Chapter 9 Chemical Quantities

(gramsA  molsA )  (molsB  gramsB ) Here I give you mass of one you tell me mass of the other key? start and end w/ grams; but must cross thru mol bridge!!! Basic method? (gramsA  molsA )  (molsB  gramsB )

example How many grams of oxygen gas are required to completely react with 14.6 g of solid sodium to form sodium oxide, Na2O?

4Na + O2  2Na2O g 14.6 g mol Na mol O2 notice that there are always non-players. but they are needed for balancing the equation!

example cont’d mol bridge remember: they can only talk mol language from the balanced equation! 14.6 g Na 1 mol Na 1 mol O2 32.0 g O2 23.0 g Na 4 mol Na 1 mol O2 mol bridge = 5.08 g O2

example When 20.4 grams of sodium metal are mixed with chlorine gas, are 52.0 g of sodium chloride produced?

2Na + Cl2  2NaCl g 20.4 g mol NaCl mol Na

example cont’d mol bridge They can only talk mol language from the balanced equation! 20.4 g Na 2 mol Na 2mol NaCl = 51.9 g NaCl 1 mol NaCl 58.5 g NaCl mol bridge 23.0 g Na 1 mol Na

example Limestone, CaCO3, is heated to produce lime, calcium oxide, CaO, and carbon dioxide. How much limestone is required to produce 10.0 g of lime?

CaCO3  CaO + CO2 g 10.0 g mol CaO mol CaCO3

example cont’d mol bridge They can only talk mol language from the balanced equation! 10. g CaO 1 mol CaO 1mol CaCO3 = 17.8 g CaCO3 1 mol CaCO3 100.1g CaCO3 mol bridge 56.1 g CaO

summary gA gB PT PT molA molB BE

9.5 Mass Calculations: Comparing Two Reactions we can use all this to compare; for example, which store-bought antacid is more effective by weight… sodium bicarbonate and magnesium hydroxide are both used as antacids if you have 1.00 g of both which will eat the most acid?

NaHCO3 + HCl  NaCl + H2O + CO2 1) sodium bicarb? NaHCO3 + HCl  NaCl + H2O + CO2 1.00 g NaHCO3 1 mol NaHCO3 1 mol HCl = 1.19 x 10-2 mol mol bridge 84.01 g NaHCO3 1mol NaHCO3

2) magnesium hydroxide? mol bridge Mg(OH)2 + 2HCl  MgCl2 + 2H2O 1.00 g Mg(OH)2 1 mol Mg(OH)2 2 mol HCl 58.33 g Mg(OH)2 1 mol Mg(OH)2 mol bridge = 3.42 x 10-2 mol

Sorry, but equations Do Not describe: 1) Exact conditions * Temperature * Pressure * Volume 2) What the atoms are doing (e.g. not all of them react)