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

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

Agenda Acids and Bases Reactions Oxidation/Reduction Reactions

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.

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+)

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.

Learning Check 3 1 2

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!

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.

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

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)

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

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

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

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) + 2H2O (l) 2H+(aq) + 2 OH-(aq)  + 2H2O (l)

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

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)

OXIDATION – REDUCTION (REDOX REACTIONS)

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.

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

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. https://www.youtube.com/watch?v=-a2ckxhfDjQ

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.

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.

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)

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.

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?

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

DISPLACEMENT REACTIONS and ACTIVITY SERIES

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?

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

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

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

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)

MOLARITY and DILLUTION

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) =

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? © 2015 Pearson Education, Inc.

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 0.500 mol / 0.500 L = 1 M 10.5 g (0.250 mol) in 100 mL 0.250 mol / 0.1L = 2.5 M © 2015 Pearson Education, Inc.

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.

Molarity Check What is the molar concentration of K+ ions in a 0.015 M solution of potassium carbonate? © 2015 Pearson Education, Inc.

Molarity Check What is the concentration of ammonia in a solution made by dissolving 3.75 grams of ammonia in 120.0 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 0.038 mol of this salt? © 2015 Pearson Education, Inc.

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.

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.

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

Using Molarities in Stoichiometric Calculations

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

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.

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.

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