Acidic, Basic & Neutral Solutions: Determining pH

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  • 0:02 What Are Acids & Bases?
  • 1:03 How Do You Know?
  • 2:40 The pH Scale
  • 3:35 Lesson Summary
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Lesson Transcript
Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

After watching this video, you will be able to explain the difference between acidic, basic, and neutral solutions and explain the concept of pH. A short quiz will follow.

What are Acids and Bases?

An acid is a type of chemical that forms solutions that taste sour due to a high concentration of positive hydrogen ions. A base is a type of chemical that forms solutions that taste bitter due to a low concentration of positive hydrogen ions. Acids will react with bases to form salts. A solution is a liquid mixture of a solute that is uniformly distributed around a solvent.

Acids sometimes have the word 'acid' in their name: like citric acid and hydrochloric acid. But lots of things are acidic: fruit juices are acidic, like oranges and lemons, so are Coca-Cola and tomatoes. Bases, on the other hand, are things like milk, potatoes, and green, leafy vegetables.

So, what about things in the middle? Water, for example, is neither particularly bitter nor particularly sour. So, water is said to be neutral. Something that is neutral is considered to be right in the middle of the scale from acids to bases.

How Do You Know?

But how do you know for sure if something is an acid or a base? If the thing you're interested in is edible, you can sometimes figure out if it's an acid or a base by tasting it and seeing if it's bitter or sour. But, that isn't very reliable.

Another way you can find out is by doing chemical reactions. If something reacts violently with a known acid, it's probably a base, and if something reacts violently with a known base, it's probably an acid. When you combine an acid and a base together, they undergo something called a neutralization reaction. This is where an acid and a base react to create a product that is neutral. When they react, they form neutral water and a salt.

But there is an easier way. We can use an indicator. An indicator is a substance that changes color in response to a particular feature of the material it's in contact with. We have indicators that tell us how acidic a substance is. Usually, they turn red for an acid, blue for a base, and green for neutral. In between those colors means that the substance is. . . in between. You can get an indicator in liquid form, where you just put a drop of the indicator on a substance and see what color it turns. You can also get indicator paper, where you put the paper inside a liquid and watch as it changes color to see how acidic or basic the liquid is. When you compare the color of an indicator with a chart that shows you what the color means, you can find out whether it's an acid, base, or neutral.

The pH Scale

But the words acid, base, and neutral are pretty vague. In science, we like to put numbers to things. And, we have a way of doing that: it's called pH. pH is a measure of how acidic or basic a substance is. A pH of 0 is the most acidic, a pH of 14 is the most basic, and a pH of 7 is perfectly neutral.

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