Chapter 4, Part II: Solution Chemistry

Properties of Solutions Solvent This is the liquid that is doing the dissolving Solute This is what is being dissolved Form a homogenous mixture

Saturated vs. Unsaturated Solutions

Solubility Two liquids that dissolve in each other are said to be miscible Immiscible liquids are insoluble in each other Think of some examples!

Immiscible vs. Miscible Solutions

Factors Affecting Solubility Solubility increases with the increase in temperature (Easier to dissolve something when the temperature is increased) Few exceptions that occur in the reverse

Concentrations of Solutions Molarity is the concentration of moles per liters Molarity (M) = moles of solute / liters of solution Dilute solution contains a low concentration of solute Concentrated solution contains a high concentration of solute

Practice Problems: Calculate the molarity of a solution which contains 0.40 mol of C6H12O6 dissolved in 1.6 L of a solution. What is the molarity of a solution containing 325 g of NaCl dissolved in 750. mL of solution?(1000 ml = 1L)

Solutions stoichiometry

Stoichiometry overview Recall that in stoichiometry the mole ratio provides a necessary conversion factor: grams (x)  moles (x)  moles (y)  grams (y) molar mass of x molar mass of y mole ratio from balanced equation We can do something similar with solutions: volume (x)  moles (x)  moles (y)  volume (y) mol/L of x mol/L of y mole ratio from balanced equation

Practice Problems 1. If I combined 15.0 grams of calcium hydroxide with 0.075 L of 0.500 M HCl, how many grams of calcium chloride would be formed? 2. If 257.8 ml of a 0.0468 M solution of lead(II) acetate is added to 156.00 mL of a 0.095 M solution of sodium sulfide, what mass of solid lead sulfide will be formed?

What Happens When a Solute Dissolves? there are attractive forces between the solute particles holding them together; likewise for the solvent Upon mixing the solute with the solvent, there are attractive forces between the solute particles and the solvent molecules if the attractions between solute and solvent are strong enough, the solute will dissolve

Table Salt Dissolving in Water Each ion is attracted to the surrounding water molecules and pulled off and away from the crystal When it enters the solution, the ion is surrounded by water molecules, insulating it from other ions The result is a solution with free moving charged particles able to conduct electricity Tro, Chemistry: A Molecular Approach

Electrolytes and Nonelectrolytes materials that dissolve in water to form a solution that will conduct electricity are called electrolytes materials that dissolve in water to form a solution that will not conduct electricity are called nonelectrolytes Tro, Chemistry: A Molecular Approach

Molecular View of Electrolytes and Nonelectrolytes in order to conduct electricity, a material must have charged particles that are able to flow electrolyte solutions all contain ions dissolved in the water ionic compounds are electrolytes because they all dissociate into their ions when they dissolve nonelectrolyte solutions contain whole molecules dissolved in the water generally, molecular compounds do not ionize when they dissolve in water the notable exception being molecular acids Tro, Chemistry: A Molecular Approach

Salt vs. Sugar Dissolved in Water molecular compounds do not dissociate when they dissolve ionic compounds dissociate into ions when they dissolve Tro, Chemistry: A Molecular Approach

Acids acids are molecular compounds that ionize when they dissolve in water the molecules are pulled apart by their attraction for the water when acids ionize, they form H+ cations and anions the percentage of molecules that ionize varies from one acid to another acids that ionize virtually 100% are called strong acids HCl(aq)  H+(aq) + Cl-(aq) acids that only ionize a small percentage are called weak acids HF(aq)  H+(aq) + F-(aq) Tro, Chemistry: A Molecular Approach

Strong and Weak Electrolytes strong electrolytes are materials that dissolve completely as ions ionic compounds and strong acids their solutions conduct electricity well weak electrolytes are materials that dissolve mostly as molecules, but partially as ions weak acids their solutions conduct electricity, but not well when compounds containing a polyatomic ion dissolve, the polyatomic ion stays together Na2SO4(aq)  2 Na+(aq) + SO42-(aq) HC2H3O2(aq)  H+(aq) + C2H3O2-(aq) Tro, Chemistry: A Molecular Approach

Classes of Dissolved Materials Tro, Chemistry: A Molecular Approach

Acid-Base Reactions also called neutralization reactions because the acid and base neutralize each other’s properties 2 HNO3(aq) + Ca(OH)2(aq)  Ca(NO3)2(aq) + 2 H2O(l) the net ionic equation for an acid-base reaction is H+(aq) + OH(aq)  H2O(l) as long as the salt that forms is soluble in water Tro, Chemistry: A Molecular Approach

Acids and Bases in Solution acids ionize in water to form H+ ions more precisely, the H from the acid molecule is donated to a water molecule to form hydronium ion, H3O+ most chemists use H+ and H3O+ interchangeably bases dissociate in water to form OH ions bases, like NH3, that do not contain OH ions, produce OH by pulling H off water molecules in the reaction of an acid with a base, the H+ from the acid combines with the OH from the base to make water the cation from the base combines with the anion from the acid to make the salt acid + base salt + water Tro, Chemistry: A Molecular Approach

Practice Write the balanced molecular and net ionic equations for the reaction between: 1. Hydrobromic Acid and Potassium Hydroxide 2. Nitric Acid and Calcium Hydroxide ****Hint: Remember what an acid-base reaction always produces!

Electrolytes Strong Acids and Strong Bases= Strong Electrolytes Weak Acids and Weak Bases = Weak Electrolytes

Red-ox Reactions other kinds of reactions involve transferring electrons from one atom to another – these are called oxidation-reduction reactions also known as redox reactions many involve the reaction of a substance with O2(g) 4 Fe(s) + 3 O2(g)  2 Fe2O3(s) Tro, Chemistry: A Molecular Approach

Oxidation and Reduction atoms that lose electrons are being oxidized, atoms that gain electrons are being reduced Leo Ger 2 Na(s) + Cl2(g) → 2 Na+Cl–(s) 2Na → 2Na+ + 2e– oxidation Cl2 + 2 e– → 2 Cl– reduction Tro, Chemistry: A Molecular Approach

Electron Bookkeeping for reactions that are not metal + nonmetal, or do not involve O2, we need a method for determining how the electrons are transferred chemists assign a number to each element in a reaction called an oxidation state that allows them to determine the electron flow in the reaction even though they look like them, oxidation states are not ion charges! oxidation states are imaginary charges assigned based on a set of rules ion charges are real, measurable charges Tro, Chemistry: A Molecular Approach

Rules for Assigning Oxidation States rules are in order of priority free elements have an oxidation state = 0 Na = 0 and Cl2 = 0 in 2 Na(s) + Cl2(g) monatomic ions have an oxidation state equal to their charge Na = +1 and Cl = -1 in NaCl (a) the sum of the oxidation states of all the atoms in a compound is 0 Na = +1 and Cl = -1 in NaCl, (+1) + (-1) = 0 Tro, Chemistry: A Molecular Approach

Rules for Assigning Oxidation States (b) the sum of the oxidation states of all the atoms in a polyatomic ion equals the charge on the ion N = +5 and O = -2 in NO3–, (+5) + 3(-2) = -1 (a) Group I metals have an oxidation state of +1 in all their compounds Na = +1 in NaCl (b) Group II metals have an oxidation state of +2 in all their compounds Mg = +2 in MgCl2 Tro, Chemistry: A Molecular Approach

Rules for Assigning Oxidation States in their compounds, nonmetals have oxidation states according to the table below nonmetals higher on the table take priority Nonmetal Oxidation State Example F -1 CF4 H +1 CH4 O -2 CO2 Group 7A CCl4 Group 6A CS2 Group 5A -3 NH3 Tro, Chemistry: A Molecular Approach

Practice – Assign an Oxidation State to Each Element in the following Br2 K+ LiF CO2 SO42- Na2O2 Tro, Chemistry: A Molecular Approach

Practice – Assign an Oxidation State to Each Element in the following Br2 Br = 0, (Rule 1) K+ K = +1, (Rule 2) LiF Li = +1, (Rule 4a) & F = -1, (Rule 5) CO2 O = -2, (Rule 5) & C = +4, (Rule 3a) SO42- O = -2, (Rule 5) & S = +6, (Rule 3b) Na2O2 Na = +1, (Rule 4a) & O = -1, (Rule 3a) Tro, Chemistry: A Molecular Approach

Oxidation and Reduction Another Definition oxidation occurs when an atom’s oxidation state increases during a reaction reduction occurs when an atom’s oxidation state decreases during a reaction CH4 + 2 O2 → CO2 + 2 H2O -4 +1 0 +4 –2 +1 -2 oxidation reduction Tro, Chemistry: A Molecular Approach

Oxidation–Reduction oxidation and reduction must occur simultaneously if an atom loses electrons another atom must take them the reactant that reduces an element in another reactant is called the reducing agent the reducing agent contains the element that is oxidized the reactant that oxidizes an element in another reactant is called the oxidizing agent the oxidizing agent contains the element that is reduced 2 Na(s) + Cl2(g) → 2 Na+Cl–(s) Na is oxidized, Cl is reduced Na is the reducing agent, Cl2 is the oxidizing agent Tro, Chemistry: A Molecular Approach

Identify the Oxidizing and Reducing Agents in Each of the Following 3 H2S + 2 NO3– + 2 H+ ® 3 S + 2 NO + 4 H2O MnO2 + 4 HBr ® MnBr2 + Br2 + 2 H2O Tro, Chemistry: A Molecular Approach