chap 11 chemical changes

Question 1

what are properties of physical changes

Answer 1

• no new substances formed
• changes are usually reversible
• properties of the products are thee same as the reactants

Question 2

what are properties of chemical changes

Answer 2

• one or more new substances formed
• changes are usually not reversible
• properties of the products are different from the reactants
• energy ( heat or light ) is taken in or given out

Question 3

Atoms are….

Answer 3

neither created nor destroyed

Question 4

Mass is ___ during a chemical reaction

Answer 4

conserved

Question 5

what is combustion and its equation

Answer 5

it is when a substance is heated in oxygen
eg: C + O2 = CO2

Question 6

what is thermal decomposition and its equation?

Answer 6

It is when a substance breaks down into two or more simpler substances upon heating
Calcium carbonate -> (heat) calcium oxide + carbon dioxide

Question 7

what is oxidation and its equation?

Answer 7

It is when a substance gains oxygen
eg: rusting ( iron reacts with oxygen and water ), respiration
Glucose + oxygen -> carbon dioxide + water

Question 8

what is neutralisation and equation

Answer 8

It is when an acid reacts with an alkali

Acid + alkali -> salt + water

Question 9

what are the physical properties of acid?

Answer 9

• sour taste
• corrosive
• turns blue litmus paper into red
  ( bc red is acidic )

Question 10

what are the physical properties of alkali?

Answer 10

• bitter taste
• feels soapy
• corrosive
• turns red litmus paper into blue
  ( blue is alkaline )

Question 11

what are the chemical properties of acid?

Answer 11

Reacts with
- metals,
- alkalis
- carbonate

Question 12

what are the chemical properties of alkalis?

Answer 12

Reacts with
- acids

Question 13

**name of acids has __ at the back

Answer 13

acid
eg: sulfuric acid

Question 14

**examples of alkali has __ at the back

Answer 14

hydroxide

Question 15

How do you test for
1) acid
2) alkali
3) what this process is called
4) equation

Answer 15

1) Check whether substance turns blue litmus paper into red
2) Check whether substance turns red litmus paper into blue
3) neutralisation
4) acid + alkali →salt + water

Question 16

**1) how do you test for hydrogen gas?
2) equation

Answer 16

1) insert a lighted splint into the test tube( containing the metal and acid ) , the lighted splint extinguishes with a “pop” sound.
2) acid + metal →salt + hydrogen gas

Question 17

*What types of metal do not react with acids?

Answer 17

copper, silver and gold ( think of the medals thing )

Question 18

why is the process called neutralisation?

Answer 18

It is because when acid and alkali is added together, the salt solution form is neutral. ( pH = 7 )

Question 19

**1) how do you test for carbon dioxide?
1.5) process of precipitate being formed.
2) equation

Answer 19

1) bubble the gas produced by blowing into the straw into limewater, white precipitate is formed if the gas is CO2.
1.5) which is a process called effervescence
2) acid + carbonate → salt + water + carbon dioxide

Question 20

pH scale, how do we define what is acidic and akaline?

Answer 20

pH <7 are acidic, the lower the pH the more acidic
pH 7> are alkaline, the higher the pH the more alkaline
pH 7 are neutral. They are neither acidic nor alkaline.

Question 21

Chemical changes can occur as a result of…. ( 5 )

Answer 21

1. Mixing
2. Heating
3. Exposure to light
4. Interacting with oxygen
5. Using an electric current.

Question 22

What are the chemical changes for
1) mixing
2) heating
3) exposure to light
4) interaction with oxygen
5) using an electric current

Answer 22

1) eg acid+alkali
2) combustion, thermal decomposition
3) photosynthesis
4) oxidation, rusting, respiration
5) electroplating

Question 23

What happens to atoms during a chemical reaction?

Answer 23

The atoms rearrange themselves to chemically combine and form new substances.

Question 24

*How do you prevent decay/decomposition?

Answer 24

Vacuum packaging can remove air (oxygen) from the package, limiting the growth of bacteria and other microorganisms.

Question 25

*how do you prevent rusting

Answer 25

Rusting can be prevented by preventing iron or steel objects from coming in contacts with water or oxygen by
1. Painting
2. Oiling
3 galvanising
4 drying

Question 26

What is the
1. Source of carbon monoxide
2. Effects

Answer 26

1. Incomplete combustion of fuels
2. Reduces the amount of oxygen taken up by blood cells, resulting in headaches and eventually death

Question 27

What is the
1. Source of sulfur dioxide
2. Effects

Answer 27

1. Burning of sulfur containing fuels (coal, petrol), Volcanic reactions
2. *dissolve in water to form acid rain, which harms aquatic life and damages buildings
   * worsens symptoms of asthma, heart diseases and respiratory problems
   - irritation of eyes, nose and lungs

Question 28

What is the
1. Source of oxides of nitrogen
2. Effects

Answer 28

1. Burning fuels at high temperatures, lightening strikes
2. *dissolve in water to form acid rain, which harms aquatic life and damages buildings
   * worsens symptoms of asthma, heart diseases and respiratory problems
   - irritation of eyes, nose and lungs