Chapter 13 Ions in Aqueous Solutions and Colligative Properties

Ratios and Molarity M 1 V 1 =M 2 V 2 M is Molarity and V is Volume – Doesn’t matter what volume is in. They just have to be the same. – How many mL of a 6M solution would you need to dilute it to 250 mL of a 3 M solution? – What is the concentration of 550 L, if you dilute 400 L of a 3.75M solution?

Compounds in Aqueous Solutions Ionic- metal and nonmetal Covalent (Molecular)- nonmetal and nonmetal Dissociation: the separation of ions that occur when an ionic compound dissolves. Reactions – s is solid – aq is aqueous – L is liquid

Dissociation (Ionic Equations) When writing reactions with ions, the equation is balanced for charge as well as for atoms. We are going to take equations and break down the compounds into their elements. Do examples

Precipitation Reactions Although no ionic compound is completely insoluble, compounds of very low solubility can be considered insoluble for most practical purposes. We are going to learn some general solubility rules. This doesn’t cover every thing, but most.

Solubility Rules Sodium potassium and ammonium compounds are soluble in water. Nitrates, acetates, and chlorates are soluble Most chlorides are soluble. – Except silver, mercury (I), and lead – Lead (II) chloride is soluble on in hot water Most sulfates are soluble – Except those of barium, strontium, lead, calcium, and mercury Most carbonates, phosphates, and silicates are insoluble – Except sodium, potassium, and ammonium Most sulfides are insoluble – Except calcium, strontium, sodium, potassium, and ammonium

Net Ionic Equations Net ionic equations include only those compounds and ions that undergo a chemical change in a reaction in an aqueous solution. To write a net ionic equation, 1.Write and balance the regular equation. 2.Determine if soluble or insoluble. 3.Only change the soluble into ions 4.Check for spectator ions

Examples Identify the precipitate that forms when aqueous solutions of zine nitrate and ammonium sulfide are combined. Write the equation for the possible double- displacement reaction. Then write the overall ionic equation, and net ionic equation for the reaction.

Examples Let’s do the practice problems on page 440

Hydronium Ion When an acid mixes with water it can form what we call a hydronium ion (H 3 O + )

Colligative Properties Properties that depend on the concentration of solute particles but not on their identity – The boiling and freezing point differ from those of the pure solvent. – To calculate the new melting point and freezing point we will be using the formulas ∆t f =K f m or ∆t b =K b m We will be using the table on your solubility sheet

Examples What is the freezing-point depression of water in a solution of 17.1 g of sucrose, C 12 H 22 O 11 in 200 grams of water? What is the actual freezing point of the solution? A water solution contain an unknown quantity of a nonelectrolyte solute is found to have a freezing point of -.23 o C. What is the molal concentration of the solution?

Examples What is the boiling-point elevation of a solution made from 20.1 g of a nonelectrolyte solute and g of water? The molar mass of the solute is 62.0 grams.

Homework Practice problems on page 450 and 451 (1-4 on both)

Electrolytes and Colligative Properties Colligative properties depend on the total concentration of solute particles regardless of the identity. The changes in colligative properties caused by electrolytes will be proportional to the total molality of all dissolved particles, not to formula units. The salts applied to icy roads are electrolytes. They lower the freezing point of water and melt the ice.

Examples What is the expected change in the freezing point of water in a solution of 62.5 g of barium nitrate, Ba(NO 3 ) 2, in 1.00kg of water?

Homework Do the practice problems on page 455