Molar Weight

Avogadro’s Number made easy!

Warm Up

1. How do you count large numbers of atoms and molecules?

2. What is a mole?3. How many things are in a mole?4. What is Avogadro’s number?

Warm Up

1. What is a mole used for?2. What is Avogadro’s number?3. Given 3.5 moles of cobalt, what is its molar mass?4. Given 5 moles of zinc, what is its molar mass?5. Given 10 moles of phosphorus, what is its molar mass?6. You have 400 grams of manganese, how many moles do

you have? 7. You have 250 grams of manganese, how many moles do

you have? 8. You have 70 grams of lithium, how many moles do you

have?

Homework

Due 2/18: practice problems 1-3, pg 311practice problems 4, page 31211.1 assessment 5-8, page 312Due 2/19: practice problems 12 a-d, page 316practice problems 14 a-e, page 318Due 2/22: practice problems 27-29, page 323practice problems 30 a-e, page 324

Warm Up

1. Given 12 moles of chromium, what is its molar mass?2. You have 1000 grams of strontium, how many moles

do you have? 3. Given 25 moles of water, what is its molar mass?4. You have 500 grams of NaOH how many moles do you

have?5. Given 50 moles of MgCl2, what is its molar mass?

6. You have 200 grams of Mn2Se, how many moles do you have?

Warm Up

1. What is the mass of sulfur if you have 2.3 x 1024 atoms of sulfur.

2. What is the mass of carbon if you have 5.6 x 1024 atoms of carbon.

3. What is the mass of iron if you have 1.8 x 1023 atoms of iron.

4. What is the mass of fluorine if you have 12.9 x 1022 atoms of fluorine.

5. What is the mass of chlorine if you have 6.7 x 1021 atoms of chlorine.

Warm Up

1. What is Avogadro’s number?2. Given 3.5 moles of cobalt, what is its molar

mass?3. You have 250 grams of manganese, how many

moles do you have? 4. You have 200 grams of Mn2Se, how many

moles do you have? 5. What is the mass of fluorine if you have 12.9 x

1022 atoms of fluorine.

Warm Up

Please write Lewis Dot Structures for the following:

1. Carbon2. Nitrogen3. Argon4. Iron5. Copper

Warm Up1. Calculate the percent composition for the following:

NaHCO3.

2. Given 200 grams of the above compound, what is the mass of each element?

3. Calculate the percent composition for the following: H2SO3.

4. Given 200 grams of the above compound, what is the mass of each element?

5. Calculate the percent composition for the following: H2S2O8.

6. Given 200 grams of the above compound, what is the mass of each element?

Warm Up

Balance the following equations and identify the type of chemical reaction involved:

____ ZnCl2 + ____ KOH ____ Zn(OH)2 + ____ KCl

____ Ba(OH)2 ____ BaO + ____ H2O

____ K + ____ H2O ____ KOH + ____ H2

____ NaBr + ____ Cl2 ____ NaCl + ____ Br2

____ MgCO3 ____ MgO + ____ CO2

____ ZnCl2 + ____ KOH ____ Zn(OH)2 + ____ KCl

Packaging

People have all kinds of ways of packaging things. Eggs come in dozens

And paper comes in reams

?????????

No one knows why hot dogs come in packs of 10 and buns come in packs of 8!

The Mole

Chemists even have a standard way to package atoms. Because atoms are so small the number of atoms per package is very large.

How many atoms are in a Standard Package?

The standard container for atoms holds 6.022 X 1023 atoms. This number is referred to by chemists as Avogadro’s number for Count Amedeo Avogadro that invented it.

Mass versus Quantity

Do all moles of a particular element weigh the same? No!! Larger heavier elements have a greater molar weight that smaller atoms, just like 10 bowling balls weighs more than ten marbles.

Molar Mass

The mass (in grams) of one mole of a substance is called its molar mass. The molar mass of an element in a.m.u.’s is the same as its molar weight in grams.

Example of molar mass

• For example, carbon’s atomic mass is 12.01 a.m.u.’s while its molar weight is 12.01 grams.

Using Mass to Count

You work in a candy store and receive a new shipment on gum balls. You are asked to put them in bags of ten. The total weight of the candy is 10 kg’s. If each gum ball weighs 20 grams, how many bags do you need?

Gum Ball Answer

• 10 kilograms is 10,000 grams. Each gumball weighs 20 grams, so 10,000/20 = 500 gumballs. Each bag will hold 10 gumballs so you’ll need (500/10) or 50 bags to pack all the gumballs.

Example #2

You have 5.5 moles of iron. The molar mass of iron is 55.85 g/ mol Fe. What is the mass of the iron that you have?

Solution to Example #2

5.5 moles Fe X 55.85 g/mole Fe = 307 g Fe1 mole Fe

Problems for You

Convert the following into weight in grams:

1. 2.50 moles of sulfur, S2. 1.80 moles of calcium, Ca3. 0.50 mole of carbon, C4. 3.2 moles of copper, Cu

Last Problem

Given 352 grams of Fe iron), how many moles of iron do you have?

Solution

352 g Fe X 1 mole Fe = 6.30 moles Fe55.85 g Fe