CHE 121: Chapter 1 - Matter and Measurements

Chapter 1: Matter and Measurements (CHE 121)

  • Core Topics Overview:
        * Elements, Compounds, and Mixtures
        * Properties of Matter
        * Metric System
        * Significant Figures
        * Dimensional Analysis

Introduction to Chemistry and Matter

  • Chemistry Definition: The study of matter, its properties, and its behaviors.
  • Matter Definition: Anything that takes up space (volume) and has mass.

States of Matter and Classification

  • States of Matter Characteristics:
        * Gas: Indefinite shape, indefinite volume, and is compressible.
        * Liquid: Indefinite shape, definite volume, and cannot be compressed.
        * Solid: Definite shape, definite volume, and cannot be compressed.
  • Pure Substances: These have distinct properties and a composition that does not vary from sample to sample.
        * Elements:
            * Cannot be broken down into simpler substances.
            * Composed of specific atoms, which are the primary building blocks of matter.
            * Each element is denoted by a specific chemical symbol (students are required to know both the symbol and the element name).
        * Compounds:
            * Substances made of two or more elements.
            * Compounded particles can be individual atoms of an element, molecules of an element, or molecules of a compound.
  • Law of Constant Composition:
        * The observation that the elements of a compound will ALWAYS be the same in every sample.
        * Example: H2OH_2O
            * Water is always composed of 11%11\% hydrogen (H) and 89%89\% oxygen (O) by mass.
  • Mixtures:
        * A combination of two or more substances where each substance retains its own chemical identity.
        * Homogeneous Mixtures:
            * The composition is uniform throughout.
            * Alloy: A homogeneous mixture of metals.
            * Air: A homogeneous mixture of gases (e.g., O2O_2 and N2N_2).
            * Solutions: Examples include salt water, sugar water, or a Cu2+ solutionCu^{2+}\text{ solution}.
        * Heterogeneous Mixtures:
            * The composition is not uniform throughout.
            * Granite: Contains different quantities of certain minerals randomly distributed.
            * Sand & Water: Consists of two different phases with a different distribution of solid and liquid.
            * Smog: Distribution has varying concentrations at different areas of a city.

Matter Classification Flow Chart

  • Logic Path for Classification:
        * Is it uniform throughout?
            * NO: Heterogeneous mixture.
            * YES: Homogeneous.
        * If homogeneous, does it have a variable composition?
            * YES: Homogeneous mixture (solution).
            * NO: Pure substance.
        * If a pure substance, does it contain more than one kind of atom?
            * YES: Compound.
            * NO: Element.

Properties of Matter

  • Physical Properties:
        * Properties that can be observed without changes to the substance's identity or composition.
        * Examples: Color, odor, hardness, melting point, boiling point, density.
        * Intensive (Intrinsic) Properties: Properties that do not depend on the amount of substance available. All listed physical properties are intensive.
        * Intensive properties are used to identify a substance (e.g., H2OH_2O boils at 100∘C100^{\circ}C).
  • Physical Change: A change in appearance but NOT in composition (e.g., transitions between water vapor, liquid water, and ice).
  • Chemical Properties:
        * Properties based on how a substance reacts.
        * Examples: Flammability, toxicity, reactivity, stability, acidity, basicity.
        * Extensive Properties: These depend on the amount of substance present.
        * Properties that are not useful for identifying a compound specifically because they change with quantity.
  • Chemical Change: When a substance undergoes a transformation into a different substance (i.e., it undergoes a chemical reaction).
        * Examples: Combustion of H2H_2 and O2O_2; dissolving a penny in nitric acid.

Separation of Mixtures

  • Filtration: A method used to separate mixtures of solids and liquids (e.g., sand and H2OH_2O).
  • Distillation: A method used to separate mixtures based on differences in boiling point.

Units and Measurements

  • Mars Climate Orbiter Warning: A 125-million-dollar climate orbiter crashed due to a conversion error between metric and English units. Use consistent units to avoid errors.
  • International System of Units (SI Units): The specific base set of metric units required for scientific measurements.
  • SI Prefixes: Used to enlarge or reduce base SI units to convenient sizes.
        * Base units include: gram, meter, mole, liter, etc.
        * 10−910^{-9} = nano
        * 10−610^{-6} = micro
        * 10−310^{-3} = milli
  • Derived Units: Obtained by multiplication or division of base units.
        * Speed: distance/time=m/s\text{distance}/\text{time} = \text{m/s}
        * Volume (V): V=(length)3=m3V = (\text{length})^3 = \text{m}^3
  • Density (d):
        * Formulated as: d=massvolumed = \frac{\text{mass}}{\text{volume}}
        * Common units: g/mL\text{g/mL} or g/cm3\text{g/cm}^3
        * Note: Density is a temperature-specific derived unit.

Temperature Scales and Conversions

  • Fahrenheit (∘F^{\circ}F): Primarily used in the USA; based on human body temperature.
  • Celsius (∘C^{\circ}C): Used globally and in scientific measurements; based on water properties (0∘C0^{\circ}C freezing, 100∘C100^{\circ}C boiling).
  • Kelvin (K): The fundamental SI unit; based on an absolute scale.
  • Conversion Formulas:
        * ∘C=59×(∘F−32)^{\circ}C = \frac{5}{9} \times (^{\circ}F - 32)
        * ∘F=95×(∘C)+32^{\circ}F = \frac{9}{5} \times (^{\circ}C) + 32
        * K=∘C+273.15K = ^{\circ}C + 273.15

Uncertainty and SigFigs

  • Measurement Types:
        * Exact numbers: Values known exactly (e.g., defined quantities).
        * Inexact numbers: Values with some uncertainty; the last measured digit is always uncertain.
  • Accuracy vs. Precision:
        * Accuracy: How close a value is to the true value.
        * Precision: How close measured values are to each other.
  • Significant Figures (SigFigs) Rules:
        1. All non-zero numbers are significant (e.g., 126 has 3 SigFigs).
        2. Zeros between non-zero digits are significant (e.g., 100,005 has 6 SigFigs).
        3. Leading zeros are NEVER significant (e.g., 0.000126 has 3 SigFigs).
        4. Zeros at the end of a number are significant IF the number contains a decimal point (e.g., 1.2600 has 5 SigFigs).
        5. Zeros at the end of a number with no decimal point are usually NOT significant (e.g., 100 has 1 SigFig; write as 1.00×1021.00 \times 10^2 for 3 SigFigs).
  • Calculations with SigFigs:
        * Addition/Subtraction: The answer matches the smallest number of decimal places.
            * Example: 20.42+1.322+83.1=104.842→104.820.42 + 1.322 + 83.1 = 104.842 \rightarrow 104.8
        * Multiplication/Division: The answer matches the smallest number of SigFigs.
            * Example: (62.21 cm)×(0.052 cm)=3.23492 cm2→3.2 cm2(62.21\,\text{cm}) \times (0.052\,\text{cm}) = 3.23492\,\text{cm}^2 \rightarrow 3.2\,\text{cm}^2
        * Rounding Rule: Round up if the next digit is ≥5\geq 5. Round down if the next digit is < 5.
        * PEMDAS Note: Follow the order of operations. Mark SigFigs as you go, but only round at the very end of the calculation.

Dimensional Analysis

  • Definition: The method of converting values of one unit into values of a different unit using conversion factors.
  • Rule: Units follow standard arithmetic operations.

Questions & Discussion

  • Exercise 1: Classify as element, compound, homogeneous mixture, or heterogeneous mixture.
        * A) Molten iron: Element
        * B) Water with dissolved sugar: Homogeneous mixture (solution)
        * C) A container of pure ethylene glycol: Compound
  • Exercise 2: Physical or Chemical changes?
        * A) Evaporation of rubbing alcohol: Physical
        * B) Burning of lamp oil: Chemical
        * C) Bleaching hair: Chemical
        * D) Formation of frost on a cold night: Physical
  • Exercise 3: Identify unit names.
        * A) 10−9 grams (g)10^{-9}\,\text{grams (g)}: nanogram (ng)
        * B) 10−6 seconds (s)10^{-6}\,\text{seconds (s)}: microsecond (μs\mu s)
        * C) 10−3 meters (m)10^{-3}\,\text{meters (m)}: millimeter (mm)
  • Exercise 4: Temperature Conversion.
        * Predict temperature 30∘C30^{\circ}C. What is it in (a) K and (b) ∘F^{\circ}F?
        * (a) K=30+273.15=303.15 KK = 30 + 273.15 = 303.15\,K
        * (b) ∘F=95(30)+32=86∘F^{\circ}F = \frac{9}{5}(30) + 32 = 86^{\circ}F
  • Exercise 5: Volume Calculation.
        * Calculate volume of 65.0 g65.0\,g of liquid methanol if density is 0.791 g/mL0.791\,g/mL.
        * Solution: V=massdensity=65.0 g0.791 g/mL=82.17 mLV = \frac{\text{mass}}{\text{density}} = \frac{65.0\,g}{0.791\,g/mL} = 82.17\,mL
  • Exercise 6: SigFigs count.
        * A) 5000: 1 SigFig
        * B) 6.02×10236.02 \times 10^{23}: 3 SigFigs
        * C) 4.003: 4 SigFigs
  • Exercise 7: SigFig Calculation.
        * 4.562×3.99870÷(452.6755−452.33)4.562 \times 3.99870 \div (452.6755 - 452.33)
        * Subtraction: 452.6755−452.33=0.3455452.6755 - 452.33 = 0.3455 (The result is significant to two decimal places: 0.35, which has 2 SigFigs).
        * Multiplication/Division: Result is limited to 2 SigFigs based on the divisor.
  • Exercise 8: How many ft are in 14.7 in?
        * 14.7 in×1 ft12 in=1.225 ft14.7\,\text{in} \times \frac{1\,\text{ft}}{12\,\text{in}} = 1.225\,\text{ft}
  • Exercise 9: Convert 525,600 min to years.
        * 525,600 min×1 hr60 min×1 day24 hr×1 yr365 days=1 year525,600\,\text{min} \times \frac{1\,\text{hr}}{60\,\text{min}} \times \frac{1\,\text{day}}{24\,\text{hr}} \times \frac{1\,\text{yr}}{365\,\text{days}} = 1\,\text{year}
  • Exercise 10: Convert 8.00 m8.00\,m to inches (Given factor: 1 in=2.54 cm1\,\text{in} = 2.54\,cm).
        * 8.00 m×100 cm1 m×1 in2.54 cm8.00\,m \times \frac{100\,cm}{1\,m} \times \frac{1\,in}{2.54\,cm}
  • Exercise 11: What is the mass, in grams, of a 2.00 in32.00\,\text{in}^3 bar of gold (d=19.3 g/cm3d = 19.3\,g/cm^3)?
        * Convert volume from in3\text{in}^3 to cm3\text{cm}^3: 2.00 in3×(2.54 cm1 in)32.00\,\text{in}^3 \times (\frac{2.54\,cm}{1\,in})^3
        * Apply density: Volume in cm3×19.3 g/cm3\text{Volume in cm}^3 \times 19.3\,g/cm^3
  • Exercise 12: What is 48 km/hr48\,km/hr in m/sm/s?
        * 48 km1 hr×1000 m1 km×1 hr60 min×1 min60 s\frac{48\,km}{1\,hr} \times \frac{1000\,m}{1\,km} \times \frac{1\,hr}{60\,min} \times \frac{1\,min}{60\,s}