Caroline's weblog

Diet coke and Mentos!

There are all kinds of cool explosive chemicals that we will explore in this blog this semester.  The first will be the diet coke and mentos reaction.

This isn't truly an explosive chemical process in the true sense of the word - because explosive kind of implies combustion and heat, which is not going on here!  But I thought that this would be a cool one to start with.  Watch this three minute video from youtube that shows a fountain effect of this reaction. 

But what is really happening here?  Well it is a physical process, the CO2 in the bubbles are more attracted to the candy than they are to the soda - so they come out of solution, and well, explode!  Here is more information of the reaction from a mythbusters episode. 

Remember, this only works with the minty kind of mentos, because they have the right kind of nucleation sites for the CO2 to be attracted to!  And it also only works with diet coke, because sugar molecules are too sticky - they hold on to the CO2 better. 

And although you probably will only get soaking wet if you chug diet coke with mentos in your mouth, it is not something I would recommend!

Posted at 05:20PM Feb 16, 2008 by CHRISTIAN, CAROLINE in Explosive chemistry  |  Comments[2]

Acid-base studies

You wake up in the morning and you enjoy a nice glass of orange juice.  (Orange juice contains citric acid and absorbic acid.)  Then you go and wash your hands with soap and water.  (Most soaps contain bases.)  While you are getting ready in the morning - your stomach is digesting your breakfast.  (Your stomach contains hydrochloric acid.) 

Almost everything we do in this life is controlled by chemistry.  One big part of chemistry is acids and bases.  Everyone has some experience with acids and bases, such as orange juice, vinegar, baking soda, and bleach.  We will be looking at these acids and bases today in class and determining their pH.  Here is a website that lists some common properties of acids and bases, and also the pH scale. 


The pH scale is an easy way to measure the amount of H3O+ in solution.  A pH of 7 = 1.0e-7M of H3O+ in solution.  (A very small amount!)  This is the pH of pure water at 298K. 

Acids when they react with bases form conjugate bases, and the bases they react with form conjugate acids.  Here is an animation that make this clearer for you.

Water is a very interesting compound that can act as either an acid or a base.  Most acids and bases (except the strong ones) will form an equilibrium when they react with water.  Therefore they have equilibrium constants associated with them.  Ka values describe acids dissolving in water, Kb values describe bases dissolving in water, and Kw values describe water reacting with itself.

Posted at 08:40AM Aug 07, 2006 by CHRISTIAN, CAROLINE in General  |  Comments[4]

Jobs in Sports Chemistry

With a degree in chemistry or in any kind of science field, you can get numerous jobs.  One of the jobs you may be interested in is in sports chemistry.  These kinds of jobs are varied in what you would be working with.  You could be working with althetes, to help them improve their performance, or you could be working on making materials to improve sports equipment. 

Maybe you are interested in getting a job at Gatorade, this is a company that works closely with althetes to develop new ways to hydrate them.  Here is a cooler website than the one above - that includes people who work in performance labs.  The Gatorade labs are located in Barrington, Illinois.

Here is a website that is more about getting a degree in sports medicine and getting a job after that. 

Here is some information about working for Sports Technology International.  They are the company that makes the polymers surfaces, that was featured in an earlier post.  They have manufacturing facilities in Pennsylvania, Shanghai, and Australia.

If you are interested in working closer to home, here is a website from BASF, and they are located in Research Triangle Park.

This is my last sports and chemistry post of the summer session.  I am going to miss writing them for you.  I have learned a lot from writing them, and also from your questions.  I hope that whatever you do with your lives, you will be happy, safe, and healthy.  Keep your eye out for one more post on Monday's lab! 

Posted at 09:57AM Aug 04, 2006 by CHRISTIAN, CAROLINE in Chemistry and sports  |  Comments[7]

Redox reactions

You start your car in the morning and you drive to school (or you get driven to school).  Did you know that your car uses a device to start up, and it is something that we will be studying this week in lab.  Do you know what it is? 

You guessed it - it is a battery!  Actually a car battery is really unique - when you start your car the chemicals in the battery are used in a redox reaction to generate electricity, but when your motor is idling - the electricity in your car goes to recharge the chemicals in the battery! Here is a "How Stuff Works" website about batteries.  It actually gives some ideas of how you can make your own batteries.

Redox reactions involve the transfer of electrons from one chemical substance to another.  This kind of reaction is called an electrochemical reaction.  This is because it involves electrons (electro) and chemicals in one reaction!  The hardest part of electrochemical reactions is remembering which is part of the reaction is oxidizing, and which part of the reaction is reducing.  Here is a pdf that might make this a little bit easier for you to remember. 

In part A of this experiment - you will be determining an order of reactivity.  This can be done easily by testing which chemical substances react with others, and then knowing how to place them in a proper order.  For this part of the lab - if a substance shows a reaction with a certain chemical - this means that it is "more active" than another substance that does not react with the same chemical.

Here is a good website that shows you something like what you will be doing, and you can determine your own order of reactivity before you get into lab.  Press Start on the first page, and then you can either do Activity 1, 2 or 4.  (You can also look at molecular level pictures - so you can visualize what is going on in these reactions.)

In part B of this experiment - you will be determing the electrochemical potential of some redox reactions.  Electrochemical potentials are what determines how much voltage you can get out of a chemical reaction.  Electrochemical potentials are also related to Gibbs Free Energy - and therefore are related to spontaneity of a reaction!

Posted at 04:55PM Aug 01, 2006 by CHRISTIAN, CAROLINE in General  |  Comments[5]

Equilibrium and Le Chatelier's Principle lab

Although we have considered reactions up to this point to go completely to products, most reactions are actually at equilibrium.  This means that when you have done a reaction, and it is sitting there on the counter - you will have products in there, and also some reactants!  What is a product or a reactant?

A reactant is listed first in a equation, and a product is listed after the arrow in a equation.

When you are at equilibrium, the rates of transformation of reactant into product, and product into reactant are equal.  Therefore the concentrations of all chemicals in the reaction remain constant.  Does this mean the concentrations equal eachother?  NO, IT DOES NOT!

Le Chatelier's principle is the way to describe what happens when an outside stress is imposed on the system.  What is an outside stress?  Well you could add some more reactant or product, or you could take them away, you could increase or decrease temperature, or pressure, or volume.  The principle says - if you add stress to a system that is at equilbrium, the equilibrium of that system will respond so as to UNDO the stress.  It is kind of like the physics principle - "For every action, there is an opposite and equal reaction".

Here is a really cool website that has an animation where you can see what happens on the microscopic level when you add a stress to a system.  It also has a guy talking to you about it, so you can hear what is happening also.

If you need more practice in setting up these type of problems - here is a website that will test you on your skills.  Just hit "New Question", and one will pop up, and it will even grade which ones you have done correct!

Posted at 09:15AM Jul 31, 2006 by CHRISTIAN, CAROLINE in General  |  Comments[2]

Sports medicine and chemistry

Chemists have helped the sporting industry also by making medicines that help althetes and spectators.  From aspirin to help a headache to polychloroprene sleeves to provide warmth and compression to promote the healing of wounds.  Here is a website that has descriptions of many sports medicine and health products.

Banned substances and doping are common words in the English language today.  Why is this?  It is because of chemists.  Olympic athletes are commonly given drug tests to test for illegal substances.  Some chemists are helping to make these substances, and some are helping to test for these substances as well. 

Some of these banned substances were originally developed for helpful purposes.  Such as Human Growth Hormone (HGH), this was originally developed for children who have metabolic growth disorders.  This is no wonder drug, and THIS DRUG IS NOT APPROVED BY ANY SPORTS ORGANIZATION!

The NSF (National Science Foundation) is starting a list of supplements that do not contain any of the banned ingredients of the sports organizations.  Here is an article from NSF about this project, and here is a list of the approved supplements so far found.  On this list will be products and companies that have complied with NSF's testing procedures.

What do you think of chemists contributions to the sporting medicine industry?  Has it been a positive one or a negative one?  If you have any comments or questions please make a comment.

Posted at 04:14PM Jul 26, 2006 by CHRISTIAN, CAROLINE in Chemistry and sports  |  Comments[10]

Measuring Enthalpy Changes

A friend of yours is working for a local fast food restaurant, and their boss tells them to throw some cleaning supplies away.  They notice one bottle has some muriatic acid (HCl) in it, and the other has some lye (NaOH) in it.  When the substances were mixed, they spilled them and it burnt them bad.  Now they are trying to sue their employer to get some of the medical costs covered.  The employer says that the substances could not have burned them because they were both at room temperature when they were mixed, after they were mixed, and they had neutral pH after they were mixed.  Your friend asks you to help them win the case because they know that you have been taking this chemistry class, and they don't have a lot of money to hire a good lawyer.  What do you tell your friend?  Do you have the knowledge to help him or not?

Some chemicals should never be mixed together as this lab will teach you.  This is because some chemical reactions either release or absorb massive amounts of heat energy.  Enthalpy is how chemists measure this heat energy at constant pressure.  Chemical reactions can either be exothermic (release heat energy) or endothermic (absorb heat energy).

Here is a cool movie about a chemical reaction that has a lot of enthalpy - the thermite reaction.  If you have never seen this done, you should watch this.

Is this chemical reaction exothermic or endothermic?  I will give you a hint - exothermic reactions release heat energy so the surroundings (what you feel) will increase in temperature.  Enthalpy (or delta H) is negative.  Endothermic reactions absorb heat energy so the surroundings (what you feel) will decrease in temperature.  Enthalpy is positive.  (Sorry about having to type Delta out - blogs have no character key!)

This is another movie about reactions that proceed that absorb a lot of heat energy.  It is about entropy of a reaction.  Entropy is  related to the number of ways that the energy of a system can be distributed or disorder.  If the disorder of a chemical system increases (increase in the number of moles, or it produces a gas), the entropy is increasing (+).  And if the disorder of a chemical system decreases (decrease in the number of moles, or it consumes a gas), the entropy is decreasing (-). 

Both of these terms - enthalpy and entropy - can be combined into one term, Gibbs Free Energy.  Delta G can be used to predict whether ANY chemical reaction will proceed as written!

If you want some practice working these type of problems visit this pdf that I made for a class a while ago!

Posted at 04:17PM Jul 24, 2006 by CHRISTIAN, CAROLINE in General  |  Comments[2]

Solid State Modeling

Have you ever used a gameboy, a cell phone, a computer?  Have you ever admired a diamond ring?  These things are made possible by the concepts you will be studying about in this lab.  The technology is made possible by the use of semiconductors - this is a atomic material that has properties between a conductor (like iron) and a insulator (like styrofoam).  Here is a cool website where you can look at the the unit cell of common semiconductors - such as Silicon (Si), Gallium Arsenide (GaAs), and Zinc Sulfide (ZnS).

Diamonds are also an example of a crystalline solid.

This is a website where you can see the structure of diamond.
Diamonds are very hard substances - people can even cut things with them, such as bone!

Speaking of biology now, protein structures are also determined by x-ray crystallography, which is a technique that uses the same theories (bond angles and lengths) as this lab does.

For this lab, it would be wise of you to FOLLOW THE DIRECTIONS CAREFULLY!

The problem that I have seen in the past people having with this lab is that they can not "see" inside their unit cell to determine how many of each type of atom there are inside.  If you have this problem, take a layer off, or build another layer so that you can answer the questions properly.

For the post lab one equation that is good to know is for the packing efficiency.
Packing efficiency = (Volume of atoms in one unit cell / Volume of one unit cell) * 100%.

Posted at 12:26PM Jul 21, 2006 by CHRISTIAN, CAROLINE in General  |  Comments[7]

Polymers in sports

Organic chemistry is the study of Carbon containing compounds.  Carbon is a essential part of polymers.  Polymers are made up of repeating monomers - which are small carbon containing covalent compounds.  Another word for polymer is plastic.  We all deal with plastics every day - in clothes, shoes, cars, soda and water containers.

There are also a lot of polymers used in sports.  From the football made from polyurethane to the football field turf made from polyethylene.  Both of these polymers are man-made polymers.  There are a lot of natural polymers also still in use in the sports industry.  For example tennis balls are usually covered in wool, which adds superior playability, consistency and durability to a tennis ball. 

So everywhere you look while watching a sporting event or playing one yourself, you will see chemistry in action.  Chemists are helping to advance sports all over the world!

Some cool websites are:
A website about sports surfaces - such as turf, playground, and track surfaces.

That doesn't interest you - then maybe a website about a polymer used in shoes and sports equipment will. 

Here is a cool pdf about lycra and kevlar - two polymers used in the Olympics but for different reasons.  Make sure you have Adobe Acrobat downloaded before you open it.

Here is a website about a new breakthrough in polymer chemistry for use in sports.  Scroll down for a description of a polymer.

And finally this a website where you can pick a sport and see what kind of plastic is in use in the sport today. 

Posted at 04:49PM Jul 19, 2006 by CHRISTIAN, CAROLINE in Chemistry and sports  |  Comments[8]

Molecular Geometry lab

Up to this point we have been talking about ionic compounds - compounds with two ions (cation- girl, and anion- boy). Now in this lab we start investigating covalent compounds. Covalent compounds will share electrons, and they are usually made up of two or more nonmetals, for example CO2.

A Lewis structure is a way to depict a covalent compound on a two-dimensional piece of paper. Here is a website that describes what I describe below. (Maybe a different way will help you learn this material.)

The steps to take when drawing a Lewis structure are:

1^{st : Count number of Valence electrons (VE) the molecule has. How do you find this out? By looking at where the atoms that make up the molecule are in the periodic table. Noble gases have 8 valence electrons (except for He, only has 2). The rest of the nonmetals valence electron count is determined by its group number. All the elements in the Fluorine column have 7, all the elements in the Oxygen column have 6, all the elements in the Nitrogen column have 5, and so forth.}

2nd: Count the number of required electrons (ER) that should be used to make up the molecule. How do you find this? Just remember that all the atoms want to fulfill the octet rule (have 8 electrons), except for hydrogen (wants to have just 2).

3rd: Find the number of shared pairs (SP) that the molecule has. This is found by taking ½ * (Required electrons - Valence electrons).

4th: Find the central atom - usually the one with the lowest electronegativity, but they can NEVER be hydrogen.

5th:  Draw it in the center and the surrounding atoms around the central atom. Place the number of shared pairs found in step 3 between the central atom and the surrounding atoms. (You can have double and triple bonds as well).

6th: Place the rest of the valence electrons around all the atoms until their octet is filled.

7th: Calculate formal charge for each atom. Formal charge for an atom = Valence electrons  - (nonbonding electrons in the lewis structure + ½ number of bonding electrons in the lewis structure).

When you have your Lewis structure drawn you can determine shape and geometry by applying VSEPR's theory, and you can determine the hybrid orbitals by determining the number of electron regions around the central atom.

In this lab you will be drawing Lewis stuctures and then looking at their three-dimensional structure. Here is a website about 3-dimensional structure of molecules.  You should be asking yourself what are the differences between the picture you drew and the three-dimensional shape. You will also be investigating bond lengths and bond angles.

I want to warn you that the pre-lab for this lab is very long. I would start it early!

Posted at 01:08PM Jul 17, 2006 by CHRISTIAN, CAROLINE in General  |  Comments[4]

Qualitative analysis

Crime Scene Investigation, Raleigh
You just learned that your chemistry T.A. has been kidnapped!  All you have to investigate this kidnapping is a little bit of liquid that was left in the chemistry lab.  Is is a clue?  Who left it?  What do you do with it?

Here is a cool forensic website from Court TV.  You can read about techniques scientists use to solve crimes.

Qualitative analysis is a big part of crime forensic scientist's techniques to solve crimes.  And although I have not been kidnapped, you should treat this lab with the same care if you were investigating someone's disapperance.

In this lab you will be seperating out ions and confirming their presence.  What are ions again?  Oh yeah they are cations (girls) and anions (boys)!  In this lab you will be separating three cations. 
Different ions have different solubilities in different solutions.  This means that some ions might precipitate out. 

*** Remember insoluble, a no in the table- means that a precipitate did form, and soluble, a yes in the table -  means that no precipitate formed. ***

The solubility rules are listed in your lab book and also with the webassign questions.  Most ionic compounds are insoluble - they will form a precipitate.  The solubility rules tell you the compounds that are soluble - no precipitate.

You will be adding chemicals - HCl (hydrochloric acid) and NH3 (ammonia) - and using a hot water bath to seperate out the ions.  You will be using a solution of KI (potassium iodide) to confirm the presence of the ions.  (All the different ions that you will be using in this lab react differently when KI is added to them.)

*** Remember that ions MUST come in pairs - for example I can not give you a bottle of just cation Na+, it must be combined with a anion, such as Cl-. (So all girls must have a boy with them!) ***

If you do get a precipitate, you need a way to seperate out the precipitate, and then you will be saving the liquid on top - or supernatant.  To seperate out the precipitate from the supernatant - you will use a centrifuge.  This is a rotor which will spin the samples at high speeds, so that the precipitate will be pushed to the bottom, and the supernatant will float on the top. 

This lab has many parts so it is important that you follow the directions carefully.  Also, you will be using as one of your solutions AgNO3 - this solution, if gotten on the skin will turn it black for about a week, so be careful with it.

Posted at 11:26AM Jul 14, 2006 by CHRISTIAN, CAROLINE in General  |  Comments[3]

Sports drinks and chemistry

Quite a few of you said that your interests included some kind of sports - from basketball to ballroom dancing to cheerleading to snowboarding.  So I will start my own sports and chemistry section of this blog.  One of my goals of this class is to have you all love chemistry!   Well if you don't love it after you come out of this, at least you can appreciate chemistry and all that chemistry does for you on a daily basis.

Remember how we said that the density of water is 1g/mL.  What does this really mean?

This means that when you sweat while exercising every kilogram that you lose of weight is really about 1L of water that you have lost while sweating!

Here is a website that describes what an electrolyte is.  Actually an electrolyte is just a fancy word for what we have been studying in class - ions!  Cations and Anions are both kinds of electrolytes.  Electrolytes is just the word for ions that are in use in your body.

Here is a website that shows the difference between what you drink while you exercise.

Here is a really cool website about the creator of Gatorade and the chemistry which they used to help develop Gatorade with.  (Some of this chemistry might be a little advanced for you - but it is still cool to look at.)

If you have any questions - you can always make a comment to this blog.

Posted at 01:09PM Jul 12, 2006 by CHRISTIAN, CAROLINE in Chemistry and sports  |  Comments[19]

Solubility test lab

(Think of ions like boys and girls - girls are the cations, positively charged, and they go first.  Boys are the anions, negatively charged and they go last!)

 
Precipitation reactions take two liquids and produce a solid.  How does this happen?? Precipitation reactions are always double displacement reactions. These are reactions where one ion will displace another and replace it. 

 
If a certain combination of ions will precipitate or not is based on solubility rules - you will be making your own up during this lab.

 
Coulomb's law predicts whether or not an ionic compound will precipitate.  F = charge 1 * charge 2 / constant * (radius)^2. 

 
The charges are important!!  If two charges are the same charge, for example two anions, they repel.  Think of two polarized magnets - when you bring the south end of two magnets together they repel. (For ions and our boy/girl analogy, think of two boys on a bus - will they ever sit in one seat together?  NO, because they repel each other!)

 
If the two charges are different charge, for example a cation and an anion, they attract. (For ions and out boy/girl analogy again, think of a boy and girl who like each other - they attract one another.)

 
The same thing is at work here with cations and anions.  As the force gets bigger and more negative - the more likely things will precipitate out.  This means that when you bring big oppositely charged particles together, they will precipitate. 

 
So which ions should always be soluble, meaning they will not precipitate out?  These are ones with small charges, such as Na+.  Can you think of any others?

 
Remember, however, that you always need a positive charged particle (cation) and a negatively charged particle (anion) to make an ionic compound.  You can NEVER have two anions in an ionic compound.

This is a cool website that shows animation of what happens in a precipitation reaction!

You will need Shockwave to run it.

 
Number 4b - prelab question amendment

 NO3- is nitrate, and you will be looking at it in the lab.  It is always soluble, and it is what the cation's salts are.  They are all nitrates.  

Posted at 09:35AM Jul 11, 2006 by CHRISTIAN, CAROLINE in General  |  Comments[1]

Flame tests

Electromagnetic radiation is all around us, it can be either natural or man made.  Some examples are sunlight, radio waves and microwaves.  Humans can only see 2% of the electromagnetic spectrum.  (For picture of this, see website below.)

Frequency (greek symbol nu) is the number of cycles that pass a given point per second.  It is measured in Hertz (Hz).  1Hz = 1 cycle/second.

Wavelength (greek symbol lambda) is the distance between successive peaks.  It is measured in meters (m). 1 nanometer (nm) = 1e-9 m, 1 Angstrom (A) = 1e-10 m.  Remember to watch the signs of the exponents!  Nanometers and Angstroms are SMALLER than meters!

Wavelength * Frequency = Speed of light (c) = 3.0e8 m/s

Therefore wavelength and frequency are inversely proportional, as one goes UP the other goes DOWN.

Energy = h * frequency.  (h is Planck's constant, h = 6.626e-34 J*s)  Energy is directly proportional to frequency, (as one goes UP, the other goes UP) and inversely proportional to wavelength, (as one goes UP, the other goes DOWN).

These are good relationships to memorize.

Here is a cool website that explains light and electromagnetic radiation, at the bottom it has a picture of the electromagnetic spectrum and a color wheel.

Something else to remember about ions - Cations are always listed first in an ionic compound, they are positively charged (+), and anions are always listed second in an ionic compound, they are negatively charged (-)!!

Posted at 10:30AM Jul 10, 2006 by CHRISTIAN, CAROLINE in General  |  Comments[0]

Moles, mass and volume

Important conversion factors

6.02e23 things = 1 mole of those things OR 6.02e23 things/1 mole

1.00 g of water = 1.00mL of water (at 25 degrees) OR 1.00g/mL = density of water

You should memorize these conversion factors!

Questions to think about

How many marbles are in a mole?
How much mass is this?
How much volume would this take up?

How could you calculate these numbers?  What other information would you need?

A mole is a BIG quantity, but molecules and atoms are so SMALL that a mole of water molecules only takes up 18ml of volume!

Posted at 05:05PM Jul 06, 2006 by CHRISTIAN, CAROLINE in General  |  Comments[1]