Tuesday, September 7

Today in Chemistry, we mainly focused on measurements. We began the class by reviewing the assignments. Mr. Henderson reiterated that Labs 1-4 and packet pages 3 and 4 are due tomorrow, Wednesday September 9; and the Intro to Measurement Lab is due on Wednesday. He then proceeded to discuss the lab from yesterday, the MM4 Separating Mixtures Lab. He used a similar (example) lab about coins to demonstrate how to find the percent composition of each element in a mixture. First it is needed to find the total mass of the mixture, and then the mass of the element whose composition you wish to find. Then, you divide the mass of the element by the total mass, and you have the percent composition of that element. Mr. Henderson multiplied the number present of each coin by the mass of that type of coin, then divided the total mass of the coin mixture to find the percent of coins which make up the mixture. He then gave us time to This link describes how to find the percent composition:
http://www.chem.tamu.edu/class/majors/tutorialnotefiles/percentcomp.htm


Next, we began the Intro to Mixtures lab, which taught us about the precision of different instrument (with some divisions), and a graduate (with many divisions). Then we had to measure the length of a blue pen with multiple rulers that had various degrees of divisions. Through these two experiments, we found out that the instruments with less divisions force you to estimate more, and therefore be less precise. After that, we weighed the mass of a penny using three different mass balances, which gave slightly varying numbers. We then discussed significant digits, which are important when communicating the precision of our measurements. Mr. Henderson stated that in regards to significant figures, one figure is one that is always estimated. In other words, it can be assumed that all of the digits are exact up until the last one (and it is important to do this when measuring something yourself in order to communicate it to others).
This link is very helpful in understanding the concept of the degree of uncertainty:
http://www.tutorvista.com/content/chemistry/chemistry-iii/chemistry-concepts/uncertainty-measurement.php

^^These are the different instruments we used to measure the volume of water.

Mr. Henderson today emphasized the importance of the difference between mass and weight. He clarified that mass is the amount of matter one object has, and gravity is the force which acts on that amount of matter. He gave the example that if a person were to go to outer space, they would have a different weight (because different planets have different amounts of gravity), but his/her mass would remain the same. He also pointed out that our scales in Chemistry calculate mass, whereas typical scales calculate weight.
This is a really good link that describes the difference between mass and weight:
http://www.colorado.edu/physics/2000/periodic_table/mass.html

Overall, today was a very informative day in Chemistry; and we learned much about measurements. Don't foget about the pop quiz on Friday!