Chem 11 Unit 9 Solutions

What kind of mixtures are solutions? What does that mean?

Homogenous: There should be no observable segregation of component substances in a solution.

What are the three types of solutions?

1: Gaseous solutions

• E.g. Air - 78% N2, 21% O2, 1% Ar, 0.03% COz

2: Solid solutions (alloys)

E.g. Sterling silver (Cu + Ag), brass (Cu + Zn)

Dental amalgam (Hg + Ag), steel (Fe + C)

3: Liquid solutions

What are the three types of liquid solutions?

liquid - liquid (e.g. vinegar)

solid - liquid (e.g. salt water)

gas - liquid (e.g. carbonated water in soda pop)

What is the solvent?

the substance present in the greater amount

What is the solute?

the component of lesser abundance (smaller amount)

How do you determine if a molecule is polar?

depending on the bond polarity (due to the differences in electronegativity of the elements involved) and the resulting dipole when electrons are displaced to one side of the molecule.

What do polar and ionic solutes tend to dissolve in?

Polar solvents

e.g. NaCl (ionic) dissolves in H20 but not CCl

NH (polar) dissolves in H20 but not CCl

What do non-polar solutes tend to dissolve in?

Non-polar solvents

e.g. L2 (non-polar) dissolves in CCl but not H20

What are solutions containing water called?

aqueous (aq).

Why is water an important solvent (2)

-Many important reactions (e.g. in living things) take place in aqueous solutions

-Water is probably the most common solvent.

Saturated

solution in which no additional solute can dissolve

Unsaturated

a solution in which additional solute can dissolve

Miscible

when there is no apparent limit to the solubility of one liquid in another

Immiscible

two liquids which do not dissolve in each other; solvation (interaction between solute and solvent particles) does not occur

What is solubility?

A measure of the amount of solute which can dissolve in a given amount of solvent.

What are some units for measuring solubility?

g/L, g/mL, g/g, mL/mL.

How to determine solubility? (2)

Adding a little at a time until saturated; or evaporating a saturated solution and measuring the mass of the solid left behind,

What does the Solubility Table defines soluble as?

> 0.1 mol/L @ 25°C

Concentration

describes the amount of solute in a given amount of solutions.

How to find percent solution?

x g/ 100 g of solution (W/W)

x mL / 100 mL of solution (V/V)

How to find molarity? and units?

# of moles of solute/litres of solution made

m = n/v

units are mol/l or molarity

Dilute solutions vs concentrated solutions?

contain less solute per litre of solution than concentrated solutions.

e.g. Dilute HCI: 0.10 M or 0.50 M

Concentrated HCl: 12 M

How are solutions often made?

by diluting a more concentrated solution.

What is the more concentrated solution called?

stock

When diluting a solution is the solvent or solute changed?

solvent: extra solvent is added but the amount (moles) of solute remains unchanged

Steps to figuring out how much water should be added to dilute a solution to your wanted molarity?

1: calculate the amount of solute in the stock

2: Calculate the amount of liquid in the diluted substance from the amount of solute (solute in stock = solute in diluted)

3: Calculate the amount of water that needs to be added

What do ionic substances (salts) form when dissolve in water?

(What reaction is this?)

ions

e.g. NaCls) (salts) → Na+(aq) + Cl-(aq)

(dissociation reaction equation)

What do square brackets mean?

molarity or concentration of

What is the concentration of ions in a solution?

can be different (or the same) from the concentrations of the ic salts.

What do you use to find the concentration of ions in solutions?

mole ratio (the coefficients of a balanced chemical equation).

What are the steps to finding concentration of ions in a solution?

1: Write a dissociation equations (mole ratio with charges)

2: Use unit conversion equations to convert moles of salts to moles of ions

3: Gives you the molarity of the ions

Dissociation reaction equation

adding solid compound to water

e.g. Pb(NO3)2(s) → Pb+(aq) + 2 NO3- (aq)

Formula reaction equation

mixing two different solutions aka double replacement. Remember that it results in one aq and one solid

Complete (Full) Ionic reaction equation

change all aq into ions

net ionic equation

Shows only the reaction species in a reaction in an aqueous environment (spectator ions are deleted) with ion form (from complete ionic equation)

eg. Pb2+ (aq) + 2I+ (aq) ---> PbI2 (s)

what are spectator ions?

The ions that are the same on both sides of the equation

Qualitative analysis

described by the procedures by which a chemist decides what substances or ions are present in a sample.

How do you decide what substances or ions are present in a sample or seperate two substances?

Use the Solubility Table to select a reagent (ion that you then make a compound with) that gives a precipitate (ppt) with some substances but not with others.

If an anion (negative ion) is added to give a ppt in Qualitative analysis what do you add to it?

an alkali metal (e.g. Nat or K+) salt of the anion (because they will not ppt with other anions.)

If adding a cation (positive ion) is added to give a ppt in Qualitative analysis what do you add to it?

use the nitrate (NO3-) salt of the cation.

Steps to seperate two substances in a solution

1: Find an ion that precipitates on substance but not the other

2: Figure out the compound for that ion and add it

3: Filter out the precipitate

4: Add something that will precipitate the other substance

5: Find a compound with that ion and add it

6: filter out the precipitate