A particulate model of an aqueous solution depicts 4 formula units of potassium sulfate ($$K_2SO_4$$) fully dissociated into ions. What is the total count of potassium ions ($$K^+$$) and sulfate ions ($$SO_4^{2-}$$) represented in this model?

8 potassium ions and 4 sulfate ions

4 potassium ions and 4 sulfate ions

4 potassium ions and 8 sulfate ions

8 potassium ions and 8 sulfate ions

A 2.00 g impure sample containing $$CaCl_2$$ is dissolved and treated with excess $$AgNO_3$$, yielding 3.50 g of $$AgCl(s)$$. Which mathematical relationship should be used to determine the mass of $$CaCl_2$$ in the original sample?

$$Mass_{CaCl_2} = Mass_{AgCl} \times \frac{MM_{CaCl_2}}{2 \times MM_{AgCl}}$$

$$Mass_{CaCl_2} = Mass_{AgCl} \times \frac{MM_{AgCl}}{2 \times MM_{CaCl_2}}$$

$$Mass_{CaCl_2} = Mass_{AgCl} \times \frac{2 \times MM_{AgCl}}{MM_{CaCl_2}}$$

$$Mass_{CaCl_2} = Mass_{AgCl} \times \frac{MM_{CaCl_2}}{MM_{AgCl}}$$

A mixture of graphite ($$C$$) and inert ash is burned completely, producing $$CO_2$$. Which expression calculates the mass of carbon in the mixture based on the mass of $$CO_2$$ collected?

$$Mass_C = Mass_{CO_2} \times \frac{12.01 \text{ g}}{44.01 \text{ g}}$$

$$Mass_C = Mass_{CO_2} \times \frac{44.01 \text{ g}}{12.01 \text{ g}}$$

$$Mass_C = Mass_{CO_2} \times \frac{12.01 \text{ g}}{32.00 \text{ g}}$$

$$Mass_C = Mass_{CO_2} \times \frac{32.00 \text{ g}}{44.01 \text{ g}}$$

A 1.00 g mixture contains only $$NaCl$$ and $$KCl$$. The total number of moles of chloride ions ($$n_{Cl^-}$$) is determined experimentally. Which system of equations allows for the calculation of the mass of $$NaCl$$ ($$x$$) and $$KCl$$ ($$y$$)?

$$x + y = 1.00$$ and $$\frac{x}{58.44} + \frac{y}{74.55} = n_{Cl^-}$$

$$x + y = 1.00$$ and $$\frac{x}{35.45} + \frac{y}{35.45} = n_{Cl^-}$$

$$x + y = n_{Cl^-}$$ and $$x(58.44) + y(74.55) = 1.00$$

$$\frac{x}{58.44} = \frac{y}{74.55}$$ and $$x + y = 1.00$$

A sample of hydrated copper(II) sulfate, $$CuSO_4 \cdot xH_2O$$, is heated until all water is lost. Which relationship correctly determines the value of $$x$$?

$$x = \frac{\text{moles of water lost}}{\text{moles of anhydrous } CuSO_4}$$

$$x = \frac{\text{mass of water lost}}{\text{mass of anhydrous } CuSO_4}$$

$$x = \frac{\text{moles of anhydrous } CuSO_4}{\text{moles of water lost}}$$

$$x = \frac{\text{mass of anhydrous } CuSO_4}{\text{mass of water lost}}$$

AP Chemistry Unit 1 Practice Test

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unit 1 unit 2 unit 3 unit 4 unit 5 unit 6 unit 7 unit 8 unit 9

Atomic Structure & Properties

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The exam experience, sized to one unit — timed like the real thing

20 Multiple Choice Questions

30 min

1 FRQ – FRQ 1 – Long Answer

15 min

1 FRQ – FRQ 4 – Short Answer

15 min

Sections run back-to-back with the same directions, timers, and scoring as the real exam

Total: 1 hr

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multiple choice questions

free response questions (choose as many as you want)

FRQ 1 – Long Answer · 15 minFRQ 4 – Short Answer · 15 minFRQ 2 – Long Answer · 15 minFRQ 3 – Long Answer · 15 minFRQ 5 – Short Answer · 15 minFRQ 6 – Short Answer · 15 minFRQ 7 – Short Answer · 15 min

Total: 30 min

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AP Chemistry Unit 1 practice questions

Try 10 multiple-choice questions from Unit 1 here. Pick an answer to see why it's right or wrong, then take the timed test above for a full AP-style set.

Question 1
A particulate model of a binary mixture shows 10 atoms of Element X (atomic mass 20 amu) and 10 atoms of Element Y (atomic mass 80 amu) distributed uniformly. What is the mass percent of Element X in this mixture?
20%
25%
50%
80%
Show answer
Answer: (A)
Calculating mass percent requires determining the total mass of each component. With 10 atoms of X (10 × 20 = 200 amu) and 10 atoms of Y (10 × 80 = 800 amu), the total mass is 1000 amu. The mass percent of X is (200/1000) × 100 = 20%.
Question 2
A particulate diagram of a gas mixture in a sealed vessel shows 3 molecules of helium ( $He$ ) and 1 molecule of neon ( $Ne$ ). Based on the particle counts, what is the mole fraction of helium in the mixture?
0.25
0.33
0.75
3.00
Show answer
Answer: (C)
Determining mole fraction involves dividing the number of particles of the component by the total number of particles. With 3 He molecules and 1 Ne molecule (Total = 4), the fraction is 3/4 = 0.75.
Question 3
A particulate representation of a reaction vessel initially contains 6 molecules of hydrogen ( $H_2$ ) and 2 molecules of oxygen ( $O_2$ ). The reaction $2H_2 + O_2 \rightarrow 2H_2O$ proceeds to completion. Which species remains unreacted and in what quantity?
2 molecules of $H_2$
2 molecules of $O_2$
4 molecules of $H_2$
4 molecules of $O_2$
Show answer
Answer: (A)
Stoichiometry dictates that 2 molecules of $O_2$ react with 4 molecules of $H_2$ (1:2 ratio). Starting with 6 $H_2$ , subtracting the 4 consumed leaves 2 molecules of $H_2$ unreacted.
Question 4
A particulate model of an aqueous solution depicts 4 formula units of potassium sulfate ( $K_2SO_4$ ) fully dissociated into ions. What is the total count of potassium ions ( $K^+$ ) and sulfate ions ( $SO_4^{2-}$ ) represented in this model?
4 potassium ions and 4 sulfate ions
4 potassium ions and 8 sulfate ions
8 potassium ions and 4 sulfate ions
8 potassium ions and 8 sulfate ions
Show answer
Answer: (C)
Dissociation of 1 unit of $K_2SO_4$ yields 2 $K^+$ ions and 1 $SO_4^{2-}$ ion. Therefore, 4 units yield $4 \times 2 = 8$ potassium ions and $4 \times 1 = 4$ sulfate ions.
Question 5
A sample of neon gas contains 9 atoms of $^{20}Ne$ (mass 20 amu) and 1 atom of $^{22}Ne$ (mass 22 amu). What is the average atomic mass of the neon in this sample, based strictly on the particles counted?
20.0 amu
20.2 amu
21.0 amu
22.0 amu
Show answer
Answer: (B)
Calculating the weighted average involves summing the total mass and dividing by the number of particles. Total mass = $(9 \times 20) + (1 \times 22) = 202$ amu. Average = $202 / 10 = 20.2$ amu.
Question 6
A particulate model represents a sample of a compound where every molecule consists of 2 atoms of nitrogen and 4 atoms of oxygen. What is the empirical formula of the compound represented by this model?
$NO_2$
$N_2O$
$N_2O_4$
$N_4O_2$
Show answer
Answer: (A)
The empirical formula represents the simplest whole-number ratio of atoms. The molecular ratio of 2 nitrogen to 4 oxygen simplifies to 1:2, resulting in $NO_2$ .
Question 7
A 2.00 g impure sample containing $CaCl_2$ is dissolved and treated with excess $AgNO_3$ , yielding 3.50 g of $AgCl(s)$ . Which mathematical relationship should be used to determine the mass of $CaCl_2$ in the original sample?
Mass_{CaCl_2} = Mass $_{AgCl} \times \frac{MM_{CaCl_2}}{2 \times MM_{AgCl}}$
Mass_{CaCl_2} = Mass $_{AgCl} \times \frac{MM_{AgCl}}{2 \times MM_{CaCl_2}}$
Mass_{CaCl_2} = Mass $_{AgCl} \times \frac{2 \times MM_{AgCl}}{MM_{CaCl_2}}$
Mass_{CaCl_2} = Mass $_{AgCl} \times \frac{MM_{CaCl_2}}{MM_{AgCl}}$
Show answer
Answer: (A)
Connecting the stoichiometry of the precipitation reaction to the mass calculation.
Question 8
A mixture of graphite ( $C$ ) and inert ash is burned completely, producing $CO_2$ . Which expression calculates the mass of carbon in the mixture based on the mass of $CO_2$ collected?
Mass_C = Mass $_{CO_2} \times \frac{12.01 \text{ g}}{44.01 \text{ g}}$
Mass_C = Mass $_{CO_2} \times \frac{44.01 \text{ g}}{12.01 \text{ g}}$
Mass_C = Mass $_{CO_2} \times \frac{12.01 \text{ g}}{32.00 \text{ g}}$
Mass_C = Mass $_{CO_2} \times \frac{32.00 \text{ g}}{44.01 \text{ g}}$
Show answer
Answer: (A)
Relating the mass of the element to the mass of the compound using molar masses.
Question 9
A 1.00 g mixture contains only $NaCl$ and $KCl$ . The total number of moles of chloride ions ( $n_{Cl^-}$ ) is determined experimentally. Which system of equations allows for the calculation of the mass of $NaCl$ ( $x$ ) and $KCl$ ( $y$ )?
$x + y = 1.00$ and $\frac{x}{58.44} + \frac{y}{74.55} = n_{Cl^-}$
$x + y = 1.00$ and $\frac{x}{35.45} + \frac{y}{35.45} = n_{Cl^-}$
$x + y = n_{Cl^-}$ and $x(58.44) + y(74.55) = 1.00$
$\frac{x}{58.44} = \frac{y}{74.55}$ and $x + y = 1.00$
Show answer
Answer: (A)
Establishing a system based on mass conservation and total moles of chloride.
Question 10
A sample of hydrated copper(II) sulfate, $CuSO_4 \cdot xH_2O$ , is heated until all water is lost. Which relationship correctly determines the value of $x$ ?
$x = \frac{\text{moles of water lost}}{\text{moles of anhydrous } CuSO_4}$
$x = \frac{\text{mass of water lost}}{\text{mass of anhydrous } CuSO_4}$
$x = \frac{\text{moles of anhydrous } CuSO_4}{\text{moles of water lost}}$
$x = \frac{\text{mass of anhydrous } CuSO_4}{\text{mass of water lost}}$
Show answer
Answer: (A)
Defining the coefficient x as the mole ratio of water to anhydrous salt.

What's on the AP Chemistry Unit 1 practice test

The standard version takes about 60 minutes and follows the timing and directions of the AP exam, sized to one unit:

20 Multiple Choice Questions (30 minutes)
1 FRQ – FRQ 1 – Long Answer (15 minutes)
1 FRQ – FRQ 4 – Short Answer (15 minutes)

Questions are drawn from 1589 multiple-choice questions and 55 FRQs written for Unit 1, Atomic Structure & Properties.

Practice AP Chemistry Unit 1 FRQs

Answer the unit's free-response questions one at a time and get a score on every part.

FRQ 1 – Long Answer (6 questions)
FRQ 2 – Long Answer (5 questions)
FRQ 3 – Long Answer (3 questions)
FRQ 4 – Short Answer (11 questions)
FRQ 5 – Short Answer (9 questions)
FRQ 6 – Short Answer (9 questions)
FRQ 7 – Short Answer (12 questions)

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