Humboldt State University ® Department of Chemistry

Richard A. Paselk

	Science 331
Fall 2004	Lecture/Activity	Office: SA560a
Notes: 17 November		Phone: x 5719 Home: 822-1116
		e-mail: rap1

Quiz 1

Investigations-Chemical Change

• How does a match work?
  Observations
• Guesses as to what's up.
  • What burns?
    • Wood
  • What makes it ignite/
    • Friction causes heat
    • Heat ignites phosphorus compound
      • strike anywhere phosphorus compound in match tip
      • strike on box phosphorus compound on striking strip
    • Phosphorous compound ignites sulfur
      • What do we smell? SO₂, Sulfur dioxide.
      • How is it formed? Sulfur burning in air combines with oxygen, giving the balanced equation below:

• Note the odor. Have you smelled it before? Volcanoes release - smell associated with "brimestone", the yellow deposit of sulfur often seen around the brim of a volcano.
• Sulfur sets off wax in match-head
• Wax sets off wood. The general formula for wood is C(H₂O), so we can write a simple equation:

Candle, test-tube and water

• Put test tube (large) over candle ­ what happens?
• Put candle in beaker with water, light and put test tube over again, but with mouth submerged ­ what happens?
  • Water is sucked up into tube. Why?
  • Candle removes oxygen from air in tube (about 20%) and thus volume of gas goes down and atmosphere pushes water up into tube.
    • Let's look at the reaction. Paraffin is a homologue of methane: Paraffin = CH₃(CH₂)_nCH₃, where n = about 100, methane = CH₄. So let's write a balanced equation for the reaction of methane as a proxy for paraffin:

• Explain observations in each case.

Vinegar and baking soda

• Put baking soda (one scoop) in beaker
• Dip in lit candle (don't touch soda). What happens?
• Pour some vinegar into beaker. What happens?
  • Baking soda is sodium bicarbonate = NaHCO₃, an ionic compound made of sodium ions (Na⁺) and bicarbonate ions (HCO₃^-). When the bicarbonate is combined with an acid (a source of hydrogen ions = H⁺) they react to create carbon dioxide and water:

• Dip in lit candle (don't touch soda). What happens?
  • Explain. The carbon dioxide is denser than air and so it fills the beaker. When the candle is dipped into it it immediately goes out since there is no oxygen to sustain the fire.

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© R A Paselk

Last modified 17 November2004