Acids and Bases Property of some aqueous solutions is their ability to act as an acid or base

Acids and Bases Acids and bases play an important part in our lives.  Proper acidity of our blood and other body fluids is vital to our health  Many products we use are acidic Citrus fruits contain citric acid Aspirin is an acid Our car batteries are filled with sulfuric acid

Acids and Bases Baking soda and milk of magnesia are basic. Antacids are basic compounds like carbonates, bicarbonates and hydroxides Dilute solutions of ammonia are used for cleaning. Caustic sodium hydroxide can be used to clean drains.

How is pH measured? We can use a scale based on the hydrogen ion concentration to express how acidic or how basic (alkaline) a particular solution is. This is called the pH scale.

We measure the Hydrogen Ions to determine the pH level

The pH scale is intended to be a convenience The pH scale ranges from 0-14

Determining pH of a solution pH = Measure of Hydrogen Ions (H+) in a solution Where do Hydrogen Ions (H+) come from? Well, it's all part of water really... Chemically acids have the ability to produce a hydrogen ion when dissolved in water How acidic a solution is depends on how easy it is to remove the hydrogen The amount of hydrogen ions produced in water allows us to determine the pH level Bases on the other hand have the ability to pick up these hydrogen ions, and the pH level is determined by their ability to pick up a hydrogen ion.

pH If the pH is less than 7, the substance is acidic. If the pH is greater than 7, the substance is basic or alkaline. If the pH is 7, the substance is neutral.

pH scale vs. Hydrogen Ions More ions Fewer Ions Lower pHHigher pH

Properties of Acids Acids may be classified as strong or weak. Depends how easily it is for the hydrogen to be removed Strong acids – sulfuric, nitric, HCl Weak acids – citric, lactic, acetic Acids are also recognized because of their sour taste. The tart taste of citrus fruits and vinegar are due to acids. React with some metals and carbonates (baking soda)

Properties of Bases A base is substance that has the ablility to pick up the H ion produced by an acid in an aqueous solution Bases are also recognized because they feel slippery or soapy. Bases also have a bitter taste. The bitter taste of milk of magnesia Do not react with metals or carbonates

Solutions may be: strongly acidic (0 - 2), weakly acidic (2 - 7), neutral (pH=7), weakly basic (7 - 12), strongly basic ( ).

How do we know whether a solution is an Acid or a Base?? To measure or determine the pH of a solution, there are several methods.

Determining pH Litmus paper can be used to indicate if a solution is acidic or basic. However, it does not indicate “how acidic” or “how basic”.

What is litmus ? Litmus is one of a large number of organic compounds (it is actually extracted from certain mosses) that change colors when a solution changes acidity at a particular point. Litmus is the oldest known pH indicator. It is red in acid and blue in base. Litmus is often impregnated onto paper to make 'litmus paper.'

Properties of Acids An acid can be identified in the laboratory because it turns a plant pigment called litmus red. A base can be identified in the laboratory because it turns a plant pigment called litmus blue.

Determining pH pH indicators can also be impregnated onto paper and used to determine pH. Paper, called pHydrion paper, is impregnated with a universal indicator. It can be used to determine the approximate pH over a full range.

Kinds of pH paper

Measuring pH The most accurate method for determining pH is using a pH meter. This consists of a electrode that measures the ionic current between the two poles. The current is then converted by the instrument into pH values. These are accurate to pH units.

Kinds of pH meters

pH & Buffers A buffer keeps something where it should be. It buffers adverse swings. It shields, cushions and protects. Is necessary to control any change in pH in some systems Especially in biological systems which need to control pH Living systems have buffering systems in place In order to maintain pH at a constant requires buffering of the system in a pond

Buffers Buffers tie up foreign acid and base There is a limit as to how much acid or base a buffer can absorb This is called buffer capacity A buffer would be used to maintain the pH of a product within a narrow range. Buffers reduce the variation in the pH of a product, as shown on the graph

Examples of Buffers Carbonate buffer system to maintain blood pH Phosphate system regulate cellular pH Proteins in the body regulate the body pH as needed Antacids – buffering and non-buffering