POGIL Moles and Balancing Equations

POGIL Moles and Balancing Equations

Essential Questions

What is a Mole?

How can we express an equation with the Law of Conservation of Mass?

What is a mole?

• A mole is a unit of measurement we use in chemistry to simplify extremely large numbers.

•  $1\ mole\ =\ 6.022\ \cdot\ 10^{23}$   
  

• This is often referred to as Avagadro's Number.

Multiple Choice

Here's a good way of thinking about it. A baker may have a recipe that says that he needs 10 sticks of butter for every 36 eggs. These numbers might be really difficult to work with, so he simplifies it to using "dozens" of eggs rather than the eggsact number. If 12 eggs are in a dozen, how many dozen eggs would the baker need for 10 sticks of butter?

• 1

• 2

• 3

• 4

From Dozens to Moles

Notice that the baker "condensed" the numbers so that it was easier to work with. 10 sticks of butter was equal to 3 dozen eggs. Now think about if we were working with atoms. You could easily fit 5 million hydrogen atoms on the head of a pin, but is that a number you'd want to work with?

Instead, we condense these numbers using the "mole" unit.

Different types of Atoms

Naturally, there are different types of atoms. Because of this, 1 mole of a particular type of atom (element) will have a different mass.

Think about it with dozens. Donuts are larger than eggs. If we have a dozen donuts, that will have more mass that a dozen eggs.

Molar Mass

Because different elements have different atomic masses, this translates to different masses at the macro level. 1 mol (mole abbreviated) of copper will have a larger mass than 1 mol of magnesium.

However, they will have the number of particles! Each of this elements has

 $6.022\cdot10^{23}$  atoms in it, but different masses!

Using the periodic table

There is an amazing mathematical relationship between the micro and macro world. If you have 1 mol,

 $6.022\cdot10^{23}$  atoms, of an element, then the atomic mass matches the molar mass (which is the number of grams of the element).

Fill in the Blank

The image to the left shows a section of the periodic table. If you can't see this, go to ptable.com. Based on what you've just learned, how many grams of Lithium (Li) would you have if you had 1 mol of Lithium? (The answer is based on ptable.com's values. Some periodic tables can have different answers based on data used).

Fill in the Blank

The image to the left shows a section of the periodic table. If you can't see this, go to ptable.com. Based on what you've just learned, how many grams of Magnesium (Mg) would you have if you had 1 mol of Magnesium? (The answer is based on ptable.com's values. Some periodic tables can have different answers based on data used).

More than 1 mol...

Logically speaking, if you increased or decreased the number of moles you had, you would have a different mass of an element. Carbon has a molar mass of 12.01 grams per mole (g/mol). If you had 2 mols of carbon, you would multiply the number of grams by 2.

 $12.01\ g\ C\ \cdot\ 2\ mol\ =\ 24.02\ g\ C$  

Multiple Choice

Oxygen has a molar mass of 16.00 g/mol (we round periodic table data to 4 significant figures). If we had 4 mols of oxygen, how many grams of oxygen would we have?

• 64.00 g O

• 4.00 g O

• 20.00 g O

• 12.00 g O

Moles of Compounds

Of course, this also means that we can add moles of elements together to make compounds. Looking at the image to the right, you can see that we add together moles of each element to find the molar mass of the entire compound. 2 hydrogen atoms translates to 2 moles of hydrogen. Likewise, one oxygen atom means 1 mole of oxygen.

Multiple Choice

You will need to use ptable.com for this question. If we had one mole of the compound MgO, how many grams would we have?

• 40.31 g MgO

• 17.45 g MgO

• 64.23 g MgO

Balancing Equations

Part 2 of the POGIL

Balancing Equations

Balancing equations just represents making sure that the Law of Conservation of Mass is being "upheld" by the number of mols that are being rearranged of both sides of the equation. We can view balancing equations on the micro side, with atoms, or on the macro side, with mols.

Example

If we were to perform the synthesis reaction below between hydrogen gas and oxygen gas, we would form water. But notice that in the first equation it's not balanced:

 $H_{2\ \left(g\right)}\ +\ O_{2\ \left(g\right)}\ \rightarrow\ H_2O_{\ \left(l\right)}$  
On the left side we have 2 mols of oxygen gas, but on the right we have only 1. This violates the Law of Conservation. We will need more moles of some elements than others, shown below:
 $2H_{2\ \left(g\right)}\ +\ O_{2\ \left(g\right)}\rightarrow\ 2H_2O_{\ \left(l\right)}$