Solutes and Solubility

Link to a set of 9 quick lessons about solutes and solubility: http://www.middleschoolchemistry.com/multimedia/chapter5/lesson1

Classification of Matter Classify according to 4 states of matter Classify by the units they are made of

Elements Matter is made up of atoms if all atoms in a sample have same identity, that matter is an element.

Examples Al Cu Ag

Compounds Made from atoms of 2 or more elements that are combined chemically (atoms are bonded together)

H2 + O (hydrogen and oxygen) Makes H2O (water)

Na + Cl (sodium and chlorine) NaCl salt

Molecules Made of 2 or more atoms that are combined chemically (atoms are bonded together) The atoms can be the same or different elements

Molecules Compounds are always molecules Elements may be individual atoms or they can be molecules H2, O2, N2 are all diatomic elements S8 is a molecule of 8 sulfur atoms

Chemical Formulas C6H12O6 is the formula for glucose Use symbols and numbers to represent the elements found in a substance and the number of each of those elements present in the substance C6H12O6 is the formula for glucose

Wrap-up Substance: an element or compound can’t be reduced to more basic components by physical processes

Mixtures Material made up of 2 or more substances that can be separated by physical means. Each substance in a mixture keeps its own properties and identity

Salt water NaCl H2O

Mixtures cont’d Don’t always contain the same amounts of the different substances that make them up

Heterogeneous mixture Different materials can be easily distinguished Not uniformly mixed

Examples Granite Concrete Inside of your locker or backpack

Solutions Homogeneous mixture Two or more substances are uniformly mixed together

Solution particles never settle to bottom of container Remain constantly and uniformly mixed

Types of solutions Solutions are classified as solid, liquid, or gas depending on their final state

Solution terms Solute: substance being dissolved, less than 50% of a solution Solvent: substance dissolving the solute, present in largest amount

Air: 78% N, 21% O, 1% Ar Solvent of air? Sterling silver: 92.5% Ag, 7.5% Cu. Solvent?

Alloy – a solution of a metal and another element (usually another metal) Ex.: brass (copper and zinc); bronze (copper and tin); cast iron (iron and carbon)

Solids dissolving in liquids Dissolving of a solid in a liquid occurs at the surface of the solid Solutes dissolve from the outside to the center

The more surface there is, the faster something dissolves A large block has less surface available (less surface area) than the same block broken into pieces

As large blocks are broken down into smaller pieces, the total surface area increases.

Animations of salt dissolving in water http://group.chem.iastate.edu/Greenbowe/sections/projectfolder/flashfiles/thermochem/solutionSalt.html animation of salt dissolving in water   http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/molvie1.swf another animation of salt dissolving in water

Rate of Dissolving Rate of solubility depends on how the solute is dissolved grams of solute/min

Stirring speeds up dissolving –brings more fresh solvent into contact with more solute, also moves solute particles around in the solvent Stirring adds kinetic energy to a solution and helps solvent and solute particles collide

Grinding a solute speeds dissolving of solid in liquid - large crystals become small ones and solvent has more surface area to work on

Increasing the temperature of solvent increases rate at which most solids dissolve - increasing temp speeds up action of molecules of the solvent and the solute

Solubility Physical property of matter that relates to the ability of a solute to dissolve in a solvent A measure of how easily or how quickly a solute dissolves in a solvent

Physical properties: Rate of Solubility Rate of solubility = mass of solute dissolved/time to dissolve To calculate the rate of solubility divide the mass of the solute by the time it takes to dissolve Rate of solubility units: g/min or g/sec

Physical properties: Rate of Solubility Rate of solubility is affected by temperature and stirring Rate of solubility is a property of a substance There are tables of solubility rates for various substances

Miscibility A measure of how easily or how quickly a liquid solute dissolves in a liquid solvent Water and oil are immiscible (they don’t dissolve in each other)

Concentration A measure of the amount of one substance in a specific volume of another substance. Concentration units: g/mL Ex. Grams of solute per mL of solvent

Concentration A solution that has 20 g of solute dissolved in 100 mL of solvent is more concentrated than a solution that has 8 g of solute dissolved in 100 mL of solvent

Types of solutions based on amt. of solute dissolved Saturated solution - solution that has dissolved all the solute it normally can hold at a given temperature

If you heat the mixture to a higher temp, more solute can dissolve - as temp. increases, amt. of solute that can dissolve increases

Unsaturated solution - any solution that can dissolve more solute at a given temp. Each time a saturated solution is heated to a higher temp, it may become unsaturated

NaCl(s) <==> Na+(aq) + Cl-(aq) Saturation point is 36g/100mL or 0.36g/mL

Supersaturated solution - contains more solute than a saturated one has at that temperature

This kind of solution is unstable - when a small crystal of the solute is added to a supersaturated solution, excess solute quickly crystallizes out

Saturation point Point where no more solute will dissolve in a solution A concentration above which the solute will no longer dissolve in the solvent, the solution is saturated and can’t take any more

Summary Add a solute crystal to solution: If crystal dissolves, solution is unsaturated If crystal doesn’t dissolve, solution is saturated (crystal just sinks to the bottom of the container) If additional solute comes out, solution is supersaturated