Unit C Lesson 2: Acids, Bases, and pH
Completion requirements
Unit C Lesson 2: Acids, Bases, and pH |
Learning Targets |
Big Question: What is pH and how does it relate to acids and bases?
Acids and bases are very common, and can be helpful and harmful depending on the situation. We compare the strength of acids and bases using the pH scale.
Acids and bases are very common, and can be helpful and harmful depending on the situation. We compare the strength of acids and bases using the pH scale.
At the end of this inquiry, you should be able to answer the following questions:
- What is an acid?
- What is a base?
- What is the range of the pH scale?
- What are some examples of acids?
- What are some examples of bases?
- How is an indicator used?
Pages 191 to 193 in your textbook will help you answer these questions about acids, bases, and pH.
Introduction
Acid Rain
Acid rain is any form of precipitation such as rain, fog, snow, or hail that contains harmful substances such as nitrogen oxides and sulfur oxides.
You have learned throughout your life from news, weather, and school that the term ”acid rain” is dangerous to the environment. However, do you have a good understanding of what an acid is and could you identify what an acid is?
Figure 1 – Acid rain diagram courtesy Siyavula Education.
Watch
Watch the following video carefully, it provides an excellent overview of acids and bases, and how to tell them apart.
The pH Scale
The pH scale is used to identify if a substance is an acid or a base. pH stands for the power of hydrogen. pH is a measurement of the hydrogen ion concentration, [H+], in a solution.
The pH scale is used to identify if a substance is an acid or a base. pH stands for the power of hydrogen. pH is a measurement of the hydrogen ion concentration, [H+], in a solution.
If there is a high H+ concentration, the pH indicates that you have a very acidic solution. If there is a low H+ concentration (which means there is a high concentration of hydroxide ion, OH–), the pH indicates that
you have a very basic (or alkaline) solution.
The pH scale runs from 0 to 14.
The pH scale runs from 0 to 14.
- An acid has a pH of less than 7.
- A base has a pH of greater than 7.
- A neutral substance has a pH of 7. It is neither an acid nor a base.
Figure 2 – Acids have high concentrations of H+ ions when dissolved in water. Bases have high concentrations of OH– ions. Images courtesy of Anatomy & Physiology, Connexions.
Acids are encountered frequently both in chemistry and in everyday living.
The word acid comes from the Latin word acere, which means "sour". All acids taste sour (although you should never taste them unless a teacher or parent indicates that they are edible). Well-known acids from ancient times were vinegar, lime juice, and sour milk.
Acids can be found everywhere. They are in your foods, your medicines, your beauty products, and your electronics. Acids are generally not dangerous unless they are strong acids, meaning their high hydrogen ion concentration is very aggressive in reacting with other substances.
Bases react vigorously with acids and will cause chemical burns.
All bases taste bitter, and most bases are extremely dangerous to taste. Some bases that are edible are mustard, baking soda and egg whites. Many medicines are bases so they taste bitter. Flavouring is added to cough syrups to cover the bitter taste.
Bases feel slippery. The slippery feeling is caused because your skin dissolves a little when you touch them. Bases react with oils and greases. For that reason, bases are used as household cleaners
Interactive
Acids and Bases
-
The BrainPOP video, reviews the concept of Acids and Bases.
Click here
to watch "Acids and Bases".
You will need a username and password to access the video.
- Username: 0099
-
Password: students
-
Click here
to complete the quiz on Acids and Bases. Remember to check your answers at the end!
Interactive
The pH Scale
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Have you ever heard of the pH scale? This BrainPOP video explains exactly how the pH Scale works.
Click here
to watch "pH Scale".
You will need a username and password to access the video.
- Username: 0099
-
Password: students
-
Click here
to complete the BrainPOP quiz on the pH Scale. Remember to check your answers at the end!
- Click here to complete the virtual lab on pH scale. There are two parts to this lab: the introduction and measuring pH. You need only to complete the introduction. Measuring pH is optional.
Acidic Solutions
The pH represents varying strengths of acids and bases. The acid side of the pH scale measures between pH = 0 to pH =7. A pH of 1 indicates a very strong acid. A pH of 6 indicates a weak acid. The closer the pH is to 7, the weaker the acid is. Therefore, a solution with a pH of 4 is less acidic than a solution with a pH of 2.
Acidic Solutions
The pH represents varying strengths of acids and bases. The acid side of the pH scale measures between pH = 0 to pH =7. A pH of 1 indicates a very strong acid. A pH of 6 indicates a weak acid. The closer the pH is to 7, the weaker the acid is. Therefore, a solution with a pH of 4 is less acidic than a solution with a pH of 2.
Acidic Solutions
| Substance |
Approximate pH
|
|
|
Battery acid is very dangerous. It is corrosive and can cause severe chemical burns.
|
1 |
|
Lemon juice will hurt if you get lemon juice on a cut or in your eye.
|
2 |
|
Orange Juice
|
3 |
|
Tomato
|
4 |
|
Coffee
|
5 |
|
Egg yolks
|
6 |
|
Bottle of Distilled Water
|
Pure distilled water is neutral and has a pH of 7
|
|
Basic Solutions
The pH represents varying strengths of acids and bases. The base side of the pH scale measures between pH = 7 to pH = 14. A pH of 8 indicates a very weak base. A pH of 14 indicates a very strong base acid. The closer the pH is to 7, the weaker the base is. Therefore, a solution with a pH of 9 is less basic than a solution with a pH of 12.
The pH represents varying strengths of acids and bases. The base side of the pH scale measures between pH = 7 to pH = 14. A pH of 8 indicates a very weak base. A pH of 14 indicates a very strong base acid. The closer the pH is to 7, the weaker the base is. Therefore, a solution with a pH of 9 is less basic than a solution with a pH of 12.
|
Solution
|
Approximate pH
|
|
Bottle of Distilled Water
|
Pure distilled water is neutral and has a pH of 7
|
|
Tap water (very weak base)
|
8 |
|
Detergents
|
9 |
|
Toothpaste
|
10 |
|
Hair remover
|
11
|
|
Household ammonia
|
12
|
|
Oven Cleaner
|
13
|
|
Drain cleaner
|
14 |
|
Very strong acids and bases are on the extreme ends of the
pH scale
. The acids and bases near the centre of the scale (closer to 7) are weaker.
Summary of Properties of Acids and Bases
Summary of Properties of Acids and Bases
| Acids | Bases |
|
pH is less than 7
|
pH is greater than 7
|
|
sour taste
|
bitter taste
|
|
react with metals to form hydrogen gas
|
do not react with metals |
|
produce hydrogen ions when dissolved in water
|
produce hydroxide ions when dissolved in water
|
|
aqueous solutions conduct electricity
|
aqueous solutions conduct electricity
|
|
feel slippery
|
|
| react with fats to produce soap |
Figure 3 – Many pH scales, such as this one, have universal indicator colours that match all of the pH levels. You can estimate the pH of an unknown substance by adding it to some universal indicator and matching colours.
How do you identify if a solution is an acid or a base?
A beaker filled with a liquid is on the counter. How would you determine if this solution is an acid or a base?
An indicator is a chemical that changes colours based on the pH of a solution. Indicators are very useful tools to measure the pH of a solution and to determine if a substance is an acid , is neutral, or is a base.
Indicator paper can be used to identify the pH of a solution. In the lower grades, you have heard of or perhaps have used litmus paper. Litmus paper turns blue when placed in a base, it turns red in an acid, and if the pH happens to be 7, then it is light purple. There are various types of indicator papers used in science labs and on the market. Universal indicator paper is able to change to a wider range of colors compared to regular litmus paper.
In addition to using indicator paper, you can add several drops of liquid indicator to find the pH of a clear fluid. The universal indicator solution is a liquid that changes various colours based on the pH of the substances it is mixed with.
Then, you would compare the colour of the resulting solution to a colour chart similar to Figure 1.12(a), provided on page 193 in the Science in Action 9 text.
A beaker filled with a liquid is on the counter. How would you determine if this solution is an acid or a base?
An indicator is a chemical that changes colours based on the pH of a solution. Indicators are very useful tools to measure the pH of a solution and to determine if a substance is an acid , is neutral, or is a base.
Indicator paper can be used to identify the pH of a solution. In the lower grades, you have heard of or perhaps have used litmus paper. Litmus paper turns blue when placed in a base, it turns red in an acid, and if the pH happens to be 7, then it is light purple. There are various types of indicator papers used in science labs and on the market. Universal indicator paper is able to change to a wider range of colors compared to regular litmus paper.
In addition to using indicator paper, you can add several drops of liquid indicator to find the pH of a clear fluid. The universal indicator solution is a liquid that changes various colours based on the pH of the substances it is mixed with.
Then, you would compare the colour of the resulting solution to a colour chart similar to Figure 1.12(a), provided on page 193 in the Science in Action 9 text.
Check Your Understanding
Universal indicator solution was added to samples of vinegar, club soda, and household ammonia. [See Figure 1.12 (b) on page 193.] Notice the various colours that have appeared. If you have any anomalies with your vision that hinder
you from identifying colours, please contact your teacher.
Figure 4 – Vinegar, club soda, and ammonia mixed with universal indicator. © Science in Action 9, page 193
Figure 5– The pH scale of universal indicator colours. © Science in Action 9, page 193
1. Using Figure 4 and Figure 5, what do you think the pH of vinegar is?
3. Using Figure 4 and 5, find the approximate pH of club soda?
5. Using Figure 4 and 5 find the approximate pH of ammonia.
Compare the colour of the beaker in front of the vinegar to the chart above.
The pH of vinegar is between 3 and 4.
3. Using Figure 4 and 5, find the approximate pH of club soda?
Compare the colour of the beaker in front of the club soda to the chart above.
The pH of club soda is between 2 and 3.
5. Using Figure 4 and 5 find the approximate pH of ammonia.
Compare the colour of the beaker in front of the ammonia to the chart above.
The pH of vinegar is between 9 and 10.
2. Is vinegar an acid or base?
4. Is club soda an acid or base?
6. Is ammonia an acid of base?
If the pH is less than 7, the solution is an acid. If the pH is above 7, the solution is a base.
Vinegar is an acid because its pH is less than 7.
4. Is club soda an acid or base?
If the pH is less than 7, the solution is an acid. If the pH is above 7, the solution is a base.
Club soda is an acid because its pH is less than 7.
6. Is ammonia an acid of base?
If the pH is less than 7, the solution is an acid. If the pH is above 7, the solution is a base.
Ammonia is a base because its pH is greater than 7.
Figure 6 lists the approximate pH values for many common substances. pH values of exactly 7 are called "neutral" solutions. If the pH is 6.99, it is an acidic solution and if the pH is 7.01, the solution is basic.
Figure 6 – Common household substances and their approximate pH values.