Water review:Take a minute and list a few of the properties you remember about our favorite liquid:• It’s a polar molecule- which means it dissolves other polar molecules.

•Water molecules are bonded to each other with which intermolecular force? Hydrogen bonds

Water review continued:

• Hydrogen bonds keep water molecules bound tightly to each other, giving water a high surface tension… lucky for Mr. water strider

Solute +

Solvent =

Solution

is the stuff being dissolved

is the stuff the solute is dissolved in *usually water… not always.

Solutions:a.k.a. homogenous mixtures.Are mixtures chemically combined?What are a few examples of solutions?

Sugar waterCarbonated water / sodaAir

Regarding solutions, we’ll consider 3 things: FIRST---

• Will your solute even dissolve into your solvent????• Remember “LIKE DISSOLVES LIKE”?– Polar solvents dissolve polar solutes AND ionic solutes.– Nonpolar solvents dissolve nonpolar solutes.

Soluble = the solute will dissolve in the solvent.Insoluble = the solute will not dissolve in the solvent.

Second---• Is the solution an electrolyte? Electrolytes are solutions that contain + or –

ions, which conduct electricityMetallic salts dissociate into ions when dissolved, so their solutions are good conductors. Most acids are also electrolytes. NaCl Na+ + Cl-

Substances which do not dissociate, but retain their molecular composition, are called nonelectrolytes and do not conduct a current. A sugar water solution is an example of a nonelectrolyte.

Gatorade ingredients

Third---

• How much solute went into how much solvent?• A little bit… we call it…• All that can normally fit, it’s...• More than it’s supposed to hold…

Dilutedsaturated

Supersaturated

Supersaturated???How do you dissolve more than normal?

• If it’s a solid in a liquid:– Saturate the solution.– Heat it up & dissolve more solute.– SLOWLY allow it to cool off.

Rate of Dissolving:

• A solid solute will dissolve faster if…1. the solvent is heated.2. the solution is agitated (i.e. stirred or shaken)3. the solute particles have greater surface area… the smaller they are, the more s.a. they have.

So how soluble is some solute?• That depends… on what?– What it is (NaCl, sucrose, KBr, etc.)– The temperature of the solvent.

Solubility is measured by seeing how many grams of solute will dissolve in 100 mL of solvent.

Question: As the temperature increases…• Should solubility increase or decrease for a

solid/crystaline solute?• Should solubility increase or decrease for a gas

solute?

Solubility CurvesAs the temp. increases, what happens to the solubility of NaCl?

It increases

Solubility CurvesAs the temp. increases, what happens to the solubility of HCl?

It decreases

Solubility CurvesHow much NaNO3 will dissolve in 100 mL of water at 30 °C?

About 96 grams.

Measuring concentration

Molarity: the number of moles of solute in one liter of solution.M = amount of solute (moles)

volume of solution (liters)

A bottle labeled 6M HCl is called “6 molar hydrochloric” and it was prepared by mixing 6 moles of HCl with enough water to make 1 liter of solution.

Molarity is always moles/1 liter.

Ex: “6M” is 6 moles HCl/ liter 6M HCl

You need molarity practice? OK!

• You’ve dissolved 4 moles of table salt (sodium chloride = NaCl) into 2 liters of water. – How concentrated is the salt water solution? • Molarity = moles solute / liters solvent• Molarity = 4 moles NaCl / 2 liters water• Molarity = 2 moles NaCl / 1 liter water• Molarity = 2M

Your turn:

• What is the concentration of a solution with 8.9 moles of sucrose dissolved in 2.5 liters of water?

8.9 moles

2.5 liters

==

3.6 M 3.6 moles

1 liter

More practice!• 234 grams of NaCl are dissolved in 2 liters of

water. How concentrated is the solution?

–How many moles of NaCl are there?• 22.99 + 35.45 = 58.44 grams / 1 mole NaCl

234 g x 1 mole = 58.44 g4.00 moles = 2 M 2 Liters

4 moles

Your turn:• 42 grams of CaO are dissolved in .78 liters

of water. How concentrated is the solution?

–How many moles of CaO are there?• 40.08 + 16 = 56.08 grams / 1 mole• 1 mole x 42 g = 56.08 g• moles = M .78 Liters

Switched up example

• How many moles of KF (potassium fluoride) are in half a liter of 7M KF solution? 7 moles KF x .5 liters = 3.5 moles KF 1 liter

Another example

• How many liters of water will you need to dissolve 9.3 moles of NaOH if you want to make a 4.0 M solution?

1 Liter

4.0 mol NaOH= Liters9.3 moles 2.3

Your turn:

• How many liters of water will you need to dissolve .63 moles of Oxygen if you want to make a 1.5 M solution?

Now to fit in some stoichiometry

• Remember those chemical equations? __Mg (s) + __HCl (aq) → __MgCl2 (aq) + __H2 (g)

Guess what the “aq” stands for…aqueous!

So the HCl in this reaction is really HCl gas dissolved in water. How much? How concentrated is it?