Explains Dimensional Analysis Simply! (skip to 1:00)

Dimensional Analysis Tutorial!

Dimensional Analysis, oooh!

Although the name can sound daunting, it's quite simple and follows basic Math 9 concepts like x/x=1

Dimensional Analysis:

ex. converting 100km/h into miles/hour

It's just like converting currencies in Chemistry, it is usually necessary to convert between units

There are FOUR SIMPLE STEPS to Dimensional Analysis, and once you have a lot of experience with this in the bag, you can skip steps!

1) Find a unit equality

2) Find the conversion factors

3) Apply the conversion factor

4) Cancel units

Sounds complicated? Here are a few examples to simplify it a bit, showing precisely how the though process works through these steps:

ex 1. How many miles are equal to 120 km?
Step 1-  1 mile = 1.6 km

Step 2- 1= 1 mile/ 1.6 km

Step 3- 120 km x 1 mile/1.6 km

Step 4- 75 miles

In Step 2, we can find that conversion factor because if we know that 1 mile= 1.6 km, then 1 mile/1.6 km must equal to 1 (just like 1/1= 1, 5/5=1)

As you can see, the 'km' isn't in the final answer, because it cancels out

Here is a slightly more complicated example (converting the top and bottom of the equation, weehoo!)

ex.2 Convert 150 kJ/h into J/s

Step 1- 1000 J = 1 kJ         3600= 1 h

Step 2- 1= 1000 J/ 1 kJ      1= 1 h/3600 s

Step 3- 150 kJ/ 1 h  x 1000J/ 1 kJ x  1 h/ 3600 s = 150 000 J/ 3600 s

Step 4- 41.7 J/s

In step 3, the 'kJ' is on the bottom (denominator) while the 'h' is on the top (numerator) because in order for the units to cancel out, it has to be opposite (ex. on the bottom if it is at the top, at the beginning) of what we are trying to convert it from.

Scientific Notation and Significant Digits

today is sept 23rd and this is our second official post and my first blog post ever! today we learned about scientific notation( SN) and significant digits(SD).Yay math! basically precision and accuracy are super important in chem so we need to make sure that we write numbers properly and only write the numbers that are important.
SDs
first lets talk about significant digits or SD. significant digits are digits that actually matter in a number
there are 3 rules for finding significant digits.

1.Non zero numbers are always significant
2. If a zero is a placeholder, it it generally not significant
3. If a number is to the right of a non-zero number, it is generally significant

ex. 0.000056 has 2 SDs5 and 6
      but 0.9000070005 has 10 SDs
a good way to find SDs is to find the first number and count to the right untill you run out of numbers: 2.0000 has 5 SDs

when you add or subtract SDs always round to the least precise number
ex. 7.4212-3.54= 3.8812 becomes 3.88
when you mulyiply or divide SDs round to the number with the fewest SDs
ex. 2.5*5.5= 13.875 becomes 14

SN
so scientific notation is making a long number like this: 1230000000000000000, into a shorter, easier to write number like this: 1.23 * 1018. its the same number but it takes up way less room.
here are some more examples


MULTIPLYING AND DIVIDING SN

when you multiply or divide SN numbers things get a little more complicated.
ex. multiplying


the answer would be 9 because you have to multiply 2 and 4 together and add the exponents together.

ex. dividing


so you divide the numbers (8.03 and 5.25) and then subtract the exponents

ADDING AND SUBTRACTING IN SN

adding and subtracting are also complicated because you have to make the exponents of both the numbers the same before you add or subtract. this depends on the exponents of each expression.
ex     5.3*104  plus  2.3*103
in this case you have to make the exponents the same so 2.3 would be changed to .23*104
then you can add them together to get 5.53*104
the problem here is that the precision has in creased so you have to take away 2 digits to get
                                                                                 5.5*104
the process is the same with subtraction except you subtract the numbers

this is a link to a video that explains everything that i have on here but with diagrams and such so if you are interested check it out
http://www.youtube.com/watch?v=l3Dv8fV12FA&feature=related

Things like chemistry

The first "official" post is now out!
It is currently September 21 and today in chem class we learned about the exciting world of the SI system and percent error (ooh fascinating), we also watched a video that made myself namely but probably pretty much everyone else feel very small. So I will try to upload it and if it doesn't work then I guess you'll just have to look it up yourselves. The video is called Powers of Ten... the unimaginable size of our universe.

Anyways though, after watching the video and before seeing the glowing pickle, we made some notes so here are the notes in a few simple points.

Experimental Accuracy
If you are measuring something and want to include the possibility that there may be an error in your measurements you write plus or minus (I can't put the symbol) 1/2 of the smallest division of your measuring device.
ie. if your are using a ruler the smallest division of measurement is 1 mm so your answer could be something like 20.2 cm plus of minus 0.05 cm.

Errors
Since no one is perfect (except for according to my brother, my brother is perfect) everyone (except my brother) makes errors. There are three reasons for errors (when you are measuring something)
1. errors in the measuring device (in which case it is not your fault)
2. sloppy measuring (now it's your fault)
3. changing conditions (ie. climate) (it's no longer your fault it's Mother Nature's fault)
Luckily for you though there are ways to calculate errors, two in fact. One however isn't very good.
The not very useful way to calculate errors is through absolute error. In absolute error the formula is simply:  measured-accepted
There is a fatal flaw in this however, because only how many units off are shown we do not know how accurate the answer is.
ie. 3 inches off of a measurement of a computers width is much less precise then 1.5 inches off of the height of
    a typical door frame. Yet the difference between the two of 3 inches and 1.5 inches seems to say
otherwise.
The far more useful way to calculate errors is with percent error, the formula is
((measured-accepted)/accepted)x100 or measured minus accepted divided by accepted, the quotient is then multiplied by 100.
This formula is far more useful then absolute error because the percent error shows how far off your measurement is in relation to the actual measurement in percentage form.
ie. you could be 42% off of the prior computer measurement but only 12.5% off of the door frames height.
 Thus showing exactly how far off your measurement is in comparison to the actual measurement.

Last but not least

SI System (or international system of units)
SI system the prefix's can change how large of small the number is
ie. gigabyte is 1,000,000,000 (and you probably have several on your itouch or whatever else you might have)
ie. a femtameter would be about 0.000000000000001 m or 1x10^-15 m.

Well that's me, good-bye and good night
(unfortunately I'm unable to figure out how to put the video on the blog at the moment so here is the link http://www.youtube.com/watch?v=aPm3QVKlBJg)

Intro

Just 3 young ladies who've got a knack for chemistry, and are on their way to becoming ultimate Chemists. We'll let you know what happens when we walk through the door to the distant land of 403, and what's stuck in our heads.
Maybe there'll be some Chem puns along the way?