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Published byKristian Bell Modified over 5 years ago

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Solution Concentration Concentration – how much solute dissolved in amount of solvent Concentration – how much solute dissolved in amount of solvent what is difference between concentrated and diluted?

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Concentration 3 different units of concentration 3 different units of concentration a)percent by mass b) molarity (M) c) molality (m)

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Percent by mass Formula FormulaOR

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Percent by mass Ex prob: If 3.6 g NaCl is dissolved in 100 g H 2 O, what is the percent by mass? Ex prob: If 3.6 g NaCl is dissolved in 100 g H 2 O, what is the percent by mass? solute What is the solute? NaCl What is the solvent? H2OH2OH2OH2O

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Percent by mass Mass of solute (NaCl) = Mass of solute (NaCl) = 3.6 g Mass solvent (H 2 O) = Mass solvent (H 2 O) = 100 g Mass solution = Mass solution = 3.6 + 100 = 103.6 g

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Percent by mass Percent by mass = 3.6 g x x 100 103. 6 g = 3.5 % NaCl

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Molarity Defn - # of moles per liter of solution Defn - # of moles per liter of solution Formula mol solute Formula mol solute L solution L solution unitmol = M (capital M) unitmol = M (capital M) L

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Molarity Ex prob #1 Molarity Ex prob #1 A solution has a volume of 250 mL and has 0.70 mol NaCl. What is the molarity? A solution has a volume of 250 mL and has 0.70 mol NaCl. What is the molarity? 2.8 mol/L or 2.8 M 0.250 L = 0.70 mol

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Molarity ex prob #2 What is the molarity of a solution made of 47.3 g NaOH in 500 mL water? What is the molarity of a solution made of 47.3 g NaOH in 500 mL water? step 1: convert grams to moles 47.3 g NaOH 40 g NaOH 1 mol NaOH = 1.1825 mol NaOH

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Molarity ex prob #2 Step 2: divide moles by volume (L) 2.37 mol/L NaOH or 2.37 M NaOH 0.500 L = 1.1825 mol

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Molarity ex prob #3 How many moles of solute are present in 1.5 L of 2.4 M NaCl? How many grams? How many moles of solute are present in 1.5 L of 2.4 M NaCl? How many grams? # moles = volume x molarity 1.5 L L 2.4 mol NaCl x = 3.6 mol NaCl

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Molarity ex prob #3 moles to grams moles to grams 3.6 mol NaCl 1 mol NaCl 58.5 g NaCl = 210.6 g NaCl

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Molality Defn - # moles of solute in one kg solvent Defn - # moles of solute in one kg solvent Formulamol solute Formulamol solute kg solvent Unitsmol = m (lower case m) Unitsmol = m (lower case m) kg kg

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Molality ex problem What is the molality of a solution with 8.4 g NaCl in 255 g of water? What is the molality of a solution with 8.4 g NaCl in 255 g of water? Step 1: convert grams to moles 8.4 g NaCl 58.5 g NaCl 1 mol NaCl = 0.14 mol NaCl

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Molality ex problem Step 2: divide by mass (kg) 0.55 mol/kg NaCl or 0.55 m NaCl 0.255 kg = 0.14 mol NaCl

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Diluting Solutions Defn – add more solvent to original solution Defn – add more solvent to original solution Formula Formula M 1 V 1 = M 2 V 2 M 1 is more concentrated than M 2

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Diluting Solutions What volume of a 2.0 M stock solution is needed to make 0.50 L of a 0.300 M solution? What volume of a 2.0 M stock solution is needed to make 0.50 L of a 0.300 M solution? M1=M1= V1=V1= M2=M2= V2=V2= 2.0 M0.300 M ? 0.50 L (2.0 M) V 1 = (0.300 M)(0.50 L) V 1 = 0.075 L

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Diluting Solutions If you dilute 20.0 mL of a 3.5 M solution to make 100.0 mL of solution, what is the molarity of the dilute solution? If you dilute 20.0 mL of a 3.5 M solution to make 100.0 mL of solution, what is the molarity of the dilute solution? M1=M1= V1=V1= M2=M2= V2=V2= 3.5 M? 20.0 mL 100 mL (3.5 M)(20.0 mL) = M 2 (100.0 mL) M 2 = 0.7 M

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