Solutions Molarity Acids & Bases

Aqueous Solutions

    Solution - a homogenous mixture mixed molecule by molecule.

Solvent - the stuff that does the dissolving.

Solute -the stuff that is dissolved.

Aqueous solution- a solution with water as the solvent.

Aqueous Solutions

       Water dissolves ionic solids and polar covalent solids best.

The rule is “like dissolves like” Polar dissolves polar.

Nonpolar dissolves nonpolar.

Oil is non polar.

Oil and water don’t mix.

Salt is ionic- salt water.

How Ionic solids dissolve

  Called solvation.

Water breaks the + and - charged pieces apart and surround them.

How Ionic solids dissolve

H H H

    Solids will dissolve if the attractive force of the water molecules is stronger than the attractive force of the crystal.

If not the solids are insoluble.

Water doesn’t dissolve nonpolar molecules because it the water molecules can’t hold onto them.

The water molecule hold onto each other and separate from the polar molecules.

Electrolytes

     Substances that conduct electricity when dissolved in water.

Must have charged particles that can move.

Ionic compounds break into charged ions.

NaCl  Na + + Cl These ions can conduct electricity.

    Non electrolytes do not conduct electricity when dissolved in water.

Polar covalent molecules such as methanol CH 3 OH don’t fall apart into ions when they dissolve.

Weak electrolytes don’t fall completely apart into ions.

Strong electrolytes do ionizes completely.

Mixtures that are NOT Solutions

     Suspensions are mixtures that slowly settle upon standing.

Particles of a suspension are more than 100 times bigger.

Can be separated by filtering.

Colloids particles are between the size of a solid and that of a liquid.

Emulsions are colloids of liquids in liquids.

Properties of solutions

     

Making solutions

What the solute and the solvent are – Whether a substance will dissolve.

– How much will dissolve.

A substance dissolves faster if It is stirred or shaken.

The particles are made smaller.

The temperature is increased.

Why?

Making solutions

 In order to dissolve the solvent molecules must come in contact with the solute.

 Stirring moves fresh solvent next to the solute.

 The solvent touches the surface of the solute.

 Smaller pieces increase the amount of surface of the solute.

Temperature and Solutions

 Higher temperature makes the molecules of the solvent move around faster and contact the solute harder and more often.

 Speeds up dissolving.

 Usually increases the amount that will dissolve.

   

How Much?

Solubility - The maximum amount of substance that will dissolve at that temperature (usually g/L).

Saturated solution - Contains the maximum amount of solid dissolved.

Unsaturated solution - Can dissolve more solvent.

Supersaturated - A solution that is temporarily holding more than it can, a seed crystal will make it come out

Liquids

 Miscible means the that to liquids can dissolve in each other.

 Immiscible means they can’t

What affects solubility?

 For solids in liquids as the temperature goes up the solubility goes up.

 For gases in a liquid as the temperature goes up the solubility goes down.

 For gases in a liquid- as the pressure goes up the solubility goes up.

Measuring Solutions

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Concentration

A measure of the amount of solute dissolved in a certain amount of solvent.

 Concentrated solution of solute.

 Dilute solution solute has a large amount has a small amount of  Sometimes g/l or g/mL of g/100 mL.

 But chemical reactions don’t happen in grams

Molarity

 The number of moles of solute in 1 Liter of the solution.

 M = moles/Liter  What is the molarity of a solution with 2.0 moles of NaCl in 4.0 Liters of solution.

 What is the molarity of a solution with 3.0 moles dissolved in 250 mL of solution.



Making solutions

Pour in a small amount of solvent  Then add the solute and dissolve it  Then fill to final volume.

 M x L = moles  How many moles of NaCl are needed to make 6.0 L of a 0.75 M NaCl solution?

 How many grams of CaCl 2 are needed to make 625 mL of a 2.0 M solution?

Making solutions

 10.3 g of NaCl are dissolved in a small amount of water then diluted to 250 mL. What is the concentration?

 How many grams of sugar are needed to make 125 mL of a 0.50 M C 6 H 12 O 6 solution?

Acids and Bases

Properties of acids

      Taste Sour (kids, don’t try this at home).

Conduct electricity.

Some are strong, some are weak electrolytes.

React with metals to form hydrogen gas.

Change indicators (litmus red).

React with hydroxides to form water and a salt.

Properties of bases

     React with acids to form water and a salt.

Taste bitter.

Feel slippery (Don’t try this either).

Can be strong or weak electrolytes.

Change indicators (litmus blue).

Water

        Water ionizes- falls apart into ions.

H 2 O  H + + OH Called the self ionization of water.

Only a small amount.

[H + ] = [OH ] = 1 x 10 -7 M A neutral solution.

In water Kw = [H + ] x [OH ] = 1 x 10 -14 Kw is called the ion product constant.

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Ion Product Constant

H 2 O H + + OH Kw is constant in every aqueous. solution [H + ] x [OH ] = 1 x 10 -14 M 2 If [H + ] > 10 -7 If [H + ] < 10 -7 then [OH ] < 10 -7 then [OH ] > 10 -7 If we know one, we can determine the other.

If [H + ] > 10 -7 If [H + ] < 10 -7 acidic [OH basic [OH ] < 10 ] > 10 -7 -7

Logarithms

        Powers of ten.

A shorthand for big, or small numbers.

pH = -log[H + ] in neutral pH = - log(1 x 10 -7 ) = 7 in acidic solution [H + ] > 10 -7 pH < -log(10 -7 ) pH < 7 in base pH > 7

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pH and pOH

pOH = - log [OH ] [H + ] x [OH ] = 1 x 10 -14 M 2 pH+pOH = 14

[H + ] 10 0 10 -1 10 -3 10 -5 10 -7 pH 10 -9 10 -11 10 -13 10 -14 0

Acidic

14 1 13 3 11 9 5 7

Neutral

9 7 5 [OH ] 11 3 13 14

Basic

1 0 10 -14 10 -13 10 -11 10 -9 pOH

Basic

10 -5 10 -3 10 -1 10 0

Polyprotic Acids

    Some compounds have more than 1 ionizable hydrogen.

HNO 3 nitric acid - monoprotic H 2 SO 4 sulfuric acid - diprotic - 2 H + H 3 PO 4 phosphoric acid - triprotic - 3 H +

How Strong

      

Strength

Strong acids and bases are strong electrolytes They fall apart completely.

Weak acids don’t completely ionize.

Concentrated much dissolved.

Strong forms may ions when dissolved.

Mg(OH) 2 is a strong base- it falls completely apart when dissolved. Not much dissolves.

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Measuring strength

Ionization is reversible.

HA H + + A makes an equilibrium.

Equilibrium constant for an acid(acid dissociation constant.

K a = [H + ][A [HA] ] Stronger acid- more products.

larger K a (pg 450)

What about bases?

 Strong bases dissociate completely.

     B + H 2 O BH + + OH Base dissociation constant.

K b = [BH + ][OH ] [B] we can ignore the water Stronger base more dissociated.

Larger K b.

Neutralization reactions

Neutralization Reactions

 Acid + Base  Salt + water  Salt = an ionic compound  Water = HOH     HNO 3 + KOH  HCl + Mg(OH) 2  H 2 SO 4 + NaOH  Really just double replacement.