CH1710-Lecture #7-Solutions/Solution Stoichiometryprofkatz.com/.../CH1710-Lecture-7-SolutionsSolution-Stoichiometry.pdf · Solutions and Solution Stoichiometry. ... Write the equation

Chapter 4

Solutions and Solution Stoichiometry

Solutions

Homogeneous mixtures are called solutions.

The component of the solution that changes state is called the solute.

The component that keeps its state is called the solvent.

If both components start in the same state, the major component is the solvent.

Gas in gas Air (O2 in N2)

Gas in liquid Carbonated water (CO2 in H2O)

Gas in solid H2 in palladium metal

Liquid in liquid Gasoline, tequila

Liquid in solid Dental amalgam (Hg in Ag)

Solid in liquid Salt water (NaCl in H2O)

Solid in solid Sterling silver (Cu in Ag)

Kinds of Solutions

Solvent and Solute in an Aqueous Solution

Solvent and Solute in an Aqueous Solution

The Solution Process

What Happens When a Solute Dissolves?

There are attractive forces between the solute particles holding them together.

There are also attractive forces between the solvent molecules.

When we mix the solute with the solvent, there are attractive forces between the solute particles and the solvent molecules.

If the attractions between solute and solvent are strong enough, the solute will dissolve.

Table Salt Dissolving in Water

In the case of an ionic compound

each ion is attracted to the surrounding water molecules and pulled off and away from the

crystal.

Sugar Dissolving in Water

molecular compounds

do not dissociate when

they dissolve

In the case of a molecular compound,

each molecule is surrounded by water

molecules and pulled off and away from the

crystal.

Electrolytes and

Nonelectrolytes

Salt vs. Sugar Dissolved in Water

ionic compounds

dissociate into ions when

they dissolve

molecular compounds

do not dissociate when

they dissolve

Ionic compounds dissociate into ions when

they dissolve.

Molecular compounds do not dissociate into ions

when they dissolve.

Electrolytes and Nonelectrolytes

Materials that dissolve in water to form a solution

that will conduct electricity are called

electrolytes.

Materials that dissolve in water to form a solution

that will not conduct electricity are called

nonelectrolytes.

ionic compounds

covalent compounds

AcidsAcids are molecular compounds that ionize when they

dissolve in water. The molecules are pulled apart by water.

The percentage of molecules that ionize varies.

Acids that ionize virtually 100% are called strong acids.

HCl(aq) ➜ H+(aq) + Cl−(aq)

Acids that only ionize a small percentage are called weak acids.

HF(aq) ⇔ H+(aq) + F−(aq)

Strong and Weak Electrolytes

Strong electrolytes are materials that dissolve completely as ions.

1) ionic compounds and strong acids 2) The solutions conduct electricity well.

Weak electrolytes are materials that dissolve mostly as molecules, but partially as ions.

1) weak acids 2) The solutions conduct electricity, but not well.

•  When ionic compounds dissolve in water, the

anions and cations are separated from each

other. This is called dissociation.

Na2S(aq) → 2 Na+(aq) + S2-(aq)

•  When compounds containing polyatomic ions

dissociate, the polyatomic group stays together

as one ion

Na2SO4(aq) → 2 Na+(aq) + SO42−(aq)

•  When strong acids dissolve in water, the

molecule ionizes into H+ and anions

H2SO4(aq) → 2 H+(aq) + SO42−(aq)

Dissociation vs IonizationWhen ionic compounds dissolve in water, the

anions and cations are separated from each other. This is called dissociation.

When compounds containing polyatomic ions dissociate, the polyatomic group stays together as one ion.

When strong acids dissolve in water, the molecule ionizes into H+ and anions.

•  When ionic compounds dissolve in water, the

anions and cations are separated from each

other. This is called dissociation.

Na2S(aq) → 2 Na+(aq) + S2-(aq)

•  When compounds containing polyatomic ions

dissociate, the polyatomic group stays together

as one ion

Na2SO4(aq) → 2 Na+(aq) + SO42−(aq)

•  When strong acids dissolve in water, the

molecule ionizes into H+ and anions

H2SO4(aq) → 2 H+(aq) + SO42−(aq)

•  When ionic compounds dissolve in water, the

anions and cations are separated from each

other. This is called dissociation.

Na2S(aq) → 2 Na+(aq) + S2-(aq)

•  When compounds containing polyatomic ions

dissociate, the polyatomic group stays together

as one ion

Na2SO4(aq) → 2 Na+(aq) + SO42−(aq)

•  When strong acids dissolve in water, the

molecule ionizes into H+ and anions

H2SO4(aq) → 2 H+(aq) + SO42−(aq)

Write the equation for the process that occurs when the following strong electrolytes dissolve in water

CaCl2

HNO3

(NH4)2CO3

CaCl2(aq) ➜ Ca2+(aq) + 2 Cl−(aq)

HNO3(aq) ➜ H+(aq) + NO3−(aq)

(NH4)2CO3(aq) ➜ 2 NH4+(aq) + CO3

2−(aq)

The Real Picture of Acid Ionization

HCl + H2O ➜ H3O+ + Cl−

hydronium ion

HCl ➜ H+ + Cl−

[ ]H Cl

H

HO O

H

H

H Cl+ +

+ -

strong acid water

chloride ion

Solubility

Solubility of Ionic Compounds

Some ionic compounds, such as NaCl, dissolve very well in water at room temperature.

Other ionic compounds, such as AgCl, dissolve hardly at all in water at room temperature.

Compounds that dissolve in a solvent are said to be soluble, where as those that do not are said to be insoluble.

Solubility Rules Compounds that Are Generally Soluble in Water

Compounds Containing the Following Ions are Generally

Soluble

Exceptions Insoluble

Li+, Na+, K+, NH4+ none

NO3-, C2H3O2 - none

Cl -, Br -, I - Ag+, Hg22+, Pb2+

SO4 - Ag+, Ca2+, Sr2+, Ba2+, Pb2+

Solubility Rules Compounds that Are Generally Insoluble in Water

Compounds Containing the Following Ions are Generally

Insoluble

Exceptions Soluble or Slightly Soluble

OH- Li+, Na+, K+, NH4+

Ca2+, Sr2+, Ba2+

S2- Li+, Na+, K+, NH4+

Ca2+, Sr2+, Ba2

CO32-, PO43-, CrO42- Li+, Na+, K+, NH4+

SO4 - Li+, Na+, K+, NH4+

Practice – Determine if each of the following is soluble in water

KOH

AgBr

CaCl2

Pb(NO3)2

PbSO4

KOH is soluble because it contains K

AgBr is insoluble; most bromides are soluble, but AgBr is an exception

CaCl2 is soluble; most chlorides are soluble, and CaCl2 is not an exception

Pb(NO3)2 is soluble because it contains NO3−

PbSO4 is insoluble; most sulfates are soluble, but PbSO4 is an exception

Solution Concentrations

Solution Concentration Qualitative Description

Dilute solutions have a small amount of solute compared to

solvent.

Concentrated solutions have a large amount of solute

compared to solvent.

Quantitative Descriptions of Solutions

One method for describing a solution is to quantify the amount of solute in a given amount of solution.

Solution Concentration - Molarity

Moles of solute per 1 liter of solution

Used because it describes how many molecules of solute in each liter of solution

mol LMolarity =

moles of solute

Liters of solution

How to prepare 1.000 L of a 1.000 M NaCl solution

First add 1 mole of NaCl to a 1.000 liter volumetric flask

--143417886.html

25.5 g KBr x

= 0.21429 mol KBr

1.00 mol KBr119.00 g KBr

1. Find the molarity of a solution that has 25.5 g KBr dissolved in 1.75 L of solution.

gKBr

molKBr

g

mol

molKBr

LKBr soln

= M

0.214

molarity, M =

= 0.12245 M KBr

0.214 mol KBr1.75 L KBr soln

0.122

2. What Is the molarity of a solution containing 3.4 g of NH3 (MM 17.03) in 200.0 mL of solution?

g NH3 mol NH3

mL sol’n L sol’n

M

Using Molarity in CalculationsMolarity shows the relationship between the moles

of solute and liters of solution.

If a sugar solution concentration is 2.0 M, then 1.0 liter of solution contains 2.0 moles of sugar.

Questions one might ask: What is the molarity of....?

How many liters contain....? How many moles....?

How many grams of....? How would I prepare....?

2.0 mol sugar1.0 L soln

1.0 L soln2.0 mol sugar

0.255 mol NaOH x = 2.04 L NaOH soln1.00 L NaOH soln0.125 mol NaOH

3. How many liters of 0.125 M NaOH contain 0.255 mol NaOH?

mol NaOH L NaOH soln

mol

L

Molarity=moles of solute

Liters of solution

4. Determine the mass of CaCl2 (MM = 110.98) in 1.75 L of 1.50 M solution.

L CaCl2 soln mol CaCl2 g CaCl2

mol

L

mol

g

1.75 L CaCl2 soln x x

= 291.32 g CaCl2

1.50 mol CaCl21.00 L CaCl2 soln

110.98 g CaCl21.00 mol CaCl2

5. How would you prepare 250.0 mL of a 1.000 M solution CuSO4·5 H2O (MM 249.69)? How many grams of CuSO4·5 H2O

are required ?

Dissolve 62.42 g of CuSO4·5H2O in enough water to total 250.0 mL

mL soln

mol CuSO4 · 5H2O

g CuSO4 · 5H2O

L soln

mol

L

mol

g

mL

L

250.0 mL soln x x

x = 62.42 g CuSO4 · 5H2O

1.000 L soln1000 mL soln

1.000 mol CuSO4 · 5H2O1.000 L soln

249.69 g CuSO4 · 5H2O1.000 mol CuSO4 · 5H2O

Dilution

DilutionOften, solutions are stored as concentrated stock solutions.

To make solutions of lower concentrations from these stock solutions, more solvent is added.

The amount of solute doesn’t change, just the volume of solution.

moles solute in solution 1 = moles solute in solution 2

( ) ·L1 = ( ) ·L2molL1

molL2

M1·V1 = M2·V2

6. What is the concentration of a solution prepared by diluting 45.0 mL of 8.25 M HNO3 to 135.0 mL?

M1V1 = M2V2

M1V1V2

= M2

( )(45.0 mL)(135.0 mL)

molL

8.25= 2.75 =2.75 Mmol

L

7. To what volume should you dilute 0.200 L of 15.0 M NaOH to make 3.00 M NaOH?

M1V1 = M2V2

M1V1M2

= V2

( )(0.200 L)( )

molL

15.0molL

3.00= 1.00 L

8. How would you prepare 200.0 mL of 0.25 M NaCl solution from a 2.0 M solution?

M1V1 = M2V2

Dilute 25 mL of 2.0 M stock solution up to 200.0 mL.

M2V2M1

= V1

( )(0.200 L)( )

molL

0.25molL

2.0 = 0.025 L

You have a bottle of 1 molar stock solution

But you WANT a 1 millimolar solution.

What will you do?

What will save your job? SERIAL DILUTION will!

“It’s a snap ! I’ll add 1.00 mL of

the stock solution to 999 mL of

water.”

“But we only need 100

microliters of the solution !!”

“Do you have any idea how much it

would cost to dispose of a liter of

that stuff?

It’s toxic !!”

Serial Dilution1.00 mL

+ 9.00 mL water

1.00 mL 1.00 mL 1.00 mL

+ 9.00 mL water

+ 9.00 mL water

+ 9.00 mL water

1.00 M 0.100 M 0.0100 M 0.00100 M 0.000100 M

stock solution

Solution Stoichiometry

Moles of A

Moles of B

Liters of a Solution of A

Liters of a Solution of B

Solution StoichiometryBecause molarity relates the moles of solute to the liters of solution, it can be

used to convert between amount of reactants and/or products in a chemical

reaction.

coefficients

mol L

mol L

mol

L

mol

mol

9. What volume of 0.150 M KCl is required to completely react with 0.150 L of 0.175 M Pb(NO3)2 in the reaction:

2 KCl(aq) + Pb(NO3)2(aq)➜ PbCl2(s) + 2 KNO3(aq)

L Pb(NO3)2 soln

mol KCl

mol Pb(NO3)2

L KCl soln

mol

L

0.150 L Pb(NO3)2 soln x x

x = 0.350 L KCl soln

0.175 mol Pb(NO3)21.00 L Pb(NO3)2 soln

2 mol KCl1mol Pb(NO3)2

1.00 L KCl soln0.150 mol KCl

10. 43.8 mL of 0.107 M HCl is needed to neutralize 37.6 mL of Ba(OH)2 solution. What is the molarity of the base?

2 HCl(aq) + Ba(OH)2(aq)➜ BaCl2(aq) + 2 H2O(aq)

L HCl soln

mol Ba(OH)2

molHCl

L Ba(OH)2 soln

mol Ba(OH)2

Molarity of Ba(OH)2 soln

0.0438 L HCl soln x

x = 0.00234 mol Ba(OH)2

0.107 mol HCl1.00 L HCl soln

1 mol Ba(OH)22 mol HCl

0.00234 mol Ba(OH)20.0376 L Ba(OH)2 soln

= 0.0623 M Ba(OH)2

The Big Picture of Stoichiometry

Moles of A

Moles of B

Mole to

Mole Ratio*

Liters of a Solution of A

Liters of a Solution of BMM

Grams of A

Grams of B

Molar Mass

Particles of A

Particles of B

Avogadro’s Number

*from balanced equation