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HKDSE Chemistry > 19: Simple Chemical Cells > Flashcards

19: Simple Chemical Cells Flashcards

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1
Q

What is the overall ionic equation of the reaction between zinc metal and copper(II) sulphate solution?

A

Zn (s) + Cu2+ (aq) -> Zn2+ (aq) + Cu (s)

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2
Q

What are the half equations of the reaction between zinc metal and copper(II) sulphate solution?

A

Zn (s) -> Zn2+ (aq) + 2e-
Cu2+ (aq) + 2e- -> Cu (s)

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3
Q

What is the definition of a diode?

A

A diode is an electronic component that only allows electrons to flow in one direction.

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4
Q

A strip of zinc metal is joined with an LED and a strip of copper metal, with both metals dipped into copper(II) sulphate solution.

What is the half equation at the end of the zinc metal?

A

Zn (s) -> Zn2+ (aq) + 2e-

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5
Q

A strip of zinc metal is joined with an LED and a strip of copper metal, with both metals dipped into copper(II) sulphate solution.

What is the path followed by the electrons?

A

The electros flow from the zinc strip in the external circuit to the copper strip, where they are gained by copper(II) ions to form copper atoms.

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6
Q

A strip of zinc metal is joined with an LED and a strip of copper metal, with both metals dipped into copper(II) sulphate solution.

What is the positive electrode?

A

Copper strip

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7
Q

A strip of zinc metal is joined with an LED and a strip of copper metal, with both metals dipped into copper(II) sulphate solution.

What is the negative electrode?

A

Zinc strip

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8
Q

A strip of zinc metal is joined with an LED and a strip of copper metal, with both metals dipped into copper(II) sulphate solution.

What is the electrolyte?

A

Copper(II) sulphate solution

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9
Q

A strip of zinc metal is joined with an LED and a strip of copper metal, with both metals dipped into copper(II) sulphate solution.

What is the expected result?

A

The LED lights up.
The mass of the zinc strip decreases while that of the copper strip increases.

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10
Q

What is the difference between the path of the electrons and that of ions in a chemical cell?

A

Electrons only flow in the external circuit while ions flow in the electrolyte.

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11
Q

What is the electrolyte in a lemon cell?

A

Lemon juice

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12
Q

A strip of zinc electrode is dipped into zinc sulphate solution, connected to a multimeter, and a copper electrode dipped into copper(II) sulphate solution by a wire.

What is the expected result and why?

A

There is a voltage, but it drops to zero quickly. The side containing the zinc metal becomes more positive and the side containing the copper metal becomes more negative. Due to the accumulation of charges, the reaction cannot proceed.

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13
Q

A strip of zinc electrode is dipped into zinc sulphate solution, connected to a multimeter, and a copper electrode dipped into copper(II) sulphate solution by a wire.

How can the circuit be completed?

A

Using a salt bridge which is dipped into the two solutions.

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14
Q

How is a salt bridge prepared?

A

A salt bridge is made from a strip of filter paper soaked in an electrolyte, usually potassium nitrate solution.

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15
Q

Why is potassium nitrate solution used to prepare salt bridges?

A

Potassium ions and nitrate ions do not react with the other ions in the solutions or with the electrodes.

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16
Q

What are the functions of the salt bridge?

A
  1. It allows the flow of ions between the two half cells to complete the circuit.
  2. It allows ions to flow into or out of the half cells to balance the charges in the half cells.
17
Q

What is the apparatus in a Daniell cell that plays the role of a salt bridge?

A

Porous pot

18
Q

In a Daniell cell, a central zinc rod dipped into a porous pot containing zinc sulphate solution, is immersed in a copper(II) sulphate solution contained in a copper can.

What is the expected result?

A

A voltage of around 1.1V is produced.
The mass of the zinc rod decreases while that of the copper can increases after some time.

19
Q

In a Daniell cell, a central zinc rod dipped into a porous pot containing zinc sulphate solution, is immersed in a copper(II) sulphate solution contained in a copper can.

What is the direction of travel of zinc(II) ions?

A

Zinc(II) ions in the zinc sulphate solution travel outwards from the interior of the porous pot to the exterior of the porous pot, to balance the build-up of negative charges in the outer chamber where copper ions gain electrons to form copper atoms.

20
Q

In a Daniell cell, a central zinc rod dipped into a porous pot containing zinc sulphate solution, is immersed in a copper(II) sulphate solution contained in a copper can.

What is the direction of travel of sulphate ions?

A

Sulphate ions in the copper(II) sulphate solution travel inwards from the exterior of the porous pot to the interior of the porous pot, to balance the build-up of positive charges in the inner chamber where zinc atoms lose electrons to form zinc ions.

21
Q

In a Daniell cell, a central zinc rod dipped into a porous pot containing zinc sulphate solution, is immersed in a copper(II) sulphate solution contained in a copper can.

What is the role of the porous pot?

A

The porous pot allows the flow of ions between the two solutions to complete the circuit, and separates the two solutions and hence prevents them from reacting with each other.

22
Q

A strip of zinc electrode is dipped into zinc sulphate solution, connected to a multimeter, and a copper electrode dipped into copper(II) sulphate solution by a wire. A positive voltage is shown.

The zinc strip is swapped for a silver strip, and the zinc sulphate solution is replaced by silver nitrate solution.

What is the expected result and why?

A

A negative voltage will be shown, as copper is placed higher in the electrochemical series than silver, and copper becomes the negative electrode in the cell.

23
Q

What is the difference between electrochemical series and metal reactivity series?

A

Calcium is less reactive than sodium and placed lower in the reactivity series, but it is more electrochemically active than sodium and placed higher in the electrochemical series.

24
Q

What is the direction of electron flow in a simple chemical cell?

A

Electrons flow from the metal higher in electrochemical series to the metal lower in electrochemical series.

HKDSE Chemistry (31 decks)

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