Chemistry Summer Science Institute

DAY 8 CHEMISTRY SUMMER SCIENCE INSTITUTE

MORE CHEMICAL CLASSES: ORGANIC vs. INORGANIC

All chemical compounds that exist in nature can be classified in two broad groups, inorganic and organic. In this activity, we will compare several inorganic and organic compounds to come to some general conclusions about their behavior.

1. Define or describe the terms below (you should have had these before):

Solubility

Conductivity

Flammability

Volatility

Melting Point

Boiling Point

We will compare inorganic and organic compounds with respect to the characteristic properties defined above. Inorganic compounds to be used are: salt, NaCl, sodium chloride; NaHCO3, sodium bicarbonate (baking soda); and a dilute acid solution. Organic compounds to be used are: rubbing alcohol, isopropyl alcohol, C3H7OH; urea, CO(NH2)2; and cyclohexane, C6H10.

2. SOLUBILITY

We will compare the solubility of inorganic and organic compounds in two solutions: water, H2O and toluene, C7H8. Place a few mL (3-5) of water in six glass vials or see-through cups. When testing a solid compound, add small amount, a pinch or a tip of the spatula, to the solvent, stir, and observe. When testing a liquid, add 2-3 mL or a few drops from a dropper slowly to the solvent and observe. Repeat this process with toluene. Complete the table using “S” for soluble, “PS” for partially soluble, and “I” for insoluble.

1 DAY 8 CHEMISTRY SUMMER SCIENCE INSTITUTE

SOLUBILITY

Water, H2O Toluene, C7H8 Inorganic - salt, NaCl

Inorganic - baking soda, NaHCO3

Inorganic - dilute H2SO4

Organic - cyclohexane, C6H10

Organic – urea, CO (NH2)2

Organic – isopropyl alcohol, C3H7OH

Complete the statements below using one of the following terms: more, less, equally.

Inorganic compounds are soluble in water than organic compounds.

Inorganic compounds are soluble in toluene than organic compounds.

3. CONDUCTIVITY

Use the already prepared solutions of the substances listed in the table below. Place the electrodes in each solution and observe the light bulb. It will light up if the solution conducts electricity; it will remain unchanged if the solution does not conduct electricity. Complete the table below using “C” for conduct, “CW” for conducts weakly (dim light), and “NC” does not conduct.

CONDUCTIVITY INORGANIC ORGANIC salt, NaCl sucrose solution

baking soda lactose solution

dilute acid benzoic acid solution

In conclusion, complete the statements below, placing conduct or do not conduct in the blank space.

Inorganic compounds typically electricity.

Organic compounds typically electricity.

4. FLAMMABILITY

Light a Bunsen burner. Place a small amount of solid on the tip of a metal spatula and into the flame. Repeat for each solid in the table below and record your observations. Does the compound burn? Does it burn readily or slowly? Does the compound leave a residue or does it burn completely?

FLAMMABILITY Inorganic – NaCl

Inorganic – NaHCO3

Organic - sucrose

Organic - Urea

In conclusion, organic compounds are flammable than inorganic compounds. (“more” or “less”)

5. VOLATILITY

Consider the liquid compounds and compare their volatility. Carefully smell the area above the compound by wafting some air above the container toward your nose.

VOLATILITY Organic – isopropyl alcohol

Organic - cyclohexane

Inorganic – dilute HC1

Organic - isobutylacetate

In conclusion, organic compounds are volatile than inorganic compounds. (“more” or “less”)

6. MELTING POINT

Using the melting point apparatus, compare the melting point of solids. Do not heat past 180oC. If the compound has not melted until 180o record >180oC. Ask your instructor for directions on how to use the apparatus,

MELTING POINT Inorganic – salt, NaCl

Inorganic – baking soda, NaHCO3 Organic - acetanilide

In conclusion, organic compounds have generally melting points than inorganic compound. (“higher” or “lower”)

7. BOILING POINT

Simply record the boiling points listed on the reagent bottles and compare.

BOILING POINT

Organic - cyclohexane

Organic – isopropyl alcohol

Inorganic - mercury

In conclusion, organic compounds have generally melting points than inorganic compound. (“higher” or “lower”)

POLYMERS: GETTING SLIMED AND WORMED

An important class of organic compounds is the polymers. These are very large molecules that are made of smaller repeating units. Polymers can be natural, like proteins and starches, or man- made, like PVC (polyvinyl chloride) or Styrofoam.

In this activity, you will make two polymers and observe their properties.

1. MAKING SLIME a. Place 25 mL (or 5 teaspoons) of the Elmer’s Glue solution into a cup or plastic sandwich bag (if you add ½ teaspoon of talcum powder at this point you can make GAK instead of slime). b. Add 5 mL (or 1 teaspoon) of the saturated borate solution to the cup (bag) and stir vigorously or mix by squeezing the bag to mix thoroughly c. After 1-2 minutes the slime should resemble silly putty

In the Classroom SLIMING THE STUDENTS 1. Build a vinylacetate molecule (C, H and O atoms) with three students (arms linked in a chemical bond) 2. Build two additional vinylacetate molecules and link all three together to make a strand of polyvinylacetate 3. Investigate its properties (movement, stretching, bending) 4. Build an identical second strand of polyvinylacetate and place it in front of the first strand. 5. “Bond” these strands with sodium borate cross-linking students 6. Investigate the properties of this cross-linked polymer (vs. the individual strand in 3 above). Specifically note that the movement of the cross-linked polymer strands is hindered (transition form-flowing liquid to flowing solid), will stretch if pulled slowly and break if pulled rapidly

Make Slime 1. Organize students into groups of four with each student assigned a number 2. Make slime as detailed above identifying students by number to do specific tasks 3. Investigate the properties of vinylacetate and polyvinylacetate as in 3 and 6 above 4. Demonstrate that slime will bounce and pick-up newsprint! Ask students to explain these phenomena!

Chemicals needed: 1. Sodium borate (20 Mule Team Borax) 2. Elmer’s White Glue (polyvinylacetate) 3. Water (tap works fine)

Solutions you need to make:

1. 50 percent (v/v) Elmers Glue solution 2. Saturated sodium borate solution 2. Calcium Alginate Worms

Sodium alginate is a polysaccharide made of D-mannuronic acid and L-guluronic acid subunits. Derived from seaweed, it is a common additive in ice cream, salad dressings, pimento slices, and some juice preparations. When a multivalent ion like Ca2+ is added to a solution of sodium alginate, the ions can interact with the acid salt on the alginate and link two sections of chain together to form a more solid and flexible polymer.

1. Obtain 25 mL of sodium alginate solution. Place 100 mL of 1% CaCl2 solution into a 150 mL beaker. Place 100 mL of saturated NaCl into a clear jar.

2. Slowly pour a thin stream of the alginate solution into the CaCl2 solution.

What happens and why?

3. Remove a few of the “worms” immediately after they form (you can use your hands) and place them in the jar of saturated NaCl. Shake the jar a few times and record your observations.

What is happening at this point and why do you think so?

MOLECULAR MODELS

A good way to visualize organic compounds is to build models. This gives you a feeling for the three dimensional qualities that often affect the way these molecules behave. In building the molecular models you will use a set in which black balls represent carbon, yellow balls represent hydrogen, red balls represent oxygen, and sticks represent chemical bonds (two electrons shared between atoms).

1. Place sticks into the holes in a carbon and add a hydrogen to each stick. This is the simplest organic molecule called METHANE.

Carbon forms (number of) bonds.

We can say that carbon is______(monovalent, divalent, trivalent, tetravalent, pentavalent, hexavalent)

______hydrogen atoms combine with one carbon to form METHANE.

Methane’s generalized formula is CxHy so it can be written as ______.

2. Now remove one hydrogen and attach another carbon. Place sticks and hydrogens on the new carbon. This molecule is called ETHANE.

Two carbons bonded to each other combine with hydrogen to form ethane.

The formula of ethane is ______.

Sketch an ethane molecule here.

3. Now add a third carbon and appropriate hydrogens to form PROPANE.

Three carbons bonded to each other combine with hydrogens to form propane.

Propane’s formula is ______. Sketch the structure of propane here.

4. Make a molecule with 4 carbons. This is BUTANE.

Four carbons bonded to each other combine with hydrogens to form butane.

Butane’s formula is ______.

Is there any other structural arrangement you can form for butane? Try making another molecule with 4 carbons and see what you can come up with. Just twisting the original model into different shapes doesn’t count! The bond arrangements must be different.

Sketch the unique structures of butane that you made.

Are they superimposable (can you place one on top of the other and match all atoms without breaking a bond)?

______

Do they have the same molecular formula (number of C’s and H’s)? ______

5. You have made a series of hydrocarbons (made from only hydrogen and carbon) called the alkanes. What is the general formula for this series? ______

What do the names have in common? ______

Are these molecules you built perfectly linear? ______

Are all the bond angles the same? ______

What do you think the value of the bond angles are?

______

So far you have been making models of hydrocarbon molecules that form only single bonds - one pair of electrons shared between two atoms. Sometimes there are not enough atoms to go around to form single bonds so atoms will share more than one pair of electrons to get to their magic number of 8. Two shared pairs of electrons form a double bond and three pairs form a triple bond.

Is it possible to make two bonds between two atoms (balls) using the wooden sticks? ______

Do you see anything in your model kits that might work to make a double bond? ______

6. Using two springs to represent a double bond (four electrons shared) connect two carbons and add hydrogens.

These two carbons combine with hydrogens to form ETHENE.

The formula for ethene is ______.

Sketch the structure of ethene here.

7. Attach a single bonded carbon with hydrogens to the two double bonded carbons.

These carbons combine with hydrogens to form PROPENE,

The formula for propene is ______.

Sketch the propene molecule here.

8. Add another single bonded carbon to the structure above.

The 4 carbons combine with hydrogens to form BUTENE.

The formula for butane is ______.

Sketch the butene molecule here.

How many different butenes can you make? Make sure they have the same molecular formula (number of C’s and H’s).

Sketch their structures here.

Are the bond angles the same for atoms attached with a double bond compared to a single bond? ______Estimate the bond angles for atoms attached with a double bond. ______

You have probably noticed that the names changed slightly for hydrocarbons with double bonds. This series is called the alkenes. How can you tell from their names? Hydrocarbons with triple bonds are called alkynes. A four carbon compound with a triple bond is called butyne.

9. Here’s a challenge for you. Make a hydrocarbon with the formula C6H12 that has only single bonds. Sketch the molecule below. What is unique about this alkane?

Not all organic molecules are hydrocarbons, although they must have carbon to be organic. Elements such as oxygen and nitrogen play a big part in the chemistry of our body systems. Let’s build some molecules with these elements.

Before we start, let’s look at expanded chemical formulas called structural formulas for organic compounds. In a structural formula the hydrogens that follow an element are attached to that element. For example:

C2H6O can be written as CH3CH2OH and has this full structural formula:

10. Make a molecule of methane but in the place of one hydrogen add an oxygen. Add any hydrogens needed to be sure all holes are complete. You have made METHANOL which is one of a series called the alcohols. Alcohols have an –OH group on a carbon atom.

Can you make butanol? (Hint: check previous models to see what “but-“ means)

What is the structural formula for the butanol you made?

Are there any other ways that you can arrange the same atoms to form a different alcohol? How many can you find?

When compounds have the same molecular formula (same number of each atom) but different structural formulas they are called isomers.

11. Have each member of your group make a different isomer of C3H6O. Be creative with the oxygen. Sketch the results for each isomer here.

12. Now, have each member of your group take a carbon atom and add 4 bonds. Add a hydrogen, chlorine (green), bromine (orange) and iodine (purple) to each stick.

Compare your molecules by trying to superimpose them on each other (all atoms line up when one molecule is placed over the other).

Did any of you make the same molecule?

If you made a molecule that is not superimposable place it across from the other form so one looks like the mirror image of the other

The mirror image compounds you made show a form of isomerism called stereoisomerism. Stereoisomers have the same bond connections but these connections differ in their arrangement in three dimensional space. Because your molecules cannot not superimposed they are also fall in a class called enantiomers. Although the atoms are the same and attached to the same carbons, properties of the isomeric compounds may differ.

Which of these things are like enantiomers (non-super-imposable mirror images)?

a. spoon b. sheet of lined paper with no holes c. student desk with side arm d. drinking glass e. automobile f. foot

Amino acids and simple sugars have two mirror image versions. Our body uses only one version and cannot metabolize the other!