Mole Conversions

Welcome to another HUMP DAAAAY, Period 5!

Scribe: Cameron B.

September 25th, 2013

Mole Conversions

The idea of today involved converting between moles, mass and particles. 

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We started off the day checking in our homework from yesterday, the Calculating Molar Mass worksheet. The sheet can be found in the Unit 2 Handouts folder. Answers are as follows:

1. CaCO3 is ionic and is named calcium carbonate. It's molar mass is 100.09 g.
2. N2O6 is molecular and is named dinitrogen hexoxide. It's molar mass is 124.02 g.
3. Na2SO4 is ionic and is named sodium sulfate. It's molar mass is 142.05 g.
4. C8H18 is molecular and is named octane. It's molar mass is 114.26 g.
5. Fe3(PO4)2 is ionic and is named Iron (II) Phosphate. It's molar mass is 357.49 g.

Some things to remember about calculating molar mass:

• Be careful with a polyatomic ion in parentheses, like (SO4)2. Since there are 2 atoms of SO4, there are 2 sulfur and 8 oxygen. 
• The masses of each element and your answer will always go to two decimal places.

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Today's Lesson: Molar Conversions

The notes worksheet we filled out (titled Mole 1) can be found in the Unit 2 Handouts section.

First of all, we defined a mole. A mole is a unit similar to a dozen. Whilst a dozen contains 12 items... A mole contains 6.022×10²³ items!

Then, we practiced a few molar mass problems. The answer to 2) is 44.01 g. The answer to 3) is 261.35 g.

It's been duly noted that sig figs don't come into play during molar mass problems, rather, every answer is rounded

to two decimal places.

Then, we started the real lesson: Mole conversions!

We wrote down a diagram to help us remember the conversion factors between moles, grams and particles. 

The important thing to remember is: MOLES ARE THE CENTER OF THE UNIVERSE!!

So, moles go in the middle of all conversions, as this picture shows. 

As you can all see, the conversion factor between mass (shown here as grams) and moles is the

molar mass and the conversion factor between moles and particles (shown here as molecules) 

is Avogadro's number. We will be using these conversion factors to solve these problems!

The first problem gave us the number 2.0 x 10-3 g of SnO2 and asked us to find how many moles were present in the sample.

First off, we need to name SnO2. It's correct name is Tin (IV) oxide.  

Next, we list what we have:  2.0 x 10-3 g of SnO2 
Because we know g (grams) is a unit of mass, and we are trying to convert to moles, the conversion factor we are using is molar mass.

We set up our equation. 2.0 x 10-3 g of SnO2    *    1 mol / ? g = our answer

But how do we know how many grams to put on the bottom of our fraction? It's our conversion factor,
the molar mass. 

We find the molar mass of SnO2 to be 150.71 g. Now, our equation reads:

 2.0 x 10-3 g of SnO2    *    1 mol of SnO2 / 150.71 g of SnO2 = our answer

Using our prior knowledge of dimensional analysis, we can solve this. Our answer is 1.3 x 10-5 mol of SnO2.

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We completed another problem in class, 5a, using the same conversion factor but going from moles to grams and not the other way around. The answer to this one is 370 g of Li2CO3.

Our next problem, 6, was a bit trickier. Given 0.0908 g of nickel (II) chloride, find the number of molecules in the sample.

Molecules = particles. So, looking back at our diagram, we need to convert twice: once from grams of nickel (II) chloride to moles, and once from moles to particles.

First, we need to name nickel (II) chloride. It's name is NiCl2.

Then, we establish what we do know: 0.0908 g of NiCl2

Our first conversion will be from mass (grams) to moles, so we will use the molar mass to convert.

The molar mass of NiCl2 is 129.59. So the first conversion is...

0.0908 g of NiCl2    *    1 mol / 129.59 g 

Now that we have converted from grams to moles, we now convert from moles to particles.

To convert from moles to particles, you use Avogadro's number. So, our full equation is...

0.0908 g of NiCl2    *    1 mol / 129.59 g    *    6.02 x 1023 / 1 mol = our answer

Canceling out the correct units and multiplying across, the answer is 4.22 x 1020.

If you still need help, check out this vid!

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Sticky Stuff

Ms. Friedmann let us know that she's busy making lesson plans and hasn't had enough time to grade our quizzes or labs yet. Don't worry, Ms. Friedmann, we all still love you!

She also briefly discussed that only covalent (molecular) compounds make true molecules. The things that ionic compounds make are called formula units, although the terms are used interchangeably. 

A tricky little thing about ionic compounds: although a compound like MgSO4 is obviously ionic, the bonding between the S and the 4 O's in the sulfate ion is molecular. 

And last but not least... thanks for the laughs today KG. Or should I say Scotty :)

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Homework

2 worksheets, Mole Conversions and Moles 1. Mole Worksheet #1 is optional, but completing it will give you extra practice!

Next scribe is Hayden N.!