Acids are the sour counterpart of Alkalis, or bases.
The scale of how sour or basic a substance is. Water is at 7 Ph, neutral. If a substance Has more than 7 Ph, it is an alkali (base). If lesser than 7 Ph, it is acidic. An indicator is something that measures Ph scales. For example, use berry tea as an indicator. If you pour in some vinegar, which is sour, acidic, the red berry tea will most likely turn white. If you mix in a teaspoon of bicarbonate, an alkali, the berry tea will turn a dark browny-greenish color. There are many types of acids. if you taste an acid such as vinegar, you will feel the sour taste on your tongue. Lemon is citric acid, while vinegar is something called Ethanoic acids(dang these horryfyingly difficult names, really). In car batteries, there is something called Sulphuric acids. But trust me, Don't bother tasting it. Sulphuric acids is the kind of liquid that carves out giant holes in mountains.
Now, for an experiment i did as part of The kitchen chemistry course with Dr Stephen Ashwort. You have a glass with some hot water. Put in a quarter of a teaspoon of Cornflower starch, commonly referred to as maizena, the brand name. This is your very own indicator! (HOORAY). Make sure you stirr it. Then, take another cup and fill it up with cold water. Now, add ten drops of iodine tincture in it. Put a teaspoon of it in your starch indicator. POOFF!! If you did everithing right, the solution will turn dark blue. And that means...(drums please)....... That iodine tincture and cold water should most surely be an alkali! Here's a link to the original experiment: https://www.futurelearn.com/courses/kitchen-chemistry/steps/8246/progress
Now, acids and alkalis are really fun and exciting to experiment with. Hope you found this article interesting!