chemical analysis

• What is a pure substance?

  A single element or compound
• How is a formulation made?

  By mixing compounds in measured quantities
• What is the purpose of alloys?

  They are harder than pure metals
• Describe the process of paper chromatography.

  1. Draw a start line on paper.
  2. Spot the mixture on the line.
  3. Fill a beaker with solvent.
  4. Hang paper in the beaker.
  5. Solvent travels up, separating components.
  6. Mark finish line before solvent reaches end.
  7. Paper is stationary phase; solvent is mobile phase.
• How is Rf calculated?

  Distance moved by the 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 different metal 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.
• How do you test for carbonate anions?

  Add dilute acid and observe fizzing
• 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}$
• How do you test for sulfate anions?

  Add Ba2+ solution and observe white precipitate
• What is the equation for the reaction of potassium sulfate with barium chloride?

  $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.

  1. Identifies metal ions in solution.
  2. Measures exact wavelength of emitted light.
  3. Allows for definite identification.
  4. Concentration found by light intensity.
  5. Intensity vs concentration graph used.
• What are cations and anions?

  Cations are positive ions; anions are negative ions