AEW week3 - Chem 209 AEW Week 3 Friday 2:30-4:25 1 Chromium...

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Chem 209 AEW Week 3 September 21, 2007 Friday 2:30-4:25 1. Chromium compounds exhibit a variety of bright colors. When solid ammonium dichromate, (NH 4 ) 2 Cr 2 O 7 , a vivid orange compound, is ignited, a spectacular reaction occurs, as shown in the two photographs below. Although the reaction is somewhat more complex, let’s assume here that the products are solid chromium(III) oxide, nitrogen gas (consisting of N 2 molecules), and water vapor. Balance the equation for this reaction. 2. Baking soda (NaHCO 3 ) is often used as an antacid. It neutralizes excess hydrochloric acid secreted by the stomach: NaHCO 3 ( s ) + HCl( aq ) → NaCl( aq ) + H 2 O( l ) + CO 2 ( aq ) Milk of magnesia, which is an aqueous suspension of magnesium hydroxide, is also used as an antacid: Mg(OH) 2 ( s) + 2HCl( aq ) → 2H 2 O( l ) + MgCl 2 ( aq ) Which is the more effective antacid per gram, NaHCO 3 or Mg(OH) 2 ? 3. Potassium chromate, a bright yellow solid, is produced by the reaction of solid chromite ore (FeCr 2 O 4 ) with solid potassium carbonate and gaseous oxygen at high temperatures. The other products of the reaction are solid iron(III) oxide and gaseous carbon dioxide. In a particular experiment 169 kg of chromite ore, 298 kg of potassium carbonate, and 75.0 kg of oxygen were sealed in a reaction vessel and reacted at a high temperature. The amount of potassium chromate obtained was 194 kg. Calculate the percent yield of potassium chromate.
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4. Element X forms both a dichloride, XCl 2 , and a tetrachloride, XCl 4. Treatment of 10.00 g of XCl 2 with excess chlorine forms 12.55 g of XCl 4 .
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