Chemistry and Measurement

Chemistry is The Basis of Life!

  • Chemistry: The study of composition, structure, properties, and reactions of matter.
    • Matter: All the substances that make up our world.
    • Definition: Anything that has mass and occupies space.
    • Examples: Apple, salt, chalk, air.
    • Chemicals: Substances that have the same composition and properties wherever they are found.

Systems of Measurement

  • Two Common Systems:
    • US (English) system: Based on inches, feet, yards.
    • Metric system: Based on the meter.
    • Includes the International System of Units (SI).

The Metric System (SI)

  • The metric system or SI is:
    • A decimal system based on 10.
    • Used in most of the world and everywhere by scientists.
    • One unit serves as the basic unit for each type of measurement:
    • Length: meter (m)
    • Volume: liter (L)
    • Mass: gram (g)
    • Time: second (s)
    • Temperature: Celsius (°C)

Units of Measurements

  • Every measurement consists of two parts:
    • A number followed by a unit.
  • Examples of Measurements:
    • 35 m
    • 0.25 L
    • 225 lb
    • 3.4 kg

Importance of Measurements in Nursing Practice

  • Example of usage in nursing:
    • Temperature, height, weight, blood pressure, and volume for IV injections must be measured accurately.
    • Accurate recording of amounts and units in patient records is essential.

Units of Measurements - Specific Types

Volume

  • Volume: Amount of space a substance occupies.
    • Metric unit: liter (L or mL).
    • SI unit: cubic meter (m³).
    • Measurement tool: Graduated cylinder.
    • Relationships between units:
    • 1 L = 1000 mL
    • 1 L = 1.06 qt
    • 946 mL = 1 qt
    • 1 mL = 1 cm³

Length

  • Length: Measured using a meterstick or ruler.
    • Metric and SI unit: meter (m).
    • Relationships between units:
    • 1 m = 100 cm
    • 1 m = 39.4 in
    • 1 m = 1.09 yd
    • 2.54 cm = 1 in

Mass

  • Mass: Quantity of material it contains.
    • Metric unit: gram (g).
    • SI unit: kilogram (kg).
    • Measurement tool: Balance.
    • Relationships between units:
    • 1 kg = 1000 g
    • 1 kg = 2.20 lb
    • 1 lb = 454 g

Temperature

  • Temperature: Indicates how hot or cold it is.
    • Metric scale: Celsius (°C).
    • Water freezes at 0 °C and boils at 100 °C.
    • SI scale: Kelvin (K).
    • Relationships between temperature scales:
    • Kelvin (K): Lowest possible temperature is 0 K.
    • Fahrenheit (°F): Water freezes at 32 °F and boils at 212 °F.

Time

  • Time measurement:
    • Unit: second (s) in both metric and SI systems.

Study Check 1

Task: Indicate whether the unit describes 1) length, 2) mass, or 3) volume.

  • A bag of tomatoes: 4.6 kg.
    • Answer: Mass
  • A person: 2.0 m tall.
    • Answer: Length
  • A medication: 0.50 g aspirin.
    • Answer: Mass
  • A bottle: 1.5 L of water.
    • Answer: Volume

Study Check 2

Task: Identify the measurement that is a metric unit.
A. Jim’s height is:
1) 1.5 yd
2) 6 ft
3) 2.1 m
B. The race was won in:
1) 19.6 s
2) 14.2 min
3) 3.5 h
C. The mass of a lemon is:
1) 12 oz
2) 145 g
3) 0.6 lb
D. The temperature is:
1) 85 °C
2) 255 K
3) 45 °F

Study Check 2 Answers

A. Answer: 3) 2.1 m
B. Answer: 1) 19.6 s
C. Answer: 2) 145 g
D. Answer: 1) 85 °C

Measurements in Scientific Notation

  • Scientific Notation: Used to write very large or very small numbers.
    • Examples:
    • Diameter of Earth: 12,800,000 m = 1.28 × 10⁷ m
    • Volume of gasoline used in the US each year: 550,000,000,000 L = 5.5 × 10¹¹ L
    • Additional examples include:
    • 8,500 L = 8.5 × 10³ L
    • Time for light to travel from the Sun to Earth: 500 s (not in scientific notation)
    • Mass of a typical human: 68 kg (not in scientific notation)
    • Diameter of chickenpox virus: 0.0000000000000000001 kg = 1 × 10⁻¹⁹ kg

Writing Numbers in Scientific Notation

  • Scientific notation consists of 3 parts:
    • Coefficient
    • Power of 10
    • Units
  • Examples:
    • Standard Number: 2400 m = 2.4 × 10³ m (3 places to the left)
    • Standard Number: 0.00086 g = 8.6 × 10⁻⁴ g (4 places to the right)

Measured Numbers and Significant Figures

  • Measured Numbers: Numbers obtained using measuring tools to determine quantities.
    • Example: “The length of the eraser is 6.5 inches.”
  • Uncertainty: There is always some uncertainty in every measurement.

Exact Numbers

  • Exact Number: Obtained from counted objects or defined relationships.
    • Examples:
    • Counted objects: 2 soccer balls, 4 pizzas
    • Defined relationships: 1 foot = 12 inches, 1 meter = 100 cm
  • Significance: Exact numbers do not affect the number of significant figures.

Significant Figures in Measurements

  • Significant Figures: In a measurement, include all known digits plus the estimated digit.
    • Nonzero digits: Always count as significant figures.
    • Zero digits: May or may not be significant, depending on their position.
  • Rules for zeros:
    • Leading zeros are not significant.
    • Sandwiched zeros between nonzero digits are significant.
    • Trailing zeros in numbers with a decimal point are significant; in numbers without a decimal point, they are usually placeholders and not significant.

Significant Figures Examples

  • Examples:
    • 38.15 cm has 4 significant figures.
    • 0.04050 kg has 4 significant figures (leading zeros not counted).
    • 25000 cm has 2 significant figures (trailing zeros are not significant without a decimal point).

Study Check 3

Task: State the number of significant figures in each measurement:

  • 0.030 m
  • 4.050 L
  • 0.0008 g
  • 2500 mi
  • 2.80 m

Study Check 3 Answers

  • 0.030 m: 2 significant figures
  • 4.050 L: 4 significant figures
  • 0.0008 g: 1 significant figure
  • 2500 L: 2 significant figures
  • 2.80 m: 3 significant figures

Rounding Off in Calculations

  • Rounding Rule for Significant Figures: The final answer must have the same number of significant figures as the measurement with the fewest significant figures.
  • Rules for Rounding Off Calculated Answers:
    1. If the first digit to be dropped is < 4 then it and following digits are dropped.
    2. If the first digit to be dropped is > 5 then the last retained digit is increased by 1.
  • Examples:
    • Calculated numbers needing three significant figures:
    • 8.4234 rounded to 8.42 (3 significant figures).
    • 3256 rounded to 3260 (3 significant figures).

Study Check 4

Task: Round off or add zeros to the following calculated answers to give three significant figures:

  • 824.75 cm
  • 0.112486 g
  • 8.2 L

Study Check 4 Answers

  • 824.75 cm: Round to 825 cm
  • 0.112486 g: Round to 0.112 g
  • 8.2 L: Already has three significant figures, but can add significant zero if needed.

Significant Figures in Calculations

  • Multiplication or Division: The final number should have the same significant figures as the measurement with the fewest significant figures.
    • Example: Calculation: 110.5 × 0.048 = 5.304, rounded to 5.3 (2 SF).
  • Addition and Subtraction: The final answer should have the same number of decimal places as the measurement with the fewest decimal places.

Prefixes and Equalities

  • Prefixes: Indicate an increase or decrease in size by a factor of ten (e.g., milli, micro).
    • Examples of metric equalities:
    • 1 kilometer (1 km) = 1000 meters
    • 1 kiloliter (1 kL) = 1000 liters
    • 1 kilogram (1 kg) = 1000 grams

Conversion Factors

  • A Conversion Factor is obtained from an equality.
  • Equalities: Use two different units to describe the same measured amount, written for relationships between units of the metric system, US units, or between metric and US units.
  • These can be inverted to give two conversion factors.
    • Example: 2.54 cm = 1 inch leads to conversion factors of:
    • 1 in = 2.54 cm
    • 2.54 cm = 1 in

Study Check 5

Task: Write conversion factors from the equality for the following.
A. Liters and mL
B. Hours and minutes
C. Meters and kilometers

  • Conversion Problem: Height of the bookcase is given as 42 inches; required is the height in feet.
    • Given unit value = 42 inches;
    • Needed unit = feet;
    • Equality: 12 in = 1 ft.

Study Check 5 Answers

  • A. Conversion factor: 1 L = 1000 mL, written as: 1 L/1000 mL and 1000 mL/1 L.
  • B. Conversion factor: 1 h = 60 min, written as: 1 h/60 min and 60 min/1 h.
  • C. Conversion factor: 1 km = 1000 m, written as: 1 km/1000 m and 1000 m/1 km.
  • Conversion of height: 42 in × (1 ft/12 in) = 3.5 ft.

Density

  • Density Equation: Density = Mass of substance / Volume of substance
  • Examples of density values:
    • Cork: D = 0.26 g/mL
    • Ice: D = 0.92 g/mL
    • Water: D = 1.00 g/mL
    • Aluminum: D = 2.70 g/mL
    • Lead: D = 11.3 g/mL
    • Density values across states:
    • Solids: Varies widely, typically higher density.
    • Liquids: Less than solids but more than gases.
    • Gases: Have the lowest densities (measured in g/L at specified conditions such as 25 °C).

Volume by Displacement

  • Volume Displacement: The volume of a solid can be determined by the water volume it displaces when completely submerged.
    • Example Calculation:
    • Water level rises from 25.0 mL to 33.0 mL; thus, volume of object = total volume - initial volume = 33.0 mL - 25.0 mL = 8.0 mL or equivalently 8.0 cm³ (Since 1 mL = 1 cm³).

Study Check 6

Task: What is the density (g/mL) of 48.0 g of a metal if the water level rises from 25.0 mL to 33.0 mL after the addition?

  • Given: Mass = 48.0 g
  • Volume of water: Initial = 25.0 mL; Final = 33.0 mL.
  • Needed: Density (g/mL).
  • Plan: Calculate volume displaced in mL for use in density calculation.
    • Compute: 33.0 mL - 25.0 mL = 8.0 mL.
  • Setup Problem:
    • Density = Mass / Volume = 48.0 g / 8.0 mL = 6.0 g/mL.