Constants & Conversion Ratios

Fundamental Constants

Understanding constants and conversion ratios is essential for solving chemistry problems and performing laboratory calculations.

• Avogadro's Number (NA): particles/mole. Used to relate moles to number of atoms, molecules, or ions.

• Common Unit Conversions:

  • 1 cm3 = 1 mL

  • 1 kg = 2.205 lb

  • 1 in = 2.54 cm

  • 1 gal = 3.785 L

  • 1 mi = 1.609 km

  • 1 g/cm3 = 1 g/mL = 1 kg/L

  • 1 mm = g

Various Equations

Basic Chemistry Formulas

These equations are frequently used in introductory chemistry for calculations involving density, temperature, volume, and percent composition.

• Density:

• Heat (q): Where m is mass, c is specific heat, and is change in temperature.

• Volume Calculations:

  • Rectangular solid:

  • Sphere:

  • Cylinder:

• Temperature Conversions:

  • Kelvin to Celsius:

  • Celsius to Fahrenheit:

• Percent Composition:

• Percent Yield:

• Mass Fraction:

Periodic Table of Elements

Organization and Use

The periodic table arranges elements by increasing atomic number and groups elements with similar chemical properties together. It is a fundamental reference for identifying elements, their symbols, atomic numbers, and atomic masses.

• Groups: Vertical columns, elements share similar properties.

• Periods: Horizontal rows, elements have increasing atomic number.

• Key Sections: Metals, nonmetals, metalloids, transition metals, lanthanides, actinides.

• Applications: Used to predict chemical behavior, electron configuration, and reactivity.

Practice Questions & Concepts

Quantitative and Qualitative Observations

Observations in chemistry can be quantitative (measured, numerical) or qualitative (descriptive, non-numerical).

• Quantitative: Involves measurements (e.g., mass, volume, temperature).

• Qualitative: Involves descriptions (e.g., color, state, texture).

• Example: "The temperature of solution A is 60°C" is quantitative; "Solution A is green" is qualitative.

Physical vs. Chemical Changes

Understanding the difference between physical and chemical changes is fundamental in chemistry.

• Physical Change: Change in state or appearance without altering chemical composition (e.g., melting, boiling).

• Chemical Change: Formation of new substances with different properties (e.g., rusting, combustion).

• Example: Dissolving sugar in water is a physical change; burning sugar is a chemical change.

Significant Figures

Significant figures reflect the precision of a measurement and are important for reporting scientific data accurately.

• Rules:

  • All nonzero digits are significant.

  • Zeros between nonzero digits are significant.

  • Leading zeros are not significant.

  • Trailing zeros in a decimal number are significant.

• Example: 33.02 cm has four significant figures.

Measurement and Uncertainty

All measurements have an associated uncertainty, which reflects the limitations of the measuring instrument.

• Uncertainty: The smallest division on the measuring instrument, typically reported as ± value.

• Example: If a graduated cylinder is marked every 1 mL, uncertainty is ±0.1 mL.

Density Calculations

Density is a physical property defined as mass per unit volume.

• Formula:

• Units: Commonly g/cm3 or g/mL.

• Example: A cube with mass 5.3875 g and volume 3.10 cm3 has density g/cm3.

Unit Conversions

Converting between units is a frequent task in chemistry, requiring knowledge of conversion factors.

• Example: To convert 0.5747 cm2 to mm2, use .

Sample HTML Table: Significant Figures in Measurements

Advice for Problem Solving

Strategies for Success

Effective problem solving in chemistry involves careful tracking of units, logical reasoning, and attention to detail.

• Write down your units and track them through problems.

• Partial credit is often awarded for correct setup, even if the final answer is incorrect.

• Percentages in chemistry problems must always add up to 100%.

Additional info:

• Periodic table image included: Use for element identification, atomic number, and atomic mass reference.

• Practice questions cover key introductory chemistry topics: observations, changes, elements, boiling point, significant figures, measurement, density, and unit conversions.