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Edexcel Chemistry > Topic 3 - Chemical changes > Flashcards

Topic 3 - Chemical changes Flashcards

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1
Q

Charges of acids & alkalis in aqueous solutions

A
  • acids produce H+ ions

- alkalis produce OH-

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2
Q

Colours of Phenolphthalein

A

Phenolphthalein

  • Alkaline = pink
  • Acidic = colourless
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3
Q

Colours of Methyl orange

A

Methyl orange

  • Alkaline = yellow
  • Acidic = red
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4
Q

Litmus solution and litmus paper

A

Litmus solution
-Alkaline = blue
- Acidic = red
○ Litmus paper
- Blue litmus paper goes red in acidic & stays blue in alkaline
- Red litmus paper goes blue in alkaline & stays red in acidic

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5
Q

What does does a strong acid and alkali mean ?

A

-higher concentration of H+ ions makes a strong acid
- higher concentration of OH- ions mean
solution is more alkaline, having a higher pH

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6
Q

Explain the terms concentrated and dilute

A
  • concentrated is the larger amount of substance in a volume of a solution
    ▪ Dilute is the lesser amount of substance in a volume of a solution
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7
Q

acid + metal reaction

A

acid + metal -> salt + hydrogen gas

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8
Q

acid + metal oxide

A

acid + metal oxide -> salt + water

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9
Q

What is a weak acid?

A
  • a weak acid partially dissociates – doesn’t produce many H+ ions, so reaction w/
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10
Q

What is a weak acid?

A
  • a weak acid partially dissociates – doesn’t produce many H+ ions, so reaction w/ substance is slow
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11
Q

acid + metal hydroxide

A

acid + metal hydroxide -> salt + water

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12
Q

acid + metal carbonate

A

acid + metal carbonate -> salt + carbon dioxide

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13
Q

Test for hydrogen

A
  • burning splint held at open end of a test tube of the gas

- Creates ‘squeaky pop’ sound

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14
Q

Test for carbon dioxide

A
  • Bubble the gas through the limewater (calcium hydroxide solution) and will turn milky (cloudy)
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15
Q

Neutralisation reaction equation

A

H+ (aq) + OH- (aq) -> H20 (l)

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16
Q

Explain how to make copper sulfate crystals

A
  • add excess of copper oxide (insoluble) to acid
  • use filter and filter paper to filter off any copper oxide that hasn’t reacted
  • evaporate off water by placing final solution in water bath
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17
Q

how to carry out acid-alkali titration, using burette, pipette
and indicator, to prepare salt

A
  • Wash burette using acid and
  • Fill burette with acid
  • Use pipette to add alkali into conical flask, drawing alkali using a pipette filler
  • Add phenolphthalein to conical flask
  • use white tile
  • Add acid from burette to alkali carefully and swirl till reaches endpoint (turns light purple)
  • Repeat experiment to gain more precise results
  • warm salt solution in water bath to evaporate the water– crystals will form
18
Q

What is titre (titration experiment)?

A

-difference between first and second readings on burette

19
Q

solubility of common sodium, potassium and ammonium

in water

A
  • all are soluble in water
20
Q

solubility of common chlorides in water

A
  • are soluble except silver and lead,
21
Q

solubility of common sulfates in water

A

-are soluble except lead, barium and calcium,

22
Q

solubility of common carbonates and hydroxides are

A

-insoluble except sodium, potassium and ammonium

23
Q

how to prepare pure, dry sample of an insoluble

salt

A
  • mix two solutions needed to form salt
  • filter mixture using filter paper, which insoluble salt will be left on
  • wash salt using distilled water
  • leave salt to dry on filter paper
24
Q

What is an electrolyte?

A

-When an ionic substance is melted or dissolved & ions are free to move about within liquid or solution

25
Q

What is electrolysis?

A
  • process which electrical energy, from a direct current supply decomposes electrolytes
  • Passing current through substances that are molten or solution means that solution can be broken down into elements– that’s electrolysis, and substance being broken down is the electrolyte
26
Q

What is the movement of ions in electrolysis?

A
  • positively charged ions (cations) move to negative
    electrode (cathode)
  • negatively charged ions (anions) move to positive
    electrode (anode).
  • Ions then discharged at electrodes producing elements
27
Q

Explain what happens at the cathode during electrolysis?

A
  • at cathode (-):
    ○ hydrogen (from H+ in water) is produced UNLESS positive ions in ionic compound are from a metal less reactive than hydrogen
    ○ if the metal is less reactive, it will be produced instead
28
Q

What happens at anode during electrolysis?

A
  • at anode (+):
    ○ oxygen (from OH- in water) will be produced UNLESS ionic compound contains halide ions (Cl-, Br-, I-)
    ○ if there are halide ions, the halogen will be produced instead (e.g. Cl2)
29
Q

What is a halide ion ?

A
  • halogen atom w/ a negative charge
30
Q

List of halide ions

A
  • fluoride, chloride, bromide, iodide and astatide
31
Q

Electrolysis of copper chloride solution?

A
  • Cu+ ions got to the cathode

- Cl- ions go to anode

32
Q

Electrolysis of sodium chloride solution

A

H+ ions go to cathode

- Cl-ions go to anode

33
Q

Electrolysis of Water acidified with sulfuric acid

A
  • H+ to cathode,

- OH- to anode

34
Q

Electrolysis of Molten lead bromide

A
  • Pb2+ to cathode, Pb is produced (not in solution so these are the only + ions present)
  • Br- to anode
35
Q

What is the reactivity series (most reactive to least)

A 
- potassium 
sodium 
calcium 
magnesium 
aluminium 
carbon
zinc
iron
tin 
lead 
hydrogen
copper
silver
gold
platinum
36
Q

Half equation of a negative electrode

A

X+ + e- -> X, electrons gained, so positive ions are reduced

37
Q

Half equation of positive electrode

A

X- -> e- + X, electrons are lost, so negative ions are oxidised

38
Q

where does oxidation and reduction occur?

A
  • oxidation at anode – loss of electrons

- reduction at cathode – gain of electrons

39
Q

How can electrolysis purify copper (experiment)?

A

-anode is made of impure copper
○ cathode is made of pure copper
○ the solution is copper sulfate
- Cu2+ ions from anode move to cathode, where they gain electrons and discharged as pure copper
○ impurities form as sludge below the anode
- cathode will increase in mass as it gains pure copper
– anode will lose mass as copper ions are lost – replace ones from CuSO4 solution & so are impurities

40
Q

Why isn’t universal indicator used in titration experiments

A
  • doesn’t show clear/ distinct change in colour

Edexcel Chemistry (7 decks)

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