Chapter 8 - Molar Conversions

Chapter 8 - Molar Conversions

Review of everything we know from chaper 8

Let's take a few minutes to review chapter 8

FIRST --> We learned how to convert between mass, moles, and molecules. This is the flowchart we've used...

REMEMBER:

• To convert your units, first identify what unit you're given in the problem and what you're being asked to convert into

• Follow the arrow from the unit you have to the unit you're asked for

• Follow the multiplication or division step written by that arrow

Let's try a simple example with a compound

Here again is the flowchart. Following will be a question for you to answer. Use the flowchart to come up with the correct answer.

Multiple Choice

How many moles of sodium are there in 20.97g?

• 0.912

• 482

• 1.26E25

• 3.48E-23

Multiple Choice

How many molecules are there in 34.5mol of beryllium?

• 3.83

• 311

• 2.08E25

• 5.73E-23

How did we do those problems? Follow the flow chart

• to convert g --> mol we divide by molar mass

• to convert mol --> molecules we multiply by Avogadro's number

Then we learned to calculate molar mass

To find the molar mass of a compound, multiply the number of atoms of each element by the molar mass and add them all together. The unit of molar mass is g/mol.

LET'S PRACTICE THIS!

Multiple Choice

Calculate the molar mass of KOH.

• 28 g/mol

• 56 g/mol

• 84 g/mol

• 112 g/mol

Multiple Choice

Calculate the molar mass of Ba(C₂H₃O₂)₂

• 255.3 g/mol

• 237.3 g/mol

• 228.3 g/mol

• 196.3 g/mol

Next we took it up a notch...

• Use the flowchart to convert g, mol, and molecules of a compound rather than an element

• This is slightly more difficult because we need to find the molar mass of the compound first before we are able to do the conversion

• REMEMBER! We do not need molar mass if converting between mol and molecules. This requires only Avogadro's number.

Multiple Choice

How many moles is 17g of water?

• 0.94mol

• 1.05mol

• 17mol

• 18.015mol

Multiple Choice

What is the mass of 6.25 mol of Cu(NO₃)₂?

• 126 g

• 785 g

• 625 g

• 1172 g

Finally, we learned how to calculate percent composition

• % Composition = (mass of element)/(molar mass of compound) x 100

• You will find the percent composition of each element within a compound

• REMEMBER - The total percent composition of all elements in the compound should add up to 100!

Multiple Choice

What percentage of the total atomic mass of carbon monoxide (CO) is composed of carbon?

• 29%

• 43%

• 57%

• 73%

Multiple Choice

What is the percent by mass of chlorine in NaCl?

• 39%
• 61%
• 35%
• 65%

Multiple Choice

What is the percent by mass of oxygen in MgO?

• 20%
• 40%
• 50%
• 60%

CONGRATULATIONS!

You have completed our chapter 8 review.