04/25/12

http://www.cmmap.org/images/learn/clouds/convection.jpg

Here is a picture of hot and cold air. Hot air rises while cold air sinks. Cole air is denser than hot air. This is why gravity makes hot air balloons rise. The denser cold air is pulled down and under the less dense hot air. The molecules are packed closer together in cold air. Hot air moves more than cold air. Technically, both are moving at the same “speed” since it is simply the movement of energy by a process. Dry air is denser compared to water vapor or humid air at the same temperature and pressure. The two components in dry air are Oxygen and Nitrogen with a combined molar mass of 28.97. The components of water are Hydrogen and Oxygen with a molar mass of 16. Hence, water vapor is lighter than dry air.

April 13, 2012

                

                            Caffeine Molecule                                 Cocaine Molecule

Both the caffeine molecule and the cocaine molecule are made of the same atoms. The formula for Cocaine is C₁₇H₂₁NO₄ and the formula for caffeine is C₈H₁₀N₄O₂. Both molecules are made from the same atoms but the configuration of how they are bonded is how each is their own species.             

April 12, 2012

The energy content (density) of materials is a very important characteristic to meet our energy demands. Human activities are dependent on several forms and sources of energy to perform work. The energy content of an energy source is the available energy per unit of weight or volume. Thus, the more energy consumed the more work that can get done. There are four types of physical work related to human activities which include: modification of the environment, appropriation of resources, processing resources and transfer. Based on the thermodynamic concepts we can rate the following from highest to lowest.

Gasoline: 45.4 MJ/Kg

Compressed Natural Gas (CNG): 53.6 MJ/Kg

Ethanol: 30.0 MJ/Kg

Lithium Ion Battery: 0.72 MJ/Kg

March 26, 2012

The problem: I started with 2.0 grams of salicylic acid and 5 grams of acetic anhydride and I got 2.1 grams of acetylsalicylic acid (aspirin). What is my theoretical yield and my percent yield? The process to solve this should be as follows:

1.       Write balanced equation

2.       Calculate number of moles in 2.1 g of salicylic acid (SA)

3.       Calculate moles of acetic anhydride

4.       Based on the amounts of reagents specified in the experiment, calculate the theoretical yield of aspirin

5.       Solve actual divided by theoretical multiplied by 100 to get the percent yield.

C₇H₆O₃ (salicylic acid) + C₄H₆O₃ (Ethanoic anhydride) à C₉H₈O₄ (Aspirin) + C₂H₄O₂ (Acetic Acid)

1 mole of SA produces 1 mole of aspirin which gives this equation a 1:1 ratio.

To calculate the number of moles of aspirin, do the following calculation:

0.0152 mole SA  X  (1 mole aspirin/ 1 mole of SA) = 0.0152 mole aspirin

Then calculate the mole of aspirin to the number of grams of aspirin.

                0.0152 mole aspirin  X  (180 grams SA/ 1 mole aspirin) = 2.74 grams aspirin

The number of moles just calculated is the theoretical yield and now you can solve for the percent yield.

% Yield = (Actual/Theoretical) X 100

(2.1 grams Aspirin)/(2.74 grams Aspirin) X 100 = 76.6 %

March 19, 2012

On March 19, 2012, we discussed limiting reagents and how it relates to making a hamburger. We had to make one double hamburger with bacon and cheese and the formula was as follows: 1 Hamburger bun + 1 Hamburger Patty + 2 Slices of Cheese + 4 Slices of Bacon = 1 Quarter Pounder. We had 10 pounds of Hamburger, 5 pounds of cheese, 4 pounds of bacon and 4 dozen buns. What we are looking to do is figure out what ingredient is the limiting reagent, or which ingredient will get run out of first when making the hamburgers. My process of figuring out how many hamburgers can I make started out by solving for how many buns I have and the number of hamburgers that can go on the buns. After this, I moved on the cheese and bacon. The first piece of information I needed was how many slices of cheese I could get from 5 pounds so in order to do so I looked up how much 1 slice of cheese weighed. This helped with the conversion factors to solve for how many slices of cheese I have. Next, I performed a similar process with the bacon. I researched how many slices of bacon I could get from 1 pound. The number of slices depended on if it was thick or thin sliced. Once I knew how many slices, the conversion factor was used and I determined the maximum number of bacon slices I will have to make as many hamburgers as possible. The maximum number of burgers depended on if you were looking at the bacon or cheese as the limiting reagent. When using thin strips over thick strips of bacon, more strips could be used and therefore more burgers could be made. This also affected weather enough cheese was available as well. I calculated how many hamburgers I could make from using thin strips of bacon so therefore bacon was the limiting reagent. I do not remember the exact number of burgers I estimated but this was my processing.

For the reaction of 2 moles of hydrogen and 1 mole of oxygen resulted in 2 moles of water, I was trying to determine the which is the limiting reagent and how much product can be made beginning with 8.5 grams of hydrogen and 40.2 grams of oxygen. The following steps can be used:

1.       Write balanced equation

2.       Calculate moles of reagents

3.       Determine limiting reagent

4.       Calculate moles of products

5.       Calculate mass of products

6.       Mass Collected

Here is the work following along with the above steps.

1.       2H₂ + O₂ à 2H₂O

2.       Moles=mass/molar mass

Moles H₂= 8.5grams/(2grams/mole)= 4.25 moles H₂

Moles O₂= 40.2grams/(32grams/mole)= 1.256 moles O₂

3.       Limiting Reagent

Two (2) multiplied by 1.256= 2.513 moles O₂

The excess of H₂ means that O₂ is the limiting reagent.

2         Moles of H₂O produced (based on limiting reagent)

1.256 moles O₂ multiplied by (2 moles H₂O/1 mole O₂)= 2.513 moles H₂O

3         Mass of H₂O

4         250 moles H₂O multiplied by (18.0 grams H₂O/1 mole O₂)= 112.5 grams of H₂O

5         Amount of H₂ remaining

4.25 – 2.513 = 1.738 grams H₂

Final Answer:

112.5 grams of H₂O

Oxygen is the limiting reagent

1.738 grams of H₂ product remaining

In Chemistry on Friday March 2, 2012, we were reviewing some of the different reactions we have been practicing in class and on OWL assignments. Some of my favorite chemical equations include precipitate, acid and base, gas forming, double replacement and redox. These are a few of the basic equations used in chemistry and it is important to understand the basics before moving on to the more complicated tasks. Below are examples of each of the following that were listed above.

Precipitate:

ZnBr₂ (aq) + 2AgNO₃ (aq) --> Zn(NO₃)₂ (aq) + 2 AgBr (s)

                2AgBr à 2Ag ⁺ + Br^-

Gas Forming:

Mg (s) + 2 HCl (aq) --> MgCl₂ (aq) + H₂ (g)

Double Replacement:

(NH₄)CO₃ (aq) + AlCl₃ (aq) --> NH₄Cl (aq) + Al₂(CO₃)₃ (aq)

Acid/Base:

2NaOH (aq) + H₂S (aq) --> Na₂S (aq) + H₂O (l)

                2OH^- + H₂S à S^2- + H₂O

H₂CO₃ (aq) + NaOH (aq) --> Na₂CO₃ (aq) + H₂O (l)

On Thursday February 23, 2012, we completed a Chemistry lab called Ion Combination which involved mixing solutions, solving out double replacement reaction equations, and net ionic equations. While completing this lab I was not surprised by any of the reactions and how precipitations were formed because I have completed a lab like this in AP Chemistry at my high school. Our lab consisted of solutions that were unlabeled and we had to combine the solutions and analyze the precipitates formed to figure out what we were mixing due to products of the reaction. An observation that led me to believe a chemical reaction was occurring is that a precipitate had formed. There were also color changes that occurred when mixing the two solutions together. These are sure signs that a chemical reaction has occurred. Also when we used the molecular substances and combined those, a chemical reaction had occurred because there was a temperature change and a gas had formed; both of which are another way of knowing that a chemical reaction has occurred. When combining solutions, there were reactions that produced different product states.  Different product states would include when two liquids were combined to form a solid precipitate. Another would include when we combined the two solutions and a gas developed. All of these observations we can conclude from this Ion Combination Lab. When sodium chloride (NaCl) is added to water (H20), the sodium and the chloride dissociate from each other resulting in sodium + ions and chloride - ions. The chemical disassociation equation would be:
NaCl -> Na+ + Cl-