Announcements
• Toxins End of Unit Assessment Retakes
– After School Today
• Last day for any retakes is THIS Friday
• Notebooks due by Monday June 1st
– NBs turned in Friday will get 5% EC in NB grade
• If you did not complete google forms(2),
you must do so or you may not get
higher than a D on your NB.
Calorimetry
• The measurement of heat-related
constants, such as specific heat.
Calorimeter: A device used to
measure the heat absorbed or
released in a chemical or physical
change.
Specific Heat of Brass Lab
• cbrass = __ _Qbrass__ _
mbrass ×∆Tbrass
cbrass : specific heat of brass
Qbrass : amount of heat transferred (J)
mbrass : mass of brass object (g)
∆Tbrass : change in temperature of brass
(oC or K)
• Object must be submerged in calorimeter
water
• You MUST know exactly how much water is in
the calorimeter (styrofoam cup)
• 3 trials should be with same amounts of water
in calorimeter
• ONLY thing you are measuring the mass of is
the brass object.
– DO NOT weigh the water in the calorimeter to find
the mass.
Styrofoam cup
calorimeter
• Hot metal placed in cold
water.
• Heat transfers from hot
metal to cold water.
• Temperature of each will
eventually reach thermal
equilibrium
– When two objects in
contact with one another
reach the same
temperature.
• Amount of heat lost by
metal is = amount of
heat gained by water.
– Qmetal = -Qwater
∆TH2O = T2 – T1
∆Tbrass = T2 – 100oC
Calculations
• Amount of heat lost by brass is = amount of
heat gained by water.
Qbrass = -QH2O
Step 1: Solving for Qwater Find out how much heat the water
absorbed from brass.
QH2O= mH2O×cH2O×∆TH2O
Step 2: Qbrass. Amount of heat lost by the brass = amount of heat
gained by the water. Qbrass = -QH2O
Step 3: cbrass. Determine the specific heat of brass.
cbrass = __ _Qbrass__ _
mbrass ×∆Tbrass
Measured in lab
cH2O = 4.18 J/g*oC
For %Error
Accepted Value for Specific
Heat of brass: 0.380 J/goC
Procedure
1. Boil ~200mL in a 400mL beaker (1/two
groups)
2. Get a brass object from Ms. Yow. Record
object # @ top of page. Find the mass of
brass object (mbrass)
3. Lower brass object into water with tongs. Be
careful not to drop it and crack the beaker.
4. Add 50-100 mL of cold water into styrofoam
cup. 1mL of water = 1g of water. (mwater =
volume of water in styrofoam cup)
1.
Need to know exactly how much water and water
needs to cover brass object in cup.
Procedure
5. Record initial temperature (T1) of water in
styrofoam cup
6. When brass object has been in boiling water
for ~3 minutes, quickly and carefully move it
into the styrofoam cup (calorimeter) with
tongs.
7. Without moving the thermometer too much,
and also not touching the thermometer to the
brass, record the highest temperature the
water reaches (T2).
8. Do 2 more trials starting with new cold water.
Conclusion (NB pg. 174)
Attach Calculations to NB pg. 175
Attach Lab handout to NB pg. 175
Summary /Conclusion on NB pg. 174 (on it’s own
page),
Write a summary of the lab and your
calculations. (guiding questions provided
on next slide)
Give 2-3 reasons why your experimental
value for the specific heat of brass was not
the same as the accepted value.
Some questions to address in your
summary/conclusion.
1. What is calorimetry? What is a calorimeter and how did we utilize
calorimetry in this lab?
2. Why do we use the ending temperature of the water as the ending
temperature of the brass?
3. Why can we assume the starting temperature of the brass is 100?
4. How do you convert from Qwater into Qbrass?
5. What are 2-3 sources of error that probably happened in your lab? Do not
just list anything that could have happened to someone doing the lab –
they need to be things that probably happened in YOUR lab.
6. Why is Q of water a positive value? Does that make it endothermic or
exothermic?
7. Why is Q of brass a negative value? Does that make it endothermic or
exothermic?
8. Did the size and shape of the brass make a difference in the specific heat
value? Why or why not?
9. How would your data change if we had put the brass in the freezer and
put hot water into the calorimeter? How would the math change? How
would your answer change?