Solutions and pH

1. Solutions and pH

2. A True Solution A true solution is like a homogeneous mixture… two or more substances are mixed together evenly. A solvent is the substance that dissolves the other substance. A solute is the substance that is getting dissolved. A common solution would be salt and water, where water is the solvent and salt is the solute.

3. Types of Solutions Gases, liquids and solids can form different combinations.

4. Water as a universal solvent Water molecules are polar – they have a negative and a positive end. Each end can them be attracted to certain solute particles. Water can dissolve most ionic solids by pulling the ions apart. Since fats and oils have few negative and positive ends they do not dissolve in water.

5. Common solvents in the home: Some common solvents found in the home: Nail polish remover Turpentine Hand cleaner Detergents

6. Factors affecting solution rate • Particle size: the greater the surface area, the faster the substance will dissolve • Temperature: the warmer the water, the more energy and the faster the substance will dissolve • Movement: stirring a solution forces more contact with surface area and speeds up dissolving

7. Factors affecting solubility The ability of one substance to dissolve in another is called solubility. Solubility varies depending on temperature. For solids, an increase in temperature increases solubility. For gases, an increase in temperature lowers solubility.

8. Practical effects of solubility • Fish prefer cold water which keeps gases dissolved better than warm water. • Soda left open to the air, will cause gas bubbles to leave the solution and give a flat taste. • In order to make crystals, you need to heat the solution first which will dissolve more solute.

9. Concentration of solutions A saturated solution contains all the solute it can hold at a certain temperature and pressure. An unsaturated solutions contains less solute than it can hold. A supersaturated solution goes beyond the saturation point. It is created by heating and then cooling the solution. Crystals are made this way.

10. Suspensions and colloids Particles settle out in a suspension; colloids have much smaller particles. The Tyndall Effect makes these smaller particles visible.

11. Properties of solution, colloids and suspensions • solution suspension colloid • Particle size molecule can be seen between • Type of mixture homo- hetero- borderline • Do particles settle out no yes no • Can be filtered no yes no • Scatter light no yes yes

12. Examples of colloids • Paint and ink • Gels • Aerosols (clouds, fog, mist, smoke) • Foams (whipped cream, marshmallows, shaving cream) • Emulsions (mayonnaise, margarine, cosmetic creams)

13. Comparing particle size

14. Acids and Bases • Acids produce hydrogen ions(H+) in a water solution. They are chemically active. They taste sour and react with metals to form hydrogen gas. Strong acids can burn your skin. Weak acids can be found in citrus fruits. • Bases produce hydroxide (OH-) ions in a water solution. They are also chemically active. They taste bitter and feel slippery. Strong bases can also give serious burns. Most weak bases are cleaning products.

15. Common acids and bases

16. pH scale

17. Types of pH indicators • Universal pH paper: red and orange/acids, blues and greens/bases • Litmus paper: red/acids, blue/bases • Bromothymol blue: yellow/acid, blue/bases • Cabbage juice, and other fruits and veggies • Phenol red: orange/base, yellow/acid, red/neutral • An indicator indicates the presence of an acid or a base by a color change.