Gen Chem I Exam 1 Study Guide

General Information about the Exam

• Subject: General Chemistry I Exam 1

• Format: Multiple Choice Questions

Mixtures and Changes

Definition of Homogeneous Mixtures

• Homogeneous Mixture: A mixture that has a uniform composition throughout.

• Example from Options:

  • A) Cola

  • Other options (B) chicken soup, (C) ice water, (D) vegetable soup, (E) salsa are not homogeneous.

Physical vs Chemical Changes

• Physical Change: A change that does not alter the chemical composition of a substance.

  • Example:

  • (D) Water is evaporated (changes state from liquid to gas, but remains H2O).

• Chemical Change: A change that results in the formation of new chemical substances.

  • Example:

  • (A) Methane gas is burned (produces CO2 and water).

Temperature Conversions

Celsius to Kelvin Conversion

• Conversion Formula: $K = C + 273.15$

• Example: If a solution has a temperature of 355 K, convert to Celsius:

  • $C = 355 - 273.15 = 81.85°C$

  • Closest Option: 82°C (E)

Kelvin to Celsius Conversion

• Given: Outside temperature is 35°C. Convert to Kelvin:

  • $K = 35 + 273.15 = 308.15 K$

  • Closest Option: 308 K (B)

Volume, Mass, and Density Calculations

Volume Calculation

• Given: Mass = 455.6 g, Density = 19.3 g/mL

• Formula: $ext{Density} = rac{ ext{mass}}{ ext{volume}} <br>ightarrow ext{volume} = rac{ ext{mass}}{ ext{density}}$

• Calculation:

  • $ext{Volume} = rac{455.6 ext{ g}}{19.3 ext{ g/mL}} <br>ightarrow 23.6 ext{ mL (D)}$

Mass Calculation

• Given: Volume = 88.6 mL, Density = 9.77 g/mL

• Formula: $ext{Mass} = ext{Density} imes ext{Volume}$

• Calculation:

  • $ext{Mass} = 9.77 ext{ g/mL} imes 88.6 ext{ mL} <br>ightarrow 865.822 ext{ g (rounded to 866 g, E)}$

Significant Figures

Rules for Significant Figures

1. Non-zero digits are always significant.

2. Any zeros between significant digits are significant.

3. Leading zeros are not significant.

4. Trailing zeros in a number containing a decimal point are significant.

Questions on Significant Figures

• Example: 109.63 mL has 5 significant figures (C).

• Example: 0.0105890 g has 6 significant figures (C).

• Expression: 3.40 x 10^4 m has 3 significant figures (A).

Convert Units and Significant Figures

• Calculate how many millimeters in 3.20 cm:

  • Conversion Formula: 1 cm = 10 mm, therefore 3.20 cm = 32.0 mm = 3.20 x 10^1 mm (A).

• Convert 244.0 cm to micrometers:

  • Conversion: 244.0 cm = 2.44 x 10^6 µm (A).

Atomic Structure

Isotopes Definition

• Isotopes: Variants of a chemical element that have the same number of protons but a different number of neutrons.

• Example of Particle Differences: D) Neutrons

Mass Number

• Definition: The mass number is defined as the total number of protons and neutrons in an atom.

• Correct Option: D) Sum of protons and neutrons.

Elements Identification and Properties

Determining Number of Subatomic Particles

• Example of determination:

  • For species with p+ = 12, n° = 25, e- = 12, identify corresponding element based on atomic numbers.

Alkali Metals

• Definition: Elements found in Group 1 of the periodic table, known for being highly reactive.

• Example of Alkali Metal: D) Lithium (Li).

Atomic Mass and Number

• Example: Atomic mass of tin is 118.71 (C).

• Calculation Example: For silver isotopes with given isotopic masses, calculate total atomic mass:

  • $ext{Atomic Mass} = ext{(mass of Ag-107 * fractional abundance)} + ext{(mass of Ag-109 * fractional abundance)}$

• Resulting Calculation Gives: A) 107.90 amu

Moles and Atomic Calculations

Mole Definition

• Definition: A mole is a unit of measurement for amount of substance in the International System of Units (SI).

• Calculation for Silver Atoms: For 3.75 moles of silver, the total number of atoms can be calculated using Avogadro's number (6.022 x 10^23).

• Example: $3.75 ext{ moles} imes 6.022 imes 10^{23} ext{ atoms/mole} = 2.26 imes 10^{24} ext{ silver atoms} (B)$

• Mass Calculation of Kr: Determine the mass of 3.99 moles of Kr using molar mass (83.8 g/mole) yielding A) 334 g.

Miscellaneous Questions

Considerations of Causality

• Statement Assessment: If a true statement says "There was a time when there was nothing," implications are explored regarding existence.

  • Options include: B) A self-existent being would exist today.

Alkaline Earth Metals

• Symbol Identification Example: C) Beryllium (Be).

Group and Period Element Identification

• Identify elements based on specific positioning in the periodic table:

  • Example: Row 5, Group 7 corresponds to Iodine (B).

• Final notes for this exam highlight major concepts in chemistry including mixtures, changes, temperature conversions, calculations involving mass and volume, significant figures, atomic structure, and classification of elements.