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Sidebar: Looking More into Dissolving the Coat of M&M Candy

In case you were wondering why the colors of the M&M candy coats did not mix when water was added and they started to dissolve, I was able to find out a bit more information.

First, here’s a summary of what the experiment looks like:

Isn’t it interesting how the different colors meet and resist mixing?

Check the comments on this blog post for a lengthy discussion of why this happens.

Lab 17: Investigating pH

We encounter acids and bases every day. Let’s find out more about them by doing some experiments.

Experimental Title: Lab 17:  Acids, Bases, and pH Indicators

Date of laboratory:  September 23, 2014

Purpose: The purpose of this laboratory is to investigate the use of pH indicators.

Introduction:

pH is a measurement of how basic or acidic a solution is based on the activity of hydronium ions (See lesson 17 for a discussion of acids and bases).

Certain molecules and substances change color when exposed to specific acidic or basic conditions, and thus can be used as pH indicators. There are over 150 different molecules that are used as pH indicators (see the excerpt from Handbook of Acid-Base Indicators by R. W. Sabnis at the bottom of this page). Examples of naturally-occurring pH indicators include litmus (a molecule extracted from certain lichens), anthocyanin (derived from red cabbage or berries), and curcumin (found in turmeric).

The pH value or range at which the pH indicator changes color is called the transition. Here are some of the known transitions:

Methyl red is red below a pH of 4.4 and yellow above 6.2. Methyl orange is red below a pH of 3.1 and orange/yellow above 4.4. Phenolthalien is pink in the range from 8.2 to 12.0. Thymol blue is red below 1.2, yellow from 2.8-8.0 and blue above pH 9.6. Turmeric is yellow/orange below 7.4 and red above 8.6.

 

Special safety concerns for Lab 17:

  • We will be using some strong acids and bases, so please bring and wear your goggles, gloves, long pants and closed-toe shoes.
  • If an acid spills, cover it with baking soda as we discussed. If a base spills, neutralize it with vinegar. If either spills on your skin, immediately wash with water.
  • If glass breaks, do not pick it up with your bare hands. Notify your instructor immediately.
  • Be sure to wash your hands when you are finished with this lab.

Materials:

  • Centrifuge tubes
  • Sharpie markers
  • Red cabbage
  • Blender
  • Distilled water
  • Acetic acid, 6M
  • Ammonia, 6M
  • Hydrochloric acid, 6M
  • Sodium hydroxide, 6M
  • Methyl red indicator
  • Methyl orange indicator
  • Phenolthalein
  • Thymol blue
  • Turmeric
  • Paper towels
  • Rubbing alcohol
  • Litmus paper
  • Wide range pH paper
  • 250 mL glass beaker
  • 100 mL graduated cylinder
  • Clear plastic cups
  • Household substances to test for pH

Procedures:

Note: I will prepare the red cabbage indicator and turmeric in advance using these simple steps:  For the red cabbage indicator, grind up fresh red cabbage in small batches with distilled water in a blender and then strain it in a colander to remove the bigger plant bits. For the turmeric, mix a little turmeric spice (used in curries) and rubbing alcohol in a small container and then dip in strips of paper towel. Allow the strips to dry (Protect the work surface, as turmeric stains).

Part 1. Acid and Base Standards

(Edit:  changed the numbering on Monday)

1. Label four centrifuge tubes, “0.1 M acetic acid”, “0.1 M ammonia”, “0.1 M hydrochloric acid”, and “0.1 M sodium hydroxide”. Place the tubes in the tray provided.
2. Measure 10 mL of distilled water to each of the four centrifuge tubes.
3. Using a pipette, transfer 0.25 mL of 6 M acetic acid to the “0.1 M acetic acid” centrifuge tube. Add additional distilled water to bring the total volume in
the tube to 15 mL. Cap the tube and swirl it gently to mix the contents.
4. Repeat that procedure in step 3 for each of the remaining centrifuge tubes, transferring 0.25 mL each of the 6 M ammonia, 6M hydrochloric acid, and 6M sodium hydroxide solutions. Be very careful and attend to any spills immediately.
5. Obtain a 24-well reaction plate and place it in the tray. Transfer 1.0 mL of 0.1 M acetic acid from the centrifuge tube into each well from A1 through A6. Recap the tube.
6. Transfer 1.0 mL of 0.1 M ammonia into each well from B1 through B6. Recap the tube.
7. Transfer 1.0 mL of 0.1 M hydrochloric acid into each well from C1 through C6. Recap the tube.
8. Transfer 1.0 mL of the 0.1 M sodium hydroxide into each well from D1 through D6. Recap the tube.

24-well-reaction-plate-template

Part 2. pH Indicators

Now we will test each type of pH indicator.

Part 2A:
1. Place 4 strips of wide-range pH paper on the lid of the 24-well plate. Using a stirring rod, obtain a drop of the fluid in well A1, acetic acid. Transfer it to a strip of pH paper. Allow the solution to react with the paper long enough so that it is no longer changing color. Record the final color and the pH that corresponds to that color in your notebook. Be sure to rinse the stirring rod carefully between samples.
2. Repeat step 1 completely, using the stirring rod to obtain a drop of the fluid in well B1, ammonia, and placing it on a strip of pH paper. Record the final color and the pH that corresponds to that color in your notebook.
3. Repeat step 1 completely, using the stirring rod to obtain a drop of the fluid in well C1, hydrochloric acid, and placing it on a strip of pH paper. Record the final color and the pH that corresponds to that color in your notebook.
4. Repeat step 1 completely, using the stirring rod to obtain a drop of the fluid in well D1, sodium hydroxide, and placing it on a strip of pH paper. Record the final color and the pH that corresponds to that color in your notebook.

Part 2B:
Now repeat part 2A using strips of red and blue litmus paper. Record your results.

Part 2C:
Repeat part 2A using the turmeric strips. Record your results.

Part 2D:
Add one drop of red cabbage indicator to each of the wells in column 2, A2 through D2. Look for color changes. If the changes are not conclusive, add another drop. Record the final color.

Part 2E:
Add one drop of methyl red to each of the wells in column 3, A3 through D3. Look for color changes. If the changes are not conclusive, add another drop. Record the final color.

Part 2F:
Add one drop of methyl orange to each of the wells in column 4, A4 through D4. Look for color changes. If the changes are not conclusive, add another drop. Record the final color.

Part 2G:
Add one drop of thymol blue to each of the wells in column 5, A5 through D5. Look for color changes. If the changes are not conclusive, add another drop. Record the final color.

Part 2H:
Add one drop of phenolthalein to each of the wells in column 6, A6 through D6. Look for color changes. If the changes are not conclusive, add another drop. Record the final color.

Now you have some idea what the range of pH values the pH indicators indicate. Keep these in the tray to use for comparison to household substances later.

 

Part 3. Phenolthalein “Titration”

Chemists use titration to determine the concentration of unknown solutions. Generally, doing a titration requires a burette, a piece of equipment that measures volume very accurately. Because we do not have access to a burette, we will simulate the process with a micropipette.

1. Place 50 mL of distilled water in a glass 250mL beaker using a 100 mL graduated cylinder.

2. Add 3 drops of phenothalein with a micropipette.

3. Using a clean micropipette, add drops of the 0.1 M ammonia from the centrifuge tube, stirring after each addition. Keep going until the solution turns pink and stays pink. Record the volume of ammonia you added.

4. Using a clean micropipette, add drops of 0.1 M acetic acid from the centrifuge tube, stirring after each addition. How much acetic acid is needed to make the solution go clear again?

 

Part 4. Determining the pH of common, household substances

Review Table 14.7 on page 507 in your textbook. We are going to check the pH of some common substances and create a similar table.

Leave space in your notebook for a table like this:

pH-table

Place substances in clear plastic cups provided. Test the pH with strips as we did in part 2 and then think about which indicator substances might verify your results. Mix indicator substances into the substances in clear cups. Try to find the transitions/color ranges for the red cabbage indicator. Record your results and the final pH values or ranges you obtain. We will compare our results.

Conclusions:

Once you have completed the four parts, sit down and write a sentence or two to explain the results of each part.

Discussion:

Record any thoughts you have about the experiments, including:

  • Possible improvements to the procedures or how to tweak techniques
  • How the results differed from your expectations
  • Suggestions for other experiments
  • What key concepts you learned about acids and bases

Excerpt from Handbook of Acid-Base Indicators by R. W. Sabnis:

Please leave a comment or send an e-mail if you have any questions before our meeting.

 

Lesson 17: Acids and Bases

Acids and bases are everywhere. They are in our food, household products, even in our own bodies! They are relevant and relatable.

Textbook Reading:  Chapter 14, Acids and Bases, pp. 487-521.

People have known for centuries that acids:

  • Taste sour (like lemons)
  • Dissolve/corrode metals
  • Turn blue litmus paper red

On the other hand, bases:

  • Taste bitter (like caffeine in coffee)
  • Feel slippery
  • Turn red litmus paper blue

In addition to these criteria, chemists have been refining and honing their definitions of acids and bases.

In 1884, Svante Arrhenius from Sweden realized an acid is a material that can release a proton or hydrogen ion (H +) when in aqueous solution and a base releases hydroxide ions.

Because this definition did not apply to non aqueous solutions, other scientists continued to refine the definition until two scientists in 1923 came up with a definition that would work for any situation. The Brønsted-Lowry definition says that an acid is a proton donor and a base is a proton acceptor.  Thus ammonia, which has no hydroxide group, still acts as a base by accepting a proton.

Some molecules, such as water, can act either as an acid or as a base according to this definition. Molecules that can act as an acid or a base are called “amphoteric.”

Some acids are defined as “strong” and some as “weak,” generally based on how much they ionize. Strong bases dissociate completely, whereas weak bases only dissociate slightly.

This short video from TED explains these terms.

pH Scale

Chemists measure how acidic or basic a substance is using the pH scale. Although no one knows for sure how the name came to be, it is acceptable to think of pH as the “power” of hydronium ions, thus how many hydronium ions are present. (A hydronium ion is a water molecule with an extra proton – H3O+. Although often used interchangeably with hydrogen ion, hydronium is more technically correct.) Thus, pH = -log [H3O+], where the brackets mean “concentration of.”

When the concentration of hydronium ions is high (pH less than 7), the substance is said to be acidic. If the pH is =7, then the substance is neutral and if the pH greater than 7, then the substance is basic.

Although the scale is often labelled from 1-14 or 0-14, there are really no limits to the ends. Substances have been found with a negative pH, but it turns out that it is very difficult to measure the hydronium ion concentration in the negative range.

pH-scale

Bozeman Science has a particularly clear overview of pH in this video:

Be sure to let me know if you have any questions about these materials.

Sidebar: More About Viscosity and the Movement of Liquids

When viscous liquids flow over a surface they often form layers of different velocity called laminar flow. Check out this demonstration of laminar flow using a Couette cell. Be patient, it is worth the wait.

Isn’t it cool how the apparatus reverses and the droplets go back to looking like how they did when they were added.

Laminar flow might have been part of what was happening in our ketchup experiment.

Lab 16: Solubility and Solutions

For this week we will be going back to the Home Scientist labs.

Reading:  Topic II. Solubility and Solutions. We will be doing Session II-1. Solubility as a Function of Temperature  pp. 42-52.

Experimental Title: Lab 16:  Solubility as a Function of Temperature

Date of laboratory:  September 16, 2014

Purpose: The purpose of this laboratory is to examine solubility of solid solutes as a function of temperature.

Introduction:

Go ahead and read through his introduction, pp. 42- 45, which covers some of the same things as the lesson and text readings. Briefly summarize the background information from the lab as for your own lab notebook introduction. The background information can be found on pp. 46-47.

Special safety concerns for Lab 16:

  • If anything spills, please clean it up immediately with a paper towel and let your instructor know.
  • If glass breaks, do not pick it up with your bare hands. Notify your instructor immediately.
  • Be careful with the hot solution.
  • Be sure to wash your hands when you are finished with this lab

Materials: See lists page 46.

Procedures:

You will find the process is somewhat similar to the recrystallization lab we did earlier. To help speed things up, I will be doing some of the preparation work for you ahead of time.

Part I. The synthesis of sodium carbonate, page 48 – 49:  I will do this at home and bring the sodium carbonate to lab already prepared. Go ahead and start with part II in your lab notebook, but be aware that we are working with washing soda and not baking soda.

Part II. Calibrate your thermometer.

There will be a laptop so we can check the local barometric pressure and use theonline-calculator.

Part III. Determine the solubility of sodium carbonate

We have the electronic scale, so we don’t need to worry about the conversions he lists in the note at the bottom of page 50. You can skip that part.

Note:  Several time he says “stir gently with the thermometer.” Please use a stirring rod instead.

Be sure to leave room in your notebook for the graph. It should look something like this:

solubilty-graph

Conclusions:

Once you have completed the lab, sit down and write a sentence or two to explain the results.

Discussion:

Record any thoughts you have about the experiments, including:

  • Possible improvements to the procedures or how to tweak techniques
  • How the results differed from your expectations
  • Suggestions for other experiments
  • What key concepts you learned

 

SMM_teasolubility

(Image public domain)
Please leave a comment or send an e-mail if you have any questions before our meeting.

Lesson 16: Solutions

Now that we have a better understanding of liquids, it is time to revisit solutions and solubility. I’m sure you will be pleased to learn you will finally be finding out what the 6M in 6M HCl means.

Textbook Reading: Chapter 13, pp. 447-477. Molarity starts on page 457.

Definitions review:

We already touched a few of these concepts in an earlier lab, so it should be review.

The solute is the smallest part of a solution, or the substance being dissolved.

The solvent is the larger part, or the part doing the dissolving.

A solution is a solute dissolved in a solvent.

The text mentions temperature can have different impacts on solubility.

You probably have direct experience trying to add sugar to a cold drink versus a hot drink. Isn’t it easier to stir in sugar when the liquid is warmer? Solids in general are more soluble at high temperatures and less soluble at low temperature.

SolubilityVsTemperature(image pubic domain)

As you can see from the graph, however, not all salts follow this general trend.

Gases

Think about how quickly a warm soda goes flat. Gases in solution react just the opposite of solids. In general, gases are more likely to stay in solution at low temperatures than high ones.

Molarity

Now it is time to learn how to quantify solutions. One way is to calculate the molarity, which is the number of moles of solute per liter of solution.

molarity-equation

More review:
Do you remember what a mole of something is?

(A mole of a substance is simply Avogadro’s number or 6.022 x 1023 items of that substance.)

Do you remember how to calculate the molar mass from Lesson 7?

(Use your periodic table to find all the atomic mass units (amus) for the atoms in the molecule and then add them together and convert to grams.)

Mr. Causey walks us through the process of calculating molarity and making dilutions in this video:

Note: Some of you skip these videos, but because molarity is such a big part of doing chemistry, I really recommend you spend the time with this one.

In addition, PhET has an awesome interactive about molarity. Be sure to click the “show values” box to really see what is going on.

Please let me know if you have any questions about your readings or this lesson.

Lab 15: Viscosity and Other Physical Properties of Liquids

Liquids have a number of interesting physical properties, such as viscosity and surface tension. Keep in mind that differences in these properties are largely due to differences in the intermolecular forces explained in Lesson 15, but length of molecules may also be a factor. For example, long molecules may change viscosity due to molecular entanglement.

Experimental Title: Lab 15:  Physical Properties of Liquids

Date of laboratory:  September 9, 2014

Purpose: The purpose of this laboratory is to investigate three physical properties of liquids:  surface tension, viscosity (including the special case of thixotropy), and evaporation.

Introduction:

Surface tension is the tendency of the molecules in liquids to interact with each other in such a way to pull together to minimize surface area. This inward pulling is due to cohesive forces.

Viscosity is how much the molecules in a liquid resist flow. Thixotropy is when certain gels or fluids are viscous (resistant to flow) under static conditions and then become less viscous when shaken, stirred or agitated.

Viscosity has a number of real world applications:

  • Food scientists study the viscosity of foods, such as the how viscous a given batch of strawberry jam is.
  • Health professionals check the viscosity of a patient’s blood.
  • Volcanologists monitor the viscosity of molten rock or magma
    to determine how easily a volcano will erupt.
  • Auto mechanics calculate the viscosity of oil needed for different engines and climates.
  • Artists pick paints for different projects based on their viscosity.

Evaporation or vaporization is a liquid changing into a gaseous state. The rate of evaporation is influenced by the strength of intermolecular forces, as well as temperature and surface area. A drop in temperature may also be an indication that a liquid is evaporating rapidly.

Special safety concerns for Lab 15:

  • If anything spills, please clean it up immediately with a paper towel and let your instructor know.
  • If glass breaks, do not pick it up with your bare hands. Notify your instructor immediately.
  • Alcohol is highly flammable, so keep it away from heat sources.
  • Be sure to wash your hands when you are finished with this lab

Materials:

  • Bowl
  • Plastic bins
  • Water
  • Graduated cylinders
  • Metal paper clips
  • Plexiglass sheet
  • Ketchup
  • Plastic chopstick for stirring
  • Dropper
  • Stand
  • Plastic cylinders
  • Glass marbles
  • Stopwatch.
  • Large bottle of light-colored shampoo
  • Sharpie marking pen
  • Rulers
  • Hot water (hot water from a faucet is fine)
  • Ice cubes
  • Paper towels
  • Thermometer
  • Temperature probe
  • Tissue
  • Rubbing alcohol
  • Calculator
  • Laundry detergent
  • Corn syrup
  • Vegetable oil

Procedures:

Note:  Today you can do the parts in any order, so go ahead to another part and come back to finish if you need to do so. No need to wait for materials.

Part 1. Determine the surface tension of water and other liquids

  1. Obtain a bowl and partially fill it with tap water.
  2. Take a metal paper clip and devise a way to float it on the surface of the water via surface tension.
  3. Answer the following questions:  How many paperclips can the surface tension hold? Does the shape of the paperclip affect its floating ability?
  4. Obtain another liquid. Using the floating metal paper clip test, compare the surface tension of that liquid to water.

Observations:

Part 2. A. Determine the viscosity of Various Liquids

1. Obtain four plastic cylinders. If there are no lines, draw a line as a starting point about 3 cm below the top of each cylinder and and a second line as a stopping point at least 3 cm above the blue part (to allow marbles to accumulate in the bottom for each run) with a Sharpie marking pen. You don’t want the ending line to be right at the bottom of the cylinder because the marble will slow down as it approaches the bottom. With the ruler, measure and record the distance between the lines in cm.

Length between marks (fall distance):

2. If the tubes provided are not already filled, fill one each with:

  • Tap water
  • Corn syrup
  • Vegetable oil
  • Laundry detergent

3. You or the helper should hold a marble at the surface of one of the liquids. The other person should zero out the stopwatch.

4. The person holding the stopwatch should say “Go!” and have the other person drop the marble. As the marble passes the starting point, which was marked in the previous section, the person holding the stopwatch should start the stopwatch. As the marble passes the ending point, which was marked in the previous section, the person holding the stopwatch should stop it.

5. Record the time elapsed in a data table. Leave the marble in the tube until the end of the trial.

6. Repeat steps 3-5 of this section, with the same liquid and cylinder four more times with four other marbles. When you have recorded the results, tip the fluid back into the original container and retrieve the marbles to wash before using with the next liquid.

7. Repeat the process for all the liquids.

viscosity-liquids-table

Note:  Technically in this experiment you are calculating velocity = distance/time rather than viscosity. Hawaii Space Grant has a more in depth viscosity experiment,  which includes calculating viscosity using this equation:

where

  • delta p = difference in density between the sphere and the liquid
  • g = acceleration of gravity
  • a = radius of sphere
  • v = velocity

Part 2. B. Investigate the effect of Temperature on Viscosity

1. Draw two lines as start and stop points all the way around the side of the shampoo bottle (about 3 cm from each end) with a Sharpie marking pen. (You don’t want the ending line to be at the bottom of the shampoo bottle because the marble will slow down as it approaches the bottom.) With the ruler, measure and record the distance between the lines in cm.

Length between marks (fall distance):
2. Uncap the bottle and insert a marble. Fill the bottle to the top with shampoo from another bottle. Take the temperature of the shampoo with the thermometer. Close the cap tightly.

Temperature of room temperature shampoo:

3. Turn the bottle upside down and observe the marble as it sinks downward. The marble should come to rest in the cap. This ensures that the marble will drop down the center of the bottle when it is inverted once more.

4. Invert the bottle once more and use the stopwatch to measure the time it takes for the marble to sink down the center of the bottle from the top line to the bottom line. Record the time.

5. Repeat step 4 four more times, for a total of five time measurements. Then calculate the average time it takes the marble to sink through the shampoo.

6. Next, investigate the viscosity of shampoo at a warmer temperature. Fill a bin with hot water from the faucet. Tighten the cap on the shampoo-filled bottle so it cannot leak. Then lay the bottle in the bin so it is completely covered. The hot water bath will heat up the shampoo. Leave the bottle in the hot water for about 1o minutes. Carefully rotate the bottle every five minutes with tongs to heat the shampoo evenly. Open the cap and take the final temperature of the shampoo with the thermometer.

Temperature of heated shampoo:

7. Repeat step 4 five times and record the data. Then calculate the average time it takes the marble to sink in warm shampoo.

8. Now cool the shampoo. Fill the bin provided with cold water and ice cubes and lay the bottle of shampoo on its side in the bin. Leave the bottle in the cold water for about 1o minutes. Carefully rotate the bottle every five minutes or so to cool the shampoo evenly. Open the cap and take the temperature with the thermometer.

Temperature of cold shampoo:

9. Repeat step 4 five times and record the data. Then calculate the average time it takes the marble to sink in cold shampoo.

shampoo-table

Part 2. C. Investigate the thixotropic Behavior of Ketchup

Remember all those commercials showing people struggling to get ketchup to come out of to bottle? Ever wonder why that is the case?

We will be investigating the question:  which is more viscous (thicker), undisturbed ketchup in the container or vigorously-stirred ketchup?

1. Look for two plastic cups labelled “undisturbed ketchup” and “stirred ketchup.” Take the plastic chopstick and stir the ketchup labelled “stirred ketchup” vigorously for at least one minute.

2. Using a dropper, gently suck up a sample from each type of ketchup and place approximately 0.5 mL dots on the piece of plexiglass as indicated. Tip the sheet of plexiglass upright against the wall in the tray provided. Record the distance each sample has moved after one minute and after five minutes.

ketchup-spots

ketchup-table

Part 3. Evaporation

 

1. Obtain the temperature probe. Wrap the probe in a small amount of tissue and then dip it into a sample of tap water. Record the initial temperature and the temperature at one minute, two minutes and three minutes.

2. Remove the wet tissue. Dry the probe and then wrap in a small amount of tissue as before. Now dip the wrapped probe in a sample of rubbing alcohol. Record the initial temperature and the temperature at one minute, two minutes and three minutes.

Compare your results.

evap-table

 

Conclusions:

Once you have completed the five parts, sit down and write a sentence or two to explain the results of each part.

Discussion:

Record any thoughts you have about the experiments, including:

  • Possible improvements to the procedures or how to tweak techniques
  • How the results differed from your expectations
  • Suggestions for other experiments
  • What key concepts you learned about the physical properties of liquids

We’ll go over the key concepts together at the end of lab.

Please leave a comment or send an e-mail if you have any questions before our meeting.

Lesson 15: Properties of Liquids and Solids

Intermolecular forces rule when it comes to liquids and solids.

Textbook Reading: Chapter 12, pages 411-437.

__________________________

 
Let’s start out with an introduction to liquids and solids by Bozeman Science.


 

Intermolecular forces

Remember the forces that hold atoms together to form molecules that we learned about in chapter 10: covalent bonds, polar covalent bonds and ionic bonds? Now we are going to find out about forces between molecules or intermolecular forces, which is what solids and liquids are all about.

The three types of intermolecular forces are dispersion forces (also called London forces), dipole-dipole forces and hydrogen bonds.

Dispersion forces were first recognized by Fritz London, which is why they are often called London forces. They are found between all molecules (both polar and nonpolar) and a formed due to temporary unequal sharing of electrons. In larger atoms or molecules, the valence electrons are, on average, farther from the nuclei than in smaller ones. The electrons are thus held less tightly and can more easily form temporary dipoles. Because of this, larger and heavier molecules exhibit stronger dispersion forces than smaller ones.

This quick video shows how the electrons move around an atom, but the forces work in a similar way around molecules as well.

Dipole-dipole forces occur between molecules that are permanently dipolar. You can figure out whether a molecule is dipolar by examining the differences in electronegativity between the atoms and also by examining the molecule’s shape.

dipole-force-graphic

Hydrogen bonds are the strongest type of intermolecular force. They form in the special case of hydrogen bonded to fluorine, nitrogen or oxygen. Although very specific, hydrogen bonds are not uncommon and in fact form important links between molecules in our DNA.

Base_pair_GC.svg

Hydrogen bonding between guanine and cytosine in DNA

(Illustration public domain from Wikimedia)

Intermolecular forces determine the physical properties of liquids and solids, such as surface tension, viscosity, melting point, boiling point, volatility, etc. We will examine some of these properties in lab.

This final video goes in depth about physical properties and intermolecular forces. Stick with it and you will find out why Kevlar is so strong!

Please feel free to contact me if you have any questions about this week’s lesson.

Lab 14: Gas Properties and Laws

For a change of pace this week we are going to do a series of activities and record our results and observations. After we are done, we are going to figure out how the gas properties and laws we learned from the lesson apply to our observations.

Experimental Title: Lab 14:  Investigation Into The Gas Laws

Date of laboratory:  Sept 2, 2014

Purpose:  The purpose of this laboratory is to examine air pressure, Boyle’s Law, Charles’s Law, and the Ideal Gas Law.

Introduction:

  1. Boyle’s Law relates pressure and volume
  2. Charles’s Law relates volume and temperature
  3. Avogadro’s Law relates volume and moles
  4. Ideal Gas Law combines these laws into the formula PV = nRT, where R is the constant 0.0821 L-atm/mol-K

Materials:

  • Empty soda can
  • Wire mesh
  • Stove
  • Oven mitts
  • Tongs
  • Ice
  • Bowl to hold ice water
  • Glass bottles or flasks
  • Wine vacuum pump with rubber stopper
  • Water balloons
  • Regular latex balloons
  • Boiled egg
  • Matches
  • Strip of paper
  • Food coloring
  • Metric ruler
  • Tap water
  • Pipette, thin stem
  • Beaker
  • Textbooks, hardcover, 6–8
  • Clamp
  • Sharpie pen
  • Measuring tape
  • Hair dryer
  • Hand boiler
  • Kitchen scale

Special safety concerns for Lab 14:

  • If anything spills, please clean it up immediately with a paper towel and let your instructor know.
  • If glass breaks, do not pick it up with your bare hands. Notify your instructor immediately.
  • Be extra careful when handling the open flame and the boiling hot water in the can on the stove.
  • Please be sure to wear goggles for the pop can (I) and egg and a bottle (III) as the containers will be under pressure.
  • Wash your hands when you are finished with this and any other lab.

Procedures:

I. “Pop” Can
1. Set the wire mesh on the burner of the stove and turn the temperature to “high.”
2. Add a small amount of water to an empty soda can, to a depth of about 1 cm.
3. Place the can upright on the burner and heat it until the water boils and steam flows out of the top opening.
4. Using oven mitts, remove the steaming can from the hot plate with tongs.
5. Invert the soda can into an ice-water bath.

Record your results and observations:

II. Balloons in a Bottle

1. Place one small water balloon filled with air and one small water balloon filled with water in the bottle provided.
2. Cap with the gray rubber seal provided.
3. Weigh the bottle.
Mass in grams:

4. Use the white wine vacuum to apply a vacuum to the bottle.

Weight the bottle again. Record your results and observations, especially comparing the air-filled versus the water-filled balloon:

5. Remove the gray stopper.

Record your results and observations:

III. Egg and a Bottle
1. Obtain a bottle or flask and a boiled egg (shell removed).
2. Light a strip of paper on fire with matches and quickly drop into the jar/flask.
3. Place the boiled egg on top.

Record your observations:

IV. Pressure on a Pipette (from Flinn Scientific)

Edit: I have removed the instructions, as they were from Flinn. You can find them as a free .pdf here.

Edit: Here is video of how to do this technique.

Number of Books             Length of air column in mm
0
1
2
3
4
5

Graph your results.

balloons1

Balloons by Teodoro S Gruhl

V. Balloon Expansion and Contraction

1. Blow up a standard latex balloon.
2. Mark a line around the middle (approximate equator) using a ruler and sharpie pen. Measure the circumference of the balloon with the measuring tape  at the line.
Circumference of balloon at room temperature:

3. Place the balloon in the freezer for about 10 minutes. Pull it out and immediately measure the circumference again.

Circumference of cold balloon:

4. Heat the balloon with a hair dryer. Measure the circumference again.

Circumference of heated balloon:

As Mr. Anderson pointed out in the video in lesson 14, you could take the temperature of each balloon and use the information to calculate absolute zero. Cool! (I couldn’t help that)

VI. Hand Boiler

1. Obtain the hand boiler. Warm it with your hands.

Observations:

Conclusions:

Once you have completed the experiment and cleaned up, sit down and write a sentence or two to explain the results. It is always a good idea to do this part while the experiment is fresh in your mind.

Discussion:

Record any thoughts you have about the experiments, including:

  • Possible improvements to the procedures or how to tweak techniques
  • How the results differed from your expectations
  • Whether the goals were met
  • Suggestions for other experiments

Please leave a comment or send an e-mail if you have any questions before our meeting.

Lesson 14: Gases

Remember the states of matter? This week we learn more about gases, next week we’re on to liquids and solids.

Textbook Reading: Chapter 11, pages 359-399.

__________________________

Kinetic Molecular Theory

The kinetic molecular theory reveals the properties of gases relative to liquids or solids. It assumes that the molecules are very small relative to the distance between them, that the molecules are in constant and random motion, and that they frequently collide with each other and with the walls of any container without interacting. The average kinetic energy of gas molecules depends on temperature.

Translational_motion

(Translational motion- Gif by A.L. Greg at Wikipedia CC BY-SA 3.0) Caption:  “The temperature of an ideal monatomic gas is a measure of the average kinetic energy of its atoms. The size of helium atoms relative to their spacing is shown to scale under 1950 atmospheres of pressure. The atoms have a certain, average speed, slowed down here two trillion fold from room temperature.”

The Simple Gas Laws

Our understanding of how gases behave started with the work of some early scientists. They are now named Boyle’s Law, Charles’s Law, and Avogadro’s Law.

gas-laws

The ABC’s of gas: Avogadro, Boyle, Charles by Brian Bennett for TED

Later, it was realized these laws were related and the same man who gave us the periodic table, Mendeleev, put them all together in the Ideal Gas Law.

PV=nRT

Note: The Ideal Gas Law ignores some factors about real gases, such as the particles do have mass and that they do interact with each other and their surroundings. Corrections have to be made to adjust for these deviations.

Mr. Anderson at Bozeman Science gives a detailed overview of gases, some cool animations and a way to estimate absolute zero!

Please feel free to contact me if you have any questions about this week’s lesson.