Acids, Bases and Natural Indicators

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INTRODUCTION:

Nowadys, indicators have become technologically advanced and can be used for the main purpose of indicating whether something is acidic, basic or neutral. This is possible because in solutions of different pH, the colour of the inidcator will change simultaneously with pH change. This is made possible by pigments in the indicators. Hand made indicators include universal indicator, methyl orange, phenolphthalein and many more.

Acids and bases are diverse in this world. They are everywhere ranging from foods to trees to rocks and many more. Indicators can be used to determine whether these substances are acidic, basic or neutral.

Manufactured indicators are one type and the second type is natural indicators. Believe it or not, the majority of fruits, vegetables and flowers contain pigments which may be used as acid-base indicators. For example, Red cabbage contains within its leaves a red pigment called anthocyanin. This is present in many other vegetables such as capsicum, carrot, tulips and many more.

This anthocyanin has the ability to change colour in a variety of pH due to certain chemical reactions that take place involving H+ and OH- ions. Read on to discover the chemistry involved in these reactions.

Anthocyanins are complex molecules that have the ability to add and/or subtract hydroxide (OH-) ions. When anthocyanin is added to acidic solutions, hydroxide (OH-) ions will leave the anthocyanin molecule. On the other hand, when anthocyanin is added to basic solutions, the OH- ions from the water will attach themselves to the anthocyanin molecule.Therefore, anthocyanin is general name given to a series of similar compounds each with a different number of OH- ions attached. Anthocyanin is an indicator for the reason that each form of the compound reacts with light differently so that each form is a different colour�

Anthocyanin can be extracted from natural plants and vegetables in many ways. A very common way of extracting anthocyanin form plants is to place the plant in low boiling point alcohols which have been acidified with HCl and boiling for a while.�

There are other methods of extracting anthocyanin from vegetables. One very common method is boiling the vegetable in distilled water and waiting till boiling starts. The water reacts with the anthocyanin pigment which allows wxperimenters to use this water as the indicator.

Anthocyanin presents many vegetables such as beets, berries, cherries, fiji apples, eggplant, grapes etc with the red-purplish colour.

Anthocyanin gives colour to plants for a reason. This colour of plants and flowers helps attract pollinating animals to the flowers and aslo animals which help in seed dispersal.�

AIM:

To perform a first hand investigation to prepare and test at least two natural inidcators

To identify the colour of these indicators in acidic, basic and neutral conditions

To use the natural indicators to classify at least five household substances as acidic, neutral or basic

MATERIALS:

MATERIALS

QUANTITY

7

1

1

1

1

1

1

100 mL

Tulip

Minimum 15

1

2 (1 pair)

1

75 mL

75 mL

150 mL

MATERIALS

QUANTITY

1

acid

100 mL

Hydroxide

100 mL

50 mL

Detergent

50 mL

50 mL

50 mL

1

1

Lab coat

1

Knife

1

Peeler

1

HYPOTHESIS:

Based on previous knowledge and personal predictions, the following results are expected.

Eggplant

Radish

Acidic

Neutral

Remains purple

Remains pink

Basic

Purple Dark green

Pink

TABLE B2: COLOUR CHANGE OF TWO COMMON INDICATORS

Bromothymol blue

Universal indicator

Acidic

Neutral

Basic

TABLE C: Trial 1 (CLASSIFYING HOUSEHOLD SUBSTANCES)

ACIDIC

NEUTRAL

BASIC

Laundry detergent

Window cleaner

Caustic soda

Vinegar

Borax

Control (distilled water)

TABLE C: Trial 2 (CLASSIFYING HOUSEHOLD SUBSTANCES)

ACIDIC

NEUTRAL

BASIC

Laundry detergent

Window cleaner

Caustic soda

Vinegar

Borax

Control (distilled water)

TABLE C: The experiment (CLASSIFYING HOUSEHOLD SUBSTANCES)

ACIDIC

NEUTRAL

BASIC

Laundry detergent

Window cleaner

Caustic soda

Vinegar

Borax

Control (distilled water)

RISK ASSESSMENT:

SUBSTANCE

RISK

SAFETY TECHNIQUE

Vinegar

When vinegar comes into contact with skin it can cause irritation and itching

Wear gloves to prevent the vinegar from touching the skin

Glass beakers

If glass beakers are dropped, they might break and experimenter might get cut.

Wear a long sleeve lab coat and gloves just as a precaution and preparation for worst case scenario. Also, handle carefully

Hot materials

After the water is boiled in the beaker, the beaker would be really hot

Wear gloves to prevent burns. Handle carefully

Knife

When cutting with a knife, hand may slip and knife will scar the experimenter

Wear glove to prevent an accidental cut

Spills

The hot water, detergent and cleaner might spill causing a slippery surface

Wear lab approved closed shoes to prevent from slipping and hurting yourself

Window cleaners

An accidental spray might result in it entering the eyes

Safety glasses must be worn to prevent entry of these cleaners

Laundry detergent

Laundry detergent might spill and trigger a slippery surface

Wear lab approved closed shoes to prevent from slipping and hurting yourself

Hydrochloric acid

Hydrochloric acid causes burn and irritation when in contact with skin

Long sleeved lab coat and gloves must be worn

Bunsen flame

The bunsen flame is really hot and a mishap would be severe

Turn the bunsen nozzle until the safety blue flame appears

Indicators

Indicators are very toxic and might be accidentally inhaled

Be really careful where you place the indicators and handle with care

All chemicals

If inhaled can cause serious intestinal pains and damage�

Keep all chemicals away from children

PROCEDURE:

PART A:

Gather the two natural substances to be used as the indicators.

Prepare the samples the way you like whether it be dicing into small pieces, or squeezing for the juice etc.

Fill a beaker with 150 mL of distilled water or demineralized water

Prepare the bunsen burner by connecting it to the gas port

Turn the gas on and use a match to light up the beaker. (Note: Make sure the flame is the safety flame which is of blue colour.)

Place the samples of the first natural substance into the beaker carefully

Allow the water with the natural substance to boil for approximately 5 -10 minutes

Once the gas supply has been shut off from the beaker, allow the water with the natural substance to cool for minimum 5 minutes

Repeat steps 5-8 but this time using the second of the natural substances

PART B:

Prepare three solutions, one acidi, the second being basic and the third being neutral.

Place 15 mL of each solution into each of three beakers.

Place some masking tape on each beaker and label with a marker each beaker as containing the acidic, basic or neutral solution.

Use a pipette to gather 10 mL of the natural substance solution from part A and place into one of the labelled beakers.

Repeat step 4 for the remaining two solutions

Observe the colour change of the indicator in each of acidic, basic and neutral conditions.

Record all results and observations

PART C:

Gather the five household substances that you would be classifying.

Gather 6 beaker ( the extra beaker would be used for the control).

Place 20 mL of each of the household substances into each of the five test tubes.

Pour 20 mL of demineralized water into the remaining beaker as the control

Collect 20 mL of the first natural substance solution from part A and add to one of the household substances

Repeat step 5 but this time for the remaining 4 household substances and the control

Repeat steps 5-6 with the solution of the second natural substance

CONTROLLED VARIABLE: The control is the beaker with the distilled water

DIAGRAM:

Radish extract solution Eggplant extract solution

BEAKERS

RESULTS:

TABLE B1: COLOUR CHANGE OF TWO NATURAL INDICATORS

Eggplant

Radish

Acidic

Purple

Pink

Neutral

Purple

Pink

Basic

Purple

Pink

TABLE B2: COLOUR CHANGE OF TWO COMMON INDICATORS

Bromothymol blue

Universal indicator

Acidic

Neutral

Basic

TABLE C: Trial 1 (CLASSIFYING HOUSEHOLD SUBSTANCES)

ACIDIC

NEUTRAL

BASIC

Laundry detergent

Window cleaner

Caustic soda

Vinegar

Borax

Control (distilled water)

TABLE C: Trial 2 (CLASSIFYING HOUSEHOLD SUBSTANCES)

ACIDIC

NEUTRAL

BASIC

Laundry detergent

Window cleaner

Caustic soda

Vinegar

Borax

Control (distilled water)

TABLE C: The experiment (CLASSIFYING HOUSEHOLD SUBSTANCES)

ACIDIC

NEUTRAL

BASIC

Laundry detergent

Window cleaner

Caustic soda

Vinegar

Borax

Control (distilled water)

COLOUR CHANGE OF TWO NATURAL INDICATORS

COLOUR CHANGE OF TWO NATURAL INDICATORS

� EMBED PBrush ���

CAUSTIC

SODA

LAUNDRY DETERGENT

WINDOW CLEANER

BORAX

VINEGAR

CONTROL

(DISTILLED WATER)

� http://www.madsci.org/posts/archives/1998-03/890795428.Ch.r.html

� � HYPERLINK "http://books.google.com.au/books?id=K8urEPJvXNsC&pg=PA503&lpg=PA503&dq=extracting+anthocyanin&source=web&ots=WqleAzLSf8&sig=KXvxGY-Fxfso6TpIGoA4uKvs3Bo&hl=en" ��http://books.google.com.au/books?id=K8urEPJvXNsC&pg=PA503&lpg=PA503&dq=extracting+anthocyanin&source=web&ots=WqleAzLSf8&sig=KXvxGY-Fxfso6TpIGoA4uKvs3Bo&hl=en�

� http://www.madsci.org/posts/archives/2001-11/1006647185.Bt.r.html

� http://www.greenfootsteps.com/vinegar-and-bleach.html

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