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

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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 C 6 H 12 O 6 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)

Making Dilutions Formula for making a dilution C 1 V 1 = C 2 V 2 (Volume must be in units of L) “Stock solution” is the same as the original solution.

Example A stock solution of HCl has a concentration of 12M. How much of the stock solution would be required to make 325 mL of a 6M solution?

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 xmolar 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 xmol/L of y mole ratio from balanced equation

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? Practice Problems

14 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

Tro, Chemistry: A Molecular Approach15 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 Approach16 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 Approach17 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 Approach18 Salt vs. Sugar Dissolved in Water ionic compounds dissociate into ions when they dissolve molecular compounds do not dissociate when they dissolve

Tro, Chemistry: A Molecular Approach19 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 Approach20 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 Na 2 SO 4 (aq)  2 Na + (aq) + SO 4 2- (aq) HC 2 H 3 O 2 (aq)  H + (aq) + C 2 H 3 O 2 - (aq)

Tro, Chemistry: A Molecular Approach21 Classes of Dissolved Materials

Tro, Chemistry: A Molecular Approach22 Acid-Base Reactions also called neutralization reactions because the acid and base neutralize each other’s properties 2 HNO 3 (aq) + Ca(OH) 2 (aq)  Ca(NO 3 ) 2 (aq) + 2 H 2 O(l) the net ionic equation for an acid-base reaction is H + (aq) + OH  (aq)  H 2 O(l) as long as the salt that forms is soluble in water

Tro, Chemistry: A Molecular Approach23 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, H 3 O + most chemists use H + and H 3 O + interchangeably bases dissociate in water to form OH  ions bases, like NH 3, 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

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

Tro, Chemistry: A Molecular Approach26 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 O 2 (g) 4 Fe(s) + 3 O 2 (g)  2 Fe 2 O 3 (s)

Tro, Chemistry: A Molecular Approach27 Oxidation and Reduction atoms that lose electrons are being oxidized, atoms that gain electrons are being reduced 2 Na(s) + Cl 2 (g) → 2 Na + Cl – (s) 2Na → 2Na + + 2e – oxidation Cl 2 + 2 e – → 2 Cl – reduction Leo Ger

Tro, Chemistry: A Molecular Approach28 Electron Bookkeeping for reactions that are not metal + nonmetal, or do not involve O 2, 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 Approach29 Rules for Assigning Oxidation States rules are in order of priority 1. free elements have an oxidation state = 0 Na = 0 and Cl 2 = 0 in 2 Na(s) + Cl 2 (g) 2. monatomic ions have an oxidation state equal to their charge Na = +1 and Cl = -1 in NaCl 3. (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 Approach30 Rules for Assigning Oxidation States 3. (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 NO 3 –, (+5) + 3(-2) = -1 4. (a) Group I metals have an oxidation state of +1 in all their compounds Na = +1 in NaCl 4. (b) Group II metals have an oxidation state of +2 in all their compounds Mg = +2 in MgCl 2

Tro, Chemistry: A Molecular Approach31 Rules for Assigning Oxidation States 5. in their compounds, nonmetals have oxidation states according to the table below nonmetals higher on the table take priority NonmetalOxidation StateExample FCF 4 H+1CH 4 O-2CO 2 Group 7ACCl 4 Group 6A-2CS 2 Group 5A-3NH 3

Tro, Chemistry: A Molecular Approach32 Practice – Assign an Oxidation State to Each Element in the following Br 2 K + LiF CO 2 SO 4 2- Na 2 O 2

Tro, Chemistry: A Molecular Approach33 Practice – Assign an Oxidation State to Each Element in the following Br 2 Br = 0, (Rule 1) K + K = +1, (Rule 2) LiFLi = +1, (Rule 4a) & F = -1, (Rule 5) CO 2 O = -2, (Rule 5) & C = +4, (Rule 3a) SO 4 2- O = -2, (Rule 5) & S = +6, (Rule 3b) Na 2 O 2 Na = +1, (Rule 4a) & O = -1, (Rule 3a)

Tro, Chemistry: A Molecular Approach34 Oxidation and Reduction 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 CH 4 + 2 O 2 → CO 2 + 2 H 2 O -4 +1 0 +4 –2 +1 -2 oxidation reduction

Tro, Chemistry: A Molecular Approach35 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) + Cl 2 (g) → 2 Na + Cl – (s) Na is oxidized, Cl is reduced Na is the reducing agent, Cl 2 is the oxidizing agent

Tro, Chemistry: A Molecular Approach36 Identify the Oxidizing and Reducing Agents in Each of the Following 3 H 2 S + 2 NO 3 – + 2 H +  S + 2 NO + 4 H 2 O MnO 2 + 4 HBr  MnBr 2 + Br 2 + 2 H 2 O

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