Solutes and Solubility

Mixture

• Mixtures: made from physically mixing two or more substances together without a chemical reaction occurring.

• Mixing ionic compounds with water forms aqueous solutions of dissolved ions.

• The polar water molecules attract to the ions, tearing them apart from other ions and holding them away from other ions.

• This is called molecule-ion attraction.

O-

2

H+

H+

O-

2

H+

H+

O-

2

H+

H+

O -2

H+

H+

O -2H

+H

+

O-2

H+

H+

O-

2H+

H+

O-

2

H+

H+

O-2H+

H+

O-

2H+

H+

O-

2H+

H+

O-2

H+

H+

O-

2

H+

H+

O-

2

H+

H+

Na+

Cl-

Na+

Cl- Na+

Cl-

Na+

Cl-Na

+Cl-

Na+

Cl-

Na+

Cl-

Na+

Cl-

Na+

Cl- Na+

Cl- Na+

Cl-

Na+

Cl- Na+

Cl- Na+

Cl-

O-2

H+

H+

O-

2

H+

H+

O-2

H+

H+ O-2

H+

H+

O-2

H+

H+

O-2

H+

H+

O-

2

H+

H+

O-2

H+

H+

O-2

H+

H+

O-2

H+

H+

Na+ Cl-

Na+ Cl-

Na+ Cl-

Na+ Cl-Na+ Cl-

Na+ Cl-

Na+ Cl-

Na+ Cl-

Na+ Cl-

Na+ Cl-

Na+

Na+ Cl-Na+ Cl- Na+

Na+ Cl-Na+ Cl-

Na+ Cl-

O-2

H+

H+

O-2

H+

H+

O-2

H+

H+

O-2

H+

H+

O -2

H +

H +

O-

2

H+

H+

O-2

H+

H+

O-2

H+

H+

O-2

H+

H+

Na+ Cl-

Na+ Cl-

Na+ Cl-

Na+ Cl-Na+

Na+ Cl-

Na+ Cl-

Na+ Cl-

Na+ Cl-Na+

Na+ Cl-Na+ Cl-

O -2H +

H +

O-2

H+

H+

O-2

H+ H+

O-2

H+

H+

O-2 H+

H+

O-2

H+

H+

O-2

H+

H+

Na+

O-2

H+

H+

O-2

H+

H+

O-2

H+

H+

Cl- O-2

H+

H+

O-2

H+

H+

O-2H+

H+

O-2

H+

H+

Na+

O-2

H+

H+

O-2

H+

H+

O-2

H+

H+

Cl-

O-2

H+H+

O-2

H+

H+

O-2H+

H+

O-2

H+

H+ Partially positive ends of

the water molecules (hydrogen) attracts to the negatively charged

chloride ions.

Partially negative ends of

molecules (oxygen) attracts to the positively charged sodium

ions.

MOLECULE – ION ATTRACTION

Solubility• The quantity of solute that can be added to a

quantity of solvent to make a saturated solution at a given temperature and pressure.

Solubility Curve• Solubility Curve – a graphical representation of

the amount of substance that can dissolve into 100 g of water at a specific temperature (Celsius)

Y-axis: Solubility of substance

(g/100 g H2O)

X-axis: Temperature (Celsius)

Substances: Compound being

dissolved in water (H2O)

Interpreting a Solubility Curve• Each point on the solubility curve shows how many

grams can be dissolved at a specific temperature:

Each line shows how much

substance can dissolve as a

function of the temperature of

the solution.

Using a Solubility CurveHow many grams of potassium bromide (KBr) can dissolve in 100 grams of water at 20°C?

70g

Answer: 70 grams of KBr can

dissolve in 100g of water at

20°C

Practice Using Solubility CurveHow many grams of potassium nitrate (KNO3) can dissolve in 100 g of water at 60°C?

Answer: 130 g of KNO3 can dissolve in 100 g of H2O

130g

Solution Concentration • Saturated: The solution

holds as many dissolved particles as it can possibly hold

• Unsaturated: The solution holds fewer solute particles than can theoretically be dissolved, can add more solute.

• Supersaturated: A very rare situation where the solution holds more solute than is theoretically possible, unstable situation where the excess will precipitate if the solution is agitated

Saturated / Unsaturated / Supersaturated

• Saturated: solute = solubility• Unsaturated: solute < solubility

• Supersaturated: solute > solubility

NaNO3

Saturated

Unsaturated

Supersaturated

Factors Affecting Solubility

1) Temperature• For solid and liquid solutes, solubility in water

increases as temperature increases• For gaseous solutes, solubility in water decreases

as temperature increases

2) Pressure• For gaseous solutes, solubility increases as

pressure increases• Pressure does not affect solid or liquid solutes

3) Nature of Solute and Solvent (Like Dissolves Like)

• Polar solutes dissolve in polar solvents• Nonpolar solutes dissolve in nonpolar solvents

Factors Affecting Solubility

Checking for understanding

1. Explain the difference between saturated, unsaturated, and supersaturated solutions2. Explain how pressure and temperature affect solubility

Concentration

Concentration and molarity• a measure of the amount of solute dissolved in

a given quantity of solvent• A concentrated solution has a large amount of

solute• A dilute solution has a small amount of solute

1. Grams of solute/100 mL of solvent

Represents

Grams of solute 100mL of solvent

2. Parts Per Million (ppm)• Number of grams of solute in

1 million gram of solvent• One unit of concentration

used in pollution measurements that involve very low concentration

g solute g solvent

= ppm X 1,000,000

• A chemical analysis shows that there are 2.2 mg of lead in exactly 500 g of water. Convert this measurement to parts per million.

mass of solute: 2.2 mgmass of solvent: 500 gparts per million = ?

2.2 mg 1000 mg 1 g

= 2.2 x 10-3 g

2.2 x 10-3 g500 g

X 1,000,000 = 4.4 ppm

g solute g solvent

= ppm X 1,000,000

• Helium gas, 3.0 x 10-4 g is dissolved in 200.0g of water. Express this concentration in ppm.

mass of solute: 3.0 x 10-4 gmass of solvent: 200.0 gparts per million = ?

200 g X 1,000,000 = 1.5ppm

3.0 x 10-4 g

g solute g solvent

= ppm X 1,000,000

3. % by mass

% mass = g of soluteg of solution

x 100 %

4. % by volume

% volume = mL of solutemL of solution

• Percent by volume is often used to describe the concentration of alcohol in alcoholic beverages or in medications containing alcohol.

x 100 %

What is the percentage by mass of a solution made by dissolving 0.49 g of potassium sulfate in 12.70 g of water?

0.49 K2SO4

12.70g water

=

0.49 g of K2SO4

12.70g water + 0.49 g K2SO4 x 100 %

=3.7% K2SO4 by mass

% mass = g of soluteg of solution

=

• A 50.0 mL sample of an aqueous ethanol solution is distilled to yield 33.2 mL of ethanol. What is the percent by volume of ethanol in this solution?

% volume= mL of solutemL of solution

x 100 %

=66.4% ethanol by volume

33.2 mL of ethanol50.0 mL solution

x 100 %=

5. Molarity (M)

• Molarity (M) is a concentration unit of a solution expressed as moles of solute dissolved per liter of solution.

M = Moles of soluteLiters of solution

• What is the molarity of a potassium chloride solution that has a volume of 400.0 mL and contains 85.0 g KCl?

solute = 85 g KCl

solution = 400 mL

74.55 g KCl

1 mol KCl= 1.14 mol KCl

1000 mL

1 L= 0.4 L

= 2.85 MM = Moles L M =

1.14 mol 0.4 L

• An aqueous solution of sodium carbonate, Na2CO3, contains 53 g of solute in 215 mL of solution. What is it concentration (M)?

solute = 53 g Na2CO3

solution = 215 mL

105.99 g Na2CO3

1 mol Na2CO3 = 0.5 mol Na2CO3

1000 mL

1 L= 0.215 L

= 2.3 MM = Moles L

M = 0.5 mol0.215 L

• How many moles of sugar are dissolved in 202 mL of a 0.150 M solution?

Molarity = 0.150 M

mol = M · L = (0.150 mol/L)(0.202 L)= 0.0303 mol C12H22O11

solution= 202ml1000ml1L = 0.202 L

M = Moles L

• A mass of 98 g of sulfuric acid, H2SO4, is dissolved in water to prepare a 0.50 M solution. What is the volume of the solution in liters ?

Molarity = 0.50 Msolute = 1.0mol H2SO4

= 2.0 L H2SO4

solute = 98 g H2SO4

98.08 g H2SO4

1 mol H2SO4= 1.0 mol H2SO4

mol = M · L

M = Moles L

L = Moles M

= 1.0mol

0.50 M

5. Molality (m or molal)

• Solute in moles and the mass of solvent in kilograms;

Density of water = 1 g/ 1 mL

1 mL = 1 g 1 L = 1 Kg 1000 g = 1 Kg

For water only!

m = Moles of solute Kg of solvent

What is the molality of a solution with 9.3 mole of NaCl in 450 g of water?mols of solute = 9.3 mol

9.3 mol

0.45 Kg = 21 m

solution= 450g1000g1Kg = 0.45kg

m = Moles kg

m =

• Determine the molality of a solution of 560. g of acetone, CH3COCH3, in 620 g of water.

9.6 mol

0.62 Kg = 15.5 m

solute = 560g CH3COCH3 58.09g1 mol

= 9.6 mol CH3COCH3

solution= 620g1000g1Kg = 0.62kg

m = Moles kg

=

Checking for understandingFormula Resulting units

g of solute/100mL of solventParts per million% by mass% by volumeMolarity Molality

Dilution

Concentration of Solution• Dilution is the process of preparing a less concentrated

solution from a more concentrated one.

moles of solute before dilution = moles of solute after dilution

MiVi = MfVf

Making a Dilute Solution

Timberlake, Chemistry 7th Edition, page 344

initial solution

removesample

diluted solution

same number ofmoles of solutein a larger volume

mix

moles ofsolute

How would you prepare 60.0 mL of 0.2 MHNO3 from a stock solution of 4.00 M HNO3?

MiVi = MfVf

Mi = 4.00 mol/L Mf = 0.200mol/L Vf = 0.06 L Vi = ? L

Vi =MfVf

Mi

=(0.200mol/L ) ( 0.06L)

(4.00 mol/L)= 0.003 L = 3 mL HNO3

3 mL of HNO3 + 57 mL of water= 60 mL of solution

How to mix a Standard Solution

Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 480

Wash bottle

Volume marker(calibration mark)

Weighedamount of solute

Process of Making a Standard Solution from Liquids

Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 483

In an experiment, a student needs 250.0 mL of a 0.100 M CuCl2 solution. A stock solution of 2.00 M CuCl2 is available.

How much of the stock solution is needed?

To make the solution:

1) Pipet 12.5 mL of stock solution into a 250.0 mL volumetric flask.

2) Carefully dilute with water to the calibration mark.

MiVi = MfVf

Mi = 2.00 mol/L Mf = 0.100mol/L Vf = 250.0mL Vi = ? L

Vi =MfVf

Mi

=(0.100mol/L ) ( 2.50L)

(2.00 mol/L)= 0.0125 L = 12.5 mL CuCl2

Preparing Solutions

How to prepare 500 mL of 1.54 M NaCl solution–mass 45.0 g of NaCl– add water until total

volume is 500 mL500 mL

volumetricflask

500 mLmark

45.0 g NaClsolute

500 mLvolumetric

flask

Preparing Solutions

500 mL of 1.54M NaCl

500 mLwater

45.0 gNaCl

– mass 45.0 g of NaCl– add water until total volume is

500 mL

– mass 45.0 g of NaCl– add 0.500 kg of water

500 mLmark

1.54m NaCl in 0.500 kg of water

molality molarity

Colligative Properties

Colligative Properties

• A property that depends only upon the number of solute particles (concentration), and not upon their identity.

• Three Important Colligative Properties of Solutions.– Vapor-pressure lowering– Boiling-point elevation– Freezing-point depression

      

 

Vapor-Pressure Lowering• Vapor pressure: is the

pressure exerted by a vapor that is in dynamic equilibrium with its liquid in a closed system.– A solution that contains

a solute that is nonvolatile (not easily vaporized) always has a lower vapor pressure that the pure solvent.

• This is true because in a solution, solute particles reduce the number of free solvent particles able to escape the liquid.

Freezing-Point Depression

• Freezing-Point Depression: The difference in temperature between the freezing point of a solution and the freezing point of the pure solvent (water).– The presence of a solute in water disrupts the

formation of the orderly pattern of ice. – Therefore more kinetic energy must be withdrawn

from a solution than from the pure solvent to cause the solution to solidify.

– Solution containing solute causes decrease in freezing point.

Freezing-Point Depression

Boiling-Point Elevation• Boiling Point: The temperature

at which the vapor pressure of the liquid phase equals atmospheric pressure.

• Boiling-Point Elevation: The difference in temperature between the boiling point of a solution and the boiling point of the pure solvent.

Boiling-Point Elevation• Because of the decrease in

vapor pressure, additional kinetic energy must be added to raise the vapor pressure of the liquid phase of the solution to atmospheric pressure to initiate boiling.

• The boiling point of a solution is higher than the boiling point of the pure solvent.

1) The higher the concentration of solute is, the higher the boiling point and the lower the freezing point will be.Which of the following solutions will boil at the

highest temperature?a) 100 g NaCl in 1000 g of water b) 100 g NaCl in 500 g waterc) 100 g NaCl in 250 g of water d) 100 g NaCl in 125 g of water

The answer is D because it has the highest concentration

2) The more particles that a solute ionizes into, the higher the boiling point and the lower the freezing point will be.

Which of the following solutions will boil at the highest temperature?

a) 1 mole C6H12O6 in 500 g of water

b) 1 mole KBr in 500 g of waterc) 1 mole MgF2 in 500 g of water

d) 1 mole AlCl3 in 500 g of water

The answer is D because AlCl3 breaks into 4 particles, the most of any of the choices.

Electrolytes vs.

Nonelectrolytes

Electrolyte

• Most ionic compounds and many acids dissolve well in water.

• These are called electrolytes, because they cause the solution to conduct electricity due to the free-moving ions.

• They ionize 100% in water to yield ions in a reaction that resembles a decomposition reaction.

• The reaction is called dissociation, and it is a physical change, not a chemical change.

• The more ions a solute breaks up into, the higher the boiling point and the lower the freezing point of the solution will be.

Electrolytes Free moving ions will conduct

electricityNaCl(s) Na+1(aq) + Cl-1

(aq)

2 moles ofdissolved ions total

Nonelectrolytes

• Substances formed from covalent bonding do not dissolve into ions upon entering the water.

• These include polar molecules that dissolve, but do not ionize.

• These include sugar (C6H12O6, C12H22O11), antifreeze (CH2OHCH2OH ) and alcohol (C2H5OH).

• These have less impact on the melting and boiling point of a solution than ionic compounds do, because they do not break up any further.

NonelectrolyteC12H22O11 (s) C12H22O11 (aq)

No ions are formed, so

no electricity can be

conducted.One mole of sucrose dissolves to form one mole of dissolved sucrose.

Checking for understandingList at least 3 characteristics for each:

ElectrolytesNonelectrolytes