Bell Work

1
Bell Work

• Why is it important to understand limiting and
  excess reactants?

2
Reactions in Aqueous Solution

• Chapter 4

3
Reactions in Aqueous Solution

• Most of the reactions considered in Chapter 3
  involved pure substances reacting with each
  other.
• Most of the reactions that occur in the world
  involve ions or molecules dissolved in water
  (aqueous solution).

4
Review

• Solution homogeneous mixture
• Solute what is being dissolved
• Solvent what is doing the dissolving

5
Molarity

• The concentration of a solute in solution can be
  expressed in terms of molarity.
• molarity (M) moles of solute
• Liter of solution
• The symbol is commonly used to represent
  the molarity of a substance in solution.

6
Molarity

• For a solution containing 1.20 moles of substance
  A in 2.50 L of solution,
• A 1.20 mole 0.480 mole/L or .480 M 2.50L
  

7
What do we use it for?

• Conversions
• What mass of K3PO4 is required to prepare 4.00
  Liters of 1.50 M solution?
• 4.00 L 1.50 mol
• -------- x ------------- x --------
• 1 1 L 1 mol

8
Molarity

• How would you prepare 0.125 M NaOH Solution?
• molarity moles
• Liter
• mole mass (g)
• molecular mass (g/mole)

9
Molarity
5 g of NaOH dissolved in 1 L of Water
10
Molality

• Similar to molarity except mols per kg
• Abbreviated as m

11
Science Bell Work

• Tell me if the following problems are molarity or
  molality problems, then solve for the unknown.
• What mass of water is required to dissolve 100 g
  NaCl to prepare 1.50 m solution?
• What volume of 0.750 M solution can be prepared
  using 90.0 g of NH4Cl?

12
Molarity (cont)

• When an ionic solid dissolves in water, the
  cations and anions separate from one another.
• This process can be represented by a chemical
  equation in which the reactant is the solid and
  the products are the positive and negative ions
  in water solution.
• Ionic solids are commonly described as strong
  electrolytes
• The ions they contain are good conductors of
  electricity in aqueous solutions.

13
Electrolytes

• Strong electrolytes soluble ionic compounds
  (those containing metals, nonmetals, and the
  ammonium ion)
• Weak electrolytes partially soluble ionic
  compounds, ionizable molecular compounds (acetic
  acid)
• Nonelectrolytes solids (insoluble ionic
  compounds), molecular compounds

14
Review with molarity and molality
15
Precipitation Reactions

• A precipitation reaction is a reaction which
  results in the formation of an insoluble product,
  or precipitate.
• A precipitation is an insoluble solid that
  separates form the solution.
• Precipitations reactions usually involve ionic
  compounds. They result from double displacement
  reactions.
• Know your solubility Rules!!!

16
Solubility Rules

• Group 1 ions and Ammonium form soluble salts
• Na NO3, NaF , K3PO4
• NH4F, (NH4)CO3
• CH3COO- All acetates are soluble.
• Na CH3COO, NH4 CH3COO , Ca(CH3COO)2
• NO3- All nitrates are soluble.
• Na NO3, NH4 NO3 , Ca(NO3)2
• CH3COO- All acetates are soluble.
• Na CH3COO, NH4 CH3COO , Ca(CH3COO)2

17
Solubility Rules

• Cl- All chlorides are soluble except AgCl,
  Hg2Cl2, PbCl2.
• CaCl2, NH4 Cl , Al Cl3
• Other Halides generally follow like Chloride
  except Fluoride
• CaI2 yes CaF2 not

18
More Solubility Rules

• SO42- Most sulfates are soluble exceptions
  include SrSO4, BaSO4, PbSO4
• CuSO4, CaSO4, Na2SO4

19
More Solubility Rules

• CO32- All carbonates are insoluble except
  those with Group 1 elements or NH4.
• Na2CO3 , (NH4)2CO3 , K2CO3 soluble
• CaCO3 , Hg2CO3 , Al2(CO3)3 insoluble

20
More Solubility Rules

• OH- All hydroxides are insoluble except those
  of the Group 1 elements, Sr(OH)2 , Ba(OH)2 ,
  and Ca(OH)2 somewhat
• KOH, Sr(OH) 2 soluble
• Al(OH)3 and Fe(OH)3 insoluble

21
More Solubility Rules

• S2- All sulfides are insoluble except those with
  Group 1 2 elements and NH4.
• Na2S, (NH4)2S, and CaS soluble
• Fe2S3, Al2S3, and CuS insoluble

22
Precipitation Reactions

• Example
• When lead (II) nitrate reacts with sodium iodide
• Molecular equation
• Pb(NO3)2 (aq) 2 NaI (aq) ? PbI2 (s) 2
  NaNO3 (aq)
• PbI2 is insoluble therefore forms a solid
  precipitate.

23
Practice

• Decide if the products produced are soluble or
  insoluble. If soluble, then no precipitate
  forms
• CuSO4 and NaNO3
• Na2CO3 and CaCl2

24
Practice with precipitation reactions
25
Reactions in Aqueous Solution

• Since the chemical equations for these reactions
  involve ions in solution they are referred to as
  a net ionic equation.

26
Net Ionic Equation

• A chemical equation for a reaction involving ions
  in which only those species that actually react
  are included.
• Atom balance- There must be the same number of
  atoms on both sides.
• Charge balance- There must be the same total
  charge on both sides.

27
Net Ionic Equation

• Molecular Equation
• Pb(NO3)2 (aq) 2 NaI (aq) ? PbI2 (s) 2
  NaNO3 (aq)
• Ionic Equation
• Pb2 (aq) 2 NO3- (aq) 2 Na (aq) 2 I- (aq)
  ? PbI2 (s) 2 Na (aq) 2 NO3- (aq)

28
Net Ionic Equation

• Ionic Equation
• Pb2 (aq) 2 NO3- (aq) 2 Na (aq) 2 I- (aq)
  ? PbI2 (s) 2 Na (aq) 2 NO3- (aq)
• Net ionic equation
• Pb2 (aq) 2 I- (aq) ? PbI2 (s)

29
Practice

• Write a balanced molecular equation for each of
  the following pairs of substances.
• BaCl2 with Na2SO4
• K3PO4 with Ca(NO3)2
• Cr(NO3)3 with NaOH
• NaCl with Mg(NO3)2
• Using your solubility chart predict if a
  precipitate will form or not.
• Write the balanced ionic equation.
• Cancel out spectator ions.
• Write the net ionic equation.

30
Acid-Base Reactions

• Acids
• Acidic solutions have a sour taste.
• Vinegar, lemon juice, and soda are acidic.
• An acid is a species that produces H ions in
  water solution.
• Bases
• Basic solutions have a slippery feeling
• Ammonia, most detergents and cleaning agents are
  basic.
• A base is a species that produces OH- ions in
  water solution.

31
Acid-Base Reactions (cont)

• Strong acids ionize completely, forming H ions
  and anions.
• HCl (aq) H (aq) Cl - (aq)
• A weak acid is only partially ionized to H ions
  in water.
• HF (aq) H (aq) F - (aq)

32
Acid-Base Reactions (cont)

• Strong bases ionize completely, forming OH - ions
  and cations.
• NaOH (s) Na (aq) OH- (aq)
• A weak base produces OH - ions in a different
  way. They react with H2O molecules, acquiring H
  ions and leaving OH ions behind.
• NH3 (aq) H2O NH4 (aq) OH - (aq)

33
Common Strong Acids And Bases
34
Equations for Acid-Base Reactions

• When an acidic water solution is mixed with a
  basic water solution, an acid-base reaction
  occurs.
• The nature of the reaction and the equation
  depend on whether the acid and base involved are
  strong or weak.

35
Equations for Acid-Base Reactions

• Strong acid strong base (neutralization
  reaction)
• Net ionic equation
• H (aq) OH (aq) H2O

36
Equations for Acid-Base Reactions

• Weak acid strong base (2-step process)
• Net ionic equation
• HB (aq) H (aq) B (aq)
• H (aq) OH (aq) H2O
• Overall equation
• HB (aq) OH (aq) B (aq) H2O

37
Equations for Acid-Base Reactions

• Strong acid weak base (2-step process)
• Net ionic equation
• NH3 (aq) H2O NH4 (aq) OH (aq)
• H (aq) OH (aq) H2O
• Overall equation
• H (aq) NH3 (aq) NH4 (aq)