January 23, 2017

Homework Help: chemistry

Posted by Gweedo8 on Monday, June 29, 2009 at 7:43pm.

I had to do this online lab and have a total of 8 questions at the end and I am stuck half way through. Can someone please walk me through the last few question?

Here is the Lab and my homework:
In this experiment, we will determine the heat of reaction for a neutralization reaction. We will then compare this to the theoretical heat of neutralization. Prior to starting, make sure you know what the products are off a neutralization reaction (general classification = double displacement reaction). Also know how to write a net ionic equation.

Obtain a calorimeter and add 10mLs of 6.00M sulfuric acid. Obtain a burette and add 50mLs of 6.00M sodium hydroxide. Right click on the calorimeter and select pH meter and collect titration data. Then right click again and choose view titration data. Start the titration by adding NaOH and watch the temperature. Continue the titration until 30.0mLs of NaOH has been added.

Using the graph, determine the maximum temperature of the reaction. (57.9721C) Use this temperature to calculate the heat absorbed by the water. Also note how many mLs of NaOH were required to reach this temperature.(19.8mL NaOH)

At the highest temperature of this titration the Volume was19.8 mL, The Ph levels was 1.4252 pH and the temperature was 58.2867C
When I stopped the titration with 30mL of NaOH the Volume was 30 mL, The Ph levels was 14.1532 pH and the temperature was 49.3241C

Calculate the experimental heat of reaction using qwater = - qreaction. (use the mass of the solution at maximum temperature to be equal to the mass of the water). (57.97C=-57.97C)

Calculate the theoretical heat of reaction. Steps..

1. Write a balanced equation, including the phase labels for each substance.
H2SO4(aq) + 2NaOH(aq) --> Na2SO4(aq) + 2HOH(l)
2. Write the net ionic equation for this reaction. This allows us to ignore the spectator ions when calculating the heats of reactions using standard enthalpies of formation.
H+ + HSO4- + 2OH- --> + SO4^2- + 2HOH(l)
3. Look up the standard enthalpies of formation for each reactant and product.
HSO4-= -887.3
2OH= -230
SO4^2-= -909.3
2HOH(l)= ???
4. Using Hess’s law, calculate the standard enthalpy for the reaction. This answer should be in kilojoules or Joules.
5. Divide the heat of reaction by the number of moles of OH- shown in the balanced chemical equation. This gives the heat evolved per 1 mole of hydroxide ion.
6. Calculate the actual number of moles of OH- used in your reaction using the formula for molarity (M = n/V). Make sure you units cancel.
7. Multiply the number of moles of OH- by the conversion factor for heat / mole. This gives you the theoretical heat of reaction for part 2.
8. Calculate the % difference between the theoretical heat of reaction and the experimental heat of reaction. Explain any differences greater than 10%.

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