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Science S2 > Ch 11 - Chemical Changes > Flashcards

Ch 11 - Chemical Changes Flashcards

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1
Q

A physical change occurs when…

A

no new subtsances are formed.

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2
Q

What are some examples of physical changes?

A
  • boiling
  • melting
  • condensation
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3
Q

Physical changes are (reversible/irreversible).

A

reversible

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4
Q

How do you reobtain salt from a salt solution?

A

Evaporate the water out.

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5
Q

A chemical change occurs when…

A

new substances are formed.

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6
Q

What is an example of chemical change?

A

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

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7
Q

Chemical changes are…

reverse

A

not easily reversed.

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8
Q
A
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9
Q

The reversal of chemical changes requires…

A

large amounts of energy.

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10
Q

What is a process used to reverse chemical changes?

A

Electrolysiss

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11
Q

What is electrolysis?

A

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

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12
Q

During both physical and chemical changes, heat energy…

A

can be taken in or given out!

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13
Q

What are the types of chemical change?

A
  1. Oxidation
  2. Combustion
  3. Thermal decomposition
  4. Neutralisation
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14
Q

What is oxidation?

A

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

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15
Q

What are examples of oxidation?

A
  • Rusting of iron
  • ‘Browning’ of apples
  • Cellular respiration
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16
Q

What is combustion?

A

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!

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17
Q

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

A

Heat and light

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18
Q

What are examples of combustion?

A
  • Burning of sparklers
  • Charcoal (carbon) in a barbecue pit burns in oxygen
19
Q

What is thermal decomposition?

A

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

20
Q

What are examples of thermal decomposition?

A
  • copper(II) carbonate –>copper (II) oxide + carbon dioxide
  • lead(II) nitratae –> lead oxide + nitrogen oxide + oxygen
21
Q

What is neutralisation?

A

It is when an acid is mixed with an alkali.

22
Q

What is produced during neutralisation?

A
  • salt
  • water
23
Q

What is an acid?

A

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

24
Q

How can you classify acids?

A
  • mineral acids
  • organic acids
25
Q

What are examples of mineral acids?

A
  • nitric acid (HNO3)
  • sulfuric acid (H2SO4)
  • hydrochloric acid (HCl)
26
Q

What are examples of organic acids?

A
  • folic acids (in avocadoes)
  • ascorbic acid (vitamin c)
  • ethanoic acid (vinegar)
27
Q

What are the physical properties of acids?

A
  1. taste sour (citric acid)
  2. change the colour of indicators
  3. corrosive (ph < 7)
  4. can conduct electricity
28
Q

What is an alkali?

A

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

29
Q

What are some example of common alkalis?

A

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

30
Q

What are the physicla properties of alkalis?

A
  1. taste bitter, slippery soapy feel
  2. change the colour of indicators
  3. corrosive (pH > 7)
  4. can conduct electricity
31
Q

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

A

0 to 14

32
Q

What does a pH value less than 7 mean?

A

the solution is acidic

33
Q

What does a pH value of 7 mean?

A

the solution is neutral

34
Q

What does a pH value greater than 7 mean?

A

the solution is alkaline

35
Q

What are examples of indicators?

A
  • litmus paper
  • universal indicator
  • pH meter
36
Q

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

A
  1. acid
  2. alkali
37
Q

What are the three reactions of acids?

A
  • with alkali
  • with metal
  • with metal carbonate
38
Q

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

A

salt and water

39
Q

Whats does the reaction of acids with metals produce?

A

salt and hydrogen gas

40
Q

How do you test for hydrogen?

A
  • 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

41
Q

What does the reaction of acids with carbonates produce?

A

salt, water and carbon dioxide gas

42
Q

How do you test for carbon dioxide?

A
  • bubble the gas through limewater
  • if carbon dioxide is present, a white precipitate will form

limewater test!

42
Q

What are the effects of rusting?

A

causes damage to iron and steel objects

43
Q

How do you prevent rusting?

A
  • painting
  • galvanising (zinc coat)
  • oiling
  • drying

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