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Chapter 1

Chapter 1 Stoichiometry.pdf

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University of Florida
CHM 2045

Chapter 1 Stoichiometry Sunday, June 30, 2013 3:32 PM 1. Unit Conversion a. 0 Celsius = 32 Fahrenheit = freezing b. 10 Celsius = 50 Fahrenheit i. -10 C = 32-18F = 14 F ii. -20 C = 14-18 F = -4 F iii. -30 C = -4 -18 F = -22 F iv. -40 C = -22 - 18 F = -40 F c. Density is a measured quantity, determined experimentally i. ρ=m/v ii. d. Specific Gravity i. Ratio of the density of a substance compared to the density (mass/sameunit volume) of a reference substance, usually water ii. e. Mass percent of a solute i. f. First step in unit conversionis determine units you are looking for g. Molar volume of a gas is 22.4 liters i. There are 22.4 liters in one mole of a substance 2. Elemental Analysis a. Fundamental process of elemental analysis involvesoxidizing an unknown completelyand collecting the products b. Mass percent of a compound i. ii. Mass percent is independent of the total mass of the sample compound 1) The mass percent of hydrogen in H20 will always be the same, regardless if you have 30 grams of H20 or 400 grams c. Mass ratio/percentcan be used to identify a specific compound in a process called combustionanalysis d. "Which of the following samples yields the MOST moles of sodium cation?" = "Which salt has the greatest mass percent of sodium?" e. Empirical formula i. Smallest whole number ratio of the atomsin a compound ii. Start by assuming a 100-gram sample iii. f. Combustion analysis i. Determinesthe mass percent of each componentelementin an unknown compound ii. Accomplished by oxidizing the unknown with excess oxygen iii. When a hydrocarbon is oxidized, CO2 and H20 are formed 1) CO2 and H20 can be separated using various methods a) Passing CO2 gas and H20 vapor across a hygroscopicsalt of known mass i) The salt absorbs the water, increasing its mass ii) The salt does not react with CO2 ii) The salt does not react with CO2 iii) A good choice for the salt is either calcium chloride or magnesium sulfate iv) The remaining gas is passed across a sample of KOH of known mass v) KOH undergoes a combination reaction with CO2 to form potassium bicarbonate KHCO3 vi) Now that we know the mass of H20 and CO2, we can determine the masses of C and H by multiplying the mass percent of each element my the mass of the oxide product that was collected vii) These numbers are then divided by the mass of the original sample b) By lowering the temperature,CO2 and H20 can be convertedinto their solid states i) Solids do not flow, so they can be collectedeasily 3. Solution Concentration a. Molarity i. Moles of a solute/literof solution b. Molality i. Moles of a solut
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