help EMF value (1 Viewer)

[AZZD]

State why the laboratory EMF value is different to the theoretical EMF value.
If this questions was a 4 marker, what would the marks be allocated to and how should i approach this question?

 

[Kurosaki]

Nonstandard conditions

 

[Kurosaki]

The observed EMF was different from the theoretical EMF due to non-standard conditions.
Standard conditions: 1 M concentration for reactants, 1 atm pressure for gases, and 25 degrees Celsius, along with pure metal electrodes.
You can see how they affect the EMF observed using the Nernst equation:
, where Q is the reaction quotient (look at equilibrium constants).

 

[HeroicPandas]

Nonstandard conditions

Yes this

I suggest that you draw up a theoretical galvanic cell such as one with: magnesium electrode, zinc electrode, magnesium nitrate electroyle, zinc nitrate electrolyte, potassium nitrate salt bridge, then write down 2 half equations. Use these 2 half equations to identify changes to the galvanic cell and how would these changes would affect electrical conductance and the standard conditions (do this first to get the idea then answer the question)

 

[strawberrye]

State why the laboratory EMF value is different to the theoretical EMF value.
If this questions was a 4 marker, what would the marks be allocated to and how should i approach this question?

I think a possible way four marks would be allocated is the following-and logically, you should structure your answers to include the four points as well
1)define theoretical EMF value-i.e. what does it mean, under what conditions it is determined
2)I think this question would be in the context of a question on galvanic cells, i.e. a part of a question, so state the threotical EMF value for the electrode couples given-using your reduction, oxidation equations and electrode potentials as evidence,
3) Highlight the disparity between the lab and theoretical value, i.e. just state them, and explain the non-standard condition-varying condition results in this variation
4)I think if you want to be safe, don't just list say, 3 non-standard conditions that were used, highlight, at least for one of them, what would be the impact on this difference from standard condition-i.e. higher concentration greater than 1 mol/L would mean a higher EMF value than theoretical could be obtained-explain the disparity using the disparities of the condition-apply the chemical knowledge to this situation

If you include the four things above-you will be guaranteed a full 4 marks