Chapter 2: Chemistry and Measurement – Section 2.1: Units of Measurement

Chapter 2: Chemistry and Measurement

Section 2.1: Units of Measurement

This section introduces the fundamental units of measurement used in chemistry, focusing on the International System of Units (SI) and their application in scientific contexts. Understanding these units is essential for accurate communication and calculation in general, organic, and biological chemistry.

International System of Units (SI)

• Definition: The International System of Units (SI) is the globally accepted standard for measurement in science, providing consistent units for length, volume, mass, temperature, and time.

• Purpose: Ensures uniformity and precision in scientific measurements worldwide.

• Common SI Units:

  • Length: meter (m)

  • Volume: cubic meter (m3), but chemists often use liter (L) and milliliter (mL)

  • Mass: kilogram (kg), but chemists commonly use gram (g)

  • Temperature: kelvin (K), Celsius (°C), Fahrenheit (°F)

  • Time: second (s)

Comparison of Common Measurement Units

Quantity	SI Unit	Common Non-SI Units
Length	meter (m)	centimeter (cm), mile (mi), inch (in), foot (ft)
Volume	cubic meter (m3)	liter (L), milliliter (mL), quart (qt), pint (pt)
Mass	kilogram (kg)	gram (g), pound (lb), ounce (oz)
Temperature	kelvin (K)	Celsius (°C), Fahrenheit (°F)
Time	second (s)	minute (min), hour (h)

Length

• Definition: Length is the measurement of distance between two points.

• SI Unit: meter (m)

• Common Laboratory Units: centimeter (cm), millimeter (mm)

• Example: A newborn infant measures 54.6 cm in length.

Volume

• Definition: Volume is the amount of space occupied by a substance.

• SI Unit: cubic meter (m3)

• Common Laboratory Units: liter (L), milliliter (mL)

• Example: A physician orders 1 L of sodium chloride solution for intravenous administration.

Mass

• Definition: Mass is a measure of the quantity of matter in an object.

• SI Unit: kilogram (kg)

• Common Laboratory Units: gram (g), milligram (mg)

• Note: Mass is independent of gravity, unlike weight.

• Example: A physician orders 1.5 g of cefuroxime for injection; an infant weighs 5.2 kg.

Temperature

• Definition: Temperature measures how hot or cold an object is.

• SI Unit: kelvin (K)

• Common Scales: Celsius (°C), Fahrenheit (°F)

• Key Points:

  • Water freezes at 0°C (32°F) and boils at 100°C (212°F).

  • Absolute zero (0 K) is -273°C.

• Example: A patient has a temperature of 38.5°C.

Time

• Definition: Time is the continuous progression of events, measured in seconds (s).

• SI Unit: second (s)

• Common Laboratory Units: minute (min), hour (h)

• Example: Medication is administered every 4 hours; a pulse is measured as 76 beats per minute.

Sample Problems and Applications

• Identifying Measurement Types:

  • Temperature: 38.5°C (body temperature)

  • Mass: 1.5 g (medication dosage)

  • Volume: 1 L (IV solution)

  • Time: every 4 h (medication schedule)

  • Rate: 76 beats per minute (pulse)

  • Length: 54.6 cm (infant length)

  • Mass: 5.2 kg (infant mass)

Key Formulas

• Temperature Conversions:

$K = ^\circ C + 273$

$^\circ F = (1.8 \times ^\circ C) + 32$

$^\circ C = \frac{(^\circ F - 32)}{1.8}$

• Volume Conversions:

$1\,L = 1000\,mL$

$1\,m^3 = 1000\,L$

• Mass Conversions:

$1\,kg = 1000\,g$

$1\,g = 1000\,mg$

Additional info: The notes have been expanded for clarity and completeness, and standard SI unit relationships have been included for reference.