Acidic, Basic & Neutral Solutions: Determining pH

Lesson Transcript
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.

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Christianlly Cena

Christianlly has taught college physics and facilitated laboratory courses. He has a master's degree in Physics and is pursuing his doctorate study.

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. Updated: 04/23/2020

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 (raw), 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.

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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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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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Additional Activities

Acids and Bases: Multiple Choice Exercise

This activity will help you assess your knowledge regarding acidic, basic, and neutral solutions.


For this activity, carefully read and select the best answer that completes each of the given statement. To do this, print or copy this page on a blank paper and circle the letter of your answer.

Multiple Choice

1) The following are examples of strong acids except __________.

A. hydrochloric acid

B. battery acid

C. vinegar

D. bleach

2) An acid is a __________-containing substance that is capable of donating a proton to another substance.

A. hydrogen

B. oxygen

C. nitrogen

D. collagen

3) A solution with a pH __________ 7 is known as an acid.

A. greater than

B. less than

C. equal to

D. multiple of

4) When an acid and a base are placed together, they undergo a __________.

A. spontaneous combustion

B. mineralization process

C. neutralization reaction

D. phase separation

5) An acid will cause an indicator solution to change color towards __________.

A. blue

B. green

C. ultraviolet

D. red

6) A neutral solution will cause an indicator solution to change color towards __________.

A. green

B. blue

C. orange

D. purple

7) Stomach acid has a pH of 4 that allows the breakdown of food for easier digestion.

A. True

B. False

8) Acids taste __________ while bases taste __________.

A. sweet, spicy

B. sour, bitter

C. salty, sour

D. bitter, sweet

Answer Key

  1. D
  2. A
  3. B
  4. C
  5. D
  6. A
  7. B
  8. B

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