Chapter 6, sci 8

Understanding Solutions

How Are Mixtures Classified?

<<A mixture is classified as a solution, colloid, or suspension based on the size of its largest particles<<

Solutions:

$Solution$ : a mixture containing a solvent and at least one solute and has some properties throughout
$Solvent$ : the part of a solution usually present in the largest amount; it dissolves in other substances; commonly water
* other solvents: gasoline - combination of gases, liquids, or solids - Air is a solution that is made up of nitrogen, oxygen and other gases - Metal alloys like bronze, brass, and steel are solutions of different solid elements
$Solute$ : the substance that is dissolved by the solvent; can be gases/liquids/solid

Colloids:

$colloid$ : a mixture containing small, undissolved, particles that do not settle out
the particles in a colloid are to small to be seen in a microscope but large enough to scatter a beam of light
fog is a colloid made up of water droplets in the air - it scatters the light that comes out of the light from your car

Suspensions:

$Suspension$ : a mixture in which particles can be seen and easily separated by settling or filtration contains visible particles that are larger than the particles in solution or colloids

How Does a Solution Form?

a solution forms when particles of the solute separate from each other and become surrounded by particles of the solvent

Ionic and Molecular Solutes

positive and negative ions of the solute are attracted to the partially charged polar water molecules
eventually water molecules will surround all of the ions and the solid crystal will be completely dissolved
* ex.Molecular compounds break up into individual neutral molecules in water. the polar water molecules attract the polar sugar molecules. This causes the sugar molecules to move away from each other. the covalent bonds within the molecule remain unbroken

Solutes and Conductivity

Ionic compounds in water conduct electric current, molecular compounds may not.

Effects of Solutes

solutes raise the boiling point of a solution above the solvent’s
* as the temp of a liquid rises the molecules gain energy and escape as gas - In a liquid solution the solute particles prevent the solvent molecules escape
* The temp must go above the boiling point of the solvent in order for the solution to boil - However the temperature increases only slightly

Review

SOLUTION: eg water and salt	COLLOIDS	SUSPENSION
solvent: → water	Small undissolved particles: If you can’t see the particles but are there	large undissolved particles: If you can see the particles
solute: will always raise the boiling point of the solvent/solution → salt	fog, shaving cream, milk, smoke, ice cream
the solute must be fully dissolved in the solvent	You know what it is because of how the light impacts it

Concentration and Solubility

How is concentration changed?

$Dilute Solution:$ a mixture that has only a little solute dissolved in a certain amount of solvent
* tree sap
$Concentrated solution:$ a mixture that has a lot of solute dissolved in the solvent
* tree syrup
You can change the concentration of a solution by adding solute. You can also change it by adding or removing the solvent
To determine the concentration of a solution, compare the amount of solute to the total amount of solution
you can report the concentration as the percent of solute in solution by volume or mass

What Factors affect solubility

$Solubility$ : a measure of how much solute can dissolve in a solvent at a given temperature
<<factors that can affect the solubility of a substance include pressure, the type of solvent, and temperature<<
$saturated solution:$ if/when there is so much solute in no longer dissolves

solubility can be helped to identify a substance

it is characteristic property of matter

Pressure:

the solubility of a gas solute in a liquid solvent increases as the pressure of the gas over the solution increases

Solvents

sometimes a solution cannot be made because the solute and solvent are not compatible
* some polar and nonpolar compounds don’t mix well
for liquid solutions acid polar compounds usually dissolve in polar solvent. Nonpolar compound do not usually dissolve in ber polar solvents, but will dissolve in nonpolar solvents

Temperature

For most solid solutes, solubility increases as temperature increases
when heated, a solution can dissolve more solute than it can at cooler temperatures
If a heated saturated solution cools slowly, the extra solute may remain dissolved to become a supersaturated solute
* it has more dissolved solute than is predicted by its solubility at the given temperature
* if one disturbs a supersaturated solution the extra solute will quickly come out of the solution
unlike most solids, gases become less soluble when the temperature goes up

Review

concentration = grams solute / ml solution
concentration mass/mass % = (# grams solute/ # grams solution) x 100
Concentration volume / volume % = (# ml solute/ # ml solution) x 100
concentration mass/volume % = (# )

3 things that affect solubility:

high pressure → more gas will dissolve = higher solubility
higher temp → will make solid will dissolve quicker = more solubility
type of solute

polar solvent will dissolve an ionic solute
polar solvent will dissolve polar solutes
nonpolar solvents will dissolve nonpolar solute

Concept Question

What are the properties of solutions and why do solutions have these properties?

the properties of a solution is that it has one solute and one solvent it has the same properties as a homogeneous mixture

###

A scientist boils water and measures its boiling point to be 100oC. She adds ZnCl2, stirs her water, and brings it to a boil again. What changes? Why?

The boiling point changes because she added a solute

After a big storm, trucks put salt on the roads. Why? What happens?

because the salt will lower the freezing point which will make the ice melt more easily.

How do you make a given solution more dilute? More concentrated?

you make a solution dilute by adding a solvent. to make it more concentrated take away the solvent or add the solute

What factors affect solubility? How?

Pressure (solubility of a gas & a liquid increases as the pressure increase), type of solvent (Ionic + polar dissolve well in polar & Nonpolar dissolve well in nonpolar), and temperature (solubility of a solid increases with temp & solubility of a gas decreases as temp increases).

What factors influence solution formation? How?

agitation (if u mix the solution dissolves faster), temperature (solid dissolves faster at higher temp), and the particle size (smaller faster dissolve).

What is a supersaturated solution? How is it made?

supersaturated solution is when there is a lot of solute in the solvent. Heat the solvent add as much solute as possible then cool the solution

What does the solubility curve show us?5t

Solubility curves show the solubility of different compounds in water at a given temperature. On these curves, pressure is constant.