CHEMISTRY 108 – Help Sheet #3 Prepared by Kelly Jetzer – Fall, 2014 – Chemistry Learning Center http://www.chem.wisc.edu/areas/clc (Resource page) Nuggets: Combustion (complete vs. incomplete), hydrocarbons (alkanes), atmospheric composition, % to ppm conversions, layers of the atmosphere, criteria pollutants, density Combustion - burning; rapid chemical reaction of a fuel with oxygen, releasing energy. Complete combustion - (of hydrocarbons) produces carbon dioxide and water Ex: Methane complete combustion: CH4 + 2O2 ! CO2 + 2H2O Incomplete combustion - (of hydrocarbons), when oxygen is in short supply, produces carbon monoxide and water Ex: Methane incomplete combustion: CH4 + 3/2O2 ! CO + 2H2O Hydrocarbons- compounds containing only carbon and hydrogen Memorize these hydrocarbons, the first four Alkanes (formula = CnH(2n+2)) Methane: CH4 Ethane: C2H6 Propane: C3H8 Butane: C4H10 Atmospheric Composition: Nitrogen (N2): 78% Oxygen (O2): 21% Argon (Ar): 0.94% Air quality is determined by the other 0.06%. ppm - parts per million = % * 10,000 (ex: 0.0395% CO2 in atmosphere = 395ppm) To convert ppm to %, divide by 10,000 (ex: 18ppm Ne in atmosphere = 0.0018%) Layers of the Atmosphere: Troposphere – where we live, from earth’s surface up to ~15km, atmospheric composition data refers to this layer. Stratosphere – from 15 – 90km above earth’s surface, includes the ozone layer Beyond the stratosphere are the mesosphere and ionosphere (which we don’t study in this course). Criteria Pollutants – atmospheric pollutants regulated by the EPA, due to their toxicity and danger to health and the environment Carbon monoxide – (CO) the silent killer, formed by incomplete combustion Natural source: forest fires Man-made source: car engine, cigarette smoking Sulfur dioxide - (SO2) “washes out in the rain” (an acid rain contributor) S + O2 ! SO2 2SO2 + O2 ! 2SO3 SO3 + H2O ! H2SO4 (This is sulfuric acid. Memorize this formula!) (Acid rain equation) Natural source: volcanoes Man-made source: coal-burning Nitrogen oxides (NOx = NO and NO2) form only at high temperatures (Atmospheric N2 and O2 don’t normally react with each other under “normal” conditions.) contributes to acid rain N2 + O2 !(HIGH TEMPS!) 2NO 2NO + O2 ! 2NO2 (occurs if NO concentration is high!) NO + O2 + VOC + •OH ! NO2 + other stuff (occurs if NO concentration is low) 4NO2 + O2 + 2H2O ! 4HNO3 (This is nitric acid. Memorize this formula!) (Acid rain equation) NO2 !(with <600nm light) O + NO (This reaction leads to tropospheric ozone!) Natural sources: lightning, forest fires, volcanoes Man-made sources: engines, industry Ozone (O3): A secondary pollutant, forms only if NO2 is present, concentration increases throughout daylight hours, then drops off when no sunlight is available to break up the NO2 See equations for NOx for the source of the O atom needed in the production of tropospheric ozone, then O + O2 ! O3 Natural source: lightning Man-made source: engines PM2.5 + PM10 particulates like soot, ash, dust, often produced as a byproduct of combustion PM2.5 Natural sources: forest fires Man-made sources: coal burning, industry, woodstoves PM10 Sources: construction, mining, agriculture, road dust, crushing & grinding mass Density (a physical property) D = volume CHEMISTRY 108 – Practice Questions for Quiz 3 Prepared by Kelly Jetzer – Fall, 2014 – Chemistry Learning Center http://www.chem.wisc.edu/areas/clc (Resource page) 1. Write the balanced chemical equation for the combustion of propane, when oxygen is in short supply. 2. Write the balanced chemical equation for the complete combustion of ethane. 3. Write the name, chemical formula, and % of the three most abundant gases in the troposphere. Name Formula % 4. Neon makes up 0.001818% of our atmosphere. State this amount in ppm. 5. What layer of the atmosphere do we live in?_______________ 6. What layer includes the ozone layer?__________________ 7. List the criteria pollutants. Underline the ones that result (either directly or indirectly) from combustion. 1. 2. 3. 4. 5. Write a balanced equation for the formation of each pollutant (except for particulate matter). State one natural, and one man-‐made source for each of the pollutants you underlined. 8. Explain how carbon monoxide can kill you. Be specific. 9. Write the balanced chemical equation for the reaction of sodium bicarbonate with hydrochloric acid. 10. Silver’s density is 10.5 g/cm3. What is the mass of a 48.4mL chunk of pure silver? Would a 48.4mL chunk of gold weigh more or less than this volume of silver? (Note: gold’s density is 19.3g/cm3.) CHEMISTRY 108 – Practice Questions for Quiz 3 - KEY Prepared by Kelly Jetzer – Fall, 2014 – Chemistry Learning Center http://www.chem.wisc.edu/areas/clc (Resource page) 1. Write the balanced chemical equation for the combustion of propane, when oxygen is in short supply. C3H8 + 7/2 O2 ! 3CO + 4H2O or 2C3H8 + 7 O2 ! 6CO + 8H2O 2. Write the balanced chemical equation for the complete combustion of ethane. C2H6 + 7/2 O2 ! 2CO2 + 3H2O or 2C2H6 + 7 O2 ! 4CO2 + 6H2O 3. Write the name, chemical formula, and % of the three most abundant gases in the troposphere. Name Formula % Nitrogen N2 78 Oxygen O2 21 Argon Ar 0.94 4. Neon makes up 0.001818% of our atmosphere. State this amount in ppm. 0.001818 * 10,000 = 18.18ppm 5. What layer of the atmosphere do we live in?_____troposphere___________ 6. What layer includes the ozone layer?_________stratosphere_________ 7. List the criteria pollutants. Underline the ones that result (either directly or indirectly) from combustion. 1. carbon monoxide (CO) from incomplete combustion forest fires, car engines C + ½ O2 ! CO 2. sulfur oxides (SOx) volcanoes, coal-‐burning S + O2 ! SO2 3. nitrogen oxides (NOx) (needs high temp!) lightning, car engines N2 + O2 ! 2NO, then 2NO + O2 ! 2NO2 4. ozone (O3) (secondary pollutant) lightning, car engines (+ sunlight, 600nm) NO2 ! O + NO, then O + O2 ! O3 5. PM2.5+PM10 forest fires, coal-‐burning (for PM2.5) mining and road dust for PM10 Write a balanced equation for the formation of each pollutant (except for particulate matter). State one natural, and one man-‐made source for each of the pollutants you underlined. 8. Explain how carbon monoxide can kill you. Be specific. Since it is odorless and colorless, you can’t sense it. If you breathe in CO (from incomplete combustion – often from faulty furnace), it binds to the hemoglobin in red blood cells, taking the place of the necessary O2 that your cells need in order to function. If exposed to too high a concentration of CO for too long, eventually you die of hypoxia (oxygen starvation). Have a CO detector in your home! 9. Write the balanced chemical equation for the reaction of sodium bicarbonate with hydrochloric acid. NaHCO3(aq) + HCl(aq) ! NaCl(aq) + H2O(l) + CO2(g) 10. Silver’s density is 10.5 g/cm3. What is the mass of a 48.4mL chunk of pure silver? Would a 48.4mL chunk of gold weigh more or less than this volume of silver? (Note: gold’s density is 19.3g/cm3.) Density =mass/volume. Mass = Density * volume m= 10.5g/cm3* 48.4cm3 mass = 508g Since gold is more dense than silver, an equal volume of gold will weigh more than the silver.