5.5 Acid and Alkali

Science Form 2

~The word acid comes from the Latin word ‘acidus’,

which mean sour.

~Acid in food gives the food a sour and tangy taste.

~Acids used in laboratory are harmful.

~Hydrochloric acid, sulphuric acid and nitric acid are

three common acids used in the laboratory.

~has a sour taste

~has a pH value less than 7

~has a corrosive nature

~turns blue litmus paper red

~Reacts with reactive metals such as

zinc, magnesium and iron to produce

hydrogen gas. The hydrogen gives

out a squeaky ‘pop' when tested with

a lighted splinter.

# Alkali is the chemical ‘opposite’ of acid

# Alkalis are often used in many household cleaners

such as in bath, sink and glass cleaners.

# Ammonia solution, sodium hydroxide solution and

potassium hydroxide solution are three common

alkalis used in the laboratory.

# has a bitter taste

# has a soapy feel

# has a pH value greater than 7

# has a corrosive nature

# turns red litmus paper blue

# reacts with ammonium salts to release ammonia

when heated

Activity with Students

Group the substance you taste

Acidic Alkaline

The properties of acid and alkali:

Properties of Acid Properties of Alkali

• Has a pH value less than7• Has a sour taste• Corrosive• Turns blue litmus to red• Reacts with most metals

• Has a pH value more than 7• Has a bitter taste and feels soapy• Corrosive• Turns red litmus to blue

Acidic and Alkaline substance in daily life

Uses of acid and Alkali in daily

AcidSulphuric acid used in car batteries used in making fertilizers, paper, plastic

Hydrochloric acid used to clean metals kill the bacteria in our stomach

Nitric Acid used to make explosives

AlkaliSodium hydroxide used to make paper make soap, detergents, plastic

Potassium hydroxide used to dye cloth used to remove varnish and paint

Properties of Acid Properties of Alkali• Has a pH value less than7• Has a sour taste• Corrosive• Turns blue litmus to red• Reacts with most metals

• Has a pH value more than 7• Has a bitter taste and feels soapy• Corrosive• Turns red litmus to blue

1. State the properties of Acid and Alkali….

State 1 use of

Hydrochloric acid Sodium hydroxide

kill the bacteria in our stomach make soap, detergents, plastic

1. Acids and alkalis may exist in solids, liquids or gases.

2. However, acids and alkali will only show their acidic and alkaline properties when dissolved in water.

3. For example, when a piece of dry blue litmus paper is added to solid citric acid, there is no change in colour.

Solid citricacid

Dry bluelitmus paper

Citric acidIn water

Blue litmus paper

Solid citricacid

Dry bluelitmus paper

Citric acidIn water

Blue litmus paperturns red

Acids need water to show its properties

Solid bariumhydroxide

Dry redlitmus paper

Red litmus paper

Solid bariumhydroxide In water

Dry blueLitmus paper

Blue litmus paperturns red

Alkalis need water to show its properties

Solid bariumhydroxide Solid barium

hydroxide In water

What happen to red litmus paper if put in solid barium hydroxide???

How to show the properties of barium hydroxide??

What happen to blue litmus paper if put in solid citric acid???

How to show the properties of citric acid??

What happen to red litmus paper after that???

What happen to blue litmus paper after that???

Aim:

To identify the properties of acid and alkali.

Problem Statement (Acid):

What are the properties of acid?

Hypothesis:

A: Acid has the pH value less than 7

B: Acid has the sour taste

C: Acid is corrosive

D: Acid will turn the blue litmus to red

E: Acid will react with metal

Materials:

pH paper, colour chart, dilute hydrochloric acid, lemon, dilute vinegar, filter paper, red litmus paper, blue litmus paper, sandpaper, concentrated hydrochloric acid, wooden splinter.

Apparatus:

Test tubes, white tile, dropper

Procedures:

A: pH value

1. Dip a piece of pH paper into a test tube with 3cm3 of dilute hydrochloric acid.

2. Compare the resulting colour with the colour chart

3. Repeat steps 1 and 2 for lemon juice and dilute vinegar.

Diagram:

Dilute hydrochloride acid Lemon Juice Dilute vinegar

B: Taste

1. Taste a lemon juice

C: Corrosive Nature (teacher’s demonstration)

Filter Paper

White tile

Concentrated Hydrochloric acid

Red litmus paper

Blue litmus paperWhite tile

Dropper

Dilute hydrochloricacid

D: Effect on litmus paper

E: Reaction with metals

Dilute hydrochloric acid

Magnesium ribbon

Sand paper

Test with lighted splinter

Problem Statement (Alkali):

What are the properties of alkali?

Hypothesis:

A: Alkali has the pH value more than 7

B: Alkali has a feels of soapy

C: Alkali is corrosive

D: Alkali will turn the red litmus to blue

Materials:

pH paper, colour chart, dilute sodium hydroxide, filter paper, red litmus paper, blue litmus paper, concentrated sodium hydroxide, distilled water

Apparatus:

Test tubes, white tile, dropper

Procedure:

A: pH value

1. Dip a piece of pH paper into a test tube with 3cm3 of dilute sodium hydroxide.

1. Compare the resulting colour with the colour chart

1. Repeat steps 1 and 2 for ammonium hydroxide and dilute barium hydroxide

Diagram:

Dilute sodium hydroxide ammonium hydroxide dilute barium

hydroxide

B: Feel

1. Feel the dilute sodium hydroxide

C: Corrosive Nature (teacher’s demonstration)

Filter Paper

White tile

Concentrated sodium hydroxide

Red litmus paper

Blue litmus paperWhite tile

Dropper

Dilute sodium hydroxide

D: Effect on litmus paper

Observation:

Acid

Alkali

Properties of Acid Properties of Alkali

• Has a pH value less than7• Has a sour taste• Corrosive• Turns blue litmus to red• Reacts with most metals

• Has a pH value more than 7• Has a bitter taste and feels soapy• Corrosive• Turns red litmus to blue

Conclusion:

Homework:

Complete the report

Do the note for

• the properties of acid and alkali

• the role of water

• the uses of acid and alkali in daily life.

That all 4 today…………..