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Chemistry > Topic 3- Chemical Changes > Flashcards

Topic 3- Chemical Changes Flashcards

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1
Q

What does the pH scale measure

A

The strenght and weaknesses of acids and bases

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2
Q

Acids on pH scale

A
  • pH 1-6
  • Form H plus ions in water
  • The higher the concentration of hydrogen ions in a solutin, the higher ot is on the pH scale
  • Coloured Red, Orange and Yellow
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3
Q

Bases on a pH scale

A
  • pH 8-14
  • Coloured blue and purple
  • Form OH minus ions in water
  • The stronger the concentration of the ions, the higher the pH
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4
Q

Alkali

A

A base that is soluble in water

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5
Q

Base

A

A substance that reacts with an acid to form salt and water

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6
Q

Indicator

A

An indicator is a substance that detects whether a substance is basic or acidic
Examples include: Universal Indicator, Phenolphthalein, Litmus and Methyl Orange

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7
Q

Universal Indicator

A

Uses the PH scale
Red when acidic
Green when neutral
Purple when basic

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8
Q

Litmus

A

Red in acid
Purple in neutral
Blue when alkaline

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9
Q

Methyl Orange

A

Red in acidic
Yellow when neutral
Yellow when alkaline

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10
Q

Phenolphthalein

A

Colourless when acidic
Colourless when neutral
Pink when alkaline

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11
Q

Neutralisation

A
  • Green on pH scale with a reading of 7
  • Salts are neutral in the reaction of an acid and base
  • H and OH ions react to form water
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12
Q

Acids in water

A
  • All acids can ionise in water

- Gives off hydrogen ions

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13
Q

Strong Acids

A
  • Ionise completely in water
  • Have a low pH
  • Sulfuric, Nitric, Hydrochloric
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14
Q

Weak acids

A
  • Do not fully ionise in solution
  • pHs around 2-6
  • Citric, Ethanoic and Carbonic
  • Reversible Reaction
  • Equilibrium lies on the left
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15
Q

Difference between strong and concentrated acids

A
  • Acid strength measures what proportion of the acid molecules ionise
  • The concentration shows how much there is of said acid in on decimetre cubed pf water
  • You can have a strong and dilute acid
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16
Q

Changing the concentration of acids

A
  • If the concentration of H plus ions increase by a factor of ten, then the pH decreases by 1
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17
Q

Reactions of acids

A
  • A salt is always formed in the reaction of an acid and a base
  • Water is always formed
  • Hydrochloric acid forms chloride salts, sulfuric acid forms sulfate salts and nitrates form nitric salts
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18
Q

Acid + Metal Oxide

A

Salt + Water

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19
Q

Acid + Metal Hydroxide

A

Salt + Water

20
Q

Acid + Metal

A

Salt + Hydrogen

21
Q

Acid + Metal Carbonate

A

Salt + Water + Carbon Dioxide

22
Q

Test for hydrogen

A

Squeaky Pop test

Lit splint sill be put out with a pop

23
Q

Test for carbon dioxide

A

Bubble it through limewater

It will turn cloudy if it is limewater

24
Q

Rules of solibility

A

The solubility of salts can be determined using the solubility rules

25
Q

Solubility of common salts of potassium, sodium and ammoniun

A

Soluble

26
Q

Solubility of nitrates

A

Soluble

27
Q

Solubility of common chlorides

A

Soluble except for silver and lead chloride

28
Q

Solubility of common sulfates

A

Soluble except from lead, barium and calcium sulfate

29
Q

Solubility of common carbonates and hydroxides

A

Insoluble except for sodium, potassium and ammonium

30
Q

What type of reaction is the making of soluble salts?

A

Precipitation

31
Q

Method for making insoluble salts

A
  • Dissolve the base in water
  • Dissolve the acid in water
  • Mix the two together
  • Filter
  • Pour the contents into the filter
  • Swill out the beaker with deionised water
  • Rinse the contents out
  • Leave it on a dry place to crystalise
32
Q

How to make soluble salts

A

Use a titration

33
Q

Titration

A
  • Wash through the pipette and burette with acid and alkali to make sure there is no residue of other acids and bases. Do not use water
  • Measure out a set amount of acid into a conical flask with a pipette
  • Slowly add the base using the burette until the indicator changes to show there has been a change
34
Q

Making a soluble salt

A
  • Use the titration
  • Repeat the experiment using the same values but without the indicator as with an indicator it is impure
  • Slowly evaporate the water and leave it to crystalise
35
Q

Electrolysis

A
  • The breaking down of a substance using electricity
  • A current is passed through an electrolyte causing it to decompose
  • Oxidation and Reduction occur
  • Positive ions (cations) are drawn towards the negative electrode (cathode) and are reduced
  • Negative ions (anions) are drawn towards the positive electrode (anode)
  • Waste products drop to the bottom of the electrolyte
36
Q

Half equations

A
  • Show what happens at each electrode
  • Add electrons to balance charges (e minus)
  • If there is gain, there is an attraction to the cathode as it is negative (Reduction)
  • 2H+ + 2e- = H+
  • If there is loss, there is an attraction to the anode as it is positive (Oxidation)
  • Na = Na + + e-
37
Q

How to perform electrolysis in a solution

A
  • Get two inert electrodes such as graphite or platinum
  • Clean the surfaces with emery paper
  • Attach them to a circuit
  • Place them into a beaker of the electrolyte
  • You may need to make the substance molten
38
Q

Molten Ionic Substances

A
  • An ionic solid can not be electrolysed as the ions are in fixed positions and can not move
  • Molten ionic compounds can move as they can move freely
  • Positive metal ions are oxidised to metal atome at the cathode
  • Negative ions are reduced to atoms or molecules at the anode
39
Q

What would be seen at the cathode

A

A silverly liquid will from

40
Q

What would be seen at the anode

A

A gas coloured to the halide so if it is bromide, a brown gas would form

41
Q

Electrolysis of aqueous solutions

A
  • In an aqueous solutions, hydrogen and hydroxide ions are present
  • Hydrogen will be attracted to the cathode if there are no less reactive metals such as the jewellery metals
  • At the anode, halide ions will be attracted unless there are none in which hydroxide will be attracted
42
Q

Results of electrolysis of aqueous sodium chloride

A

Hydrogen gas
Chlorine
Sodium Hydroxide
The electrolyte needs to have sodium in it

43
Q

Electrolysis of Copper Sulfate

A
  • Produces oxygen
  • Copper metal is produced
  • No halides present so water is formed
44
Q

Using Copper Electrodes

A
  • Non-inert copper electrodes could be used to purify copper
  • The electrolyte needs to contain copper
  • Copped ions will be separated from the anion as it is separated in the electrolyte
  • They will be attracted to the cathode as they are positivley charged and it is negatively charged
  • This will cause the anode to lose mass and the cathode to gain mass
45
Q

How to increase the rate of electrolysis

A

Increase the current

46
Q

How does the electrical supply act in electrolysis

A
  • Pulls off electrons

- Offers electrons

Chemistry (9 decks)

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