StoichiometryAlyson and Heather

Conversions using moles

•You first need a balanced equation •The coefficients in the equation represent how many moles there are for that molecule or compound •Ex: 2 Zn (there are 2 moles of zinc )

Mole-Mole

• This is used to take given number of moles of an element/compound and converting them to the number of moles of a different element/compound

• Ex: Zn + 2 HCl ZnCl2 + H2 How many moles of hydrogen are produced from the reaction of 3 moles of zinc with an excess of hydrochloric acid.

• You have to use the 3 moles of zinc given to find how many moles of hydrochloric acid would be produced.

Zn + 2 HCl ZnCl2 + H2

• Since you’re given 3 moles Zn, this is what you have to start with on top3 moles Zn

• You then multiply this by putting how many moles of the one you’re given (zinc) on the bottom and the number of moles of the element you’re looking for on the top. You find the number of moles of each from the equation in the equation. (from the equation)

3 moles Zn x 2 moles HCl = 6 moles HCl (from the equation) 1 mole Zn

Mass-Mass• This is used when you’re given the mass of an

element/compound and have to convert it to the mass of another element/compound.

• You start with the mass given, convert it to moles, change it to the moles of the element/compound you’re looking for and convert those moles to the mass of the element/compound you’re looking for

• g of known element/compound moles of known element/compound moles of unknown element/compound g of unknown element/compound

• Ex: 2KClO3 2KCl + 3O2 How many grams of potassium chloride are produced if 25g of potassium chlorate decompose?

• 25 g KClO3

• To convert this to moles, you have to put the number of grams of one mole of KClO3 on the bottom when you multiply

• (To find how many grams are in 1 mole of KClO3,

just add the atomic mass of K, Cl and O3...remember to multiply oxygen’s atomic mass by 3)

• Adding the atomic masses of KClO3

• K = 39.1 g• Cl = 35.5 g

• O3 = + 16x 3 g

122.6 g ...So there are 122.6 g in 1 mole of KClO3

So back to the example...25 g KClO3 x 1 mole KClO3 there are 122.6 in 1 mole of KClO3!

122.6 g KClO3

2KClO3 2KCl + 3O2

Now we multiply the amount of moles from theequation of the compound that we want over the amount of moles of the element given from the

equation25 g KClO3 x 1 mole KClO3 x 2 moles KCl

122.6 g KClO3 2 moles KClO3

To cancel the moles of KCl, and get grams, we have to multiply it by the number of grams in 1 mole

• Finding grams in KCl... K = 39.1 g Cl = + 35.5 g 74.6 g... So there are 74.6 g of

KCl in one mole25 g KClO3 x 1 mole KClO3 x 2 moles KCl x 74.6 g KCl = 15.21

gKCl 122.6 g KClO3 2 moles KClO3 1 mole KCl

Volume-Volume

• You can do this conversion using either STP or SATP. This information will be given in the equation.• You’re given a volume of a gas, you must

convert it to the moles of that gas, then to the moles of the gas you’re looking for and finally to the volume of the gas you’re looking for.

• There are 22.4 L in 1 mole at STP.• There are 24.8 L in 1 moles at SATP.

Ex. N2 + 3H2 2NH3 What volume of hydrogen at SATP is necessary to react with 5 L of nitrogen to produce ammonia?

• To cancel the L of nitrogen and find the number of moles, you have to multiply it by 1 mole divided by 24.8 L (because 1 mole= 24.8 L at SATP)

5 L N2 x 1 mole N2

24.8 L N2

• You now have to do the mole conversion...multiply the

number of moles in the equation of the element/compound that you weren’t given in the question over the number of moles from the equation of the element/ compound given from the question.

N2 + 3H2 2NH3

5 L N2 x 1 mole N2 x 3 moles H2

24.8 L N2 1 mole N2

• Finally, you must convert the moles of the element/compound you want to find into volume (remembering 1 mole = 24.8 L at SATP)

5 L N2 x 1 mole N2 x 3 moles H2 x 24.8 L H2 = 15 L H2

24.8 L N2 1 mole N2 1 mole H2