Test 1: Fundamental Concepts and Calculations in GOB Chemistry

Classification of Matter and Its Properties

Pure Substances and Mixtures

Understanding the distinction between pure substances and mixtures is foundational in chemistry. Pure substances have a uniform and definite composition, while mixtures consist of two or more substances physically combined.

• Pure Substance: A material with a constant composition (e.g., aluminum foil, water).

• Mixture: A combination of two or more substances where each retains its own properties (e.g., air, glass of water with pebbles, milk, sugar granules, brass).

Homogeneous vs. Heterogeneous Mixtures

Mixtures can be classified based on the uniformity of their composition:

• Homogeneous Mixture: Uniform composition throughout (e.g., air, milk, brass).

• Heterogeneous Mixture: Non-uniform composition; different parts are visible (e.g., glass of water with pebbles, sugar granules).

Chemical and Physical Properties and Changes

Properties and changes of matter are classified as either chemical or physical:

• Physical Property/Change: Does not alter the chemical composition (e.g., banana sliced into pieces, water boils, sugar dissolves).

• Chemical Property/Change: Alters the chemical composition (e.g., iron rusting, copper turning green, hair burning, something smells).

Significant Figures and Scientific Notation

Understanding Place Value

Each digit in a number has a specific place value, which is important for reporting measurements accurately.

• Ones, tens, hundreds, thousands, tenths, hundredths, thousandths are common place values.

Scientific Notation

Scientific notation expresses numbers as a product of a coefficient and a power of ten, which is useful for very large or small numbers.

• Example: $1,044,000 = 1.044 \times 10^6$

• Example: $0.0000098 = 9.8 \times 10^{-6}$

Counting Significant Figures

Significant figures reflect the precision of a measurement.

• All nonzero digits are significant.

• Zeros between nonzero digits are significant.

• Leading zeros are not significant; trailing zeros after a decimal point are significant.

Rounding to Significant Figures

When reporting measurements, round to the correct number of significant figures as required by the context.

• Example: 3.1567 rounded to 2 significant figures is 3.2.

Exact Numbers and Relationships

Exact numbers are defined values, not measured, and have infinite significant figures.

• Examples: 1 inch = 2.54 cm (by definition), 1 liter = 1000 milliliters.

Units, Prefixes, and Conversions

SI Prefixes

Prefixes are used to denote multiples or fractions of units in the metric system.

• kilo- ($10^3$), centi- ($10^{-2}$), milli- ($10^{-3}$), micro- ($10^{-6}$), nano- ($10^{-9}$), pico- ($10^{-12}$), mega- ($10^6$), giga- ($10^9$), tera- ($10^{12}$), deci- ($10^{-1}$).

Unit Equality and Conversion Factors

Equality statements relate two units and are used to create conversion factors for dimensional analysis.

• Example: 1 meter = 100 centimeters ($1 \text{ m} = 100 \text{ cm}$)

• Example: 1 mile = 1.609 kilometers ($1 \text{ mi} = 1.609 \text{ km}$)

Common Unit Conversions

From	To	Conversion Factor
Kilometers	Meters	1 km = 1000 m
Milliliters	Liters	1000 mL = 1 L
Inches	Centimeters	1 in = 2.54 cm
Seconds	Picoseconds	1 s = 1 \times 10^{12} ps

Density and Specific Gravity

Density

Density is the mass per unit volume of a substance.

• Formula: $\text{Density} = \frac{\text{Mass}}{\text{Volume}}$

• Units: g/mL, g/cm3, kg/L

Specific Gravity

Specific gravity is the ratio of the density of a substance to the density of water (at 4°C, 1.00 g/mL).

• Formula: $\text{Specific Gravity} = \frac{\text{Density of Substance}}{\text{Density of Water}}$

Temperature Scales and Conversions

Temperature Scales

The three main temperature scales are Celsius (°C), Kelvin (K), and Fahrenheit (°F).

• Kelvin is the SI unit for temperature.

Conversion Formulas

• Celsius to Kelvin: $K = ^\circ C + 273.15$

• Celsius to Fahrenheit: $^\circ F = (^\circ C \times \frac{9}{5}) + 32$

• Fahrenheit to Celsius: $^\circ C = (^\circ F - 32) \times \frac{5}{9}$

Energy, Calories, and Nutrition

Calories and Joules

Energy can be measured in calories (cal), kilocalories (kcal), or joules (J).

• 1 Calorie (food calorie, with capital C) = 1 kilocalorie = 1000 calories

• 1 calorie = 4.184 joules

Energy Content in Food

The energy provided by food is calculated based on the macronutrient content:

• Carbohydrates: 4 kcal/g

• Proteins: 4 kcal/g

• Fats: 9 kcal/g

To calculate total energy:

• Multiply grams of each macronutrient by its energy value and sum the results.

• Example: 5.5 g fat × 9 kcal/g = 49.5 kcal from fat

Summary Table: Key Conversion Factors

Quantity	Conversion
Length	1 in = 2.54 cm
Volume	1 L = 1000 mL
Mass	1 kg = 1000 g
Energy	1 cal = 4.184 J
Temperature	K = °C + 273.15

Additional info: Some explanations and examples have been expanded for clarity and completeness, as the original material was in question/answer format.