Galvanic cells

Question 1

What is oxidation?

Answer 1

The process where by a substance loses electrons.

There will be an increase in oxidation numbers.

Question 2

What is reduction?

Answer 2

The process where by substance gains electrons.

There will be a decrease in oxidation numbers.

Question 3

What is the reductant?

Answer 3

The reductant is the species that causes the reduction of another species, but is itself oxidised as it loses electrons.

Question 4

What is the oxidant?

Answer 4

The oxidant is the species that causes the oxidation of another species, but is itself reduced as it gains electrons.

Question 5

What is the method for writing half equations? (8)

Answer 5

1. sperate into 2 half equations
2. balance Key elements (not O2 + H2)
3. balance O2 by adding H2O
4. balance H2 by adding H+
5. balance overall charge by adding Electrons
6. Multiple each half equation by a factor so that they have equal no. of electrons
7. add 2 half equations and cancel out
8. add in States

Question 6

In a redox reaction from which species do the electrons flow to?

Answer 6

Electrons flow from the reductant to the oxidant.

anode - cathode

Question 7

What is a spontaneous reaction?

Answer 7

A redox reaction is spontaneous if the standard electrode potential for the redox reaction is positive.
That is, if the oxidant and the reductant on the electrochemical series creates a negative gradient the reaction occurs spontaneously.

Question 8

What is a salt bridge and what is its purpose?

Answer 8

A salt bridge is a bridge consisting if an electrolyte, forming the internal circuit.
The salt bridge provides cations and anions for reduction and oxidation sites to maintain electrical neutrality. This is to balance consumed or produced ions.

Question 9

Why is a salt bride required?

Answer 9

When the cations are produced at the anode, this begins to create a positive charge when the anode would otherwise be negative. If this continues to occur, electrons won’t be attracted to the cation and there will be no flow of electrons. Thats why the sat bridge is used to provide ions that will maintain the balance and overall polarity of each electrode.

Question 10

What direction do the cations from the salt bridge flow to?

Answer 10

The cations will always be flow to the cathode.

Question 11

What direction do the anions from the salt bridge flow to?

Answer 11

The anions will always flow to the anode.

Question 12

At what conditions was the electrochemical series produced at and why is this important?

Answer 12

At standard laboratory conditions, 25°C and 1atm.
Important because comparisons can be made about reactions that have also occurred at SLC. Otherwise comparisons can not be made if no at SLC as different temps and pressures can effect the outcome.

Question 13

True or false?

Each oxidation/ reduction site or each beaker is a half cell.

Answer 13

True .

Question 14

What is a galvanic cell?

Answer 14

Galvanic cells harness the electrical energy available from the electron transfer in a redox reaction to perform useful electrical work.

Question 15

How to write a redox reaction using the electrochemical series? (4)

Answer 15

1. list species present
2. classify species as reductant/ oxidant
3. find strongest oxidant (highest on the left) and wrote equation- cathode
4. find strongest reductant (lowest on right) write equation from right to left- anode

Question 16

How to determine max cell voltage for a spontaneous reaction?

Answer 16

E˚ cell = E˚ cathode - E˚ anode

Question 17

What are the features f a galvanic cell? (4)

Answer 17

1. 2 seperate half cells containing electrolytes
2. 1 electrode in each half cell
3. connecting wire for flow of electrons
4. salt bridge for internal circuit

Question 18

What is the equation for oxidation and reduction?

Answer 18

Anode- red: Red = Red y+ + ye-

Cathode- ox: ox x+ + xe- = ox

Question 19

What are the words used to describe redox reactions

Answer 19

• An OIL Ox
  anode- oxidation is loss- oxidation
• Red Cat RIG
  cathode- reduction is gain- reduction

Question 20

What are the different types of galvanic cells?(3)

Answer 20

• metal ion-metal half cell
• solution half cell (inert electrode)
• gas-non meal ion half cell (inert electrode)

Question 21

What is a dry cell?

Answer 21

An electrochemical cell in which the electrolyte is a paste rather than a liquid.

Question 22

What are the properties of dry cells? (3)

Answer 22

Oxidants and reductants:

• far enough apart
• not react with water too quickly
• inexpensive

Question 23

What is the purpose of a porous fibre separator?

Answer 23

Prevents mixing of anode and cathode components.

Question 24

What is a fuel cell?

Answer 24

An electrochemical cell that produces electrical energy directly from a fuel.
Fuel cells use a continuous supply of fuel to produce a flow of electrons.

Question 25

How do fuel cells produce electricity?

Answer 25

Combine fuels such as hydrogen and oxygen in the presence of an electrolyte

Question 26

What are the differences between fuel cell and galvanic cell? (2)

Answer 26

• electrode in fuel cell is porous in nature

- fuel cell do not run out of reactants

Question 27

What are the advantages of a porous electrode? (2)

Answer 27

• high surface area

- enable catalysts to be present

Question 28

What is a battery?

Answer 28

A collection of one of ore cells whose chemical reactions create a flow of electrons in a circuit.

Question 29

What are the similarities between fuel cells and batteries? (2)

Answer 29

• combined in groups

- obtain usable voltage and power output

Question 30

What are the differences between fuel cells and batteries? (3)

Answer 30

• GC has limited chemical energy and when depleted cell can’t be recharged, while FC has continuous supply of fuel
• FC do not release energy stored in the cell
• FC don’t have to be recharged
• FC release few emissions and can be cheap

Question 31

What are the features of a fuel cell? (3)

Answer 31

• use spontaneous redox reactions to produce energy
• have continuous supply of reactants
• products continuous removed

Question 32

What are the features of electrodes in fuel cell?

Answer 32

• site of oxidation and reduction
• separates reactants and products
• act as catalysts
• are porous to allow reactant gases to come into contact with electrode
• conduct electricity

Question 33

What us a the % efficiency of a fuel cell equation?

Answer 33

produced charge÷ theoretical charge x 100

or

(it) ÷ (ne-F) x 100

Question 34

What are the disadvantages of fuel cells?

Answer 34

• expensive to produce
• difficult to store and transport fuel reactants
• slow rate of reactions at electrodes, requiring catalyst
• potential poisoning of the catalytic electrodes and consequent costs

Question 35

Why would there be a potential difference in observed cell voltage and predicted cell voltage?

Answer 35

• concentration of solutions is less than 1M
• temperature other then 25˚c
• if electrodes had same surface area but made of different metals

Question 36

How would connecting electrodes to the wrong terminal of the voltmeter effect cell?

Answer 36

Incorrectly connecting the electrodes would result in a negative reading on the voltmeter, not an altered numeric value

Question 37

What are 4 observations which could be made in the beakers to indicate the cell is operating?

Answer 37

• increase in mass of cathode
• decrease in mass of anode
• a possible change in ph
• gas produced

Question 38

What could be done to cause galvanic cell reaction to take place?

Answer 38

• add a suitable catalyst

- increase temperature

Question 39

Why might there be no observable reactions occurring in a galvanic cell?

Answer 39

• concentrations of reactants may not be at 1M, therefor not at SLC, meaning slower reaction rate
• reaction may be occurring at such a slow rate
• salt bridge dried up
• anode could possible have been used up; no more reactants
• chemical neutrality has not been maintained.

Question 40

What factors influence your choice of reactant?

Answer 40

• not insoluble ions that participate in secondary reactions
• highly soluble ions with low reactivity
• cheap and readily avaliable
• weather it will form a precipitate