1. Reactions in Aqueous Solutions
Unit 4:
Reactions in Aqueous Solutions
Day 8: Metathesis Reactions and Gravimetric Analysis

2. Warm Up TIME: 4 MINUTES WHEN DONE: Show me for a stamp
WITHOUT LOOKING AT YOUR FLASH CARDS, FILL OUT THE FOLLOWING TABLE:
TIME: 4 MINUTES
WHEN DONE: Show me for a stamp
Name
Formula
Charge
NO2
Phosphate
NH4
Cyanide OH
HCO3
Hypochlorite

3. Agenda
Acids and Bases Reactions
Oxidation/Reduction Reactions

4. Acids
The Swedish physicist and chemist S. A. Arrhenius defined acids as substances that increase the concentration of H+ when dissolved in water.
Both the Danish chemist J. N. Brønsted and the British chemist T. M. Lowry defined them as proton donors.

5. Bases
Arrhenius defined bases as substances that increase the concentration of OH− when dissolved in water.
Brønsted and Lowry defined them as proton acceptors (react with H+)

6. Strong or Weak?
Strong acids completely dissociate in water; weak acids only partially dissociate.
Strong bases dissociate to metal cations and hydroxide anions in water; weak bases only partially react to produce hydroxide anions.

7. Learning Check 3 1 2

8. Strong vs. Weak Electrolytes
If we remember the common strong acids and bases (table 4.2) and that NH3 is a weak base, we can make reasonable predictions about the electrolytic strength of a lot of compounds!

9. Acid-Base Reactions
In an acid–base reaction, the acid (H2O above) donates a proton (H+) to the base (NH3 above).
Reactions between an acid and a base are called neutralization reactions.
When the base is a metal hydroxide, water and a salt (an ionic compound) are produced.

10. Ways to Write Metathesis Reactions
Molecular
Neutralization Reactions
(Not all form precipitate!)
Net Ionic
Complete Ionic

11. Neutralization Reactions
When a strong acid (like HCl) reacts with a strong base (like NaOH), the net ionic equation is circled below:
HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l)
H+(aq) + Cl−(aq) + Na+(aq) + OH−(aq) 
Na+(aq) + Cl−(aq) + H2O(l)
H+(aq) + OH−(aq)  H2O(l)

12. K+ and NO3–. H+ and OH–. H+ and NO3–. K+ and OH–.
Learning Check When nitric acid is neutralized by potassium hydroxide, the spectator ions are
K+ and NO3–.
H+ and OH–.
H+ and NO3–.
K+ and OH–.
Answer: a

13. Which compound below is not a strong acid?
HC2H3O2
H2SO4
HNO3
HBr
Answer: a

14. Learning Check
a) Write the balanced molecular equation for the reaction between aqueous solutions of acetic acid, HC2H3O2, and barium hydroxide, Ba(OH)2.
b) Write the net ionic equation for this reaction

15. Learning Check
a) Write the balanced molecular equation for the reaction between aqueous solutions of acetic acid, HC2H3O2, and barium hydroxide, Ba(OH)2.
2HC2H3O2(aq) + Ba(OH)2 (aq)  Ba(C2H3O2)2(aq)+2H2O(l)
b) Write the net ionic equation for this reaction
2H+(aq) + 2 C2H3O2-(aq) + Ba2+(aq) + 2 OH-(aq)  Ba2+(aq) + 2 C2H3O2-(aq) H2O (l)
2H+(aq) + 2 OH-(aq)  + 2H2O (l)

16. Metathesis Reactions Gas Forming Molecular Neutralization Reactions
(Not all form precipitate!)
Complete Ionic
Net Ionic

17. Gas-Forming Reactions
Some metathesis reactions do not give the product expected.
When a carbonate or bicarbonate reacts with an acid, the products are a salt, carbon dioxide, and water.
CaCO3(s) + 2 HCl(aq) CaCl2(aq) + CO2(g) + H2O(l)
NaHCO3(aq) + HBr(aq) NaBr(aq) + CO2(g) + H2O(l)
Na2S(aq) + H2SO4(aq)  Na2SO4(aq) + H2S(g)

18. OXIDATION – REDUCTION (REDOX REACTIONS)

19. Oxidation-Reduction Reactions
Loss of electrons is oxidation.
Gain of electrons is reduction.
One cannot occur without the other.
The reactions are often called redox reactions.

20. Oxidation-Reduction Reactions
Way to remember!!!!!!

21. Oxidation Numbers
To determine if an oxidation–reduction reaction has occurred, we assign an oxidation number to each element in a neutral compound or charged entity.

22. Rules to Assign Oxidation Numbers
Elements in their elemental form have an oxidation number of zero.
The oxidation number of a monatomic ion is the same as its charge.

23. Rules to Assign Oxidation Numbers
Nonmetals tend to have negative oxidation numbers, although some are positive in certain compounds or ions.
Oxygen has an oxidation number of −2, except in the peroxide ion, in which it has an oxidation number of −1.
Hydrogen is −1 when bonded to a metal, +1 when bonded to a nonmetal.

24. Rules to Assign Oxidation Numbers
Nonmetals tend to have negative oxidation numbers, although some are positive in certain compounds or ions.
Fluorine always has an oxidation number of −1.
The other halogens have an oxidation number of −1 when they are negative; they can have positive oxidation numbers, most notably in oxyanions (ex. Chlorate)

25. Rules to Assign Oxidation Numbers
The sum of the oxidation numbers in a neutral compound is zero.
The sum of the oxidation numbers in a polyatomic ion is the charge on the ion.

26. Look at Oxidation Number Rules
What is the oxidation state of Phosphorous in P2O5?
What is the oxidation state of Hydrogen in NaH?
What is the oxidation state of Chromium in Cr2O72- ?
What is the oxidation state of tin in SnBr4?
What is the oxidation state of Oxygen in BaO2?

27. What is the oxidation state of Phosphorous in P2O5
What is the oxidation state of Phosphorous in P2O5? = +5, because each oxygen has a -2 charge.
What is the oxidation state of Hydrogen in NaH? = -1, because hydrogen bonded to a metal is -1, +1 when bonded to a non-metal
What is the oxidation state of Chromium in Cr2O72- ? = +6, because each oxygen is -2 and the charge of the ion is -2 overall
What is the oxidation state of tin in SnBr4? = +4, because Br oxidation state is -1
What is the oxidation state of Oxygen in BaO2? = +2, because O2 is the peroxide ion -1

28. DISPLACEMENT REACTIONS and ACTIVITY SERIES

29. Displacement Reactions
In displacement reactions, ions oxidize an element.
In this reaction, silver ions oxidize copper metal:
Cu(s) + 2 Ag+(aq)  Cu2+(aq) + 2 Ag(s)
The reverse reaction does NOT occur. Why not?

30. Activity Series
Elements higher on the activity series are more reactive.
They are more likely to exist as ions.
Any metal on the list can be oxidized by the ions of the metal below it

31. Metal/Acid Displacement Reactions
The elements above hydrogen will react with acids to produce hydrogen gas.
The metal is oxidized to a cation.

32. Learning Check
Which of the following metals will be oxidized by Pb(NO3)2?
Zn, Cu, or Fe?
Write the balanced molecular equation for one.
Write the net ionic equation

33. Learning Check
Which of the following metals will be oxidized by Pb(NO3)2?
Zn, Cu, or Fe? Because Fe and Zn are above Pb on the activity series.
Write the balanced molecular equation for one:
Pb(NO3)2 (aq) + Zn(s)  Pb(s) + Zn(NO3)2 (aq)
Write the net ionic equation
Pb2+(aq) + Zn(s)  Pb(s) + Zn2+(aq)

34. MOLARITY and DILLUTION

35. volume of solution in liters
Molarity
The quantity of solute in a solution can matter to a chemist.
We call the amount dissolved its concentration.
Molarity is one way to measure the concentration of a solution:
moles of solute
volume of solution in liters
Molarity (M) =

36. Molarity Check
Which is more concentrated, a solution prepared by dissolving 21.0 grams of NaF (0.500 mol) in enough water to make 500 mL of solution, or a solution prepared dissolving 10.5 g (0.250 mol) of NaF in enough water to make 100 mL of solution?
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37. Molarity Check
Which is more concentrated, a solution prepare by dissolving 21.0 grams of NaF (0.500 mol) in enough water to make 500 mL of solution, or a solution prepared dissolving 10.5 g (0.250 mol) of NaF in enough water to mak 100 mL of solution? 21.0 g (0.500 mol) in 500 mL mol / L = 1 M 10.5 g (0.250 mol) in 100 mL mol / 0.1L = 2.5 M
© 2015 Pearson Education, Inc.

38. Mixing a Solution
To create a solution of a known molarity, weigh out a known mass (and, therefore, number of moles) of the solute.
Then add solute to a volumetric flask, and add solvent to the line on the neck of the flask.

39. Molarity Check
What is the molar concentration of K+ ions in a M solution of potassium carbonate?
© 2015 Pearson Education, Inc.

40. Molarity Check
What is the concentration of ammonia in a solution made by dissolving 3.75 grams of ammonia in L of water? How many grams of Na2SO4are there in 15 mL of 0.50 M Na2SO4? How many mL of 0.50 M Na2SO4 solution are needed to provide mol of this salt?
© 2015 Pearson Education, Inc.

41. Dilution One can also dilute a more concentrated solution by
using a pipet to deliver a volume of the solution to a new volumetric flask, and
adding solvent to the line on the neck of the new flask.

42. Dilution
The molarity of the new solution can be determined from the equation
Mc  Vc = Md  Vd,
where Mc and Md are the molarity of the concentrated and dilute solutions, respectively, and Vc and Vd are the volumes of the two solutions.

43. Dilution: Check 1.75 mL 8.75 mL 48.6 mL 57.1 mL 28570 mL
What volume of a 1.00 M stock solution of glucose must be used to make 500 mL of a 1.75 x 10-2 M glucose solution?
1.75 mL
8.75 mL
48.6 mL
57.1 mL
28570 mL

44. Using Molarities in Stoichiometric Calculations

45. Titration
A titration is an analytical technique in which one can calculate the concentration of a solute in a solution.

46. Titration
A solution of known concentration, called a standard solution, is used to determine the unknown concentration of another solution.
The reaction is complete at the equivalence point.

47. Making Hot Chocolate!
Make a cup of hot chocolate using exactly 28.0 g of chocolate mix in 200 mL of hot water. Then do the following calculations:
According to the nutrition label, there are exactly 23.0 g of sucrose (sugar) in the sample. What is the molar concentration of sucrose in your drink?
According the the nutrition label, there are 5.0 mg of “sodium” in your sample. This “sodium” is NaCl. Calculate the molarity of the sodium ion in your drink.

48. Warm Up Go get a chromebook and log in to webassign Agenda:
Webassign Q&A
Lab Preparation work