Calculating Molar Enthalpy of Sodium Hydroxide in a Calorimeter

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Also, make sure to include any sources of error that could have affected your results.In summary, the conversation was about a lab experiment to calculate the molar enthalpy of sodium hydroxide using water in a calorimeter. The procedure involved using varying volumes and masses of water and sodium hydroxide in three trials. The calculations were done to find the enthalpy for each trial and a conclusion was made by averaging the two closer values. However, it was advised not to disregard the third trial and to include it in the calculation and also to mention any sources of error in the experiment. It was also recommended to draw a diagram of the apparatus and to compare the experimental value with the theoretical value.
  • #1
losethefire
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This is basically the lab I typed up tonight to hand in tomorrow. I'm wondering:
1. Does it look okay?
2. Is there any additional information I should add/anything to take out?
3. Is my third calculation totally off or is it just experimental error?

Purpose: To calculate the molar enthalpy of the compound sodium hydroxide by using water in a calorimeter.

Materials: An insulated coffee cup with a fitted lid
Water (varying volumes in each trial)
Solid sodium hydroxide (varying masses in each trial)
A thermometer

Procedure: 1. Fill the coffee cup with 100ml of water. Find and record the temperature fdsof the water.
2. Weigh 9.36g of sodium hydroxide.
3. Add the sodium hydroxide to the water and quickly place the lid on top of the cup.
4. Lift the lid a bit and stir with the thermometer until the sodium hydroxide dissolves. Record the temperature of the solution.
5. Pour out the solution and clean the coffee cup thoroughly.
6. Repeat steps 1-5 twice. In the second trial, use 100ml of water and 29.27g of sodium hydroxide. In the third trial, use 75ml of water and 71.52g of sodium hydroxide.

Observations:

Trial Volume of Water Mass of Sodium Hydroxide Temperature initial Temperature final
1 100ml 9.36g 22°C 40°C
2 100ml 29.27g 23°C 70°C
3 75ml 71.52g 22°C 85°C

Calculations:
ΔHNaOH=qwater
nH=vcΔt
H=vcΔt
n
For trial 1
H= 0.1L* 4.19kJ *18°C *40g
L ● °C * 9.36g * 1 mol
= 32.23 kJ/mol


For trial 2
H= 0.1L* 4.19kJ *47°C* 40g
L ● °C *29.27g *1 mol
=26.91 kJ/mol



For trial 3
H= 0.075L * 4.19kJ * 63°C * 40g
L ● °C *71.52g *1 mol
=11.07 kJ/mol



Conclusions: I found that the third trial seemed to be abnormal and so I won’t include it in an average. By averaging the two closer enthalpies, I got 29.57 kJ/mol as the molar enthalpy for sodium hydroxide.



Thanks in advance!

EDIT: Sorry if the math and the charts are a little illegible. It's hard to communicate math over the internet.

And I think I may have posted it https://www.physicsforums.com/showthread.php?t=133445" originally, sorry!
 
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  • #2
Well if I was you I wouldn't disregard a data point just because it is abnormal. You have to include it in your calculation. It's not a favourable result obviously and some error was probably made to get an out of whack answer, but it is important not to leave it out of your calculation. What I recommend is that you do a calculation of enthalpy including that point and then do the calculation leaving the point out as well. That way you can compare the two values with the theoretical value and give reasons as to why your experimental value might not be right.

I'm not sure if you did draw a diagram of your apparatus, but if you didn't it would be good to include that in your procedure.
 
  • #3


1. Overall, your lab appears to be well-written and organized. The purpose, materials, and procedure are clearly stated and the observations and calculations are presented in a logical manner.
2. One suggestion would be to include the units for the masses of sodium hydroxide in the observations table. Also, in the calculations, make sure to include the units for the specific heat capacity of water (kJ/kg°C) and the molar mass of sodium hydroxide (g/mol). This will make it easier for the reader to follow your calculations.
3. It is possible that the third trial yielded a lower molar enthalpy due to experimental error. It could be helpful to include a discussion of potential sources of error in your lab report, such as heat loss to the surroundings or incomplete dissolution of the sodium hydroxide. Additionally, you could repeat the third trial to see if you get a similar result or try to troubleshoot any potential errors in your procedure. Overall, it is important to acknowledge any potential sources of error and discuss how they may have affected your results.
 

What is molar enthalpy?

Molar enthalpy is a measure of the amount of energy released or absorbed during a chemical reaction, per mole of the reacting substance.

Why is it important to calculate molar enthalpy in a calorimeter?

Calculating molar enthalpy in a calorimeter allows us to accurately determine the amount of energy released or absorbed during a chemical reaction, which can help us understand the nature of the reaction and its potential uses.

What is a calorimeter?

A calorimeter is a device used to measure the amount of heat released or absorbed during a chemical reaction. It typically consists of an insulated container, a thermometer, and a stirrer.

How do you calculate molar enthalpy of sodium hydroxide in a calorimeter?

The molar enthalpy of sodium hydroxide in a calorimeter can be calculated by measuring the change in temperature of the solution before and after the reaction, and using the formula q = mCΔT, where q is the heat released or absorbed, m is the mass of the solution, C is the specific heat capacity of the solution, and ΔT is the change in temperature.

What are some potential sources of error when calculating molar enthalpy in a calorimeter?

Potential sources of error when calculating molar enthalpy in a calorimeter include heat loss to the surrounding environment, incomplete mixing of the reactants, and heat capacity of the calorimeter itself. It is important to take these factors into consideration and make appropriate corrections to ensure accurate results.

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