Solutions Review

Spring Final Exam

Definitions• Solution - homogeneous mixture

Solvent - present in greater amount

Solute - substance being dissolved

soluble: “will dissolve in”

miscible: refers to two liquids that mix evenly in all proportions

-- e.g., food coloring and water

Factors Affecting the Rate of Dissolution

1. temperature

2. particle size

3. mixing

4. nature of solvent or solute

With more mixing,rate

As temp. , rate

As size , rate

We can’t controlthis factor.

Solubility vs. Temperature

Timberlake, Chemistry 7th Edition, page 297

KI

NaNO 3

KN

O 3

Na 3PO 4

NaCl

Temperature (oC)

Sol

ubili

ty (

g so

lute

/ 10

0 g

H2O

)200

180

160

140

120

100

80

60

40

20

020 40 60 80 100

Gas SolubilityCH4

O2

CO

He

Temperature (oC)

Sol

ubili

ty (

mM

)

2.0

1.0

0 10 20 30 40 50

Higher Temperature

…Gas is LESS Soluble

Solubility

Temp. (oC)

Solubility(g/100 g

H2O)

KNO3 (s)

KCl (s)

HCl (g)

SOLUBILITYCURVE

unsaturated: sol’n could hold more solute;

saturated: sol’n has “just right” amt. of solute;

supersaturated: sol’n has “too much” solute dissolved in it;

how much solutedissolves in a givenamt. of solvent at agiven temp.

below the line

on the line

above the line

sudden stresscauses thismuch ppt

Describe each situation below.(A) Per 100 g H2O, 100 g NaNO3 @ 50oC.

(B) Cool sol’n (A) very slowly to 10oC.

(C) Quench sol’n (A) in an ice bath to 10oC.

unsaturated;all solute dissolves;clear sol’n.

supersaturated;extra solute remainsin sol’n; still clear

saturated; extra solute (20 g)can’t remain in sol’n and becomes visible

Concentration• A measure of the amount of solute

dissolved in a certain amount of solvent.• Concentrated solution has a large

amount of solute.• Dilute solution has a small amount of

solute• Separate from Saturated / unsaturated

Molarity

• The number of moles of solute in 1 Liter of the solution.

• M = moles/Liter• What is the molarity of a solution with 2.0

moles of NaCl in 4.0 Liters of solution.

Molarity

• What is the molarity of a solution with 3.0 moles dissolved in 250 mL of solution.

12 M

Making solutions

• 10.3 g of NaCl are dissolved in a small amount of water then diluted to 250 mL. What is the concentration?

0.70 M

Dilution

Adding solvent to a solution

Dilution• The number of moles of solute doesn’t

change if you add more solvent.• The moles before = the moles after

• M1 x V1 = M2 x V2

• M is concentration and V is volume.• Stock solutions are pre-made to known M

Practice

• 2.0 L of a 0.88 M solution are diluted to 3.8 L. What is the new molarity?

0.46 M

Making solutions

• How many grams of CaCl2 are needed

to make 625 mL of a 2.0 M solution?

139 g

Electrolytes

• Substances that conduct electricity when melted or dissolved in water.

• Conducting is charged pieces moving• Ionic compounds are electrolytes

– Fall apart into ions• When dissolved• When melted

Electrolytes

Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

(a) Nonelectrolyte (b) Weak electrolyte (c) Strong electrolyte