Burning Candle Investigation
Background
Have you ever wondered if that expensive candle you bought
would really burn as many hours as the label claimed? In this
investigation, you will calculate the amount of moles that will burn
in 8 minutes. You will practice finding the amount of molecules in
the candle that you burn for 8 minutes. Avogadro’s number is
6.022 × 1023 atoms or molecules are equal to 1 mole of the
element or compound you are investigating. You must also
remember that 1 mole is = to the molar mass of the element or
compound. The chemical formula for candle wax is C25H52.
KNOW: What do you know about molar calculations?
Objectives
-Calculate the molar mass of candle wax.
-Perform stoichiometry calculations involving mass, moles, and
molecules.
-Calculate the time to burn one mole of candle wax.
Materials
Goggles, matches, candle, glass plate, stopwatch
Procedure
1. Weigh a glass plate
2. Weigh the candle BEFORE burning
3. Place the candle on the glass plate and burn the candle for 8
minutes.
DO NOT TOUCH THE MELTED WAX OR YOUR
CALCULATIONS WILL BE INCORRECT.
Make sure to let your candle burn on the glass plate so no product
is lost during the reaction.
4. Blow out the candle, and measure the mass of the candle and the
glass plate(we want the mass of any dripped wax which is why we
use the plate)
5. Subtract the glass plate and calculate the mass of the candle
again.
6. Subtract the candle after burning from the candle before burning
to find the mass of the wax burned.
Data
Mass plate
Mass candle
before burning
Mass candle
after burning
Mass burned
wax
1.Calculate the molar mass of candle wax. You will need to add
the masses up using the periodic table. Remember that candle wax
is C25H52. This means you will need to add up the masses of 25
carbon atoms and 52 hydrogen atoms.
2. Calculate the number of moles of the candle before it burned:
___g candle before burning × 1 mole= _______ moles candle
g(molar mass of candle wax)
3. Calculate the number of molecules of the unlit candle.(use your
answer from #2 for the moles of the candle)
___moles candle × (6.022 × 1023 molecules)=_____molecules
1mol
4. Calculate the number of moles of the wax burned.
___g wax burned × 1 mol=____moles burned
g(molar mass of candle)
5. Calculate the number of molecules of wax burned. Use your
moles from #4 of wax burned.
___moles wax burned × (6.022 × 1023 molecules) = _____molecules burned
1mole
6. Calculate the amount of time it will take to burn 1 mole of
candle wax (remember to solve by cross multiplying because this
is a proporation)
g burned wax = molar mass of candle wax
time burned
x(time to burn 1 mole of candle)
WHAT: What did you learn about molar calculations?
Answer two analysis questions with complete sentences.
1. What are the two conversions factors in this lab? You do not
need to use complete sentences on this question.
2. Describe the process to find the molar mass of a compound.
3. Why did you weigh the candle on the glass plate?
LEARN: What do you still want to learn about molar
calculations?