chemical analysis

• What is a pure substance?

  A pure substance is a single element or compound
• What is a formulation and how is it made?

  • A formulation is a mixture of compounds in measured quantities.
  • Designed as a useful product.
  • Examples: fuels, cleaning agents, paints, medicines, alloys, fertilizers, foods.
• Why are alloys harder than pure metals?

  Alloys are mixtures of metals with specific purposes
• Describe the steps of paper chromatography.

  1. Draw a start line near the bottom of the paper.
  2. Spot the mixture on the line.
  3. Fill a beaker with solvent (below the start line).
  4. Hang paper in the beaker.
  5. Solvent travels up, separating components.
  6. Mark finish line before solvent reaches the end.
  7. Paper is dried.
• What is the stationary phase in paper chromatography?

  The paper is the stationary phase
• What is the mobile phase in paper chromatography?

  The solvent is the mobile phase
• How is Rf calculated?

  Rf = distance moved by spot / distance moved by solvent
• What does an Rf value of 0.85 indicate about a compound?

  It has a higher affinity for the solvent
• Describe the tests for hydrogen, oxygen, carbon dioxide, and chlorine.

  • Hydrogen: pop with burning splint.
  • Oxygen: glowing splint relights.
  • Carbon dioxide: turns limewater milky.
  • Chlorine: bleaches damp litmus paper white.
• What are the flame test results for lithium, sodium, potassium, calcium, and copper compounds?

  • Lithium: crimson red flame.
  • Sodium: yellow flame.
  • Potassium: lilac flame.
  • Calcium: orange red flame.
  • Copper: green flame.
• Describe the sodium hydroxide test results and write the equations.

  • Copper(II): blue precipitate; $Cu^{2+} +$$2OH^{-} \rightarrow Cu(OH)_{2}$
  • Iron(II): dirty green precipitate; $Fe^{2+} +$$2OH^{-} \rightarrow Fe(OH)_{2}$
  • Iron(III): brown precipitate; $Fe^{3+} +$$3OH^{-} \rightarrow Fe(OH)_{3}$
  • Al3+, Ca2+, Mg2+: white precipitates; Al(OH)3 dissolves in excess NaOH.
• What happens when dilute acid is added to carbonate anions?

  Fizzing occurs as CO2 is released
• What is the equation for the reaction of sodium carbonate with hydrochloric acid?

  $Na_{2}CO_{3} +$$2 HCl \rightarrow 2 NaCl +$$H_{2}O +$$CO_{2}$
• Describe the test for sulfate anions and provide an equation.

  • Add Ba2+ solution (e.g., BaCl2).
  • White precipitate of BaSO4 forms.
  • Equation: $K_{2}SO_{4} +$$BaCl_{2} \rightarrow 2 KCl +$$BaSO_{4}$
• Describe the test for halide anions using silver nitrate.

  • Add AgNO3 (acidified with HNO3).
  • Chlorides: white precipitate (AgCl).
  • Bromides: cream precipitate (AgBr).
  • Iodides: yellow precipitate (AgI).
• What are instrumental methods?

  Accurate, sensitive, and rapid methods
• Describe flame emission spectroscopy.

  • Identifies metal ions in solution.
  • Measures exact wavelength of emitted light.
  • Allows for definite identification.
  • Concentrations found by measuring light intensity.
  • Intensity vs concentration graph provides values.
• What are cations and anions?

  Cations are positive ions; anions are negative ions