Review
A solution is a homogeneous mixture.The solvent is the major component of the
solution.The solute is the minor component and active
ingredient.A saturated solution holds the maximum
amount of solute that is theoretically possible for a given temperature.
Solution Concentration
Is one glass of tea stronger than the other?– What’s true about the “stronger” glass of tea?– How much tea does it have in it compared to
the other glass?
Concentrated vs. Dilute
How do we know how strong a solution is?Concentrated – LOTS of solute, little solventDilute – little solute, lots of solvent
Concentrated and dilute are not quantitativeMeasurements are needed to get precise
data
Concentrated vs. Dilute
Concentrated solution
Dilute solution
= solute particles
Solution Concentration
Concentration – a ratio comparing the amount of solute (the part) to the amount of solution (the whole).
Concentration is expressed by:– % by weight (% w/w)
– Mass of solute x 100 Mass of solution
– % by volume (% v/v)– Volume of solute x 100
Volume of solution
Solution Concentration
• parts per million (ppm) or parts per billion (ppb) for very low concentrations• Mass of solute x 1,000,000 Mass of solution
• molality (m)• Moles of solute Mass(kg) of solution• Used for high-concentration solutions or where
temperature changes significantly
Molarity
– Molarity (M) –The most common unit of concentration in chemistry
– Unit = moles per liter (mol/L)– Or just M
Formula:
– Example: 1.500 mol/L = 1.500 M– read as “1.500 Molar”
solution of Liters
solute of moles Molarity
Molarity
What is the Molar concentration of a sol’n if 0.198 mol KNO3 is dissolved in enough water to make 0.800 L?
M 0.248L 0.800
KNO mol 0.198 Molarity 3
Molarity
What is the Molar concentration of a sol’n if 292 grams of NaCl (MM = 58.44 g/mol) is dissolved in enough water to make 800. mL? Convert g of NaCl to mol of NaCl
Convert mL to L
Determine Molarity
292gNaCl x 1mol NaCl 58.44g NaCl
= 5.00mol NaCl
800.mL x 1 Liter 1000mL
= 0.800L
Molarity = 5.00mol 0.800L
Molarity = 6.25M
Molarity
What is the Molar concentration of a sol’n if 10.5 grams of glucose (Molar Mass = 180.18 g/mol) is dissolved in enough water to make 20.0 mL of sol’n?
– Convert g of glucose to mol of glucose.
– Convert mL to L.
– Determine Molarity
10.5g glucose x 1mol glucose 180.18g glucose
= 0.0583mol glucose
20.0mL x 1 Liter 1000mL
= 0.0200L
Molarity = 0.0583mol 0.0200L
Molarity = 2.92M
Boiling Point Elevation & Freezing Point Depression
• Concentration affects boiling points and freezing points• The greater the concentration, the greater the effect
• Increasing concentration raises the boiling point• Adding salt to boiling pasta cooks it at a hotter temperature
• Increasing concentration lowers freezing point• Adding salt/brine to icy roads causes water to freeze at a
lower temperature, melting ice and snow• Some solutes have greater affect than others
• Ionic compounds dissociate into multiple ions, increasing the number of particles in solution
• C12H22O11(s) → C12H22O11(aq)
• NaCl(s) → Na+(aq) + Cl-(aq)
• CaCl2(s) → Ca2+(aq) + 2Cl-(aq)
1 particle
2 particles
3 particles
Normal Freezing Point
Freezing Point and NaCl Concentration
Percent by Weight
% by weight (% w/w)
What is the % w/w of a solution if 3.00 grams of NaCl are dissolved in 17.00 g of water?– mass of solute = 3.00 g
– mass of solution = 3.00 g + 17.00 g = 20.00 g
– (3.00 g / 20.00 g) x 100% = 15.0% w/w
100% x solution of mass total
solute of mass %w/w
Percent by Volume
% by volume (% v/v)
What is the % v/v of a solution if 20.0 mL of alcohol are dissolved in 50.0 mL of solution?– volume of solute = 20.0 mL
– volume of solution = 50.0 mL
– (20.0 mL / 50.0 mL) x 100% = 40.0%
100% x solution of volume total
solute of volume %v/v