Ch 204 Lab Help

Atmospheric Gases

The report should include a short intro and the usual methods section. There isn't really a discussion here - the best way to do this report is to break each section up as follows:

1. Preparation of oxygen

• Equation (using symbols)
• Equation (using words)

2. Reactions with oxygen

• Equation (using symbols)
• Equation (using words)

You will be expected to show your observations on your yellow sheets - DO NOT type them in your lab report!

You are to write balanced equations for each reaction performed. Here are a few hints to help you along:

• Most, if not all, reactions can be found in your textbook - use the index! Also, we'll do most (if not all) of these reactions in our studies of Chapters 7, 3, and 4 in Ch 201. Don't hesitate to get out your Ch 201 materials!
• In the preparation of oxygen, the iron (III) chloride is a catalyst in the decomposition of H₂O₂(aq) to oxygen gas and water - it does not appear in the overall reaction!!
• Is the decomposition of hydrogen peroxide a redox reaction? How do you know?
• For the reactions with oxygen, note the following:
  -carbon is just C(gr) (graphite carbon)
  -sulfur is S₈ (it forms 8-membered rings at room temp.)
  -Iron is most likely to be oxidized to the +3 state under the conditions in our experiment.
  -what general class of reaction is the reaction between Mg(s) and O₂ (and the reaction between Fe(s) and oxygen)? What should be the products of these reactions?
  recall that metal oxides are basic - that is, they form metal hydroxides in aqueous solution. Pay attention to this - why are you told to put some water on the product of the combustion of Mg and then add an indicator?

• For the reactions of CO₂:
• Do a double-displacement reaction between NaHCO₃ and HCl; you should form H₂CO₃. Recall our discussion of D-D reactions which are driven by gas formation. This is an example of such a reaction - the carbonic acid formed decomposes into carbon dioxide gas and water.
• Recall that nonmetal oxides, such as CO₂, are acidic - they form acids is aqueous solutions. What acid do you suppose we form when we bubble carbon dioxide in water?
• For the reaction between CO₂(g) and Ca(OH)₂: we form a carbonate and water. What do you recall about the solubility of carbonates from chapter 4?

• For the SO₂ reactions:
• First, do the double displacement between sodium sulfite and sulfuric acid; you will form H₂SO₃. Sulfurous acid (H₂SO₃) is unstable and behaves much like carbonic acid - it falls apart to give water and SO₂.
• When you pull some SO₂ from the baggie and bubble it into water, write the reaction as SO₃ + H₂O(l) --> (what acid do you think you get?) We do this because SO₃ is also a product of the reaction in the baggie and it is much easier to balance the acid formation reaction using sulfur trioxide.

• For the NO₂ reactions:
• the oxygen generating reaction is just like you did before (decomposition of hydrogen peroxide)
• The metathesis reaction between potassium nitrite and sulfuric acid will give a salt and nitrous acid
• NOTE THIS: aqueous nitrous acid disproportionates rapidly to give nitric acid, water, and NO(g). A disproportionation reaction is a redox reaction in which the same species is oxidized and reduced, Calculate the oxidation number of nitrogen in this reaction and see what's happening!
• the NO(g) produced by the disproportionation of nitrous acid then reacts with the oxygen gas produced above to give NO₂ (the brown death gas.)
• NO₂(g) reacts with water to give nitric acid and NO(g). Does this explain why the water solution with NO₂ bubbled into it is so acidic? Is this a disproportionation reaction? How do you know?

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