One of the main differences between acids and bases is that acids have a pH that is less than 7 and bases have a pH that is greater than 7. When dissolved in water, acids are substances that will cause the concentration of hydrogen ions (H+) to increase. Bases, when dissolved in water, will instead cause the number of hydroxide ions (OH-) to increase.
There are additional physical and chemical differences between acids and bases. Acids taste sour while bases have a bitter taste. If a wound comes in contact with an acid, it will produce a stinging pain. Bases feel slippery. Acids react with metals to produce hydrogen gas, and will produce carbon dioxide gas when they react with a carbonate compound. Acids in an aqueous solution will turn litmus test paper red, while bases in an aqueous solution will cause it to turn blue.