Chem Chapter 5: Solution Concentration

concentration

the strength of a solution: the ratio of the amount of solute to the amount of solution

amount of solute / amount of solution

concentration formula

percent concentrations

the amount of solute in 100 mL of solution (grams or mL)

weight per volume (w/v)

solute is a solid, the amount is given in grams; # of grams of solute per 100mL

ex. concentration of glucose = 5.0% w/v glucose which means 5.0g glucose / 100 ml solution

volume (v/v) percentage

solute is a liquid, the number of mL of solute per 100 mL of solution

ex. concentration of alcohol = 5.0% (v/v) which means 5.0mL alcohol / 100mL of solution

general procedure for calculating concentration

1. determine the type of concentration you must calculate and the units you must use for the solute and solution

2. convert the amount of solute and the amount of solution into correct units if needed

3. divide the amount of solute by amount of solution

4. if concentration is a % multiply answer by 100

amount of solute / volume of solution (mL) x 100

percent concentration formula

can be in (w/v) or (v/v)

concentrations are expressed in many other ways

1. mass per volume

2. parts per million

3. parts per billion

mass per volume

the concentration of a solute can be expressed as the mass of the solute in any chosen amount of solution

ex. mass / deciliter (dL = 100mL) so 1g/dL = 1% (w/v)

parts per million

1/1,000,000g of solute in 1mL of solution

parts per billion

1/1,000,000,000g (1ng) of solute in 1mL of solution

solubility

the maximum possible concentration of a solute; upper limit to the mass that we can dissolve in a given volume of water 

unsaturated solution

a solution that contains less than the maximum concentration of solute

ex. NaCl solubility = 360g (if you use less than 360 g)

insoluble

cannot dissolve to a significant extent; compound that the solubility is less than 1g/L

soluble

able to dissolve to a significant extent; compound that the solubility is @ least 10g/L

temperature and pressure

solubility depends on…

temperature for solids

solubility of a solid in water INCREASES as you INCREASE the temperature

temperature for gas

solubility of a gas DECREASES as the temperature INCREASES

• gas dissolves better in cold water than in warm water

pressure for gas

solubility of a gas INCREASES as you INCREASE the pressure (torr)

relationship between solubility and molecular structure

the ability to dissolve in water depends on the structure of the entire molecule

molecule structure

1. hydrophobic region

2. hydrophilic region

hydrophobic

unable to mix with water / little attraction for water (not ionized and cannot participate in hydrogen bonds)

hydrophillic

attracted to and able to mix with water (ionized or have ability to participate in hydrogen bonds)

hydrophobic region

contains no atoms that can form hydrogen bonds (oygens and nitrogens)

hydrophilic region

contains atoms that can form hydrogen bonds with water (oxygens and nitrogens)

molarity (molar concentration)

the ratio of moles of solute to liters of solution

moles of solute / liters of solution

molarity formula (M or mol / L)

how to calculate molarity of solution

1. know or calculate how many liters of solution

2. know or calculate how many moles of solute are dissolved in it

3. divide the moles by liters to get the molarity

specific molarity

calculate the number of grams of solute that we will use to prepare the solution

diffusion

the spontaneous mixing of liquids or gases by random molecular motion (mixes a solute evenly throughout a solvent)

semipermeable membrane

a barrier that allows only certain types of molecules or ions to pass through it (allows water and small molecules)

osmosis

the net movement of solvent molecules through a semipermeable membrane (occurs when 2 solutions have unequal concentrations)

predicting direction of osmosis

1. if solution contains 2 or more solutes we add up molarities of all solutes

2. we multiply the molarity of the electrolyte by the number of ions in chemical formula

osmotic pressure

the pressure required to prevent osmosis; the pressure exerted on the membrane when 2 solutions have reached equilibrium (concentration difference becomes larger, the osmotic pressure will increase)

osmotic pressure is affected by

dissociation

if solution contains 2 or more solutes we add up molarities of all solutes

ex. if solution contains 0.1 moles of glucose + 0.1 moles of fructose = 0.2M per liter of solution

we multiply the molarity of the electrolyte by the number of ions in chemical formula

ex. Mg(NO₃ )₂ is strong electrolyte with 0.2M

theres 3 ions so 0.2M x 3 = 0.6M (total molarity of solution)

tonicity

relationship between the overall concentration of solutes in a solution and the normal concentration of solution in intracellular fluid

isotonic

having some solute concentration as that in intracellular fluid

hypertonic

having solute concentration higher than that in intracellular fluids

hypotonic

having solute concentration lower than that in intracellular fluid

dialysis

movement of solute through a membrane

equivalent

the amount of any ion that has the same total charge as a mole of hydrogen ions (H+)

• the # of equivalents equals the number of moles times the charge

equivalents formula

ex. Mg²⁺ = 1 mole x 2 = 2Eq of Mg²⁺

mEq

1 eq / 1000 meq

number of equivalents of solute / volume of solution

concentration of ions can be expressed in mEq/ L 

dilution

adding solvent to reduce the concentration of a solution

Inverse proportion

relationship between the volume of a solution and its concentration is an

volume of solution and its concentration formula

C₁ x V₁ = C₂ x V₂ 

C₁

initial concentration

V₁

initial volume

C₂ 

final concentration

V₂

final volume