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Measuring the enthalpy change between Zn and CUSO4


akr1

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In this lab I had several problems:

* Concentration of CuSO4 was 0.2 M.

*No major changes in temperature. Min: 28 Max: 34

*Huge percentage error of 207.38%

*We had to increase the amount of CuSO4 and Zn to be able to read the temperature because the thermometer couldn´t reach it.

* We used an old polyestirene cup and a normal thermal cup's lid.

*Lab instructions told me to use 25 ml of 1.0 M of CuSO4 and 6 grams of zinc, but I used 75ml of 0.2M of CuSO4 and 18 grams of zinc.

*The graph I plotted with the data I got from the experiment is awful. Also, I was asked to trace a perpendicular line from when the zinc was added and a tangent line from the maximum point and using the temperature found at the intersection point which was 38 ºC, find the enthalpy change. The problem is that the result was horrible.

*I was given a theorical value of -217

Can you explain me how these problems could have affected my experiment and why I had a huge percentage error. Also if Ive got any mistakes I would really appreciate someone pointing them out.

Thank you everyone!

Edited by akr1
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I've sent you a few comments to your inbox. as soon as you see this please remove your file because people can take it and plagiarise (although i don't think anyone would in this case...) just to stay safe.

is it DCP only or also CE?

hahaaha! yeah I think NO ONE will want to plagirize what I did! hahaha! thank you although! and yes I do have to conclude and evaluate...

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ok, so firstly your graph is supposed to look like this:

tempgraph2.gif

can't find a simpler picture, sorry, but it's something like that, which means after it increases significantly, you need to still record the temperature when it goes down until you get enough data points (I'd say at least 5) that you can extrapolate it. so you can talk about this in the evaluation and suggest to record the temp for a longer time period.

and then you used wrong amounts of reactants so you definitely have to admit this mistake.

and you used a lot more zinc than required (look at the numbers of moles...) and this mass of (excess, unused) zinc adds to the mass of your thing and this excess zinc absorbs some heat, causing systematic errors because the required amount of zinc for your used CuSO4 is only 1 g. the 17 g of zinc was just sitting there absorbing heat with some unknown specific heat capacity...

We had to increase the amount of CuSO4 and Zn to be able to read the temperature because the thermometer couldn´t reach it.

what do you mean the thermometer couldn't reach it? :o

oh well you can suggest to use data logger with temperature sensor instead. more precise.

it's also true to use more amount of reactants, to reduce the uncertainties.

We used an old polyestirene cup and a normal thermal cup's lid.

woah, nice. but then why were there still a lot of errors?

you can still talk about heat loss to surroundings i guess?

one of the most important things you should mention (probably the largest source of error) is the assumption of density of both CuSO4 & Zn are 1 g/ml and their specific heat capacity is 4.18 J/gK and then you can talk about measuring their real values.

your cup still absorbs heat no matter what.

did you mix them at the exact same time? like did you pour the solid all at once or did you pour little by little?

I guess that's all? good luck hey!

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so  I did the experiment few week ago and this is what I got hope it helps

Zn(s)  + CuSO4(aq)    Cu(s) + ZnSO4(aq)

Procedure: 

  1. The bench scale was turned on and 1.30g of Zn(s) were measured with the help of a watch glass 

  2. With a volumetric cylinder 25ml of  CuSO4(aq)  were measured

  3. The CuSO4(aq) was added into a paper coffee cup 

  4. The thermometer was added into the paper coffee cup and the temperature was measured with time intervals of every 30 seconds up to 3 minutes

  5. At the 3 minutes the paper coffee cup was opened as quickly as possible and the powdered zinc was added

  6. The solution was stirred up to 5 minutes while recording the temperature every 30 seconds

Equipment

Materials

Watch Glass

25ml of  CuSO4(aq)

Volumetric Cylinder

1.30g of Zn(s)

Thermometer

 

Paper Coffee Cup 

 

Bench Scale

 

Stop Watch

 

Table 1: Equipment and Materials used

Raw Data:

Time (sec)

Temperature (°C)

0 sec

24 (°C)

30 sec

24 (°C)

1.00 sec 

24 (°C)

1.30 sec

23 (°C)

2.00 sec

23 (°C)

2.30 sec

23 (°C)

3.00 sec 

23 (°C)

Table 2: Data Collected from experiment up to 3 min 

Time (sec)

Temperature (°C)

0 sec

37 (°C)

30 sec

38 (°C)

1.00 sec 

38 (°C)

1.30 sec

39 (°C)

2.00 sec

40 (°C)

2.30 sec

41 (°C)

3.00 sec 

43 (°C)

3.30 sec

44 (°C)

4.00 sec

44 (°C)

4.30 sec

44 (°C)

5.00 sec

45 (°C)

5.30 sec

45 (°C)

6.00 sec 

44 (°C)

Table 3: Data Collected from experiment up to 5 min

Mass of Zn(s) (g)

1.3g of  Zn(s)   0.01g

Mass of  CuSO4 (ml)

25 ml of  CuSO4(aq) 0.05ml

Mass of Copper sulfate solution (g)

27.83g 0.01g

Initial Temperature (°C)

24°C 0.01

Final Temperature   (°C)

44 °C 0.01

Change in Temperature T(Final) - T(Initial)

44°C - 24°C = 20°C 0.02

Table 4: Results and data used for the reaction 

Calculating Heat Energy (ΗΕ):

HE=mcΔT= 27.83*4.18*20 = 2326,588 = 2,326588 = 2,337 kJ

m =  mass of solution

c = specific heat capacity

ΔT = Change in Temperature

Calculating limiting reactant:

n=m/mr=1.3/65.38= 0.01988 mol

Zn(s)  + CuSO4(aq)    Cu(s) + ZnSO4(aq)

1 mol + 1 mol -->  1 mol + 1 mol

0.01988 mol --> x mol

1x= 1 0.01988 x= 0.01988 mol

Limiting Reactant Zinc

Calculating Enthalpy Change (ΔΗ): 

ΔΗ=-HE/n=-2.337/0.01988=117.2 kJmol-1

Calculating Percentage Uncertainty for Mass:

Percentage Uncertainty Zn = 0.01/1.3 *100% = 0.00769% 

Percentage Uncertainty Mass of Copper sulfate solution =0.01/27.83*100% =0.000359%

Total Mass Percentage Uncertainty= Uncertainty Zn + Uncertainty Copper sulfate=

= 0.00769% + 0.00769% =0.0001538%

Calculating Percentage Uncertainty for Volumetric Cylinder:

25ml 0.05ml

100ml x?

25x= 0.05 *100

25x= 5

x=525=15=0.2%

Total Percent Uncertainty = Percent Uncertainty Volumetric Cylinder + Percent Uncertainty Mass

Total Percent Uncertainty=0.0001538% +0.2% =0.002001538 %

Calculating Percentage Deviation:

Percentage Deviation=actual-theoretical/theoretical*100=117.2 - (-217)-2171*00=154%

Conclusion:

We conducted an experiment to calculate the enthalpy change in a reaction of Zinc between copper sulfate. From the results found we can conclude that the experiment that took place was an exothermic reaction due to the increase of the temperature from 24°C to 44°C  with a temperature change of 20°C. We took measurements of 30 second intervals up to 3 minutes without the zinc and 30 second intervals up to 5 minutes with the zinc which is when the temperature started increasing.

Some errors that could have occurred during the experiment are the incorrect amount of time the reaction took place, the incorrect measurements of either elements, and inconsistent environment for the reaction to occur in. The amount of time for the reaction could have been longer or shorter than the optimal amount of time in which the reaction should have occurred. The reactants were both solids so it was very difficult to measure exactly five grams of each element. The environment of the reaction was not temperature controlled; also other chemicals from surrounding experiments could possibly tamper with results.


 

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On 2/16/2014 at 7:40 AM, Simran Venkatraman said:

What are the standard values (theoretical result) for this experiment? I need to compare my result and draw evaluations based on that. Can someone help me?

look at mine

 

Edited by anabelito234
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