Chemistry Grades and Chemistry Help

Here are a couple of books which will help improve your chemistry grades.

In the ideal gas law pressure and temperature are fairly easy to understand from a molecular point of view.  Pressure is when gas molecules hit the wall and bounce off.  Temperature is how fast they move.  P and T are essentially independent of each other.  Volume can be more difficult to interpret.  The question “how big of a container do you need to hold this much gas” is certainly a good test question, but in a real experiment you start with a container and ask questions about what is inside it.  It has almost no microscopic relevance.  The microscopic feature which is relevant is:  how close are the gas molecules to each other ?

Volume and amount are closely coupled together, and perhaps a better form of the ideal gas law would be  n/V = P/RT where n/V is the molar density.  Molar density is the number of moles per unit volume, which is directly related to the typical distance between molecules.  It’s measured in moles/liter and sounds a lot like molarity (the units are the same).  But molarity usually refers to a dilution of some compound dissolved in water.  The molar density of a gas says how many moles are in a standard volume.  For 1 atm at 298 oK the molar density of a gas is 1/22.41 or 0.04462 moles/liter.

If you measure pressure and temperature as independent variables then molar density is a result.  Only 2 of these 3 variables can be independent. As soon as you measure 2 of them the 3rd can be calculated.

If molar density confuses you think about water solutions.  You would almost never ask “how many liters do I need to hold 0.34 grams of a liquid with density 1.119 g/cm3 ?”  While this is an excellent test question, it’s not a real problem we will ever face.  A much more realistic problem is to ask, if 101.2 grams of liquid has a volume of 100 cm3 then how much will 1 gallon weigh ?

This is a good test question :  At 1 atmosphere and 298 oK what is the density of air?

n/V = P/RT = 1/.08206/298.15 = 0.4462 moles/liter,  now just convert moles to grams.  Since air is 80% N2 and 20% O2 a good molar mass to use is 29 g/mole.  So the density of air is about 29 * 0.4462 = 1.3 g/liter.  So an empty 1 liter Coke bottle has 1.3 grams of air inside of it.  1L can hold 1000 g of H2O.  So water is about 770 times as dense as air (1000/1.3).

I have made some chemistry help videos which explain properties of gases, including pressure and temperature. These videos are currently free but will soon become part of the protected content of this membership site.

The first 3 videos are on the properties of gases, the 4th describes the 6 typical versions of ideal gas law problems you will see on a test or homework.  Then the 6 homework videos go through each type of problem in careful detail, with an added bonus.  I tried to point out common mistakes you will make when you work these problems.  If you are prepared for these mistakes then your grades should improve.

Please respond to this post on these videos, are they useful, are there any mistakes, what is missing, what other topics should I cover for ideal gases? Are there any web problems (bad URL, no file, 404 code) ?

http://media.chemistrygrades.com/IdealGas_Intro.swf
http://media.chemistrygrades.com/IdealGas_Intro2.swf
http://media.chemistrygrades.com/IdealGas_Intro3.swf
http://media.chemistrygrades.com/IdealGas_questions.swf
http://media.chemistrygrades.com/IdealGas_homework1.swf
http://media.chemistrygrades.com/IdealGas_homework2.swf
http://media.chemistrygrades.com/IdealGas_homework3.swf
http://media.chemistrygrades.com/IdealGas_homework4.swf
http://media.chemistrygrades.com/IdealGas_homework5.swf
http://media.chemistrygrades.com/IdealGas_homework6.swf

While I work on generating my own chemistry videos I’ll link some videos from You Tube.

Here’s the first:   The Ideal Gas Law

Hopefully this will provide you with some chemistry help.

Frank Cardulla is a retired high school chemistry teacher. He has created a video series of chemistry lectures, most are available on Amazon.  A complete set is available for a lower price from www.teach12.com

A new article in Nature from the Putterman lab at UCLA shows how peeling scotch tape in a vaccuum emits XRays.

http://www.nature.com/news/2008/081022/full/news.2008.1185.htm

Camara, C. G. , Escobar, J. V. , Hird, J. R. & Putterman, S. J. Nature 455, 1089–1092 (2008).

In almost every chemistry lecture the nearly magical molecule of water is present. For acid-base titrations, electrochemistry, thermodynamics, hydrogen bonding, covalent bonding, solvation, boiling….the list goes on nearly forever.

In my videos I will frequently use H2O as the example. It can be a gas, a liquid, a solid, a solvent, a solute, a reactant, and a product. It has so few electrons it’s reasonable to count all of them. It has so few atoms we can calculate where they are.

Here is one example, what happens when you open the cap on a bottle of soda water? What is dissolved in the water, what is in the gas above the water, and why does opening the cap change the liquid?

The answer is that when you release the pressure of the cap, a lot of excess CO2 leaves the bottle. This CO2 is used to keep the dissolved CO2 in equilibrium. When the cap is removed the partial pressure of CO2 above the water drops to nearly zero, and LeChatlier’s principle pushes the dissolved CO2 to leave.  But it does not simply evaporate from the surface, because the solution is now supersaturated with CO2. If this bottle held perfectly pure water and the inside walls of the bottle were perfectly smooth then we might never see bubbles. But nothing is perfect, the water has tiny particles floating around which act as nucleation sites for CO2 bubbles. The CO2 “knows” it is now supersaturated and it wants to leave. It aggregates on the particle surface as a gas, and soon a bubble lifts off from the particle.

Now, why does shaking the bottle make more bubbles? The number of particles in the liquid isn’t changing. Or is it? (probably not).

www.chemistrygrades.com

The goal of my website is to offer help to those chemistry students who need it the most, to those who cannot afford expensive tutors. For a $25 fee I will offer a full month of access to all the chemistry videos on this site and to the forums. That’s about the price of a 30 minute session with a chemistry tutor. If you want a full year of access the annual rate will be $150, the same as 6 months. You are welcome to join for a month before finals each semester if you prefer.

Within a few weeks this site will host videos with simple explanations of the most confusing concepts in chemistry including moles, redox reactions, Lewis structures, counting electrons for the octet rule, orbitals, and weak acid buffer solutions. If your topic is not yet here send a request, but understand that we will schedule the video release to meet the syllabus of a typical chemistry course. The video should online a few weeks before you need it.

The level of these topics is targeted for high school chemistry students and for freshman college chemistry. Teachers may also use it as a private chance to enhance their understanding of a few topics which always seemed a little challenging.

Students who want someone else to do their homework are advised not to join. The comments in the forum will be monitored for this situation. If you post a specific question we may delete or change the response to avoid any hint of cheating on homework or take-home exams.

This website is a resource, a reference which should sit alongside your books, your notes, and Google. It cannot replace your teacher or your own hard work. My goal is to bump you up 1 or 2 letter grades, from a C to a B, or maybe to an A. I doubt this website will help you improve 3 letter grades, meaning that if you are going to fail chemistry this website might lift you to a D or a C, but almost certainly not to a B.

If you work hard and study and use this site then your understanding of chemistry homework, tests, and concepts will improve. I can’t make any moneyback guarantees because I’m not there to see how hard you worked. I can guarantee you that if you don’t work hard your grade will not improve. That will be true with or without my videos. If you are not satisfied with the content please contact me and we will work out an answer.