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Chemical Solutions (aqueous = water is the solvent)
Types of vessels (least to most precise):
Beaker Erlennmeyer flask Graduated cylinder Volumetric flask
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Goals
• Make solutions
• Dilute solutions
• Convert between different concentrations of solutions
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Facts of Life
• Mass is measured in Grams, mg, μg1g = 1000mg = 1000000µg
• Volume is measured in liters, mL, μL1L = 1000mL = 1000000 μL
• Density of water is 1 g / mL
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Facts of life (cont’d)
• Concentration means: amount of solute in a volume of solution
• Expressed 3 ways:– 1. percent – 2. mg/ mL– 3. molar
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Percent Solutions
• Per means “for every one”
• Cent means 100
• Example: a 5% sugar solution has
5 grams of sugar for 100g of solution
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Make 250 mL of a 3% starch solution
3 g / 100 g = 3 g / 100 mL because density of water is 1 g / mL
Set up a ratio:
3 g / 100 mL = ?g / 250 mL
Use 7.5 g of starch and bring to a volume of (BTV) 250 mL with water
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• 5 mg/mL has 5 milligrams of solute in 1 milliliter of solution
mg / mL Solutions
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Set up a ratio:
3 mg / 1 mL = ?mg / 250 mL
Use 750 mg of starch and bring to a volume of (BTV) 250 mL with water
Make a 250 mL of a 3 mg /mL starch solution
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Molar Solutions
• 1 mole is 6.02 x 1023 items
• Molecular weight or Formula weight is really the mass of 1 mole of molecules (see periodic table)
Example: 1 mol of sodium chloride (NaCl) has a mass of 58.44 g.
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A 1 Molar solution is 1 mol of solute /Liter of solution
• Make 250 mL of a 3 molar NaCl solution
Set up a ratio:
58.44 g /1 mol = ? g / 3 mol
3 moles has a mass of 175.3 g
3M = 3mol/L = 175.3g/1000mL = ? g/250mL
? = 43.8g
BTV of 250 mL
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Diluting Solutions
• Conc A x Vol. A = Conc B x Vol B
• Usually want 1 X solutions
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Example: Frozen Orange Juice
• Solution A is the frozen concentrate
• Solution B is the 1X juice you drink
• How concentrated is it?
• CA VA = CB VB
• (250mL)(?X) = (1000 mL)(1X)
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Answer:
Frozen OJ is 4X because ¼ of the final volume is the concentrated oj