+ types of reactions ch. 4 part ii. + types of chemical reactions (3) precipitation reactions...

+

Types of Reactions

Ch. 4 Part II

+Types of Chemical Reactions (3)

Precipitation Reactions

Acid-Base Reactions

Oxidation-Reduction Reactions

+Precipitation Reactions

A precipitation reaction can also be called a double displacement reaction.

When ionic compounds dissolve in water, the resulting solution contains the separated ions.

If a solid forms from a combination of selected ions in solution, the solid must contain an anion part and cation part, and the net charge on the solid must be zero.

There are some simple solubility rules to help predict the products of reactions in aqueous solutions.

+Simple Rules for Solubility 1. Most nitrates (NO3

-) salts are soluble.

2. Most salts containing the alkali metal ions (Li+, Na+, K+, Cs+, Rb+) and the ammonium ion (NH4

+) are soluble.

3. Most chloride, bromide, and iodide salts are soluble. Notable exceptions are salts containing the ions Ag+, Pb+, and Hg2+

4.Most sulfate salts are soluble. Notable exceptions are BaSO4, PbSO4, HgSO4, and CaSO4

5.Most hydroxide salts are only slightly soluble. The important soluble hydroxides are NaOH and KOH. The compounds Ba(OH)2, Sr(OH)2, and Ca(OH)2 are slightly soluble.

6.Most sulfide (S2-), carbonate (CO32-), chromate (CrO4

2-), and phosphate (PO4

3-) salts are only slightly soluble.

Page 144

+Solubility Memorization Requirements for AP Exam

All sodium, potassium, ammonium, and nitrate salts are soluble in water.

**Memorization of “solubility rules” is beyond the scope of this course and the AP Exam.**

Rationale: Memorization of solubility rules does not deepen understanding of the big ideas.

+Predicting Reaction Products

To begin, focus on the ions in solution before any reaction occurs.

Complete and balance the following reactions, determining in each case, if a precipitate is formed.

KCl(aq) + Pb(NO3)2(aq)

AgNO3(aq) + MgBr2(aq)

Ca(OH)2(aq) + FeCl3(aq)

NaOH(aq) + HCl(aq)

+Describing Reactions in Solution

Formula Equation (overall reaction – does not identify ions)

2AgNO3(aq) + Na2S(aq) Ag2S(s) + 2NaNO3(aq)

Complete Ionic Equation (includes ions in solution)

2Ag+(aq) + 2NO3

-(aq) + 2Na+

(aq) + S2-(aq) Ag2S(s) + 2NO3

-(aq)

+ 2Na+(aq)

Net Ionic Equation (identifies species that undergo chemical change)

2Ag+(aq) + S2-

(aq) Ag2S(s)

+Writing Equations for Reactions Example Write the formula, complete ionic, and net ionic forms

for each of the following equations. Aqueous nickel (II) chloride reacts with aqueous sodium

hydroxide to give a nickel (II) hydroxide precipitate and aqueous sodium chloride.

Solid potassium metal reacts with water to give aqueous potassium hydroxide and hydrogen gas.

Aqueous sodium hydroxide reacts with aqueous phosphoric acid to give water and aqueous sodium phosphate.

+Practice Problems

Page 173 # 37, 39, 41, and 43

15 Minutes

+Stoichiometry of Precipitation Reactions

Steps: 1. Identify the species present in the combined solution, and

determine what reaction occurs. 2. Write the balanced net ionic equation for the reaction. 3. Calculate the moles of reactants. 4. Determine which reactant is limiting. 5. Calculate the moles of product or products, as required. 6. Convert to grams of other units, as required.

**No two examples are alike, the PROCESS to solving will be similar**

+Solution Stoichiometry Example

What mass of Fe(OH)3 is produced when 35. mL of a 0.250 M Fe(NO3)3 solution is mixed with 55 mL of a 0.180M KOH solution?

Individual Practice Problem Page 173 #49 and 50

+Check for UnderstandingPrecipitation Stoichiometry

Please complete the following on a sheet of paper to turn in.

When aqueous solutions of Na2SO4 and Pb(NO3)2 are mixed, PbSO4 precipitates. Calculate the mass of PbSO4 formed when 1.25 L of 0.0500 M Pb(NO3)2 and 2.00 L of 0.0250 M Na2SO4 are mixed.

+Acid-Base Reactions

The Bronsted-Lowry Definitions

Acid is a proton donor.

Base is a proton acceptor.

An acid-base reaction is often called a neutralization reaction.

+Acid-Base Example

How many mL of a 0.800M NaOH solution is needed to just neutralize 40.00mL of a 0.600M HCl solution? (Hint: Write down the reaction and convert to moles, and relate moles of acid to moles of base.)

Individual Example Problems 65 page 171 – 8 Minutes

+Acid-Base Titrations Volumetric analysis

A technique for determining the amount of a certain substance by doing a titration.

Titration Involves delivery (from a buret) of a measured volume of a

solution of known concentration (the titrant) into a solution containing the substance being analyzed (analyte).

Equivalence point (Stoichiometric point) Point in titration where enough titrant has been added to react

exactly with the analyte

Indicator A substance added at the beginning of the titration that

changes color at (or very near) the equivalence point Point at which indicator actually changes color is the endpoint

of the titration.

+Acid-base titration (Standardizing)

You wish to determine the molarity of a solution of sodium hydroxide. To do this, you titrate a 25.00mL aliquot of your sample, which has had 3 drops of phenolphthalein indicator added so that it is pink, with 0.1067 M HCl. The sample turns clear after the addition of 42.95 mL of the HCl. Calculate the molarity of your NaOH solution.

Individual Example Problems 63 and 65 page 174 – 10 Minutes

+Oxidation Reduction Reactions

Reactions in which one or more electrons are transferred (redox reactions)

Example: H2(g) + Cl2(g) 2HCl(g)

Electrons are transferred from the hydrogen to the chlorine.

Table 4.2 Rules for Assigning Oxidation States (pg 156)

Remember: The sum of the oxidation states in a neutral compound must equal zero.

+Oxidation States

Assign oxidation states to each of the atoms in the following compounds:

Hint: Check that oxidation states sum up to the charge on the compound/ion.

CaF2

C2H6

H2O

ICl5

KMnO4

SO42-

+Practice- Oxidation States

Fe2O3 + 2Al Al2O3 + 2Fe

THE IRON GAINED ELECTRONS. IT HAS BEEN REDUCED.

THE ALUMINUM LOST ELECTRONS. IT HAS BEEN OXIDIZED.

OIL – Oxidation Involves Loss (of electrons)

RIG- Reduction Involves Gain (of electrons)

+Tricky…Tricky…

Oxidizing agent Something that is reduced (it causes something else to oxidize)

Reducing agent Something that is oxidized (it causes something else to reduce)

Fe2O3 + 2Al Al2O3 + 2Fe

Iron was reduced. Aluminum was oxidized. Iron (II) oxide was the oxidizing agent. Aluminum was the reducing agent.

+OIL RIG Practice For each reaction, identify the atoms that undergo

reduction or oxidation (and charges). Also, list the oxidizing and reducing agents.

2H2(g) + O2(g) 2H2O(g)

Zn(s) + Cu2+(aq) Zn2+

(aq) + Cu(s)

2AgCl(s) + H2(g) 2H+(aq) + 2Ag(s) + 2Cl-(aq)

+Balancing Oxidation-Reduction Equations (Half-Reaction Method) Steps: Acidic

1. Write separate equations for the oxidation and reduction half-reactions.

2. For each half-reaction Balance all the elements except hydrogen and oxygen. Balance oxygen using H2O.

Balance hydrogen using H+. Balance the charge using electrons (e-).

3. If necessary, multiply one or both balanced half-reactions by an integer equalize the number of electrons transferred in the two half-reactions.

4. Add the half-reactions, and cancel identical species. 5. Check that the elements and charges are balanced.

+Balancing Oxidation-Reduction Equations (Half-Reaction Method) Steps: Basic

The same as acidic and then… 6. Add a number of OH- ions to both sides so that you just

balance excess H+ ions. 7. H+ and OH- will form H2O on the side with excess H+. Free

OH- will appear on one side of the equation. 8. Double check atoms and charges!

+Balancing Redox Example - Acid

Cu(s) + HNO3(aq) Cu2+(aq) + NO(g)

Copper is being oxidized:

Nitrogen is being reduced:

+Balancing Redox Reactions - Base

Cr2O72-

(aq) + 2NO(g) + 6H+(aq) 2Cr3+

(aq) + 2NO3-(aq) +

3H2O(l)

**Already balanced in acid**

+Practice Time!

Page 174, # 67, 69, 71, 73, and 75

Be sure to show your work!

+Chemistry of Copper Lab - _______ Pre-lab: REQUIRED FOR ENTRY INTO LAB!!

Read lab handout thoroughly. Set-up data organization

What data are you collecting for each step? Complete procedure component of lab

Safety: Safety goggles at ALL times! Concentrated acids will be used!!

Can cause severe burns No touching your face! Wash your hands after completing lab. Read thoroughly…carefully pour acids and remove hot

beakers from hot plate with tongs! (A hot beaker looks like a cold one!)

Avoid congestion around the fume hood (Step 5 should be done in fume hood!).

Keep lab stations cleaned through multistep procedure.

+Copper Lab Partners

Group 1:

Group 2:

Group 3:

+Step 1: Copper Lab Task

Label beaker with tapeBlock Student group initials

+Bleach Redox Lab PRE-LAB DUE ___________!!

Read handout thoroughly! (in black binder)

Complete the pre-lab questions Hint: Dilution, Concentration, Stoichiometry

Required for entry into lab.

Also for _________… Begin working on Lab Report for Cu Lab Continue practice with Precipitation, Acid-Base,

and redox reactions. Begin reading Ch.5 Gases

+

+Today’s Agenda

Review Expectations for Tomorrow

Check Pre-Lab for Bleach Redox Lab.

Review Bleach Redox Lab

Take final copper mass reading for Lab C.

Complete/Collect Data for the Bleach Redox Lab Watch Time.

+Due for Tomorrow…

Copper Lab Report (Heavily Qualitative) Date when data was collected

Read Ch. 5 Gases

Begin completing Bleach Redox Lab Report Due _________ at the BEGINNING of class.

+Bleach Redox Lab Pre-lab

Safety: Bleach is a 5% solution of sodium hypochlorite. This

solution is a corrosive liquid; it can cause skin burns. The solution reacts with acid and with heat to evolve chlorine gas. The solution is moderately toxic by ingestion and inhalation. Keep away from skin and clothing. Hydrochloric acid solution is toxic by ingestion or inhalation. It is corrosive to skin and eyes.

CAUTION: Adding hydrochloric acid to bleach may cause chlorine gas to be given off. Step 6 is completed in the fume hood!

Wear your goggles at ALL times! Do NOT touch your face. Wash your hands with soap before leaving the lab.

+Data Collection

Collect mass of copper. This may be placed in the trash and the cleaned beaker back on the drying rack.

Complete the 3 titrations of bleach. READ INSTRUCTIONS CAREFULLY!

ALL glassware must be away from the edge of the tables.

Practice caution in the lab! Be aware of your surroundings.

When finished clean lab station and return to seat and begin working on the reports or reading Ch. 5.

+Up Next…. GASES!! Ch. 5