3. Monday, Nov. 4th: “A” Day Tuesday, Nov. 5th: “B” Day Agenda
Check lab write-ups
Lab Discussion/Safety Items
Conduct lab and begin calculations: “Calorimetry and Hess’s Law”
Homework: Concept Review
We will finish the lab calculations
next time and the lab will be due…

4. “Calorimetry and Hess’s Law” Discussion
There are 3 different reactions you will be running, all using hydrochloric acid (HCl) and sodium hydroxide (NaOH).
Be sure to CLOSE the NaOH container when done using it because it is hygroscopic, meaning it will absorb moisture from the air and gain mass.
Make sure to use the glass beaker inside the metal calorimeter – DO NOT pour the acids and bases directly into the metal calorimeter – they are corrosive and will damage (pit) the calorimeter!

5. “Calorimetry and Hess’s Law” Safety Issues
You do not have to wear gloves when handling the NaOH, but you must use the porcelain scoop. Do not touch the pellets!
HCl is hydrochloric acid – be careful when handling it.
Make sure you are using the correct solution; there are 3 different solutions used in this lab.
READ THE LABELS!

6. “Calorimetry and Hess’s Law”
Rinse off the thermometer probe and stirring rod thoroughly with distilled water each time after recording the temperatures. DO NOT touch the metal probe until it’s been rinsed off.
The actual laboratory part of this lab is not difficult, it’s the calculations that will take some time.
We will go through the calculations
together back in the classroom…

7. “Calorimetry and Hess’s Law”
In the Analysis section: you need to complete
#1-#4 TODAY!
Follow all directions carefully and
have

8. Lab: “Calorimetry and Hess’s Law”
Analysis
1. Organizing Data
Write a balanced chemical equation for each of the 3 reactions.
#1: NaOH(s) + H2O(l) → NaOH(aq) + H2O(l)
#2: HCl(aq) + NaOH(aq)→ NaCl(aq) + H2O(l)
#3: HCl(aq) + NaOH(s)→ NaCl(aq) + H2O(l)

9. Lab: “Calorimetry and Hess’s Law”
2. Analyzing Results
Add the first 2 equations from question #1 to get the equation for reaction #3:
#1: NaOH(s) + H2O(l) → NaOH(aq) + H2O(l)
+ #2: HCl (aq) + NaOH(aq)→ NaCl(aq) + H2O(l)
#3 NaOH(s) + HCl(aq)→ NaCl(aq) + H2O(l)

10. Lab: “Calorimetry and Hess’s Law”
3. Explaining Events
Why does a plastic-foam cup make a better calorimeter than a paper cup?
A good calorimeter must insulate and not transfer (lose) heat. Plastic-foam cups are better insulators than paper cups and therefore make a better calorimeter.

11. Lab: “Calorimetry and Hess’s Law”
4. Organizing Data
Calculate the change in temperature (ΔT) for each of the reactions.
ΔT = Tfinal – Tinitial
Example:
ΔT1 = 26.5°C – 21.5°C = 5.0°C
ΔT2 =
ΔT3 =