Acids Bases They are everywhere In your food
Acids & Bases They are everywhere. . In your food In your house EVEN IN YOU!!!!!
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.
Properties of an Acid § § § Picture from BBC Revision Bites http: //www. bbc. co. uk/schools/ks 3 bitesize/science/chemistry/acids_b ases_1. shtml 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
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
What is a base? § A base is a solution that has an excess of OHions. § Another word for base is alkali. § Bases are substances that can accept hydrogen ions
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. § §
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.
p. H Scale § p. H is a measure of how acidic or basic a solution is. • The p. H scale ranges from 0 to 14. § Acidic solutions have p. H values below 7 § A solution with a p. H of 0 is very acidic. § A solution with a p. H of 7 is neutral. • Pure water has a p. H of 7. • Basic solutions have p. H values above 7.
p. H Scale • A change of 1 p. H unit represents a tenfold change in the acidity of the solution. • For example, if one solution has a p. H of 1 and a second solution has a p. H of 2, the first solution is not twice as acidic as the second—it is ten times more acidic.
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.
Acid – Base reactions § Each salt listed in this table can be formed by the reaction between an acid and a base.
Acid-Base Indicators
Measuring p. H § Now that we know what p. H of a solution is, how do we measure it in the lab? § The following slides will provide numerous examples of ways to measure p. H in the laboratory.
p. H testing § There are several ways to test p. H § § § § Blue litmus paper (red = acid) Red litmus paper (blue = basic) p. H paper (multi-colored) p. H meter (7 is neutral, <7 acid, >7 base) Universal indicator (multi-colored) Indicators like phenolphthalein Natural indicators like red cabbage, radishes
Paper testing § Paper tests like litmus paper and p. H 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.
p. H paper
p. H meter § Tests the voltage of the electrolyte § Converts the voltage to p. H § Very cheap, accurate § Must be calibrated with a buffer solution
p. H 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 p. H. 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
Choosing the Correct Indicator § Not all indicators shift colors at p. H 7. § Many change colors over a wide range of p. H values. § When testing a sample for acidity or basicity it is best to choose an indicator that has a color change close to p. H 7 § Or use p. H paper § Or use a p. H meter to get a digital reading
Sample Indicator p. H Ranges § § § § Crystal Violet = yellow (p. H 1) blue Cresol Red = red (p. H 2) yellow (p. H 8) red Thymol Blue = red (p. H 3) yellow (p. H 8) green/blue Bromophenol blue = yellow (p. H 4) blue Methyl orange = red (p. H 4. 5) orange/yellow Bromcresol green = yellow (p. H 4. 5) green/blue Methyl red = pink (p. H 5. 5) yellow Bromcresol purple = yellow (p. H 6) purple Alizarin = yellow (p. H 6. 5) red (p. H 12) purple Bromthymol blue = yellow (p. H 7 ) green/blue Phenol red = yellow (p. H 7. 2) red Phenolpthalein = clear (p. H 8. 3) pink Thymolphtalien = clear (p. H 10) blue Alizarin yellow GG = orange (p. H 10. 5) red Universal Indicator = red (p. H 4) orange (p. H 6) yellow (p. H 7) green (p. H 8) blue (p. H 9) purple
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