4.2: solutions and dilutions
solution: a homogenous mixture of two or more pure substances
the solvent is present in the greatest amount possible
all other substances are solutes
suspension: a heterogeneous mixture in which solute-like particles settle out of a solvent-like phase after mixing
colloid: a solution that has particles which remain evenly distributed throughout the solution; the particles do not settle to the bottom of the container, and they do not filter
term | meaning | example (bolded) |
|---|---|---|
solute | what is being dissolved | sugar in water |
solvent | what does the dissolving | sugar in water |
soluble | can be dissolved | sugar can dissolve in water |
insoluble | cannot be dissolved | sand cannot dissolve in water |
“like dissolves like”—the more similar the solvent and solute molecules are, the more likely one substance is to be soluble in another
polar water molecules are able to dissolve an ionic compound like NaCl
polar water molecules are not able to dissolve a non-polar compound like propane
electrolytes
electrolyte: a substance that forms ions (charged particles or species) when dissolved in water
ionic compounds are electrolytes
strong electrolytes dissociate completely when dissolved in water (lots of ions)
weak electrolytes only partially dissociate when dissolved in water (fewer ions)
non-electrolyte: a substance that does not form ions when dissolved in water
covalent compounds are non-electrolytes
eg. sugar—dissolves in water but doesn’t form ions
solutions are categorized into one of three groups: saturated solutions, unsaturated solutions, and supersaturated solutions
these are based on the amount of solute dissolved within them
unsaturated solution: a solution that has less than the maximum amount of solute dissolved in the solvent (for that temperature)
you can continue to add solute and it will continue to dissolve
saturated solution: a solution in which the solvent holds as much solute as is possible at that temperature
saturation is dependent on temperature
supersaturated solution: a solution in which the solvent holds more solute than is typically possible at a given temperature
factors that affect how fast a substance dissolves
factor | definition |
|---|---|
agitation | stirring helps solute particles dissolve faster because it increases the rate at which the solute particles come in contact with solvent particles |
particle size | generally, the smaller the solute particle size, the faster it will dissolve. smaller particle size = more surface area = increased rate of contact with the solvent |
temperature | some solutes dissolve faster at higher temperatures. higher temperature = more kinetic energy = higher rate of contact with solvent |
concentration | a measurement of the amount of solute dissolved in the volume of solvent. there are many different ways to measure concentration, eg. molarity, percent by mass, percent by volume |
finding percent by mass and percent by volume of a solution
percent by mass: ([solute mass/solution mass] x 100)
percent by volume: ([solute volume/solution volume] x 100)
dilutions
dilution: the process of adding more solvent to a solution without adding more solute, which decreases the concentration of a solution
eg. only adding water to the solution; that means that the number of moles of solute stays the same, only the volume of the solution changes
used to weaken the properties of the solute
“dilution” can also be used to describe the liquid itself that has been diluted
solution: a homogenous mixture of two or more pure substances
the solvent is present in the greatest amount possible
all other substances are solutes
suspension: a heterogeneous mixture in which solute-like particles settle out of a solvent-like phase after mixing
colloid: a solution that has particles which remain evenly distributed throughout the solution; the particles do not settle to the bottom of the container, and they do not filter
term | meaning | example (bolded) |
|---|---|---|
solute | what is being dissolved | sugar in water |
solvent | what does the dissolving | sugar in water |
soluble | can be dissolved | sugar can dissolve in water |
insoluble | cannot be dissolved | sand cannot dissolve in water |
“like dissolves like”—the more similar the solvent and solute molecules are, the more likely one substance is to be soluble in another
polar water molecules are able to dissolve an ionic compound like NaCl
polar water molecules are not able to dissolve a non-polar compound like propane
electrolytes
electrolyte: a substance that forms ions (charged particles or species) when dissolved in water
ionic compounds are electrolytes
strong electrolytes dissociate completely when dissolved in water (lots of ions)
weak electrolytes only partially dissociate when dissolved in water (fewer ions)
non-electrolyte: a substance that does not form ions when dissolved in water
covalent compounds are non-electrolytes
eg. sugar—dissolves in water but doesn’t form ions
solutions are categorized into one of three groups: saturated solutions, unsaturated solutions, and supersaturated solutions
these are based on the amount of solute dissolved within them
unsaturated solution: a solution that has less than the maximum amount of solute dissolved in the solvent (for that temperature)
you can continue to add solute and it will continue to dissolve
saturated solution: a solution in which the solvent holds as much solute as is possible at that temperature
saturation is dependent on temperature
supersaturated solution: a solution in which the solvent holds more solute than is typically possible at a given temperature
factors that affect how fast a substance dissolves
factor | definition |
|---|---|
agitation | stirring helps solute particles dissolve faster because it increases the rate at which the solute particles come in contact with solvent particles |
particle size | generally, the smaller the solute particle size, the faster it will dissolve. smaller particle size = more surface area = increased rate of contact with the solvent |
temperature | some solutes dissolve faster at higher temperatures. higher temperature = more kinetic energy = higher rate of contact with solvent |
concentration | a measurement of the amount of solute dissolved in the volume of solvent. there are many different ways to measure concentration, eg. molarity, percent by mass, percent by volume |
finding percent by mass and percent by volume of a solution
percent by mass: ([solute mass/solution mass] x 100)
percent by volume: ([solute volume/solution volume] x 100)
dilutions
dilution: the process of adding more solvent to a solution without adding more solute, which decreases the concentration of a solution
eg. only adding water to the solution; that means that the number of moles of solute stays the same, only the volume of the solution changes
used to weaken the properties of the solute
“dilution” can also be used to describe the liquid itself that has been diluted
