Galvanic Cells Prac Question

[esha.ajmera]

Hi guys,
This is my first time on the forum to make a post, please do help me out if this post is not in the chemistry thread.
I am a current year 12 student who studies chemistry and biology for science subjects.

My question is regarding the following dot point:
Perform a first-hand investigation and gather first-hand information to measure the difference in potential of different combinations of metals in an electrolyte solution

We did this practical very briefly in class 2 months ago and I have no clue what was going on hence kept delaying the lab report, until I discovered this forum. I have attached my results along. We used the following metals in zinc sulfate solution.

My question is:
1. are these readings realistic? We had to change voltmeters quite often as they were not fully collaborated and gave us various results each time. 
2. what are these results telling me? and what dot points should I cover in the discussion and conclusion?

Thank you,
Esha

[clovvy]

Do you have the actual worksheet for these? I might want to have a look

[RuiAce]

1. are these readings realistic? We had to change voltmeters quite often as they were not fully collaborated and gave us various results each time. 

This is an extremely hard question to answer, or at least answer correctly. As you should know, in a discussion you must talk about the validity, reliability and accuracy of the experiment. Here, you're basically just asking us "is it accurate" (and to some extent is it valid as well).

And we can not answer this, because we did not do the prac using the exact same equipment you used. The only time in which we can tell whether or not they are accurate is if we know the EXACT conditions your experiment was performed under.

Of course, if you had a dodgy voltmeter, impurities in the metal or anything else affecting the apparatus, then your experiment would have had problems to begin with. But other than that, your experiment must be performed under the standard conditions (or something extremely close to them) to really get anything out of the accuracy:
- 1M solutions used (i.e. 1 mol L^-1)
- 1 atm pressure
- 25 deg-Celsius temperature
This is because, we want our values to be as close as possible to the actual (theoretical) value. But in the HSC, we can ONLY obtain those values under standard conditions.

2. what are these results telling me? and what dot points should I cover in the discussion and conclusion?

The results tell you the voltage produced by forming a Galvanic cell between the two electrodes|electrolytes you've provided. As an example, in your second one, you built a cell between the Pb|Pb²⁺ half cell, with the Zn|Zn²⁺ half cell. The resulting cell produced a voltage of 0.55V. It is quite important that you understand the theory of galvanic cells first before you can really make sense out of your practical - you should ask about that if you do have problems with the theory.

The relevant syllabus dot points:
- perform a first-hand investigation to identify the conditions under which a galvanic cell is produced
- perform a first-hand investigation and gather first-hand information to measure the difference in potential of different combinations of metals in an electrolyte solution

[esha.ajmera]

Do you have the actual worksheet for these? I might want to have a look

Hi,
No we haven't got anything from the teacher. There was no point of reference for us. :/

[esha.ajmera]

This is an extremely hard question to answer, or at least answer correctly. As you should know, in a discussion you must talk about the validity, reliability and accuracy of the experiment. Here, you're basically just asking us "is it accurate" (and to some extent is it valid as well).

And we can not answer this, because we did not do the prac using the exact same equipment you used. The only time in which we can tell whether or not they are accurate is if we know the EXACT conditions your experiment was performed under.

Of course, if you had a dodgy voltmeter, impurities in the metal or anything else affecting the apparatus, then your experiment would have had problems to begin with. But other than that, your experiment must be performed under the standard conditions (or something extremely close to them) to really get anything out of the accuracy:
- 1M solutions used (i.e. 1 mol L^-1)
- 1 atm pressure
- 25 deg-Celsius temperature
This is because, we want our values to be as close as possible to the actual (theoretical) value. But in the HSC, we can ONLY obtain those values under standard conditions.The results tell you the voltage produced by forming a Galvanic cell between the two electrodes|electrolytes you've provided. As an example, in your second one, you built a cell between the Pb|Pb²⁺ half cell, with the Zn|Zn²⁺ half cell. The resulting cell produced a voltage of 0.55V. It is quite important that you understand the theory of galvanic cells first before you can really make sense out of your practical - you should ask about that if you do have problems with the theory.

The relevant syllabus dot points:
- perform a first-hand investigation to identify the conditions under which a galvanic cell is produced
- perform a first-hand investigation and gather first-hand information to measure the difference in potential of different combinations of metals in an electrolyte solution

Ok makes sense. I was unaware of 
- 1M solutions used (i.e. 1 mol L^-1)
- 1 atm pressure
- 25 deg-Celsius temperature

Thank you