Ch 11 - Chemical Changes

Question 1

A physical change occurs when…

Answer 1

no new subtsances are formed.

Question 2

What are some examples of physical changes?

Answer 2

• boiling
• melting
• condensation

Question 3

Physical changes are (reversible/irreversible).

Answer 3

reversible

Question 4

How do you reobtain salt from a salt solution?

Answer 4

Evaporate the water out.

Question 5

A chemical change occurs when…

Answer 5

new substances are formed.

Question 6

What is an example of chemical change?

Answer 6

Reaction of potassium metal with water –> potassium hydroxide & hydrogen

Question 7

Chemical changes are…

reverse

Answer 7

not easily reversed.

Question 9

The reversal of chemical changes requires…

Answer 9

large amounts of energy.

Question 10

What is a process used to reverse chemical changes?

Answer 10

Electrolysiss

Question 11

What is electrolysis?

Answer 11

It is the breakdown/decomposition of the product using electricity.

Question 12

During both physical and chemical changes, heat energy…

Answer 12

can be taken in or given out!

Question 13

What are the types of chemical change?

Answer 13

1. Oxidation
2. Combustion
3. Thermal decomposition
4. Neutralisation

Question 14

What is oxidation?

Answer 14

It is the chemical change whenn a substance reacts wih oxygen.

Question 15

What are examples of oxidation?

Answer 15

• Rusting of iron
• ‘Browning’ of apples
• Cellular respiration

Question 16

What is combustion?

Answer 16

It is when a substance is heated in the presence of oxygen to form one or more new substances.

It’s another example of oxidation!

Question 17

( ) & ( ) are usually given out during combustion.

Answer 17

Heat and light

Question 18

What are examples of combustion?

Answer 18

• Burning of sparklers
• Charcoal (carbon) in a barbecue pit burns in oxygen

Question 19

What is thermal decomposition?

Answer 19

It is when a substance breaks down into two or more simpler substances upon heating.

Question 20

What are examples of thermal decomposition?

Answer 20

• copper(II) carbonate –>copper (II) oxide + carbon dioxide
• lead(II) nitratae –> lead oxide + nitrogen oxide + oxygen

Question 21

What is neutralisation?

Answer 21

It is when an acid is mixed with an alkali.

Question 22

What is produced during neutralisation?

Answer 22

• salt
• water

Question 23

What is an acid?

Answer 23

A substance that dissolves in water and dissociates to give hydrogen ions, H+

Question 24

How can you classify acids?

Answer 24

• mineral acids
• organic acids

Question 25

What are examples of mineral acids?

Answer 25

* nitric acid (HNO3) * sulfuric acid (H2SO4) * hydrochloric acid (HCl)

Question 26

What are examples of organic acids?

Answer 26

* folic acids (in avocadoes) * ascorbic acid (vitamin c) * ethanoic acid (vinegar)

Question 27

What are the physical properties of acids?

Answer 27

1. taste sour (citric acid) 2. change the colour of indicators 3. corrosive (ph < 7) 4. can conduct electricity

Question 28

What is an alkali?

Answer 28

A substance that dissolves in water and dissociates to give hydroxide ions, OH-

Question 29

What are some example of common alkalis?

Answer 29

Group 1 metal hydroxides: sodium _ NaOH, potassium _ KOH Group 2 metal hydroxides: calcium _ Ca(OH)2, barium _ Ba(OH)2

Question 30

What are the physicla properties of alkalis?

Answer 30

1. taste bitter, slippery soapy feel 2. change the colour of indicators 3. corrosive (pH > 7) 4. can conduct electricity

Question 31

What is the range of a pH scale/universal indicator?

Answer 31

0 to 14

Question 32

What does a pH value less than 7 mean?

Answer 32

the solution is **acidic**

Question 33

What does a pH value of 7 mean?

Answer 33

the solution is **neutral**

Question 34

What does a pH value greater than 7 mean?

Answer 34

the solution is **alkaline**

Question 35

What are examples of indicators?

Answer 35

* litmus paper * universal indicator * pH meter

Question 36

What do the color changes of litmus paper mean? 1. turns/remains red 2. turns/remains blue

Answer 36

1. acid 2. alkali

Question 37

What are the three reactions of acids?

Answer 37

* with alkali * with metal * with metal carbonate

Question 38

What does the reaction of **acids** with **alkalis** (neutralisation) produce?

Answer 38

salt and water

Question 39

Whats does the reaction of acids with metals produce?

Answer 39

salt and hydrogen gas

Question 40

How do you test for hydrogen?

Answer 40

* place a lighted splint at the mouth of the test tube * if hydrogen is present, the lighted splint will be extinguished + 'pop' sound | POP test

Question 41

What does the reaction of acids with carbonates produce?

Answer 41

salt, water and carbon dioxide gas

Question 42

How do you test for carbon dioxide?

Answer 42

* bubble the gas through limewater * if carbon dioxide is present, a white precipitate will form | limewater test!

Question 42

What are the effects of rusting?

Answer 42

causes damage to iron and steel objects

Question 43

How do you prevent rusting?

Answer 43

* painting * galvanising (zinc coat) * oiling * drying