Acids and bases

Acids, bases Part 1

M. Kennedy

https://www.youtube.com/watch?v=KfWvdSyW6Io

https://www.youtube.com/watch?v=KfWvdSyW6Io

pH

► The acidity or basicity of a substance, a

measurement of how many hydrogens or
hydroxides ionize when dissolved in water

► Scale is from 1-14

► pH is a measurement or description of a quality.

► The pH of cola is about 2, this is because it is

acidic, it is not acidic because it has a pH of 2

pH

► Acids: substances with pH below 7 produce hydrogen ions in

water, the more hydrogen ions produce the lower the pH

► Bases: substances with pH above 7 produce hydroxide ions

in water

► When in solution, you can say bases produce hydroxide ions

► you cannot say they neutralize a solution, or raise the pH unless

you know what type of solution to which the base has been
added

pH

►
A pH of 7 is neutral

► The hydrogen ions and hydroxide ions cancel each other out,

forming water

►
Neutralization reaction occurs when an acid and base are
added together

► the ions cancel each other

► forming water

► a salt precipitate

► Some produce a gas (this is important in leavening)

►
When the number of H+ and OH- are equal the end point or
equivalence point of the neutralization reaction is reached

Multiple Choice

On the pH scale, _____

• a neutral solution has a value of 14

• lower values indicate greater acidity

• higher values indicate greater acidity

• all of these are correct

pH in food

► The pH in our food has many different functions.

Understanding how to manipulate or control the pH of
the system, will help control the chemical reactions and
overall quality of the end product (your food).

► Example- Kale has a very bitter taste (basic) but is not so

bitter with a vinegar based dressing.

Poll

pairing acids and bases in foods will counter the flavors of each, giving the food great flavors (such as kale and vinaigrette)

• true

• false

In food

► Color: pigments change color or intensity with a

difference in pH

► Cocoa- regular Hershey’s cocoa powder vs special

dark. The special dark is more neutral, regular cocoa
is more acidic

► Indicator: natural pigments change color with a

change in pH, can be used to measure pH

► Taste:

► Acids- sharp, tangy, sour (think lemons)

► Bases- bitter (think unsweetened coffee)

Measuring pH

►
pH indicator- a protein that changes color with a change in pH

► Anthocyanins are one type of protein- this is the red or purple

pigment in plants

►
pH papers- contain indicator pigments

► Litmus paper- only indicates an acid or a base

► pH paper- more accurate than litmus paper, with a wider

range, compare the color to a standard

►
pH meter- most accurate measurement of pH

► Think of the difference between someone feeling your

forehead and a thermometer to determine if you have a fever

Multiple Choice

A substance that changes color with a change in pH is called ____.

• unstable

• an indicator

• an acid

• a base

Strength

►
Strength of an acid or base is based on the percentage of
molecules that do ionize.

► A small percentage will be described as weak, such as vinegar

(pH 2)

► A large percentage will be described as strong such as

hydrochloric acids (pH 2)

►

strong acids are very corrosive

►
Acids and bases in our food are weak and pose little health risk
(not corrosive)

►
pH and strength measure different properties of acids and bases

► like temperature and humidity both are important for a heat

index

Multiple Choice

Acids in foods pose little health risk becasue ____.

• they are weak

• they are not used often in food

• they are highly soluble

• all of these are correct

• none of these are correct

Multiple Choice

A base in which few molecules ionize is called ____.

• neutral

• dilute

• weak

• all of these

In food

► In food, pH increases food safety

► pH below 4.6 inhibits microbial growth

► Used in cheese production- curdles milk

► Acids are used as meat tenderizers

► Acids are used to “cook” seafood

► Acids and bases are used as chemical leavening

agents and provides texture

Multiple Choice

The pH of a solution and the strength of an acid describe different properties of the same solution.

• true

• false

Open Ended

How can pH be used for food safety?

Multiple Choice

pH is important for the quality of food because it contributes to ____.

• color

• taste

• texture

• safety

• all of these

Multiple Select

Acids can be used to "cook" seafood and fish because ____.

• Acids enhance the flavor of seafood
• the acid causes the same type of chemical changes as heat

• they will prevent burned food

• Acids make seafood more tender

pH and eggs

►

Fresh eggs have a pH of 6.4-7

►

Older eggs may be as high as 9.7

►

Fresh egg whites can be as low as 5.6

►

The pH of eggs has an impact on the quality of your product and the
overall process of leavening.

►For example, if a recipe depends on eggs to provide the acid needed for
baking soda, older eggs (basic) could cause a recipe to fail

Multiple Choice

The freshness of eggs changes the pH of the egg because eggs are still living and metabolism of the egg causes the changes.

• true

• false

pH and type of cake

Cake type

pH range

Fruit cake

4.4-5.0

Angel food cake ( uses only egg whites)

5.2-6.0

Pound cake

6.6-7.1

Yellow layer cake

6.7-7.5

White layer cake

7.0-7.5

Sponge cake

7.3-7.6

Chocolate cake

7.5-8.0

Open Ended

Evaluate the table with types of cake and pH.

What relationship do you see with pH and type of cake?

Examples of the pH scale