solutions unit teview

Solution

A solution is a homogeneous mixture of a solvent and solutes

Solvent

The solvent is the substance present in the largest amount

Solute

Is the substance present in the lesser amount

Solution examples

Solid dissolved in a solid = steel (carbon dissolved in iron)

Solid dissolved in a liquid = sea water

Liquid dissolved in a liquid = hydrogen peroxide dissolved in water

Gas dissolved in a solid = air dissolved (trapped) in ice

Gas dissolved in a liquid = carbonated beverages

Gas dissolved in a gas = air (nitrogen is the solvent)

Dissolution

During dissolution, existing attractions are broken and new attractions are formed. This can be endothermic process (absorbs heat) or an exothermic process (releases heat).

Hydration

During hydration, ions and polar molecules are surrounded by water molecules

Solubility

Solubility is the maximum amount of solute that will dissolve in a given quantity of solvent at specific temperatures (e.g., the solubility of sodium at 10•c)

Unsaturated solution

A solution that could dissolve more solute (more solute dissolves)

Saturated solution

A solution that cannot dissolve more solute (full) (no more solute dissolves)

Supersaturated solution

A solution that contains more dissolved solute than a saturated solution at the same temperature (becomes unstable, crystals form)

Temperature and solubility

Most, but not all, ionic solids, are more solvable at higher temperatures.

Solubility

The maximum amount of solute that will dissolve in a given quantity of solvent at a specific temperature

Solubility is determined by

The forces between particles:

• attraction of solute particles to each other

• Attraction of solute particles to solvent

• Attraction of solvent particles to each other

• When a solution forms, particles of solute are attracted to particles of solvent and intermolecular forces are broken between solutes and between solvents.

Solubility in water

Water is polar thus can dissolve many types of solutes

Ionic compounds in water

• Water molecules break apart lattice and hydrate ions

• Ionic compounds will dissolve if ions are more attracted to water than to each other

Molecular compounds in water

• dipole-dipole attractions may occur between polar compounds and water

• E.g., ethanol is hydrated by water molecules

• Non-polar molecules do not dissolve in water because absence of strong dipole-dipole attractions

• Molecule size also has an effect on solubility

  example: methanol -CH3OH

  ethane - CH3CH7OH

  pentanol - CH3CH2CH2CH2CH2OH

Like dissolves like

1) non-polar solvents will dissolve non-polar solutes

2) polar solvents will dissolve polar solutes

3) molecules with both polar and non-polar components can dissolve in both polar and non-polar solvents

Temperature

• At higher temperatures, solvent particles will have more kinetic energy this will collide with solute particles more often

  a) solids in aqueous solution: higher temperature will increase solubility

  b) liquids in aqueous solution: solubility is not affected by temperature

  c) gases in aqueous solution: higher temperatures will decrease gas solubility

Pressure

• solubility of a gas in a liquid is directly proportional to the pressure of that gas above the liquid

• By increasing pressure above the gas, the gas will stay dissolved in water

  scuba divers

• Breathe more compressed air thus breathing in air at a higher pressure

• More gases in the air will dissolve in the divers blood

• When they surface, gases come out of the blood but this needs to be done slowly or bubbles form = THE BENDS!

Concentration

The amount of solute per quantity of solvent

1) mass/volume percentage percent (m/v)

Mass of solute dissolved in a volume of solution, expressed as a percent

%m/v = mass of solute (in g) / volume of solution (in ml) x 100%

2) mass/mass percentage percent (m/m)

Mass of solute divided by the mass of solution, expressed as a percent

%m/m = Msolute / Msolution x 100%

3) volume/volume percentage percent (v/v)

Volume of the solute divided by the volume of solution, expressed as a percent

%v/v = Vsolute / Vsolution x100%

4) parts per million and parts per billion

Ppm = any combo of m/m, m/v, v,v x10^6

Ppb = any combo of m/m, m/v, v/v x10^9

Molarity

A measure of concentration based upon the mole is used, termes molar concentration

C = n/V

C is the molar concentration measured in mol/L or (M)

n is the amount of solute in mol

V is the volume of solution in L

In some cases you may first need to convert the solute from a mass into an amount in miles using n = m/M

Making a solution

Forming ions

• ionic compounds refer to positive ions and negative ions held together by electrostatic attractions

• This can be a:

  metal + non-metal e.g., Nacl, MgF2

  metal + poly atomic ion e.g., NaOH, NaNO3

• For salts (aq) means the salt exists as a solution

• NaCl(aq) is the same as NaCl(aq) — Na+(aq) + Cl-(aq)

• Acids form ions: HCl(aq) — H+(aq) + Cl-(aq)

• Bases form ions: NaOH(aq) — Na+(aq) + OH-(aq)

Types of chemical equations

Equations can be divided into 3 types: 1) Molecular, 2) Ionic, 3) Net ionic

Here is a typical molecular equation:

Pb(NO3)2(aq) + 2KI(aq) — PbI2(s) + 2KNO3(aq)

We can write this as an ionic equation (all compounds that are (aq) are written as ions):

Pb2+(aq) + 2NO3-(aq) + 2K+(aq) + 2I-(aq) — PbI2(s) + 2K+(aq) + 2NO3-(aq)

To get the NET ionic equation we cancel out all terms that appear on both sides:

Net: Pb2+(aq) + 2I-(aq) — PbI2(s)

Spectator ions: NO3-(aq), K+(aq)

Net ionic continued

• there are two conditions that must be met for molecular, ionic, and net ionic equations

  Materials balance

  both sides of an equation should have the same number of each type of atom

  Electrical balance

  both sides of a reaction should have the same net charge

Acid

Hydrochloric acid (HCl)

• Conducts electricity

• Reacts with magnesium (Mg) = bubbles (H2)

• Reacts with baking soda (NaHCO3) = bubbles (CO2)

• Bromothymol blue = orange/yellow

• Litmus paper = red

• Phenolphthalein = no change

• pH paper = <7

• forms hydrogen ions

Base

Sodium hydroxide (NaOH)

• Doesn’t conduct electricity

• Doesn’t react with magnesium (Mg)

• Doesn’t react with baking soda (NaHCO3)

• Bromothymol blue = blue

• Litmus paper = blue

• Phenolphthalein = pink

• pH paper = >7

• Forms hydroxide ions