RED CABBAGE PH INDICATOR

THE PURPOSE OF THIS EXPERIMENT IS TO SHOW HOW TO MAKE YOUR OWN PH INDICATOR USING

CABBAGE JUICE

Why use cabbage juice?

• By boiling the red cabbage leaves, we extracted a class of pigment molecules called anthocyanins into solution. Anthocyanin molecules will change their color depending upon the pH of their environment and can indicate the pH of a solution.

What is pH?

• The pH scale measures how acidic or basic a substance is.

• It ranges from 0 to 14. • A pH of 7 is neutral. • A pH less than 7 is acidic, and a

pH greater than 7 is basic.

What is the pH scale?• The pH

scale measures

how acidic or basic a solution is.

Red Cabbage pH scale

neutralStrong

acidStrong alkali

Investigation

• Identify each solution as either an acid, base, or neutral.

Solution 1

Vinegar

pH: 3-4 (acid)

Solution 2

Soda

pH: 3 (acid)

Solution 3

Tap Water

pH: 7 (neutral)

Solution 4

Baking Soda

pH: 8-9 (base)

Solution 5

Milk

pH: 6 (acid)

Solution 6

Soapy Water

pH: 12 (base)

Solution 7

Lemon Juice

pH: 2-3 (acid)

Solution 8

Hand Sanitizer

pH: 7 (neutral)

RED CABBAGE JUICE CAN BE USED TO TEST THE PH OF COMMON HOUSEHOLD CHEMICALS.

RED CABBAGE JUICE CONTAINS A NATURAL PH INDICATOR THAT CHANGES COLORS ACCORDING

TO THE ACIDITY OF THE SOLUTION. 

ADD A LEMON TO THE GLASS OF CABBAGE JUICE

We noticed the color changed to red, which indicated that lemon

juice is classified as an acid.

ADD A LITTLE VINEGAR TO THE GLASS

OF CABBAGE JUICE

We noticed the color changed to red, which

indicated that vinegar is classified as an acid.

ADD A TEASPOON OF LAUNDRY DETERGENT

TO THE GLASS OF CABBAGE JUICE

We noticed the liquid turns green, indicating that this

chemical is a base.

ADD A TEASPOON OF OVEN CLEANER

TO THE GLASS OF CABBAGE JUICE

We noticed the color changed to green, which indicated that the oven

cleaner is classified as an base.

ADD A TEASPOON OF ALKA-PRIM TABLETS

TO THE GLASS OF CABBAGE JUICE

We noticed the color changed to green, which indicated that alka-prim

tablets are classified as an base.

DURING OUR EXPERIMENT THE PURPLE CABBAGE JUICE TURNED RED WHEN IT

WAS MIXED WITH SOMETHING ACIDIC AND TURNED GREEN WHEN IT WAS MIXED WITH SOMETHING BASIC. RED CABBAGE JUICE

IS CONSIDERED TO BE AN INDICATOR BECAUSE IT SHOWED US SOMETHING

ABOUT THE CHEMICAL COMPOSITION OF OTHER SUBSTANCES.

RED CABBAGE CONTAINS A WATER-SOLUBLE PIGMENT CALLED ANTHOCYANIN THAT CHANGES

COLOR WHEN IT IS MIXED WITH AN ACID OR A BASE.

THE PIGMENT TURNS RED IN ACIDIC ENVIRONMENTS WITH A PH LESS THAN 7 AND THE

PIGMENT TURNS BLUISH-GREEN IN ALKALINE (BASIC) ENVIRONMENTS WITH A PH GREATER

THAN 7.

Characteristics Of Acids

Acids can be characterized by:

1. A sour taste.

2. It turns blue litmus paper red

3. It tastes sour. Try drinking lemon juice (citric acid)

Characteristics of Bases

A Base is characterized by:

1. A bitter taste. (Milk of Magnesia)

2. It feels slippery. (Soapy Water)

3. It turns Red Litmus Blue.

Why Learn about Acids & Bases?

• What do you think is the pH level of NYC tap water?

• The pH of a swimming pool must be checked periodically. Why?

• Is it important for Lakes & Rivers to maintain a certain pH?

Properties of an Acid

Tastes Sour Conduct Electricity Corrosive, which means

they break down certain substances. Many acids can corrode fabric, skin,and paper

Some acids react strongly with metals

Turns blue litmus paper red

Picture from BBC Revision Bites http://www.bbc.co.uk/schools/ks3bitesize/science/chemistry/acids_bases_1.shtml

Uses of Acids

Acetic Acid = Vinegar Citric Acid = lemons,

limes, & oranges. It is in many sour candies such as lemonhead & sour patch.

Ascorbic acid = Vitamin C which your body needs to function.

Sulfuric acid is used in the production of fertilizers, steel, paints, and plastics.

Car batteries

What is a base?

A base is a solution that has an excess of OH- ions.

Another word for base is alkali.

Bases are substances that can accept hydrogen ions

Properties of a Base

Feel Slippery Taste Bitter Corrosive Can conduct electricity.

(Think alkaline batteries.) Do not react with metals. Turns red litmus paper

blue.

Acid – Base Reactions

A reaction between an acid and a base is called neutralization. An acid-base mixture is not as acidic or basic as the individual starting solutions.