Week 1

This past week in AP Chemistry we learned about molarity, or concentration of solutions, being the number of moles of a substance in a liter of given solution. This number can be used to calculate the mass of solute in a solution. Given the equation: M1(V1)=M2(V2), we learned how to calculate either the molarity (M) or volume (V) of a solution before (1) or after (2) dilution with the solvent, given the other three values. We used this equation when calculating the concentration of Blue #1 in each solution we made of a known ratio of stock solution and distilled water. Knowing this new concept of molarity and how to calculate it allowed us to develop a linear regression equation that related molar concentration to the absorbance of light by the solution. Absorbance is a measure of the percent of light of a particular wavelength impeded by the solution, related to transmittance. Transmittance is the percent of light of a particular wavelength allowed through a solution.

We were detailed on all of the aspects involved in a lab experiment. I learned that you must always follow the step-by-step process in order to succeed in the testing. This includes completing pre-lab and thinking through all aspects of the experiment before arriving in class on the specified day. During the lab, it was very apparent who had prepared before class and who had not, as seen by the many puzzled faces of those who watched others starting before beginning their own experiments. You must also stay organized and follow the rubric formatting in order for your lab to look professional and presentable. Neglecting this seems to run a higher risk of error. Your responses to the post lab questions

We also explored the ways in which you can identify the molar concentration of a solute in distilled water if there is only one solute, through the application of light. This requires the use of a colorimeter (see figure below) which can accurately measure the absorbance of light of a particular wavelength by the solution being tested. With this data you could find many important details about the solution, which can have many practical details outside of this controlled school experiment. These applications could include the measurement of dissolved minerals in lake or ocean waters of certain areas in which fluctuations could result in catastrophic changes to the life in that area.

We came to know most of the information in class from guides this week. To understand both the principles of light transmittance and absorbance and the instructions for the colorimeter we read through the Vernier Colorimeter manual, which detailed these by describing the units of each term, the use for each and how they relate to each other physically and mathematically. In class we also had discussions on how to calculate the concentration of the stock solution using beer's law and known absorbance and molar extinction coefficient. These calculations were carried throughout the entire experiment and were therefor very important to the success of the experiment as a whole.

Here is a reference for the use of notebooks throughout experimentation:
http://www.ruf.rice.edu/~bioslabs/tools/notebook/notebook.html

This is an overview of the mathematical relationships for light transmittance in solutions:
http://teaching.shu.ac.uk/hwb/chemistry/tutorials/molspec/beers1.htm

Vernier Colorimeter for measuring absorbance (Left) and standard lab notebooks (Right)