Significant Figures and Zeroes

Another topic we learned about recently in class are "sig figs"; this is short for significant figures. This is one of the more challenging topics of this unit, so I decided it would be a good idea to make a post about it, so if I need help reviewing/remembering how to use them, I can refer back to this.

Sig figs are the digits that were actually measured, and we pay close attention to them when rounding. When we estimate something using sig figs, we can estimate 1 digit past the calibration on the instrument. 

Take the number:   0.004004500

0.004004500= this zero before the decimal is not significant

0.004004500= these zeroes directly after the decimal are not significant

0.004004500= this 4 is significant

0.004004500= these zeroes stuck in between two numbers are significant

0.004004500= these numbers are significant

0.004004500= these trailing zeroes are significant

The above example shows the rule to follow when determining which numbers are significant. Here is a useful website that I found that describes these rules more clearly: rules for finding significant numbers

Here are a few more examples: 

123 = 3 sig figs

0.123= 3 sig figs

40.506= 5 sig figs

9,800. x 10^4= 4 sig figs

600.= 3 sig figs

4.5600= 5 sig figs

98000= 2 sig figs

The last thing we learned about dealing with significant figures was how to add/subtract and multiply/divide with them. Here is a great website that explains how to do this: adding/subtracting and multiplying/dividing sig figs

Chemical vs. Physical Changes and Properties

The other day in class, we learned about/reviewed chemical and physical changes and properties. Here is a brief outline of the most important things that I learned, that I think will be helpful to know for future tests/quizzes:

Physical Properties: can be observed without changing one substance into another.

-Boiling point

-Density

-Mass

-Volume

-Smell

Chemical Properties: can only be observed when a substance changes into another.

-Flammability

-Corrosiveness

-Reactivity with acid

Here is a helpful website that I found to explain the differences between the two in a more in-depth way: chemical vs. physical properties

Physical Change: changes in matter that don't change composition/identity.

-Change of state

-Change in temperature

-Change in volume

Chemical Change: result in new substances.

-Acid base

-Redox

-Double replacement reactions

-Burning

Here is a helpful website that I found to explain the differences between the two in a more in-depth way: chemical vs. physical change

Make-a-Mole Reflection

This past Friday, we celebrated National Mole Day in Chemistry class, which is explained here: "What is National Mole Day?". We all sewed moles, brought them in, and had a party. I spent several hours spread out over several days creating my mole. I cut out lots of colorful 2x2 inch squares, then sewed them all together to make patchwork fabric to make my mole out of.

Above photo was taken by myself

After lots and lots of cutting, pinning, sewing, and stuffing, my mole was complete!!

Above photo was taken by myself

This project was fun and I really loved seeing everyone's finished products and how creative they were. It also helped improve my sewing skills!

Aspirin Lab Reflection

The week before we went on fall break, we took a pre-lab quiz to see which groups would get to participate in the aspirin lab. My partner and I were the only ones out of the Day 2 groups to pass it and get to carry out the lab. This was rewarding, because I took time to thoroughly study the lab before-hand, and it paid off. The first thing we did was combine all of the different chemicals in a flask:

Above photo was taken by myself

After several more steps, the chemicals were put into a beaker and we heated it up:

Above photo was taken by myself

When we came back to the lab the next day, the aspirin crystals had formed:

Above photo was taken by myself

After we drained all the water out and transferred the crystals out of the beaker, this was the finished product:

Above photo was taken by myself

Overall, this aspirin lab was fun yet very educational, and I got to experience using several chemicals and pieces of equipment that I have never used before, so I learned a lot.

After I completed the lab, I wanted to learn more about aspirin and the chemicals/methods used to make it, so I did some research. Here is a very insightful website that I found to help with my curiosity:  more about aspirin

Unit Test Reflection

Today in class, we took the Atomic Structure and Radioactivity unit test. Luckily, it was not as bad as I thought it would be, and I think that is partially thanks to the blog posts I have made this unit. I actually used them as a resource while studying, and they were very helpful. However, there were still a couple things that I was confused about on the test:

-How to calculate the percent abundance of one isotope atom when you are given the individual masses and the amu of the element

-Which type of radioactive decay can penetrate the human body the furthest

To help me learn about the above questions for future exams, I researched each of them. Hgere is a link I found giving the answer to my second question:

Strength of Radioactive Decays

Overall, I knew most of the material on the test, thanks to these blog posts, and I will be sure to keep it up, in order to continue doing well on the tests.

Half-Life

Recently, in class, we learned about half-lives: their meaning and how to calculate them in real-life examples. Half-life is the time it takes for half of a sample to decay into a stable form. Here is a link to a helpful website that goes more into depth on what a half-life is and relates it to radioactive decay:

Half-Lives Explanation

Here are a couple examples of problems dealing with half-lives that I might see something similar to on a test:

Q: How much of a sample of Uranium with a mass of 150 grams is left after 7 half lives? 

A: 150/(2^7)= 1.17 grams

Q: Radium-225 has a mass of 2.59 grams and decays for 135 days. What was the mass of the original sample?

A: 135 days x 1HL/1.5 days = 9 HL passed

(2.59g)(2^9)= 1326.08 grams

Q: The half-life of radium-255 is 15 days. What percentage of radium is left after 3 months?

A: 3 months x 30 days/1 month x 1 HL/15 days = 6 HL

1=50%

2=25%

3=12.5%

4=6.25%

5=3.125%

**6=1.5625%

Overall, this post will serve as a great resource to look back at when I have to solve half-life problems, because the three examples above accurately represent and explain all of the different types of half-life questions that I will probably see on tests or class work.