Acids & Bases

1. Acids & Bases They are everywhere.. In your food In your house EVEN IN YOU!!!!!

2. What is an acid? • An acid is a solution that has an excess of H+ ions. It comes from the Latin word acidus that means "sharp" or "sour". • The more H + ions, the more acidic the solution.

3. Properties of an Acid • Tastes Sour • Conduct Electricity • Corrosive, which means they break down certain substances. Many acids can corrode fabric, skin,and paper • Some acids react strongly with metals • Turns blue litmus paper red Picture from BBC Revision Bites http://www.bbc.co.uk/schools/ks3bitesize/science/chemistry/acids_bases_1.shtml

4. Uses of Acids • Acetic Acid = Vinegar • Citric Acid = lemons, limes, & oranges. It is in many sour candies such as lemonhead & sour patch. • Ascorbic acid = Vitamin C which your body needs to function. • Sulfuric acid is used in the production of fertilizers, steel, paints, and plastics. • Car batteries

5. What is a base? • A base is a solution that has an excess of OH- ions. • Another word for base is alkali. • Bases are substances that can accept hydrogen ions

6. Properties of a Base • Feel Slippery • Taste Bitter • Corrosive • Can conduct electricity. (Think alkaline batteries.) • Do not react with metals. • Turns red litmus paper blue.

7. Uses of Bases • Bases give soaps, ammonia, and many other cleaning products some of their useful properties. • The OH- ions interact strongly with certain substances, such as dirt and grease. • Chalk and oven cleaner are examples of familiar products that contain bases. • Your blood is a basic solution.

8. pH Scale • pHis a measure of how acidic or basic a solution is. • The pH scale ranges from 0 to 14. • Acidic solutions have pH values below 7 • A solution with a pH of 0 is very acidic. • A solution with a pH of 7 is neutral. • Pure water has a pH of 7. • Basic solutions have pH values above 7.

9. pH Scale • A change of 1 pH unit represents a tenfold change in the acidity of the solution. • For example, if one solution has a pH of 1 and a second solution has a pH of 2, the first solution is not twice as acidic as the second—it is ten times more acidic.

10. Acid – Base Reactions • A reaction between an acid and a base is called neutralization. An acid-base mixture is not as acidic or basic as the individual starting solutions.

11. Acid – Base reactions • Each salt listed in this table can be formed by the reaction between an acid and a base.

12. Acid-Base Indicators

13. Measuring pH • Now that we know what pH of a solution is, how do we measure it in the lab? • The following slides will provide numerous examples of ways to measure pH in the laboratory.

14. pH testing • There are several ways to test pH • Blue litmus paper (red = acid) • Red litmus paper (blue = basic) • pH paper (multi-colored) • pH meter (7 is neutral, <7 acid, >7 base) • Universal indicator (multi-colored) • Indicators like phenolphthalein • Natural indicators like red cabbage, radishes

15. Paper testing • Paper tests like litmus paper and pH paper • Put a stirring rod into the solution and stir. • Take the stirring rod out, and place a drop of the solution from the end of the stirring rod onto a piece of the paper • Read and record the color change. Note what the color indicates. • You should only use a small portion of the paper. You can use one piece of paper for several tests.

16. pH paper

17. pH meter • Tests the voltage of the electrolyte • Converts the voltage to pH • Very cheap, accurate • Must be calibrated with a buffer solution

18. pH indicators • Indicators are dyes that can be added that will change color in the presence of an acid or base. • Most are large molecules that act as weak acids. The color changes occur when the molecules is ionized (acting as an acid) or un-ionized (acting as a base). • Some indicators only work in a specific range of pH. Choosing the right one is important! • Once the drops are added, the sample is ruined • Some dyes are natural, like radish skin or red cabbage

19. Choosing the Correct Indicator • Not all indicators shift colors at pH 7. • Many change colors over a wide range of pH values. • When testing a sample for acidity or basicity it is best to choose an indicator that has a color change close to pH 7 • Or use pH paper • Or use a pH meter to get a digital reading

20. Sample Indicator pH Ranges • Crystal Violet = yellow (pH 1) blue • Cresol Red = red (pH 2) yellow (pH 8) red • Thymol Blue = red (pH 3) yellow (pH 8) green/blue • Bromophenol blue = yellow (pH 4) blue • Methyl orange = red (pH 4.5) orange/yellow • Bromcresol green = yellow (pH 4.5) green/blue • Methyl red = pink (pH 5.5) yellow • Bromcresol purple = yellow (pH 6) purple • Alizarin = yellow (pH 6.5) red (pH 12) purple • Bromthymol blue = yellow (pH 7 ) green/blue • Phenol red = yellow (pH 7.2) red • Phenolpthalein = clear (pH 8.3) pink • Thymolphtalien = clear (pH 10) blue • Alizarin yellow GG = orange (pH 10.5) red • Universal Indicator = red (pH 4) orange (pH 6) yellow (pH 7) green (pH 8) blue (pH 9) purple