DISSOLVING AND SOLUBILITY

Transcription

1 DISSOLVING AND SOLUBILITY QUICK REVIEW: Homogeneous mixtures: a solution of substances in which no settling occurs (looks like one thing). A solution occurs when the particles of the components slip in between each other in an even distribution throughout the entire mixture. Heterogeneous mixtures: contains two or more materials that are still visible (can see the different phases). Can be further classified based on the size of their components. 1

2 QUICK REVIEW: In-Between Mixtures: Suspension heterogeneous mixture in which some particles settle after mixing (can be filtered). Examples: orange juice with pulp, salad dressing, paint, dust Colloids heterogeneous mixture in which particles do not settle. Examples: fog or hairspray (liquid dispersed in a gas), smoke or smog (solid dispersed in a gas), jelly or jello (liquid dispersed in a solid) shaving cream or whipped cream (gas dispersed in a liquid). Emulsion a special colloid, with an emulsifying agent to keep particles suspended. Example: mayo WHAT MAKES MATERIALS DISSOLVE? Dissolving is forming a solution by mixing two or more materials together. Example: salt dissolved into water. But how does it dissolve?? Draw 4 beakers in your journal. 2

3 HOW DOES SUGAR DISSOLVE IN WATER? R Remember the particle model!! Particles can attract each other and they are always moving! WHAT MAKES MATERIALS DISSOLVE? As water particles pass by the nearest (or outermost) sugar particle, the water particles can pull a sugar particle away from the other sugar particles and then the motion of the water particles carries it away. This leaves room for more water particles to move in and attract another sugar particle. This process will continue until all of the sugar is dissolved. The particles will move around until they are evenly mixed throughout. 3

4 BUT WAIT What if the attraction between the different particles is stronger than the attraction bond between the same particles? NO DISSOLVING!! LET S TALK ABOUT SOLUTES AND SOLVENTS A solute is the substance that dissolves in a solvent Example: sugar. A solvent (usually more than the solute) is the substance that dissolves a solute. Example: water. 4

5 Example Air Made up of Oxygen, nitrogen Soda water Carbon dioxide in water Vinegar Ocean water Acetic acid in water Various salts in water States of Matter Solute Gas nitrogen Gas - carbon dioxide Liquid acetic acid Solvent Gas oxygen Liquid - water Liquid water Solid salts Liquid - water WATER = UNIVERSALLY LOVED (BY MOST SOLUTES) Water : sometimes referred to as the universal solvent WHY? Because it dissolves so many materials Think about it: Your body is made up of a lot of water The water portion of your blood dissolves and transports Food Nutrients Waste Minerals Vitamins The same things are dissolved and transported in water in plants 5

6 MAYBE NOT SO UNIVERSAL Soluble vs. Insoluble If a certain solute is able to be dissolved in a particular solvent, it is said to be soluble in that solvent. Soluble means able to be dissolved in a particular solvent. Example: sugar is soluble in water. If a certain solute is not able to dissolve, it is said to be insoluble. WHAT DO YOU THINK CAN INCREASE THE RATE AT WHICH SOMETHING DISSOLVES? There are many factors that can influence the rate of dissolving of a substance: 1. Agitation (stirring/shaking) can increase the interactions of the solvent with the solute. It moves to fresh solvent particles close to the solute particles. 2. Increased surface area of solute provides more area where dissolving can occur. 3. Increased temperature increases particle movement which increases the rate of dissolving. 4. Increased pressure moves particles closer together, increasing their interactions. Doesn t matter much for solids and liquids but greatly affects gases. 6

7 HOW MUCH CAN BE DISSOLVED? Solubility refers to the mass of a solute that can dissolve in a given amount of solvent to form a saturated solution at a given temperature. A saturated solution is one in which NO more solute will dissolve in a specific amount of solvent at a specific temperature. An unsaturated solution is one in which more solute could still be dissolved in that amount of solvent at that temperature. HOW MUCH CAN BE DISSOLVED? 7

8 YOU CAN GRAPH SOLUBILITY HOW DOES THAT LOOK ON A GRAPH? 8

9 THE LINE ITSELF ALSO REPRESENTS A PERFECT SOLUTION; THAT IS, A SOLUTION WITH THE EXACT AMOUNT OF SOLUTE THAT WILL SATURATE 100 ML OF WATER: At any temperature, any LESS solute than the value on the line would produce an UNSATURATED solution à points below the line! If 5 grams of mix were added to 40 o water, the solution would not be saturated, as shown by the point BELOW the saturation line 9

10 At any temperature, any MORE solute than the value on the line would produce an SUPERSATURATED solution à points above the line If 70 grams of mix were added to 100 o water, the solution would be more than saturated, as shown by the point ABOVE the saturation line BEYOND THE LIMIT Supersaturated: A solution that contains more solute than would normally dissolve at a certain temperature. 10

11 WHAT ABOUT A NEGATIVE SLOPE As temperature increases 11

12 BACK TO THE TABLE! What if we want more than 100mL? Say 200mL Amount (g) = 100mL x 200mL Example: salt 35.7g = x 100mL 200mL x = 71.4g 12