10^{24}$ atoms

Question 7

Which experiment led to the discovery of the nucleus in the atom?

Accepted Answer

Rutherford’s gold foil experiment

Question 8

A sample contains $2.70 	imes 10^{22}$ atoms and has a mass of 1.96 g. What is the molar mass of the element?

Accepted Answer

$\frac{1.96\ \mathrm{g}}{2.70 	imes 10^{22}\ 	ext{atoms}} 	imes 6.022 	imes 10^{23}\ 	ext{atoms/mol} = 43.7\ \mathrm{g/mol}$

Question 9

Which of the following is true about ions?

Accepted Answer

Anions are negatively charged ions formed by gaining electrons.

Question 10

A chlorine atom has 17 protons and 18 neutrons. What is its chemical symbol and mass number?

Accepted Answer

$^{35}\mathrm{Cl}$

Question 11

Which of the following best describes the law of conservation of mass?

Accepted Answer

The total mass of substances before and after a chemical reaction is always the same.

Question 12

How many significant figures are in the result of $14.79\ \mathrm{cm} 	imes 12.11\ \mathrm{cm} 	imes 5.05\ \mathrm{cm}$?

Accepted Answer

3 significant figures

Question 13

Which of the following is a correct application of the law of multiple proportions?

Accepted Answer

If two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in ratios of small whole numbers.

Question 14

A student calculates $32.44 + 4.9 - 0.3$. What is the answer with the correct number of significant figures?

Accepted Answer

$37.0$

Question 15

Which of the following best describes a pure substance?

Accepted Answer

A material with a fixed composition and distinct properties.

Question 16

What is Avogadro’s number and what does it represent?

Accepted Answer

$6.022 	imes 10^{23}$, the number of particles in one mole of a substance.

Question 17

Which of the following is the correct symbol for an ion with 11 protons and 10 electrons?

Accepted Answer

$\mathrm{Na}^+$

Question 18

A cube of a certain element has a mass of 1.96 g and a volume of $1.075\ \mathrm{cm}^3$. What is its density?

Accepted Answer

$\frac{1.96\ \mathrm{g}}{1.075\ \mathrm{cm}^3} = 1.82\ \mathrm{g/cm}^3$

Question 19

Which of the following best describes the result of Rutherford’s gold foil experiment?

Accepted Answer

Most alpha particles passed through, but some were deflected, indicating a small, dense nucleus.

General Chemistry Fundamentals: Significant Figures, Dimensional Analysis, Atomic Theory, and Classification of Matter

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