Chemical Changes

Question 1

what is the difference between Chemical and Physical changes

Answer 1

1. Physical changes have no new substances formed
2. The changes can usually be reversed and get their constituents by using separation techniques
3. Chemical changes occur when one or more substances are formed.
4. The changes are not easily reversible and cannot get the reactants back very easily.

Question 2

How do we represent Chemical reactions?

Answer 2

1. Use word equations to show the substances that are involved in chemical reactions.
2. A word equation includes the reactants used and the products formed in a chemical reaction.
3. The reactants are on the left and the products are on the right side.
4. They are connected by an arrow

Question 3

What happens during a chemical change?

Answer 3

The atoms rearrange themselves to form products

Question 4

Give me some some examples of word equations

Answer 4

Hydrogen + Oxygen = Water

Question 5

What happened to the numer of atoms before and after the reaction?

Answer 5

1. They remain the same.
2. The mass of the reactants is also the same as the mass of the products.
3. Mass is conserved

Question 6

What are some types of chemical changes

Answer 6

Combustion, Thermal Decomposition, Oxidation and Neutralization

Question 7

What are the properties of acids

Answer 7

1. Sour taste
2. May burn the skin.
3. Turns blue litmus paper red.
4. Reacts with alkalis , metals, and carbonates.

Question 8

Give an example a of strong acid

Answer 8

Acid in car battery

Question 9

Give an example of a strong alkali

Answer 9

Oven cleaner

Question 10

What happens when alkalis react with acids

Answer 10

1. Neutralisation
2. Acid + Alkali = Salt + Water

Question 11

What is the term salt used for?

Answer 11

‘Salt’ is a general term for a compound containing an element that is a metal.

Question 12

What is the word equation that represents chemical reactions between acids and metals

Answer 12

acid + metal = salt + hydrogen

Question 13

What can we do to test for hydrogen?

Answer 13

1. Use a lighted splint and insert it in the test tube without it touching the solution
2. It should extinguish with a pop sound

Question 14

What is the word equation that represents chemical reactions between acids and carbonates

Answer 14

acid + carbonate= salt + carbon dioxide + water

Question 15

How can we test for carbon dioxide?

Answer 15

1. Use limewater
2. If white precipitate is formed, there is carbon dioxide

Question 16

What are the ways we can determine the acidity or alkanity of a solution?

Answer 16

pH scale, litmus paper, universal indicator soloution.

Question 17

What happenes when alkalis or acids come into contact with blue or red litmus paper.

Answer 17

1. Acids turn blue litmus red
2. Alkalis turn red litmus blue

Question 18

What are some applications of neutralisation

Answer 18

1. Antacids (to neutralise excess gastric acid).
2. Toothpaste (helps neutralise acids that cause tooth decay)

Question 19

State some of the ways chemical changes occur

Answer 19

1. Mixing
2. Heating
3. Exposure to light
4. Exposure to oxygen
5. Using an electric current ( electroplating)

Question 20

How does the knowledge of chemical reactions help us in our daily lives.

Answer 20

1. Cooking
2. Respiration
3. Decomposition (decay)
4. Rusting
5. Combustion

Question 21

What are the properties of Alkalis

Answer 21

1. Have a bitter taste
2. Soapy feel
3. May burn the skin
4. Turns red litmus paper blue.
5. Reacts with acids to neutralise

Question 22

Give an example of a weak acids

Answer 22

Citric acid found in orange juice

Question 23

Give an example of a weak alkali

Answer 23

Baking soda