Monday, Nov. 4th: “A” Day Tuesday, Nov. 5th: “B” Day

AgendaCheck lab write-upsLab Discussion/Safety ItemsConduct lab and begin calculations:

“Calorimetry and Hess’s Law”

Homework: Concept ReviewWe will finish the lab calculations next time and the lab will be due…

“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!

“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!

“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…

“Calorimetry and Hess’s Law” In the Analysis section: you need to complete #1-#4 TODAY!

Follow all directions carefully and

have

Lab: “Calorimetry and Hess’s Law”Analysis1. 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)

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)

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.

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 =