2B: The Chemical Formula - Lab-Aids · 2B: The Chemical Formula What is a chemical formula, and how...

Name:________________________________Section:_________Date:_______

2B: The Chemical FormulaWhat is a chemical formula, and how is it used?

Part 1: Setting up your modelLook at the molecular model kit. Assigncolors to the different atoms, and writethem down in the table on the right. Makesure you have at least the following four:carbon, oxygen, hydrogen, and nitrogen.

One color in particular should be assignedto a specific element. Which one and why?

Part 2: Making some models and “spelling” them1. Pick any four atoms. Use the plastic

bonds to connect them.2. Draw the molecule you have made in the

diagram below.3. Use the yellow and blue boxes to work

out the chemical formula for your molecule.

4. Write the completed formula on the line.

Paper, glass, plastic, metal, skin, leaves, etc. are all matter. Although differentsubstances are made of different combinations of elements, there are only 92elements on Earth from which all substances are made. In fact, only six elementsmake up almost everything around us. How does such incredible variety comefrom only a few elements? Compare elements to letters in the alphabet. How doso many words come from only 26 letters? The answer for matter is very similar,and the chemical formula is how we “spell” all the different kinds of matter withthe same few elements.

Materials• Molecular

model kit• Calculator• Periodic table

A NATURAL APPROACH TO CHEMISTRY 11

Investigation 2B: The Chemical Formula

Part 3: Bigger molecules1. Using six atoms, build a molecule with two pairs. A pair is two of the same atom.

2. Using six atoms, build a molecule that has three of the same type of atom

Part 4: Reflecting on what you learned a. How many atoms in total are there in a glucose molecule?

b. Write the chemical formula for glucose.

c. Methane has the chemical formula CH4. Draw a possible chemical diagram for a methane molecule. (Hint: Carbon makes four bonds with other atoms.)

d. Write a chemical formula for a molecule that has four hydrogen atoms, two carbon atoms, and two oxygen atoms.

Part 5: Rules for bonding atomsIn most situations, elements tend to form a specific number of bonds when they make molecules. Forexample, each carbon atom needs to make four bonds, a nitrogen atom needs to make three, and an oxygenatom needs to make two. This is one of the most important ways the elements are different from each other.They are different because they form different numbers of bonds with other elements.

12 A NATURAL APPROACH TO CHEMISTRY


Molecules can have single bonds, double bonds, and even triple bonds! Here are some examples of each.

Let’s reassign the colors and set up the rules for bonding a few elements

1. Build one possible structure for each of the following molecules. Make sure you follow the rules for how many bonds connect each atom.

2. Draw a possible structural diagram for each molecule you build. There may be many possible structures for each molecule.

3. Leave the “formula mass” lines blank until the next step.

NH3

Formula mass____________

Diagram

CO2


Diagram



H2S


Diagram

CCl2F2


Diagram

CH3OH


Diagram

C6H6


Diagram

H2CO3


Diagram

HCN


Diagram



Part 6: The formula massThe formula mass follows these rules:

1. Each atom has a unique mass.2. The masses are different for atoms of different elements.3. Each molecule must also have a mass that depends on both its chemical formula and the mass of

its individual atoms.

The chart is now expanded to include the average mass of each atom in atomic mass units (amu). Anatomic mass unit is roughly equal to the mass of a single hydrogen atom. Carbon is about 12 times as heavyas hydrogen, oxygen is about 16 times as heavy, and so on.

Use your diagrams and chemical formulas to calculate the mass of each of the molecules you built. Recordthe masses under the chemical formulas. You can use the diagram below as an example for one of them.


Investigation 2B: Notes and Calculations


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2C: One in a MillionDrinking water can contain up to 1.3 parts per million (ppm) of copper and still be considered safe. What does parts per million mean?

Part 1: Making solutions1. Using the 1 mL pipette, add 1 mL of red food coloring to test tube #1.2. Add 9 mL of water to the test tube.3. Take 1 mL of solution from test tube #1 and put it in test tube #2. (If you use the same pipette,

make sure to clean it well before reusing it.)4. Add 9 mL of water to test tube #2.5. Take 1 mL of solution from test tube #2 and put it in test tube #3.6. Add 9 mL of water to test tube #3.7. Now take 1 mL of solution from test tube #3 and put it in test tube #4.8. Add 9 mL of water to test tube #4.

Both living things and the environment can be greatly affected bysmall concentrations of certain substances. Sometimes theamounts are so small that we use parts per million (ppm) or partsper billion (ppb) to describe them. For example, fish live byextracting oxygen dissolved in water. Fresh water bass thrive whenthe concentration of dissolved oxygen is above 4 ppm. By releasingeven very small amounts of hazardous substances, we affect theenvironment and sustainability. We can protect the environment bynot releasing hazardous substances and by using varioustechnologies to monitor environmental quality. In this activity, youwill make solutions and measure concentrations in parts per millionto understand the techniques and the skills used by scientists tomonitor our environment.

Materials• Five clean cuvettes• Four 30 mL test tubes• Cuvette rack• Red food coloring• Tap water• 1 mL and 3 mL pipettes• Lab-Master system


2B: The Chemical Formula - Lab-Aids · 2B: The Chemical Formula What is a chemical formula, and how...

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