S Acids and Bases

Question 1

Where does the word ‘acid’ come from?

Answer 1

The word acid comes from the Latin word ‘acidus’ meaning sour.

Question 2

Give some examples of everyday substances that contain acid

Answer 2

Hydrochloric acid in the stomach
Sour milk contains lactic acid
Acid drop sweets or lemons and grapefruits contain citric acid.

Question 3

What do we use to test for the presence of an acid?

Answer 3

We use a substance called an indicator to test for the presence of an acid.

Question 4

What colour does acid turn litmus?

Answer 4

Acid turns litmus from blue to red

Question 5

What do indicators do and give an example of an indicator?

Answer 5

Indicators tell us/indicates if a substance is an acid. An example of such a substance is litmus.

Question 6

What substances also work well as indicators?

Answer 6

The juices from red cabbage and blueberries also work well.

Question 7

What is a base?

Answer 7

A base is a chemical opposite to an acid

Question 8

What are bases that dissolve in what called? Give an example of one

Answer 8

Bases that dissolve in water are called alkalis. Soap is an example of an alkali. 
Sodium hydroxide (caustic soda) is an alkali. It dissolves in water and is very corrosive.

Question 9

What colour do bases turn litmus?

Answer 9

bases turn litmus from red to blue.

Question 10

Give examples of other common indicators. What colours do they turn when in the presence of an acid and base?

Answer 10

Methyl orange: It is red in an acidic solution and yellow in a basic solution.
Phenolphthalein: It is colourless in an acidic solution and pink in a basic solution.

Question 11

Indicator definition

Answer 11

An indicator is a compound that shows by means of a colour change whether a substance is acidic or basic.

Question 12

What is a neutral substance? Give examples of neutral substances.

Answer 12

A neutral substance is neither an acid nor a base. Examples are sugar, water and salt.

Question 13

When there is no colour change, we say that a substance is _____?

Answer 13

When there is no colour change, we say that a substance is neutral

Question 14

What colour does litmus turn when with a neutral substance?

Answer 14

In neutral substances, red litmus stays red and blue litmus stays blue.

Question 15

What is the pH scale used for?

Answer 15

A pH scale is used to tell us how acidic or basic a substance is.

Question 16

What is the scale of the pH scale and what does it indicate?

Answer 16

The pH scale goes from 0 to 14. This scale indicates the level of acidity or basicity in a solution.

Question 17

List at what level is a substance neutral, acidic or basic (alkaline) on the pH scale.

Answer 17

A solution whose pH is 7 is neutral.
A solution whose pH is less than 7 is acidic.
A solution whose pH is greater than 7 is basic (alkaline).

Question 18

What is it important to know about litmus and pH?

Answer 18

Litmus tells us if a substance is acidic or basic. It does not tell us the pH of the substance.

Question 19

How can we find the pH of a substance?

Answer 19

pH can be measured using pH paper or universal indicator solution. We can use a pH sensor attached to a data logger and a computer as well.

Question 20

Give some examples of everyday substances that contain bases.

Answer 20

Drain cleaner contains a base called sodium hydroxide (caustic soda).
Indigestion tablets contain magnesium hydroxide.
Toothpaste contains a base called hydrogencarbonate.