Tuesday, May 17, 2011

Final Exam Review #12 and #31

They say that all good things must come to an end, and so it seems as summer draws so near and this school year draws to a close. Yet, at the end of any school year are the dreaded final exams, late nights of studying, and hours spent reviewing all that we have learned throughout the aforementioned year. Then there are the exam reviews. Though helpful, these lengthy packets often take extended lengths of time to complete, unless there is collaboration. So lets split it up!!


How about one on colligative properties?


12) In a solution of water, what would decrease the freezing point the most: adding 1.00 mole of aluminum nitrate, adding 3.00 moles of sugar, C6H12O6, or adding 2.00 moles of magnesium nitrate? Please explain why this freezing point depression occurs and why you selected the solute you did.

Colligative properties are those that are dependent upon the number of particles in a solution, not the type of particles. There are three main colligative properties of solutions: boiling point elevation, freezing point depression, and vapor-pressure lowering. They all have their roots in that fact that these foreign particles disturb the order and function of the native particles of the solvent.
This is a graph of the differences in the relations of pressure and temperature for pure water versus water with a dissolved solute in it.







Now lets look specifically at freezing point depression!

For a substance to freeze, the individual molecules must be able to arrange themselves in an orderly manner (to form an often crystalline structure) and bond. When foreign molecules/atoms are put into the mix however, they disrupt this orderly arrangement and make it more difficult for the particles of the solvent to make the needed bonds with each other to solidify. For the solution to freeze it must be at a lower temperature where the particles have less kinetic energy.

Recall that we are talking about colligative properties, characteristics that are dependent upon the number of solute particles in a solvent, not they type or size of these particles. Thus, as the number of solute molecules/atoms that are added to the solvent increase, the freezing point will decrease. In this manner, the answer boils down to the question of which solute, when dissolved in water, will create the largest number of specific particles:

  • 1.00 mol of Al(NO3)3 - According to the solubility rules, aluminum nitrate is soluble and will dissociate in water yielding Al3+ and 3 NO3-, or 4.00 mol of particles. 

  • 3.00 mol of sugar - Sugar is a general name for a variety of organic molecules, most commonly sucrose (C12H22O11) and glucose (C6H12O6).  Both of these are covalently bonded and will not dissociate. Thus, 3.00 mol of sugar will yield 3.00 mol of particles.

  • 2.00 mol of Mg(NO3)2 - Magnesium nitrate is also soluble and will dissociate in water to yield Mg2+ and 2 NO3-.  Thus, 2.00 mol of Mg(NO3)2 will yield 6.00 mol of particles.


The 2.00 mol of Mg(NO3)2 will cause the largest freezing point depression.


31) Did we cover it all? Think of a topic or question from this past trimester that you think should have been covered more by this review, and respond to it.

For me, one topic, or better, on focus of a topic that I believe the review covered only briefly was a some of the special cases regarding decomposition reactions. As these cases are less common than that of acid decomposition or salt decomposition, they are often put to the side and forgotten. Here are the special cases of decomposition reactions:

    • Metal halate --> metal halide + oxygen gas
      • Cu(BrO3)2 --> CuBr2 + 3O2 
    • Metal peroxide --> metal oxide + oxygen gas
      •  2MgO2 --> 2MgO + O2 
    • Metal carbonate --> metal oxide + carbon dioxide gas
      • Ag2CO3 --> Ag2O + CO2   

Hopefully this can clear a few things up. Thanks!!! and Good Luck!!!

Image Citations: 
http://www.chem.queensu.ca/people/faculty/mombourquette/firstyrchem/colligative/index.htm 
http://theslolane.wordpress.com/2009/05/11/stephens-big-day/

Saturday, April 9, 2011

Just Nuke It!! - Food Irradiation and Nuclear Chemistry

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Food Irradiation: Weaponizing meals or making them safe for the masses?

In this post we will discuss what food irradiation actually is and how it can be achieve and described through nuclear chemistry.  This "Xtranormal" video serves as a brief introduction to what food irradiation is and why not to be afraid of it:




Next, this "Prezi" contains all sorts of information about food irradiation, from the decay of cobalt-60 to create gamma rays needed for the process, to the risks and benefits of irradiating food.

Enjoy!!!




(Works and Images Cited are at the end of the the Prezi)

Saturday, February 5, 2011

How about some "Creative Chemistry"?....Anyone?...

So how about short "artsy" post to stimulate the mind? Maybe a Haiku and a cool slide show? What do you think?

Well, if I could actually hear your responses, I would hope that the answer would be, "Yes! Go for it!" So without further ado:

Here is a Haiku about why and how atoms form covalent bonds by sharing electrons:


Photobucket

Because the electron configurations of noble gasses (8 valence electrons and completely full outer shells) are the most stable of all configurations, when forming compounds, atoms strive to gain an octet.  Thus, they will share the number of electrons needed for all atoms to have eight electrons in their highest energy level shells.


The image to the left shows how two Group 17 (7A) elements (two atoms with 7 valence electrons) can combine to create one single bond and a diatomic molecule.


Works Cited:
Background Image for Haiku: http://205.243.100.155/frames/lichtenbergs.html
Animated .gif: http://teachers.pasd.k12.pa.us/hs/plavcand/Ionic%20and%20Covalent%20Bonds.htm

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Now, here is a short Animoto (an juiced up slide show) about five or six of the simplest molecular geometries and some household items that resemble these shapes.  Enjoy!!



Works Cited:
See last slide of movie.