chapter nine chemical reactions in aqueous solutions

A solution is a homogeneous mixture Gas example: air Liquid liquid: salt water Solid example: brass

Solute: substance being dissolved Typically lesser in quantity

Solvent: substance doing the dissolving Typically greater in quantity

Electrolyte: substance that when dissolved in water conducts electricity Sodium Chloride (or table salt) Has ions in solution (dissociation)

Nonelectrolyte: substance that when dissolved in water does NOT conduct electricity Sucrose (or sugar) Does NOT have ions in solution, but molecules

All water-soluble ionic compounds will dissociate completely Therefore, they are strong electrolytes

(i.e. substances that completely dissociate)

There are only 7 molecular compounds that are also considered strong electrolytes▪ HCl, HBr, HI, HNO3, HClO3, HClO4, H2SO4

Most molecular compounds are weak electrolytes OR nonelectrolytes Weak electrolytes produce some ions

upon dissolving but exist mostly of molecules that aren’t ionized

Acids are electrolytes (they produce H+ ions) HCl(g) H+(aq) + Cl-(aq)

Bases are electrolytes (they produce OH- ions) NH3(g) NH4+(aq) + OH-(aq)

For acids/bases that are WEAK, the reaction goes in both directions simultaneously

HC2H3O2(l) H+(aq) + C2H3O2-

(aq)

“” reaction occurs in both directions

Dynamic Chemical Equilibrium

A + B2 AB2

Sucrose (C12H22O11)

Fructose (C6H12O6)

Sodium Citrate (Na3C6H5O7)

Potassium Citrate (K3C6H5O7)

Ascorbic Acid (H2C6H6O6)

Reaction where a “precipitate” forms

Maximum amount of solute that will dissolve in a given quantity of solvent at a specific temperature

Pb(NO3)2(aq) + NaI(aq)

Ionic Equation: Shows equation with ions dissociated

Net Ionic Equation: Shows only what’s involved in the reaction Removes “Spectator Ions”

For the following reaction, correctly predict the products to write the balanced molecular equation. Then write the ionic equation and the net ionic equation.

Aqueous solutions of Lead Acetate and Calcium Chloride

Arrhenius Model: Acids produce H+ ions Bases produce OH- ions

Bronsted Model: Acids are H+ donors (or proton donors) Bases are H+ acceptors (or proton

acceptors)

Reaction between an acid and base Produce water (most of the time) and a

salt (ionic compound)

A.K.A. “Redox” Reactions

Chemical Reaction where electrons are being transferred from one reactant to another.

Consider Zn(s) + CuCl2(aq) ZnCl2(aq) + Cu(s)

Oxidation is loss of electronsReduction is gain of electrons

“OIL RIG”

Oxidizing Agent: species that causes oxidation Takes the electrons

Reducing Agent: species that causes reduction Gives the electrons

A.K.A. Oxidation State (or charge)

Help us determine what elements were oxidized and reduced

In order to determine an element’s oxidation number, you must follow the guidelines on the next two slides:

What is the oxidation number of each atom in the following:

SO2

NaH

CO32-

H2SO4

2Fe + 6HBr 3H2 + 2FeBr3

N2 + 3H2 2NH3

2KClO3 2KCl + 3O2

What is the oxidation number for chlorine in the compound HClO4?

What species is the reducing agent in the following equation? Mg(s) + 2HCl(aq) MgCl2(aq) + H2(g)

Does the following equation represent a redox reaction? Why? 2Mg(s) + O2(g) 2MgO(s)

Measure of amount of solute dissolved in a certain amount of solvent or solution

More solute: Concentrated

Less solute: Diluted

Molarity = moles of solute/ L of solution A.K.A. molar concentration Represented by “M” ex: 1.5 M

If you have exactly 1 L of 1.5 M glucose, it contains 1.5 moles of glucose

Suppose you wanted to make a 0.150 M solution of KMnO4 using a 25o.00 mL volumetric flask. How would you do this?

You need to make 500. mL of a 0.650 M solution of Sodium Hydroxide (NaOH). What mass of NaOH do you need to use?

What is the molar concentration (M) of a solution prepared by dissolving 58.50 g of Copper Chloride (CuCl2) in water to yield a 1.50 L solution?

Preparing less concentrated solutions Typically done by adding water to

concentrated solution

Dilution formula: McVc = MdVd

C = concentrated D = diluted

What volume in mL of a 1.20 M HCl solution must be diluted in order to prepare 1.00 L of 0.0150 M HCl?

How much water was added?

Recall: Soluble Ionic Compounds dissociate completely (all ionize)

If you have 0.500 M of KMnO4, then there is 0.500 M of K+ and 0.500 M of MnO4- (1:1 ratio between ions)

[ ] are usually used to show concentration [KMnO4] = 0.500 M, [K+] = 0.500 M, [MnO4-] =

0.500M

If you have soluble ionic compounds with ratios other than 1:1 for ions, use subscripts to determine ion concentration

Ex: Na2SO4

[Na2SO4] = 0.35 M, [Na+] = 0.70 M, [SO4

2-] = 0.35 M

Suppose you had a 1.55 L solution of this ionic compound. How many moles of each ion do you have? How many individual ions do you have?

Analytical technique based on mass Uses percent composition

Ex: A 0.8633-g sample of an ionic compound containing chloride ions and unknown metal cations is dissolved in water and treated with excess AgNO3. If 1.5615 g of AgCl precipitate, what is the percent by mass of Cl in the original compound?

Process where Solution of known concentration

(standard solution) is added gradually to Another solution of unknown

concentration till The reaction is complete

▪ Equivalence point: # of moles of H+ ions equals # of moles of OH- ions

▪ End point: Color change in solution (visually indicates the equivalence point)

What volume of a 0.203 M NaOH solution is needed to neutralize 25.0 mL of a 0.188 M H2SO4 solution?

If it takes 26.79 mL of 0.560 M HCl solution to neutralize 85.70 mL of Ba(OH)2, what is the molarity of the base?

What is the molar mass of a diprotic acid if 30.5 mL of 0.1112 M NaOH is required to neutralize a 0.1365-g sample?

How many milliliters of a 1.89 M H2SO4 solution are needed to neutralize 91.9 mL of a 0.336 M KOH solution?

Explain the difference between an endpoint and an equivalence point.