Empirical & Molecular Formulas + Percent Composition!

Welcome back Beryllium Chemist followers! Today we will be talking about a few things. Firstly, the difference between empirical and molecular formulas. Then, we will move on to percent composition! (That's a lot!) I hope you'll survive through this blog!

In chemistry, there are two types of formulas that you MUST know: molecular and empirical

Empirical Formula

• shows the RATIO of the atoms or moles in LOWEST-TERMS 
• when you form ionic compounds on the periodic table, they are in empirical formulas since they're in lowest terms
• to get to empirical formula, divide molecular formula by its greatest factor
• you can calculate the empirical formula from percent composition and by mass
  
  eg. NaCl is an empirical formula but Na2Cl2 is not

Molecular Formula

• shows the total atoms each element are present in the molecule of the compound
• it is a MULTIPLE and not in lowest terms
• formula of the ionic and covalent compounds
  
  for example, C3H6 is a molecular formula because it's simplest form is CH2

Here is the key to converting:

Empirical Formula x whole number = Molecular Formula
Empirical Formula MASS x whole number = Molecular Formula MASS
Empirical Formula Mass (GRAMS) x whole number = mass of ONE MOLE of the compound


So if carbon and hydrogen are present in a compound in a ratio of 1:2, then the EF would be CH2. What is the molecular formula if 28.0g is the mass of one mole?

Step 1: Find the empirical formula mass.
12.0 + 2(1.0) = 14.0g/mol

Step 2: Divide the molar mass with the empirical formula mass.
(remember molecular formula mass = EF mass x whole number)

28.0 / 14.0 = whole number = 2

Step 3: Multiply whole number by the empirical formula.
Recall: Molecular formula = empirical formula x whole number

2(CH2) = C2H4


Now lets try some questions where we try to determine the EF with a given mass!
If you are given the question: Determine the empirical formula with the given 30.4g Nitrogen and 69.6g Oxygen. Follow through with these steps.

Step 1: Convert grams to moles.
Nitrogen: 30.4g x 1mole/14g N = 2.1714 mol
Oxygen: 69.6g x 1mole/16g = 4.35 mol


Step 2: Divide each molar mass by the smallest molar amount.
Nitrogen: 2.1714/2.1714 = 1
Oxygen: 4.35/2.1714 = 2.003
And voila! Your final empirical formula is NO2.


BUT, if after step 2 your answers don't round easily to a whole number, you have to multiply them by a whole number.
For example: If you have 1.7344 Carbon and 4.2332 Nitrogen

Multiply by 2, and keeping going till you get a number close enough to a whole number
Carbon: 1.7344 x 2 = 3.4688. 1.7344 x 3 = 5.2032. 1.7344 x 4 = 6.9376
Nitrogen: 4.2332 x 2 = 8.4664. 4.2332 x 4 = 12.6996. 4.2332 x 4 = 16.9328Therefore your empirical formula will be C7N17


Hope this helps guys:)
-Kimberly

MORE CONVERSIONS! (2-Steps!)

Are you overwhelmed with moles yet? Maybe this might brighten your day..

One day on the Tonight Show, Jay Leno showed a classified ad that read: "Do you have mole problems? If so, call Avogrado at 602-1023!" ha-ha! get it? 6.02x10²³ :p

Back to business..

Here's a mole map.. treat it as your BEST FRIEND!! (very helpful)

Today we learned how to do two-step conversions! Fun eh?
How would you convert particles to grams? Let's refer to the mole map!

you would have to go from particles → moles → grams

Eg. What's the mass of 4.35 x 10²¹ atoms of Au (Gold)?

4.35 x 10²¹atoms  x  1mol/6.022x10²³atoms  x  197.0g/1mol = 1.42g  of Au

** Make sure that you find the formula/molecular mass beforehand if it's a compound or it has more than one atom**


How would you convert grams to particles? Let's refer to the mole map! (again)
this time, you'd have to go from grams → moles → particles (opposite as the first!)

Eg. How many atoms of Au (Gold) are there in 5.72g of Au?

5.72g  x  1mol/197.0g  x  6.022x10²³atoms/1mol = 1.75 x 10²² atoms of Au

---------------------------------------------------------------------------------------------------------
Here's some extra practice for you!
1) What's the mass of 7.7 x 10²² atoms of Carbon?
2) How many formula units of potassium sulphide are there in 20.1g of potassium sulphide?
3) What would be the mass of 6.32 x 10²¹ molecules of 
Ca(NO3)2?
4) How many molecules of BF3 are there 3.3g of boron trifluoride?

Answers:

1) 1.5g
2) 1.10x10²³ f.u
3) 1.72g
4) 2.9x10²² molecules

And voila! You're an expert in mole conversions! (What a relief!) ;)

CONVERSIONS WITH THE MOLE >:(

What can i say? its just that good.

:D

So, what if you have this mole.

And you, being the nosy person you are, want to know how much it weighs.

So you put it on this scale.  (After you kick the sheep off, of course!)

So then you got the mole's weight in grams!! Yay!
...But wait. Teachers aren't that nice.  So picky picky, they want the weight in moles!! How ever will you do that?!?!

Well, with a handy-dandy calculator and the supreme knowldege of the mole conversion chart, you should be just fine.

Since I'm technologically challenged, this chart isn't very pretty.  Boo hoo.

Grams to moles: x (1mol / grams)
Moles  to grams: x (grams / 1 mol)

Moles to Formula Units: x (6.022x(10 to the 23rd) / 1 mol )   [hahaha my intimite knowlegde of blogger is clearly displayed here]
Formula Units to Mole: x(1 mol / 6.022x(10 to the 23rd))

F.U. (hah...) to atoms: x (#of atoms / 1 molecule)
atoms to F.U.: x (1 molecule / # of atoms)


*molar unit is g/mol
*label all your conversions incase you forget what you're doing and don't want to start ALLLL OVEERRR AGAAAAIIINNN

Memorising that chart would probably be helpful.  My advice would be to draw that chart at the top of the test paper, and refer to that throughout the test to avoid that awkward moment when you begin to doubt yourself and then you change all your answers and then get everything WRONNNGGG. Not that that has ever happened to mee... anyways if you have that memorised the conversions are pretty basic.

here are some examples for your pleasure...

convert 5.0g of carbon to moles.
                mass of carbon (according to periodic table) = 12.0
                5.0g C x (1/12) = .416666666666666666666666666666666666666666666
                and there were 2 sigfigs in the question... so your answer would be .42mol
easy peasy shampoo squeezy

lets try the other way:
20.0mol nitrogen to formula units
                              20.0g N x (6.022 x (10 to the 23rd)) = 1.20 x 10 to the 25th

comprendez-vous?
if not, ask someone else.

funneh kitteh.

no, not morbid at all.

-A

ha just kidding its heather. im just dying to finish this blog so i can watch pretty little liars hahahaha

All About Moles!

The Mole

.. and no, I'm not talking about the "beauty" mark or the animal!!!


Then what is it?!

it is a unit of measurement! (a counting unit) that allows chemists to count large quantities such as atoms and molecules by weighing its mass
- mole has same number of particles found in 12g of carbon-12




- Volumes that are equal of different gases have a constant ratio, 
 
  For example:   Oxygen : Hydrogen    16:1
             
when they have the same # of particles, the ratio of oxygen to hydrogen will always be 16:1      
 
Avogadro's Hypothesis

 
Avogadro's hypothesis states that equal volumes of different gasses, at the same temperature and pressure, contain the same number of particles.
 
- If they have the same number of particles, the mass ratio is due to the mass of particles.
- principle for the relative masses of all atoms are on the periodic table of elements


To understand the hypothesis better, imagine two boxes with oranges in one and apples in the other. You believe that there are equal number of fruits in each box. Not counting the masses of the boxes, you can find the mass of each of the fruit and determine the ratio between the oranges and apples. This is the relative mass since it is a comparison. 

Relative Mass
 
- Relative masses are expressed when comparing it mathematically to the mass of another object.
- Currently, we compare it to the mass of carbon-12 (1 atom is one twelfth the mass of carbon)


 
Molar Mass
 
- The molar mass is the mass of ONE mole of particles.
- The molar mass of an element is the mass shown on the periodic table which is expresssed in grams. (same value as molecular mass, formula mass, or atomic mass)
 
  For example:    1 mole of Oxygen = 16.0 g/mol
                         1 mole of Sodium = 23.0 g/mol
                          1 mole of CO = 28.0 g/mol

 
* All of these have the same number of particles.
 
- Molar atomic mass is the mass of 1 mole of that element.
- "Grams per mole" is the unit for molar mass.
 
Atomic Mass
 
- The mass of 1 atom of the element in amu (u)


eg. atomic mass of Iron (Fe) is 55.8u



Formula Mass
- Total mass of all atoms in the formula of an ionic compound
- in atomic mass units (u)
 
  For example:    Manganese Oxide
                               Mn           O
                            54.9    +   16.0
                             MnO     =   70.9 u
 
Moledular Mass
 
- All atoms of a formula in covalent compound.
 
  For example:    Nitrogen Oxide
                              N       O 
                           14.0  +  16.0
                           NO  =  30.0 u
 
Avogadro's Number
 
Do you want Avogadro's number?! 
 
- Well it's....
 
6.022 × 10^{23    =}  particles per mole   * memorize it!
 
- This is the number of particles in 1 mole of any amount of substances.

How big is it?


Have Avogadro's number of pennies placed in a rectangular stack of about 6m by 6m at the base and it would stretch 9.4 x 10¹²km and extend outside of our solar system. It'd take light approximately a year to travel from one end of the stack to the other!! That's a LOT of pennies!!

 

Now that you learned about mole, you should learn the mole song!
You will love it...

LAB DAYY! (DENSITY)

Our lab today was determining aluminum foil thickness.

The objectives for this lab was:

• to calculate the thickness of a sheet of aluminum foil and express the answer in the terms of scientific notation and significant figures.

All supplies that were used were 3 sheets of aluminum foil, 15cm by 15cm large, a metric ruler, and a centigram balance.

The steps to doing this lab correctly is very simple.

1. Take the sheets of aluminum foil and number them 1,2 and 3.
2. Use the metric ruler and measure the length and width of each sheet.
   * REMEMBER TO RECORD ALL YOUR DATA*
3. Then use the centigram balance to find out the mass of each sheet.
   *always use significant digits!*

Your table should have these labels: Sheet; Length(cm); Width(cm); Mass(g), and te numbers 1,2,3, for the aluminum foil.

To calculate for thickness, use the following formulas:

Volume = Length x Width x Height

Volume = Mass/Density

ex. 

• Take your information for sheet #1: length-17.11cm; width-17.91cm; mass-1.27g
• With the given density, find out the volume with the formula highlighted blue with green font.
• Then with the volume you just calculated, plug it into the formula in above in pink!
• After all calculations are done, voila! You have your height aka thickness.

To find the experimental error, here is another colorful the formula:

Experimental Error = |(your average thickness) - (given average thickness)| / (given thickness)

hope this helped guys:)

GRAPHING TIME! and Lab next day!

Fun comic of the day!

Ha-Ha! Hopefully that wont happen on the lab the next day...



Today, we went to the computer lab to... *drum rolls*


MAKE GRAPHS!
and interpret them...

Anywho, we made graphs using Microsoft Excel and it was FUN! We got to decorate and customize it however way we want! :) 
Why do we make graphs? Graphs are one of the key tools to present our data! It helps us visualize the relationship between the x and y values.

How do you make a graph on MS Excel, you ask?
Well here is a visual step-by-step procedure that may help!

1) On the second row of column B and C, make a table of values.

2) Click "Insert" at the top and then click "Scatter". From there, click on the first diagram.

 3) Now you will have a graph! Make a title and make sure to label your axis! Click on "Text Box" on the top to create your labels.

 4) Right click on one of the points on the graph then click on "Add Trendline". Examine the graph and determine what type of graph it is. In this case, it is "Linear". Also, click on "Display Equation on chart".

 5) You can play around with the graph by customizing it with shadows and colors. Right click on the chart or the plot (actual graph), then click on "Format". From there, play around with the designs and make your graph beautiful!

AND YOUR DONE! Wasn't that fun?!
Now to calculate the slope, just look at the equation! It's that easy :)

A REMINDER TO ALL THAT WE HAVE A LAB THE NEXT DAY! (YAY FOR LABS!)
Don't forget to do your PRE-LAB and also dress appropriately for the lab!!



Hopefully, nothing goes wrong and all will go well! ..... Hopefully.....

DENSITAAYYY

You are soo dense. ha.
Just thought I'd get that in there.



Density is a physical property of matter that measures mass per unit volume.
Anyways here are some formulas you maayy want to store in the old memory bank.  They may come in handy sometime. You never know.

Density = Mass/Volume

Volume = Mass/Density

Mass = (Volume)(Density)


Density helps determine different components in a mixture as the denser component will sink.
If the density of an object is more than the density of the liquid, it SINKS. If it doesnt, it FLOATS.
It is also handy to know that 1cm³ = 1mL so 1000cm³ = 1L (in case you need to convert!)
The density of water is 1.0g/mL or if you convert, it would be 1000g/L (1.0g/mL x 1000mL/L)

So here is an example of how you may see or find density in life. It is also the best experiment you will ever do. 

You're gonna need some OREOS (noooww i have your attention...), some milk (i used 75mL), something to put the milk in, a calculator, and a pen and paper.

So the first thing you need to calculate the density of an OREO is it's mass.  You can't really tell from the picture, but it says that 2 OREOS = 24g.  According to my calculator, that means each OREO has a mass of 12g.  Well that was easy.

The next thing you need is to calculate the volume.  I started with 75 mL of milk in the measuring cup shown below.  Again, stupid flash makes it difficult to read.  The smallest division on the cup was 25mL, I measured to the nearest 2.5mL.   I dropped in the cookie...

And voila!  From what I saw with my own eyes (not the camera) the cookie plus milk had a total volume of 97.5mL. 
volume of milk = 75
total volume = 97.5
97.5 - 75 = 22.5mL (volume of OREO)

Alright now that we have all that figured out...

Notice how I rounded to 2 sig figs? Smarty pants.

Oh that's weird... where did the oreo go? ;)

You also need to know how to calculate the expression of error. This is done by taking your three measurements, and calculating the average (using the correct number of SigFigs, of course).  You then find out what the accepted measurement is, and use the below equation to find the percent of error:

[(your measurement - accepted measurement) / accepted measurement] x 100

ta da!

See you later alligater

In a while crocodile

See you soon big baboon

XOXO

Beryllium Chemists

Heather is over and out.