ACADEMIC CHEMISTRY NAME:
PERIOD: DATE:
THE MOLE
ABOUT A MOLE’S WORTH OF CALCULATIONS
INTRODUCTION
Please complete the following background questions about units as your prelab assignment.
1. When you buy eggs you usually ask for a ______. You know that one dozen of any items is ______items.
2. Paper is not packaged by the dozen. Paper is packaged by the ream. A ream of paper has 500 sheets. Why is it useful to use these units like a dozen or a ream?
3. What determined how many items should make up a particular unit? (Think about the paper and the eggs)
4. If you were asked to design a new unit to count something, what would you consider when choosing how many items should be included in your new counting unit?
5. The MOLE is defined as (see your notes or textbook):
The word MOLE is derived form the Latin “moles” which means “a mass.”
6. What other unit is based on carbon – 12 as the standard? Write the unit and the definition here.
7. One mole of items contains ______of that item.
8. The number associated with the mole is known as ______number.
9. If you had one mole of carbon, how many atoms would be present?
10. How much would a mole of carbon weigh? ______This is known as the molar mass of carbon and it has the same value as the atomic mass only it has units of grams.
OBJECTIVES
To discover a method of counting “things” that you are not able to see such as atoms, molecules or formula units of compounds.
To use Avogadro’s number and molar mass as a bridge between mass of a sample and number of atoms, molecules, or formula units in that sample.
MATERIALS
Electronic balance
Calculator
Pencil
Various chemical samples
Small beaker, pipet, water
Introductory Lab data and Density Lab data – bring with you to class.
PROCEDURE
Please weigh all samples first and then perform the calculations and analysis questions.
PART I: ATOMS OF CARBON IN A SAMPLE
Objective: to determine the number of atoms used while using your pencil during lab.
Pencils have a graphite core that is commonly referred to as “lead.” However, graphite is actually an allotrope of carbon. Define allotrope:______
1. Obtain a piece of graphite from a mechanical pencil.
2. Guess how many atoms of C are in the sample. Write your guess in pen.
3. Find the mass the graphite rod.
4. Measure the length of the graphite rod.
5. Complete the calculations below showing work in the space provided
DATA PART I:
DESCRIPTION
/ VALUE / UNITSEstimated number of C atoms in the graphite rod
Length of graphite rod
Density of graphite
Mass of graphite rod
Molar mass of graphite
Moles of graphite
Number of carbon atoms
Radius of graphite
% error between your estimated value and your calculated value of the number of atoms of C.
Calculations:
Moles of graphite used:
Number of carbon atoms:
Volume of graphite rod:
Radius of graphite rod:
% error calculation:
Please show all work, units, and sig figs for these mid-lab questions:
1. How much would 1 atom of carbon weigh in grams?
2. How much would 1 mole of carbon atoms weigh in grams?
3. How much would 1 atom of carbon weigh in amu?
4. Given 5.0 x 1027 atoms of carbon, what is the mass of carbon present?
PART II: MOLECULES OF WATER IN A DROP?
Objective: To calculate the number of water molecules in a single drop of water.
1. Guess the number of water molecules in a drop of water. Write your guess in pen.
2. obtain a small beaker or cup and find its mass
3. use a dropper pipet to deliver 50 drops of water to the beaker
4. find the mass of the beaker and 50 drops of water
5. complete the calculations and data table below
DATA PART II:
Description / Value / UnitsEstimated number of water molecules in a drop
Mass of empty beaker
Mass of beaker and 50 drops of water
Mass of 50 drops of water
Average mass of 1 drop of water
Molar mass of water
Moles of water in 1 drop
Calculated number of water molecules in 1 drop
% error comparing the estimated and the calculated number of water molecules in a drop
Calculations:
Molar mass of water = 2 x molar mass of H + molar mass of O =
Moles of water in 1 drop:
Molecules of water in 1 drop:
% error
Please show work for the following mid-lab questions.
1. If you drink 10 (8.0 oz.) glasses of water a day, how many molecules of water do you drink? Set up as a single conversion problem.
30 ml = 1 fluid ounce
2. The Pacific Ocean has an area of 165.25 million square kilometers. Given an average depth of 12100 ft, determine the number of water molecules in the Pacific Ocean (disregard the aqueous salts).
PART III: MOLES and ATOMS in a SAMPLE
Objective: To become familiar with mole amounts of different substances.
1. Fill in the following data table for 5 different substances in the lab.
2. Subtract the mass of the container to find the mass of the sample in the container.
3. Perform calculations to complete the table.
Qualitative observations of the sampleName of substance
Chemical formula/ element symbol
Molar mass of element/ compound
Mass of sample and the container
Mass of container
Mass of the sample
Moles of the sample
Number of atoms/ molecules
Calculations:
Show one sample calculation to find the number of moles in a sample starting with the mass of the sample in grams.
Show one sample calculation to find the number of atoms or molecules in a sample starting with the number of moles of the sample.
Please show work for the following mid-lab questions.
5. Determine the number of atoms in a 5.0 mg sample of iron.
6. Determine the number of grams that would register on the balance if you had 4.5 x 1027 atoms of sulfur.
PART IV: MOLES and MOLECULES BURNED IN A CANDLE
Objective: To calculate the number of moles of C25H52 and the number of molecules used when a candle burns for a set amount of time.
Use your data from the first lab.
Description / Value / UnitsMass of plate
Mass of candle and plate before burning
Mass of candle before burning
Mass of candle and plate after burning
Mass of candle after burning
Mass of wax used
Molar mass of wax
Moles of wax used
Molecules of wax used
Calculations:
1. Calculate the molar mass of wax C25H52 (hint: 25 x molar mass of C + 52 x molar mass of H)
2. Calculate the moles of wax used.
3. Calculate the molecules of wax used.
Please show work for the following mid-lab questions.
1. Given a candle with dimensions d = 2.0 inches and h = 8.0 inches and the density of wax = 0.93 g/cm3, determine the mass of the candle.
2. How many molecules of paraffin would be contained within the candle in #1?
3. If the whole mass of the candle was consumed in a combustion reaction, determine the total amount of energy that would be released in kJ. (see wax lab post lab for heat of combustion of wax)
PART V: CALCULATE THE NUMBER OF ATOMS THAT SPAN THE THICKNESS OF AN ALUMINUM FOIL PIECE
Use your data from the density lab or recalculate the thickness of aluminum foil if needed.
When Rutherford performed the gold foil experiment, he shot positive alpha particles towards the thin gold foil in an attempt to probe the structure of the atom. His thought was that having a thin gold foil would minimize the number of atoms that spanned the thickness so he could probe fewer atoms at one time. Understand that the gold foil was much thinner than our aluminum foil, but the calculation of the number of atoms that would span the thickness is the same.
Description / Value / UnitEstimated number of atoms that would line up across the thickness of aluminum foil.
Length of the foil piece
Width of the foil piece
Height/ thickness of the aluminum foil in m
Mass of the foil piece
Volume of foil piece
Total number of atoms in the foil piece
Radius of an aluminum atom
Radius of an aluminum atom in m
Number of atoms of aluminum that could be lined up across the height of the aluminum foil
% error comparing your estimated value and the calculated value
Calculations:
Height of foil piece in m:
Volume of foil piece:
Total number of atoms in the foil piece (based on mass of foil piece)
Radius of the aluminum atom in meters
Number of atoms of aluminum that could be lined up across the height of the aluminum foil
Please show all work, units, and sig figs for these mid-lab questions:
1. Back to the gold foil experiment: Typical gold leaf, like the gold foil used in Rutherford’s experiment has a thickness of about 0.10 microns. A stack of 1000 sheets of gold leaf would be about the same thickness as a typical piece of printer paper. Convert this thickness to meters.
2. What property of gold allows it to be formed into sheets?
3. Determine the number of gold atoms across the thickness on 0.10 microns after finding the radius of a gold atom.
4. Which is a bigger atom, aluminum or gold? Suggest a reason for this? What makes atoms larger/ smaller?
5. Given a 5.0 x 5.0 cm x 10.0 cm stack of gold leaf, determine the mass of gold contained within.
6. Calculate the number of gold atoms in the stack of gold leaf in the last problem.
POST LAB QUESTIONS
1. Write a numerical value or calculation under each of the following. You do one side, your partner does the other. Then enter a greater than, less than, or equal to in the middle column
Atoms of carbon in a mole of carbon / Atoms of aluminum in a mole of aluminumMass of one mole of carbon / Mass of one mole of aluminum
Moles of carbon given 10.00 g carbon / Moles of aluminum given 10.00 grams of aluminum
Grams of carbon present given 1.2 x 1024 atoms of carbon / Grams of aluminum present given 1.2 x 1024 atoms of aluminum
Grams of carbon given 3.0 moles of carbon / Grams of aluminum given 3.0 moles of aluminum
Atoms of aluminum that fit across the thickness of aluminum foil (see calculation in data table above. / Atoms of gold that fit across the thickness of gold foil (see mid-lab problem above)
Molecules of C25H52 in a mole / Molecules of H2O in a mole
Mass of one mole of C25H52 / Mass of one mole of H2O
molecules of C25H52 in a 200.0 gram piece of wax / Molecules of water in 18.0 ml of water
Atoms of hydrogen in 1 molecule of C25H52 / Atoms of hydrogen in 1 molecule of H2O
2. If everyone in the world (research the current population) counted 1 particle per second, how long would it take to count up to 6.02 x 1023 (in years)?
3. Research and explain: Amadeo Avogadro is the name associated with the 6.02 x 1023 value, but he did not determine the actual value. Who discovered the number of particles in a mole? How was it determined? Why is the mole named after Avogadro if he did not actually determine the numerical value? List sites visited.