College Chemistry Quiz: Elemental Composition Of Pure Substances

What this quiz covers

This quiz focuses on Elemental Composition Of Pure Substances, giving you a quick way to practice the rules, question types, and explanations that matter most for College Chemistry.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

Question 1

1. Atomic mass equals 12.00 amu because C-12 defines the element and excludes other isotopes.
2. Atomic mass is a weighted average slightly above 12 because C-13 occurs naturally in smaller amounts. (correct answer)
3. Atomic mass equals 13.00 amu because the heaviest isotope determines periodic table placement.
4. Atomic mass varies with temperature because isotopes interconvert during ordinary chemical reactions.

Question 2

1. They have the same number of valence electrons, leading to similar bonding and ion formation. (correct answer)
2. They have identical numbers of protons, so they are the same element with different names.
3. They have the same atomic radius, so all physical and chemical properties match exactly.
4. They have the same neutron number, so they form the same isotopes and compounds.

Question 3

1. $C_2H_4$
2. $CH_2$ (correct answer)
3. $C_3H_4$
4. $CH$
5. $C_6H_{14}$

Question 4

1. 3
2. 4
3. 5
4. 6 (correct answer)
5. 8

Question 5

1. $PCl$
2. $PCl_2$
3. $PCl_3$ (correct answer)
4. $PCl_4$
5. $PCl_5$

Question 6

1. $C_3H_6O_3$
2. $C_6H_{12}O_6$ (correct answer)
3. $CHO$
4. $C_2H_4O_2$
5. $C_{12}H_{24}O_{12}$

Question 7

1. 1.42 g
2. 2.84 g (correct answer)
3. 4.25 g
4. 5.67 g
5. 8.51 g

Question 8

1. $CH_2Cl$
2. $C_2H_4Cl_2$ (correct answer)
3. $C_3H_6Cl_3$
4. $C_4H_8Cl_4$
5. $C_2H_3Cl$

Question 9

1. $SO$
2. $SO_2$ (correct answer)
3. $S_2O_3$
4. $SO_3$
5. $S_2O$

Question 10

1. 5
2. 6
3. 7 (correct answer)
4. 9
5. 12

Question 11

1. $C_3H_6O_3$
2. $C_2H_4O_2$
3. $CH_2O$ (correct answer)
4. $C_6H_{12}O_6$
5. $CHO$

Question 12

1. 27.0 u (correct answer)
2. 52.0 u
3. 55.8 u
4. 58.9 u
5. 63.5 u

Question 13

1. $C_2H_4O$
2. $C_4H_8O_2$ (correct answer)
3. $C_6H_{12}O_3$
4. $C_8H_{16}O_4$
5. $CHO$

Question 14

1. 3
2. 4
3. 5 (correct answer)
4. 6
5. 7

Question 15

1. $CH$
2. $CH_2$ (correct answer)
3. $CH_3$
4. $C_2H_6$
5. $C_3H_8$

Question 16

1. $C_2H_6O_2$ (correct answer)
2. $CH_3O$
3. $C_2H_4O_2$
4. $CH_2O$
5. $C_3H_6O_3$

Question 17

1. 2
2. 4
3. 6
4. 8 (correct answer)
5. 10

Question 18

1. Reactivity decreases because atoms gain valence electrons down the group, stabilizing the outer shell.
2. Reactivity increases because one valence electron is held less tightly as atomic radius increases. (correct answer)
3. Reactivity increases because electronegativity increases down the group, pulling electrons inward.
4. Reactivity stays the same because all Group 1 elements have identical atomic sizes and shielding.

Question 19

1. Al³⁺ and O²⁻ balance in a 2:3 ratio, producing the empirical formula Al₂O₃. (correct answer)
2. Al²⁺ and O³⁻ balance in a 2:3 ratio, producing the empirical formula Al₂O₃.
3. Al³⁺ and O²⁻ balance in a 3:2 ratio, producing the empirical formula Al₃O₂.
4. Al and O form covalent molecules, so the formula depends on temperature and pressure.

Question 20

1. One C and two O form a bent molecule, so bond dipoles add to make CO₂ strongly polar.
2. One C and two O form a linear molecule, so bond dipoles cancel and CO₂ is nonpolar overall. (correct answer)
3. Two C and one O form a linear molecule, so bond dipoles cancel and CO₂ is nonpolar overall.
4. One C and two O form an ionic lattice, so polarity is irrelevant to its physical properties.