Wednesday Lecture

Another week, another unit. This week we were introduced to the concept of acids and bases and how they behave. Wednesday we mainly focused on the basic types of acids and bases: arrhenius and Bronstead-Lowrey. In arrhenius acids and bases, the acid or base breaks apart into their separate ions. On the other hand, Bronstead-Lowrey acids donate a proton and bases accept a proton. B-L acids produce conjugate bases and its bases produce conjugate acids; these types of reactions can also be performed backwards, but don't to it backwards unless, it specifically says to in the problem. Acids have varying strengths depending on the ratio of oxygens to hydrogens; if the oxygens outnumber the hydrogens by 2 or more, then the acid is strong.

A few strong acids are:
HCl
HBr
HI
HClO4
HClO3

Vitamin C Lab

Beginning this week in Chemistry, we started and finished a lab which tested the concentration of Vitamin C in different juices by using a technique called a titration. Iodine was used as an indicator to turn the solution a dark blue to signal the endpoint of the reaction, as seen below:

Hamming and I were the ones who created the standard for this experiment which was used by everyone in this class, so hopefully it produced consistent enough results across the class. We found that it took the least amount of iodine to react with the pear nectar and the most amount of iodine to react completely with unsweetened grapefruit juice.  

Hydrogen Peroxide Lab

Since our teacher was out last Friday and was unable to set up the lab, we were given the data we would've collected during the lab and filled out the calculations based on that data. I was a little bummed that we weren't able to do the lab ourselves, but it was nice to not have to worry about the pre-lab question and to not worry about the red lines on my face from the indent of the goggles. The calculations were fairly easy after doing the practice calculations when I prepared for the lab. Plus, the one where we were told to do conversions, we were given the steps to follow along with which made it a lot easier to understand. The follow-up questions helped me to visualize the lab as well and better understand what we were exactly calculating without actually doing it. I also thought it was beneficial that we completed all of this in class because it gave us a sense of urgency to complete the task, and it gave us a chance to ask questions and reason through each problem instead of putting it off and having to worry about it later when we got home.

This what commercial hydrogen peroxide looks like (what we were testing in lab):

Murder Investigation Lab

This was actually a pretty fun lab! After Hamming and I finished our outline of a  procedure, we ventured back to the lab station to start our experiment. We began by testing .5 mL of the unknown solution with .5mL of each of the test solutions (NaCl and Na2CO3). We determined that the murder substance was silver nitrate because the reaction produced a precipitate and we were able to do the reaction on a larger scale. We measured out 10mL of the silver nitrate and 10mL of NaCl and reacted it in the flask while filtering the precipitate into the filter paper. The liquid produced wasn't filtered nearly enough, so we made sure to run it through the filter again to get the best results. After obtaining all of the data needed, we made sure to calculate the molarity of the solution to catch the killer, which was Mr. Green. We completed a lab write-up as well to turn in a few days later, complete with our materials used, our procedure, our calculations, and a conclusion summing up what our data told us.

Below is our substance being filtered the first time into the first flask:

And here is the culprit:

1st Lecture of 2nd Semester

Welcome back! Today we jumped right in to introduce our new unit: aqueous solutions. We hit mostly on how to calculate molarity and what composes a solution.

You can use the formula:
M= mol of solute/L of solution
to determine the molarity of a substance (can be used as a conversion factor).

Also the formula:
M1V1=M2V2
comes in handy when you are given molarity and volume of a solution. That way you are able to solve for a single variable in the equation.

You can be given a molarity problem in many different ways:

1. originally given molarity
2. # of moles of chloride ions
3. grams of a substance that needs to be prepared

These are all being used to determine concentration of ions in a solution.

This whole unit elaborates on a majority of what we learned last semester and building upon it little by little, testing our knowledge of past topics as we move through the rest of the year.

This image provides a good visual of the comparison of concentration of a solution and molarity of a solution: