Q: A sample of magnesium reacts with oxygen to form magnesium oxide. If 24.3 g of magnesium reacts completely with 16.0 g of oxygen, what is the mass of magnesium oxide formed, according to the Law of Conservation of Mass?

$$24.3\ \text{g} + 16.0\ \text{g} = 40.3\ \text{g}$$

Q: Which of the following is the correct molar mass of calcium carbonate ($$\text{CaCO}_3$$)? (Atomic masses: Ca = 40.1, C = 12.0, O = 16.0)

$$40.1 + 12.0 + (3 \times 16.0) = 100.1\ \text{g/mol}$$

Q: If you have 18.0 g of water ($$\text{H}_2\text{O}$$), how many moles of water do you have? (Molar mass of $$\text{H}_2\text{O} = 18.0 g/$$mol)

$$\frac{18.0\ \text{g}}{18.0\ \text{g/mol}} = 1.00\ \text{mol}$$

Q: A sample of copper contains $$1.20 \times 10$$^{24}$$ atoms. What is the mass of this sample? (Molar mass of Cu = 63.5 g/mol, Avogadro’s number = 6.02$$ \times $$10^{23})$$

$$\frac{1.20 \times 10$$^{24}$$}{6.02 \times 10$$^{23}$$} \times 63.5 = 126.6\ \text{g}$$

Question 1

Which of the following statements best describes the Law of Definite Proportions?

Accepted Answer

A compound always contains the same elements in the same proportion by mass.

Question 2

A sample of magnesium reacts with oxygen to form magnesium oxide. If 24.3 g of magnesium reacts completely with 16.0 g of oxygen, what is the mass of magnesium oxide formed, according to the Law of Conservation of Mass?

Accepted Answer

$$24.3\ 	ext{g} + 16.0\ 	ext{g} = 40.3\ 	ext{g}$$

Question 3

Which experiment led to the discovery of the electron?

Accepted Answer

Cathode ray tube experiment

Question 4

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 5

A neutral atom of chlorine has an atomic number of 17 and a mass number of 35. How many neutrons does it have?

Accepted Answer

$$35 - 17 = 18$$

Question 6

Which of the following best describes the difference between a cation and an anion?

Accepted Answer

A cation has more protons than electrons, while an anion has more electrons than protons.

Question 7

Which of the following elements is a metalloid?

Accepted Answer

Silicon (Si)

Question 8

According to Dalton’s Atomic Theory, which statement is NOT correct based on modern understanding?

Accepted Answer

Atoms are indivisible and indestructible.

Question 9

Which of the following correctly represents the nuclear symbol for an isotope of carbon with 6 protons and 8 neutrons?

Accepted Answer

$$^{14}_{6}	ext{C}$$

Question 10

A sample contains $$3.01 	imes 10$$^{23}$$ atoms of sodium. How many moles of sodium are present?

Accepted Answer

$$0.500\ 	ext{mol}$$

Question 11

Which of the following statements about the periodic table is correct?

Accepted Answer

Elements in the same group have similar chemical properties.

Question 12

Which of the following is the correct molar mass of calcium carbonate ($$	ext{CaCO}_3$$)? (Atomic masses: Ca = 40.1, C = 12.0, O = 16.0)

Accepted Answer

$$40.1 + 12.0 + (3 	imes 16.0) = 100.1\ 	ext{g/mol}$$

Question 13

If you have 18.0 g of water ($$	ext{H}_2	ext{O}$$), how many moles of water do you have? (Molar mass of $$	ext{H}_2	ext{O} = 18.0 g/$$mol)

Accepted Answer

$$\frac{18.0\ 	ext{g}}{18.0\ 	ext{g/mol}} = 1.00\ 	ext{mol}$$

Question 14

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.

Question 15

Which of the following elements is a noble gas?

Accepted Answer

Neon (Ne)

Question 16

A sample of copper contains $$1.20 	imes 10$$^{24}$$ atoms. What is the mass of this sample? (Molar mass of Cu = 63.5 g/mol, Avogadro’s number = 6.02$$ 	imes $$10^{23})$$

Accepted Answer

$$\frac{1.20 	imes 10$$^{24}$$}{6.02 	imes 10$$^{23}$$} 	imes 63.5 = 126.6\ 	ext{g}$$

Question 17

Which of the following is a correct statement about alkali metals?

Accepted Answer

They are highly reactive and form $$+1$$ ions.

Question 18

Which of the following best explains the Law of Multiple Proportions?

Accepted Answer

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

Question 19

How many atoms are present in 0.250 mol of iron? (Avogadro’s number = $$6.02 	imes 10$$^{23}$$)

Accepted Answer

$$0.250 	imes 6.02 	imes 10$$^{23}$$ = 1.51 	imes 10$$^{23}$$ atoms

Question 20

A patient is given 0.500 g of potassium iodide ($$	ext{KI}) as a $$treatment. How many moles of $$	ext{KI}$$ did the patient receive? (Molar mass of $$	ext{KI} = 166.0 g/$$mol)

Accepted Answer

$$\frac{0.500\ 	ext{g}}{166.0\ 	ext{g/mol}} = 0.00301\ 	ext{mol}$$

Atoms, Elements, and the Structure of Matter: Study Notes for General Chemistry

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