Exam 3 Information and Problem Solving Guidelines for General Chemistry

Exam 3 Information and Preparation

Exam Logistics

This section provides essential information about the logistics and rules for Exam 3 in Chem 136. Understanding these details ensures a smooth exam experience and compliance with course policies.

• Date and Time: Exam 3 is scheduled for Friday, April 10, from 6:00 to 7:30 pm in room SLRC 1010.

• Coverage: The exam will cover Chapters 17 and 18 (Acids and Bases, Aqueous Ionic Equilibrium).

• Allowed Materials: Only nonprogrammable, nongraphing calculators are permitted. No sharing of calculators or use of cell phones is allowed.

• Required Items: Bring your UMID and a dark pen or pencil.

• Provided Materials: Scantrons, periodic table, and scrap paper will be provided.

• Personal Belongings: Place backpacks, books, and papers at the front or along the walls. Remove caps and jackets and store them in your backpack.

• Electronic Devices: Turn off and put away all electronic devices, including cell phones.

• Seating: Exams and seats are numbered; match your exam number with your seat number.

• Restroom Use: Use the restroom before the exam begins.

Exam Format and Study Recommendations

The exam will assess your understanding through a variety of question types and will require thorough preparation.

• Format: Multiple choice, short answer, and show-your-work problems. The exam is worth 100 points.

• Study Materials: Review all lecture material, homework, lecture slides, in-class exercises (ICEs), quizzes, and MastChem homework.

• Practice Resources: An optional Exam Review and a Practice Test are available on MastChem. Use the Practice Test as a final check of your understanding, not as your primary study tool.

• Reference Information: Equations, constants, conversions, metric prefixes, and a periodic table will be provided during the exam.

Problem Solving Guidelines

General Approach to Show-Your-Work Problems

Follow these guidelines to ensure clarity, accuracy, and full credit on show-your-work problems in general chemistry exams.

• Equations: If an equation is used, write the equation explicitly, substitute the numbers and units, and provide the answer with correct significant figures. Box your final answer.

• Dimensional Analysis: For problems not involving equations (such as unit conversions, grams-moles-number of particles, and stoichiometry), solve using dimensional analysis.

• Decimal Notation: Always include a zero before the decimal point for numbers less than one (e.g., 0.23, 0.00510).

• Atomic Masses: Use the atomic masses as given on the periodic table; do not round off these values.

• Significant Figures: Do not round off intermediate steps. Only round the final answer to the correct number of significant figures. Unit conversions should not be used to determine significant figures.

• Scientific Notation: Use scientific notation only for very large or very small numbers. Do not use exponents of 1, 0, or -1. Write numbers in standard scientific notation (e.g., $2.15 \times 10^4$, not $21.5 \times 10^3$).

• Neatness: Write your work clearly and neatly. Points may be deducted for messy work. Use scrap paper for rough work, then rewrite your final answers.

Examples and Applications

• Unit Conversion Example: To convert 5.00 grams of NaCl to moles, use the molar mass from the periodic table and set up the dimensional analysis as follows: $5.00\ \mathrm{g\ NaCl} \times \frac{1\ \mathrm{mol\ NaCl}}{58.44\ \mathrm{g\ NaCl}} = 0.0856\ \mathrm{mol\ NaCl}$

• Scientific Notation Example: Express 21,500 in scientific notation: $2.15 \times 10^4$

• Significant Figures Example: If multiplying 2.34 (3 sig figs) by 1.2 (2 sig figs), the answer should have 2 significant figures: $2.34 \times 1.2 = 2.8$

Summary Table: Problem Solving Guidelines

Guideline	Explanation	Example
Write the equation	State the equation before substituting values	$n = \frac{m}{M}$
Dimensional analysis	Use for unit conversions and stoichiometry	$5.00\ \mathrm{g} \times \frac{1\ \mathrm{mol}}{58.44\ \mathrm{g}}$
Show the zero	Include zero before decimal for numbers < 1	0.23, 0.00510
Significant figures	Round only the final answer	2.34 × 1.2 = 2.8
Scientific notation	Use only for very large/small numbers; standard format	$2.15 \times 10^4$