Chemistry · Unit 4 · Paper 2

Chemical Reactions unit test

A test on this unit alone, marked as a percentage and a letter grade — for the test your class is actually sitting, rather than for May. Answer everything, then submit once: seeing the answer to question 3 before attempting question 4 makes the final percentage meaningless.

Paper 1 Paper 2 Paper 3

Each paper is built from this unit’s 17 terms and is the same for everyone, so a teacher can assign “Unit 4, Paper 2” and every student sits the identical test. Multiple choice is marked objectively; the written sections you mark yourself against the model answer and rubric.

Suggested time 37 min 34 points0/17 attempted

Precipitation reaction

Limiting reactant

Acid-base neutralization

Net ionic equation

Identifying reaction type

Gravimetric analysis

Titration

Percent yield

Back titration

Balancing redox in acid

Redox identification

Equivalence vs endpoint

Short answer 1. Define or explain: Oxidation number rules

3 pts

Short answer 2. Define or explain: Titration calculation

3 pts

Short answer 3. Define or explain: Solubility rules

3 pts

Short answer 4. Define or explain: Stoichiometry road map

3 pts

Free response

10 pts

A 0.750 g sample of impure calcium carbonate is treated with excess hydrochloric acid: CaCO₃(s) + 2 HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g). The CO₂ produced is collected over water at 25 °C, where the total pressure is 755 torr and the collected volume is 155 mL. The vapor pressure of water at 25 °C is 23.8 torr.

Calculate the partial pressure of CO₂ in atmospheres.

Calculate the number of moles of CO₂ collected.

Calculate the mass percent of CaCO₃ in the original sample.

Explain the direction in which the calculated mass percent would be biased if the student forgot to subtract the water vapor pressure.

Describe one experimental observation that would confirm the HCl was truly present in excess.