Use Avogadro’s number and molar amounts 0.05 mol (NH 4 ) 2 SO 4 6.02 x 10 23 molecules CaSO 4 1 mol CaSO 4 x 3 mol CaSO 4 3 mol (NH 4 ) 2 SO 4 x = 3.01 x 10 22 molecules CaSO 4
20 In Summary Using only balanced reaction equations , the periodic table and Avogadro’s number one can find: - Formula mass (molar mass) of any reactant/product - Number of moles of any reactant/product (used/produced) - Mass of any reactant/product used/produced - Number of atoms of any reactant/product (used/produced) - The limiting reagent and the excess reagent(s) An immense amount of information comes from something so simple as a written reaction equation!!
21 Solutions • A solution is a homogeneous mixture of some solute and some solvent – Homogeneous – cannot be separated by filtration, single phase – Usually we deal with aqueous solutions • The component of the solution that changes state is called the solute – Generally, “what gets dissolved” • The component that keeps its state is called the solvent – Generally, “what does the dissolving” • If both components start in the same state, the major component is always the solvent
22 Describing Solutions • Because solutions are mixtures, the composition can vary from one sample to another – pure solutions have constant composition – water samples from different bodies of water have different amounts of salt • An accurate description will tell you how much of each component is present – Usually described as a concentration • Often a “ percentage” or “parts”
23 Solution Concentration • Solutions are simplistically described as dilute or concentrated • Dilute solutions have a small amount of solute compared to solvent • Concentrated solutions have a large amount of solute compared to solvent – Not necessarily intuitive
24 Concentrations—Quantitative Descriptions of Solutions • A more precise method for describing a solution is to quantify the amount of solute in a given amount of solution • Concentration is the amount of solute in a given amount of solution – Occasionally based on solvent amount • Not very useful or common
25 Molarity • Most common unit of concentration is molarity (M) • Defined as moles of solute per 1 liter of solution • Used because it describes, in a way, how many molecules of solute are in each liter of solution Moles solute L solution M = * Molarity can be used as a conversion factor between moles and L *
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