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OCR B A Level Chemistry > developing metals > Flashcards

developing metals Flashcards

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1
Q

what is meant by the term ‘end point’? (acid/base)

A

the point where the alkali is exactly neutralised and the indicator changes colour

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2
Q

describe how a redox titration using Manganate(VII) ions is performed

A
  • measure out quantity of reducing agent e.g. Iron(II) ions
  • add dilute sulfuric acid (xs)
  • add aqueous MnO4, swirl
  • stop when the mixture is tainted with pink
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3
Q

describe how an electrochemical cell can be constructed

A

two different metals dipped in salt solution dipped in salt solutions of their own ions and connected by a wire

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4
Q

what process occurs at the anode?

A

oxidation

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5
Q

what process occurs at the cathode?

A

reduction

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6
Q

in which direction does the flow of electrons go?

A

from the most reactive metal to the least

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7
Q

how do you construct a salt bridge?

A

soak a piece of filter paper in salt solution and draping it between two beakers

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8
Q

what does a negative electrode potential represent?

A

oxidation

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9
Q

what electrode potential represents the forward reaction?

A

positive

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10
Q

what is the definition of standard electrode potential?

A

the voltage measured under standard conditions when the half cell is connected to standard hydrogen electrode

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11
Q

what is the equation for the reaction at the hydrogen electrode?

A

2H+ + 2e- -> H2

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12
Q

which way does a reaction with a more positive standard electrode potential go?

A

forwards

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13
Q

how do you calculate Ecell?

A

(more positive-more negative)

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14
Q

which way do electrons flow in an electrochemical cell?

A

from the most reactive metal to the least

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15
Q

when might a prediction using Ecell be wrong?

A
  • if reaction has a high activation energy

- rate is so slow reaction does not appear to happen

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16
Q

what is rust?

A

Fe2O3.xH2O

17
Q

what is the equation for rusting?

A

2H2O + O2 + 2Fe -> 4OH- + 2Fe2+

18
Q

how does Fe2+ and OH- combine to form rust?

A
  • Fe2+ and OH- combine to form Fe(OH)2
  • Fe(OH)2 is oxidised further to form Fe(OH)3
  • Fe(OH)3 gradually turns into hydrated Iron(III) Oxide
19
Q

why is rust less likely to occur in alkaline conditions?

A

when OH- ions are added, equilibrium of the reaction between O2 and H20 moves left, equilibrium of iron half reaction moves right to get rid of electrons

20
Q

describe two ways to prevent rusting

A
  • painting or coat with a polymer
  • oiling
  • coating with a more reactive metal (sacrificial metal)
21
Q

what is a transition metal?

A

a d block element that can form at least one stable ion with an incomplete d sub shell

22
Q

why do transition metals have a variable oxidation state?

A

the energy levels of the 4s and 3d subshells are very close together
this means different numbers of electrons can be gained or lost using similar amounts of energy

23
Q

what is a complex ion?

A

a central metal atom or ion surrounded by co-ordinately bonded ligands

24
Q

what is a ligand?

A

an atom or molecule that donates a pair of electrons to a central transition metal ion to form a co-ordinate bond

25
Q

what is meant by coordination number?

A

the number of co-ordinate bonds that are formed to the central metal ion

26
Q

what form do transition metals take in aqueous solutions?

A

[M(H2O)6]n+

27
Q

what is the ion present when copper(II) sulfate is dissolved in water?

A

[Cu(H2O)6]2+

28
Q

what is formed when Copper(II) ions are dissolved in water? what is the colour change?

A

Cu(OH)2

light blue to blue

29
Q

what is formed when Iron(II) is dissolved in ammonia? what is the colour change?

A

Fe(OH)2

light green to dark green

30
Q

what is formed when Cu(OH)2 is added to an excess of dilute NH3? what colour change occurs?

A

a complex [Cu(NH3)4(H2O)2] is formed

turns dark blue

31
Q

what is formed when Iron(III) is dissolved in water? what is the colour change?

A

Fe(OH)3

yellow to orange

32
Q

why are transition metals such good catalysts?

A

because they can change oxidation states easily, transferring electrons to speed up reactions

OCR B A Level Chemistry (12 decks)

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