Fundamental Concepts and Measurements in General Chemistry

What are Matter and Mass?

Definitions and Examples

Understanding the basic concepts of matter and mass is essential in chemistry, as these form the foundation for all chemical studies.

• Matter: Anything that occupies space and has mass.

• Mass: A measure of the amount of matter in a sample.

Law of Conservation of Mass

The law of conservation of mass states that the total mass of a system remains constant during any process.

• Example: 1.85 g of wood is placed in a sealed vessel with 9.45 g of air. After burning, the resulting ash weighs 0.28 g. The total mass of gases remaining is: $1.85 + 9.45 - 0.28 = 11.02$ g

Additional info: This principle is fundamental in chemical reactions and stoichiometry.

What are the Basic States of Matter?

States and Their Properties

Matter exists in three primary states, each with distinct physical properties.

• Solid:

  • Closely packed particles

  • Incompressible

  • Particles vibrate in fixed positions

  • Fixed volume and shape

• Liquid:

  • Closely packed particles

  • Incompressible

  • Particles can move past one another

  • Fixed volume, no fixed shape

• Gas:

  • Particles far apart

  • Compressible

  • Particles move freely

  • No fixed volume or shape

The state of matter can be changed by increasing or decreasing temperature or pressure.

How Can Matter Be Classified by Composition?

Classification of Matter

Matter can be classified as pure substances or mixtures, each with further subdivisions.

• Pure Substance: Cannot be separated physically.

  • Element: Cannot be separated chemically.

  • Compound: Made from two or more elements, can be separated chemically.

• Mixture: Made from two or more substances.

  • Homogeneous Mixture (Solution): Uniform composition.

  • Heterogeneous Mixture: Non-uniform composition.

What are the Differences Between Physical and Chemical Changes?

Types of Changes in Matter

Changes in matter can be classified as physical or chemical, depending on whether the chemical identity is altered.

• Physical Change: Does not involve a change in chemical identity (e.g., phase changes, appearance).

• Chemical Change: Involves a change in chemical identity (e.g., chemical reactions).

What are the Differences Between Physical and Chemical Properties?

Properties of Matter

Properties of matter are observed and measured to characterize substances.

• Physical Properties: Observed without changing chemical composition.

  • Examples: Density, melting point, color.

• Chemical Properties: Observed by changing chemical composition.

  • Examples: Reactivity, flammability.

What are cgs and mks (SI) Units?

Measurement Systems in Science

Scientific measurements use standardized units for consistency and accuracy.

• mks (SI) units: Meter (length), kilogram (mass), second (time).

• cgs units: Centimeter (length), gram (mass), second (time).

Quantity	mks (SI) unit	cgs unit
Length	meter (m)	centimeter (cm)
Mass	kilogram (kg)	gram (g)
Time	second (s)	second (s)

What are Some SI Base and Derived Units?

Units Used in Chemistry

SI base units are fundamental, while derived units are combinations of base units.

Quantity	Unit	Abbreviation
Mass	kilogram	kg
Length	meter	m
Time	second	s
Temperature	kelvin	K
Amount of Substance	mole	mol
Charge	Coulomb	C

Derived units:

Quantity	Definition	SI unit	cgs unit
Volume	L × W × H	m3	cm3
Velocity	distance/time	m/s	cm/s
Density	mass/volume	kg/m3	g/cm3

How Do I Express Numbers Using Scientific Notation?

Scientific Notation

Scientific notation is used to express very large or very small numbers using powers of ten.

• Move the decimal point until the number is between 1 and 10.

• Multiply by 10 raised to a power that represents the magnitude.

Example:

• 93,000,000 = $9.3 \times 10^7$

• 0.000000486 = $4.86 \times 10^{-7}$

How Do I Use SI Prefixes with Units to Express the Size of a Number?

SI Prefixes

SI prefixes are used to represent powers of ten for numbers in scientific notation.

Prefix	Symbol	Definition
Million	Mega- (M)	$10^6$
Thousand	Kilo- (k)	$10^3$
Hundredth	Centi- (c)	$10^{-2}$
Thousandth	Milli- (m)	$10^{-3}$
Millionth	Micro- ($\mu$)	$10^{-6}$
Billionth	Nano- (n)	$10^{-9}$
Trillionth	Pico- (p)	$10^{-12}$

What is the Difference Between Measured and Exact Numbers?

Types of Numbers in Chemistry

Numbers in chemistry can be measured or exact, affecting the precision of calculations.

• Measured numbers: Obtained from instruments; precision is limited.

• Exact numbers: Defined values or numbers from formulas; considered to have infinite precision.

Exact Numbers	Examples
Numbers in formulas	$T = 59$ (TF-32)
Conversions within a unit system	$1 \text{ in} = 2.54 \text{ cm}$
"Defined" values	$1 \text{ L} = 1.00 \text{ mL}$

What are Significant Figures?

Significant Figures in Measurement

Significant figures (sig figs) reflect the precision of a measurement. Zeros can be significant or placeholders.

Sig. Figs	Placeholders
All interior zeros	All leading zeros
Trailing zeros with a decimal point	Trailing zeros in a number without a decimal point

How Do I Adjust the Sig Figs of My Final Answer After I Perform Calculation?

Rounding and Calculations

Calculated numbers must be rounded so that they are not more precise than the least precise measurement used in the calculation.

• Multiplication and Division: Round the final answer so that it has the same number of sig figs as the least precise measurement.

• Addition and Subtraction: Round the final answer to the same number of decimal places as the least precise measurement.

Example:

• $3.2903 \times 3 = 9.9$ (2 sig figs)

• $17.70 - 3.863 = 13.84$ (hundredth place)

• For multi-step calculations, round only after the last operation.

How Can I Use Unit Conversion Techniques to Help Me Solve Problems Involving Measured Numbers?

Dimensional Analysis

Dimensional analysis (factor label method) is used to convert units and solve problems with correct units.

• Example: Convert 2235 ft/s to km/hr $2235 \frac{\text{ft}}{\text{s}} \times \frac{1 \text{mi}}{5280 \text{ft}} \times \frac{1.6093 \text{km}}{1 \text{mi}} \times \frac{3600 \text{s}}{1 \text{hr}} = 2452 \text{km/hr}$

• Example: The average US farm occupies 435 acres. How many square kilometers is this? $435 \text{ acres} \times \frac{43560 \text{ ft}^2}{1 \text{ acre}} \times \frac{(1 \text{ mi})^2}{(5280 \text{ ft})^2} \times \frac{(1.6093 \text{ km})^2}{(1 \text{ mi})^2} = 1.76 \text{ km}^2$

How Can I Use Unit Conversion Techniques to Solve Problems Involving Measured Numbers? (cont.)

Using Measurements as Conversion Factors

Measurements can be used as conversion factors to solve complex problems.

• Example: The space shuttle used 227,641 lb of liquid hydrogen during takeoff. Determine the volume of the fuel tank in gallons. The density of liquid hydrogen is 0.07085 g/cm3. $227641 \text{ lb} \times \frac{452.59237 \text{ g}}{1 \text{ lb}} \times \frac{1 \text{ cm}^3}{0.07085 \text{ g}} \times \frac{1 \text{ mL}}{1 \text{ cm}^3} \times \frac{1 \text{ L}}{1000 \text{ mL}} \times \frac{1 \text{ gal}}{3.785411384 \text{ L}} = 3.85 \times 10^6 \text{ gal}$

Additional info: These foundational concepts are essential for success in General Chemistry and provide the basis for more advanced topics such as stoichiometry, thermodynamics, and chemical kinetics.