Solution Concentration. Concentration – how much solute dissolved in amount of solvent what is difference between concentrated and diluted?. Concentration. 3 different units of concentration a) percent by mass b) molarity (M) c) molality (m). Percent by mass. Formula OR .
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Solution Concentration • Concentration – how much solute dissolved in amount of solvent what is difference between concentrated and diluted?
Concentration • 3 different units of concentration a) percent by mass b) molarity (M) c) molality (m)
Percent by mass • Formula OR
Percent by mass • Ex prob: If 3.6 g NaCl is dissolved in 100 g H2O, what is the percent by mass? What is the solute? NaCl What is the solvent? H2O
Percent by mass • Mass of solute (NaCl) = 3.6 g • Mass solvent (H2O) = 100 g • Mass solution = 3.6 + 100 = 103.6 g
Percent by mass Percent by mass = 3.6 g x 100 103. 6 g = 3.5 % NaCl
Molarity • Defn - # of moles per liter of solution • Formula mol solute L solution • unit mol = M (capital M) L
Molarity Ex prob #1 • 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 0.70 mol = 0.250 L
Molarity ex prob #2 • 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 1 mol NaOH 1.1825 mol NaOH = 40 g NaOH
Molarity ex prob #2 Step 2: divide moles by volume (L) 1.1825 mol 2.37 mol/L NaOH or 2.37 M NaOH = 0.500 L
Molarity ex prob #3 • How many moles of solute are present in 1.5 L of 2.4 M NaCl? How many grams? # moles = volume x molarity 2.4 mol NaCl 1.5 L x = 3.6 mol NaCl L
Molarity ex prob #3 • moles to grams 58.5 g NaCl 3.6 mol NaCl = 210.6 g NaCl 1 mol NaCl
Molality • Defn - # moles of solute in one kg solvent • Formula mol solute kg solvent • Units mol = m (lower case m) kg
Molality ex problem • 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 1 mol NaCl 0.14 mol NaCl = 58.5 g NaCl
Molality ex problem Step 2: divide by mass (kg) 0.55 mol/kg NaCl or 0.55 m NaCl 0.14 mol NaCl = 0.255 kg
Diluting Solutions • Defn – add more solvent to original solution • Formula M1V1 = M2V2 M1 is more concentrated than M2
Diluting Solutions • What volume of a 2.0 M stock solution is needed to make 0.50 L of a 0.300 M solution? M1= 2.0 M M2= 0.300 M V1= ? V2= 0.50 L (2.0 M) V1 = (0.300 M)(0.50 L) V1 = 0.075 L
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? M1= 3.5 M M2= ? V1= 20.0 mL V2= 100 mL (3.5 M)(20.0 mL) = M2 (100.0 mL) M2 = 0.7 M