Introduction to Matter, Energy, and Measurement

This chapter introduces the foundational concepts of measurement in chemistry, including the metric and SI systems, units, significant figures, and the use of scientific notation and dimensional analysis. Mastery of these topics is essential for accurate scientific communication and laboratory work.

Units of Measurement

Scientific measurements require standardized units to ensure consistency and accuracy. The metric system and the International System of Units (SI) are universally used in chemistry.

• SI Units: The SI system has seven base units, each corresponding to a fundamental physical quantity.

• Metric System: Uses prefixes to indicate multiples or fractions of base units, making it easy to express very large or small quantities.

Metric System Prefixes

Prefixes are used to convert base units into more convenient units for measurement. Each prefix represents a specific power of ten.

• Examples: 1 kilometer (km) = meters (m); 1 milligram (mg) = grams (g).

• Common Prefixes: Giga (G), Mega (M), Kilo (k), Deci (d), Centi (c), Milli (m), Micro (), Nano (n), Pico (p), Femto (f).

Temperature Scales

Temperature is a measure of the average kinetic energy of particles in a sample. The Celsius and Kelvin scales are most commonly used in scientific contexts.

• Celsius (°C): Water freezes at 0°C and boils at 100°C.

• Kelvin (K): The SI unit for temperature; absolute zero is 0 K. Conversion:

• Fahrenheit (°F): Used in the United States; water freezes at 32°F and boils at 212°F.

Volume and Its Measurement

Volume is the amount of space occupied by a substance. The liter (L) and milliliter (mL) are common units of volume in chemistry.

• Equivalences: 1 L = 1 dm3; 1 mL = 1 cm3 = 1 cc

• Conversions: ;

Measuring Volume in the Laboratory

Different glassware is used to measure and deliver specific or variable volumes of liquids.

• Graduated Cylinder: Used for variable volumes.

• Syringe and Burette: Used for precise delivery of variable volumes.

• Pipette and Volumetric Flask: Used for delivering or holding specific volumes.

Volume by Displacement

The volume of an irregular object can be determined by the displacement of a liquid in a graduated cylinder.

Density

Density is a physical property defined as mass per unit volume. It is commonly expressed in g/mL or g/cm3.

• Formula:

• Solving for Mass or Volume: ;

• Application: Used to identify substances and convert between mass and volume.

Uncertainty in Measurement

All measurements have some degree of uncertainty, especially in the last digit. Numbers in science are classified as exact or inexact.

• Exact Numbers: Defined values (e.g., 12 eggs in a dozen).

• Inexact Numbers: Measured values with uncertainty (e.g., 2.49 mL ± 0.01 mL).

Accuracy and Precision

Accuracy refers to how close a measurement is to the true value, while precision refers to how close repeated measurements are to each other.

• Poor Accuracy, Poor Precision: Measurements are scattered and far from the true value.

• Poor Accuracy, Good Precision: Measurements are close to each other but far from the true value.

• Good Accuracy, Good Precision: Measurements are both close to each other and to the true value.

Significant Figures

Significant figures reflect the precision of a measured or calculated quantity. Rules for determining significant figures:

• All nonzero digits are significant.

• Zeroes between significant digits are significant.

• Leading zeroes are not significant.

• Trailing zeroes are significant if a decimal point is present.

Significant Figures in Calculations

• Addition/Subtraction: The result should have the same number of decimal places as the measurement with the fewest decimal places.

• Multiplication/Division: The result should have the same number of significant figures as the measurement with the fewest significant figures.

Scientific Notation

Scientific notation is used to express very large or small numbers in a compact form. It consists of a coefficient (between 1 and 10) and a power of ten.

• Example: 3820 = ; 0.0478 =

• Move the decimal to the right for negative exponents (small numbers), and to the left for positive exponents (large numbers).

Dimensional Analysis

Dimensional analysis (unit analysis) is a method for converting between units using conversion factors derived from equivalence statements.

• Example: To convert 8.00 m to inches:

Using Scientific Calculators

Scientific calculators are essential for handling powers of ten and scientific notation. The exponent key (EXP or EE) is used to enter numbers in scientific notation.

Ladder Method for Metric Conversions

The ladder method is a visual tool for converting between metric units by moving the decimal point or adjusting the exponent in scientific notation.

Summary Table: SI Base Units

Summary Table: Metric Prefixes

Practice Problems

• Calculate the volume of 65.0 g of liquid methanol if its density is 0.791 g/mL.

• How many grams of methanol are needed for 5.25 mL if density is 0.791 g/mL?

• Convert 3.5 Gbyte to kbyte.

• What is the mass in grams of a 325 mg aspirin tablet?

• Convert the average speed of a nitrogen molecule (515 m/s) to miles per hour.

• Calculate the volume of Earth's oceans (1.36 × 109 km3) in liters.

Additional info: These problems reinforce the application of dimensional analysis, significant figures, and unit conversions in real-world chemistry scenarios.