Please cut this paper in half and tape it into your chemistry comp bookl.
1112 Counting by Measuring Mass (excerpt from text, page 304)
Purpose
To determine the mass of several samples of chemical compounds and use the data to
count particles.
Materials
chemicals
water – dihydrogen monoxide – H2O
isopropyl alcohol – C3H7OH
sodium chloride – NaCl
sucrose – C12H22O11
calcium carbonate – CaCO3
sodium hydrogen carbonate – NaHCO3
plastic spoons
portion cups for holding and massing chemicals
centigram balance
Procedure / Analysis
(1) Measure the mass of one level teaspoon of each of the chemicals.
For this lab – and this lab only – you may return the chemical you use to its original
container.
Record your values in your data table (provided).
(2) Calculate the molar mass of each compound and record it in your data table. The
molar mass is the number of grams in one mole of the substance. Show your work
and circle your answer. Be sure to include units on your answer.
[How do you do this? Use the periodic table to find the atomic mass (to the tenths place)
of one of the elements in the compound. Multiply this atomic mass by the number of
atoms in the compound. Do the same for every element in the compound and then add
the totals together to get the molar mass. The units are g/mol.]
(3) Determine how many moles of each compound are in your samples. Show your
work and circle your answer. Be sure to include units on your answer.
[How do you do this? Take the mass of the sample (#1) and divide it by the molar mass
of the compound (#2). The result will be the number of moles in the sample.
number of moles = mass / Molar mass or
n = mass / Molar mass
Using dimensional analysis, this looks like:
mass of sample (g)
1 mol
mass from PT (g)
=
mol]
Please cut this paper in half and tape it into your chemistry comp bookl.
(4) Determine how many particles of each compound are in your samples. Show
your work and circle your answer. Be sure to include units on your answer.
[How do you do this? Take the number of moles in your sample (#3) and multiple it by
Avagadro’s number. The result will be the number of particles in the sample.
number of particles = # moles x 6.02 x 1023 particles*
Using dimensional analysis, this looks like:
amount of sample (mol)
6.02 x 1023 particles
1 mol
=
particles*]
* If you are dealing with a covalent compound, the particles are molecules.
If you are dealing with an ionic compound, the particles are formula units.
If you were dealing with an element, the particles are atoms (or molecules if the element is one
of the seven diatomic elements: H2, N2, O2, F2, Cl2, Br2, I2)
Conclusion(s)
(5) Which of the six samples contains the greatest number of moles? Support your
answer with evidence.
(6) Which of the six samples contains the greatest number of particles
(molecules/formula units? Support your answer with evidence.
(7) THINK: Which of the six samples contains the greatest number of atoms? How
would you go about determining this?
(8) Write a statement or two that summarizes the big ideas from this lab activity.
Include (and underline) the following words:
mass
number
mole(s)
molar mass
particles
Avagadro’s
Practice what you learned:
(9) Sally measures out 7.5 grams of sodium carbonate – Na2CO3. Calculate the number of
moles of sodium carbonate and the number of particles (formula units) in her sample. You
will need to determine the molar mass of sodium carbonate first.
(9) Sally measures out 0.60 grams of glucose – C6H12O6. Calculate the number of moles of
sodium carbonate and the number of particles (formula units) in her sample. You will need
to determine the molar mass of glucose first.