Lab – Lauric Acid Cooling and
Heating Curve
‘Cause paradichlorobenzene is just
too stinky…
What You’ll Be Using
• Lauric acid, a solid (at room temperature) fatty
acid with the formula C12H22O2.
• It’s found in many cosmetic products and
soaps/shampoos.
What You’ll Be Doing
• Because lauric acid is solid at room temperature,
you’ll be heating it first.
– There’s no way to measure the temperature if you
don’t have a thermometer in it.
• So the first heating requires no measurement.
• We’ll be heating it in a hot water bath.
– In other words, attach it to a ring stand with a utility
clamp.
– The clamp is above the beaker which is on wire mesh
on a ring above the Bunsen burner.
What You’ll Be Doing
• Once the acid liquefies, you’ll remove it from the hot
water bath and stick a thermometer in it to record
the temperature every 20 seconds until it reaches 40
°C.
– If it “needs help” getting that low in temperature, trying
using a beaker of room temperature water from the sink.
– If it still “needs help” getting that low in temperature, I
have an ice bath ready for it.
– IMPORTANT: Make sure you can read the thermometer!
• At that point, you’ll transfer it to a hot water bath
again and record the temperature every twenty
seconds as it rises.
– HEAT GENTLY FOR QUALITY DATA.
What You’ll Be Doing
• So think about it:
– First you heat it so it becomes a liquid and you can put
a thermometer in it.
– Then you cool it (and take measurements).
– Then you heat it (and take measurements).
• At that point you can clean up and start making a
graph of the data.
– You will need two curves on the same axis.
• One for cooling, one for heating.
• You’ll also be answering discussion questions.
– And speaking of…
Pre-Lab Questions
• In official chemistry terms, what is the process of
going from a solid to a liquid called? What about
the reverse?
– Fusion (reverse: solidification)
• Given the fact that we will be letting a liquid cool
into a solid (and vice versa), how many
“segments” will each line on your graph have?
– Three
• Liquid cooling, solidification, solid cooling
• Solid warming, fusion, liquid warming
Pre-Lab Questions
• According to kinetic theory, when you add
heat without changing phase, what happens?
– Particles move at increasing speed.
• When you add heat during a phase change,
what happens?
– Particles gain energy needed to escape their
current state.
– Example: When boiling water, when enough heat
is added, water molecules escape to the gas state
(and move at a faster speed).
Quick Safety Notes
• Lauric acid isn’t too toxic, relatively speaking.
That said, if it gets overheated and aerosolized, it
can be a little irritating to the lungs.
– Once it’s liquid, you’re ready to go. Don’t overheat.
• Use hot mitts! And safety glasses!
• When you’re done, put the lauric acid in the ice
bath.
• Unrelated:
– Lauric acid’s real melting/freezing point is…?
Lauric Acid Freezing/Melting Point
• 43.2 °C.