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By, Abby Leung & Peggy FungBy, Abby Leung & Peggy FungBlock ABlock A

What is Stoichiometry?What is Stoichiometry?

Stoichiometry is the relationships Stoichiometry is the relationships between the amount of reactants between the amount of reactants used in a chemical reaction and used in a chemical reaction and the amount of products produced the amount of products produced by the reaction.by the reaction.

Confused when stoichiometry Confused when stoichiometry involves molar concentration? involves molar concentration?

MOLARITY?MOLARITY?

MOLES?!MOLES?!

STOICHIOMETRY!STOICHIOMETRY!

Just Remember This!Just Remember This!

WWe e BBake ake FFresh resh

MMagnificent agnificent MMuffins!uffins!

5 5 REALLYREALLY EASY STEPS EASY STEPS

1. W1. Write an Equationrite an Equation

2. B2. Balance the Equationalance the Equation

3. F3. Find the mole of the given quantityind the mole of the given quantity

4. M4. Molar Ratio olar Ratio

5. M5. Molarity- Use equation to Solve Your olarity- Use equation to Solve Your QuestionQuestion

FACTS YOU SHOULD KNOWFACTS YOU SHOULD KNOW

STP = 22.4 L/mol STP = 22.4 L/mol Molar Concentration = MolarityMolar Concentration = Molarity

c= n/v c= n/v

-or--or-

Molarity =mole/volume (in L)Molarity =mole/volume (in L)

KEEP TRACK OF SIG FIGS DURING KEEP TRACK OF SIG FIGS DURING YOUR CALCULATIONS!YOUR CALCULATIONS!

1. Write the Equation1. Write the Equation

Put reactants on the left side of Put reactants on the left side of equation & products on the right equation & products on the right side.side.

Reactants Reactants Products Products

2. Balance Equation2. Balance Equation

Make sure that each element Make sure that each element has the same number of has the same number of atoms on both sides!atoms on both sides!

3. Find mole of given quantity3. Find mole of given quantity

Convert given quantity to # of mol of quantityConvert given quantity to # of mol of quantity

If given quantity in L: use STP to convertIf given quantity in L: use STP to convertSTP= 1 mol/ 22.4 LSTP= 1 mol/ 22.4 L

If given quantity in particles: Use Avogadro’s If given quantity in particles: Use Avogadro’s Number to convertNumber to convert6.02 × 10^23 6.02 × 10^23

4. Molar Ratio4. Molar Ratio

Use molar ratio to convert moles of given Use molar ratio to convert moles of given quantity to wanted quantityquantity to wanted quantity

*Note: Coefficients in balanced equation *Note: Coefficients in balanced equation represent molar ratio.represent molar ratio.

Molar ratio used in fraction formMolar ratio used in fraction formE.g. 3:4 =3/4E.g. 3:4 =3/4

Which mol quantity in Which mol quantity in molar ratio is the molar ratio is the

denominator?denominator? Denominator:Denominator: mole ratio of the given quantity mole ratio of the given quantity

Numerator:Numerator: mole ratio of wanted quantity mole ratio of wanted quantity

5. Molarity 5. Molarity Use step 4’s answer & molar concentration to Use step 4’s answer & molar concentration to

answer question.answer question.This step turns mol of a quantity to the This step turns mol of a quantity to the

answer of the question.answer of the question.

Molarity given in form: ? M (mol/L) Molarity given in form: ? M (mol/L) Depending on question, you may need to Depending on question, you may need to

rearrange molarity equation.rearrange molarity equation.c=m/v c=m/v equals equals v=m/cv=m/c equals equals m=cvm=cv

Let’s Try It Together!Let’s Try It Together!A student wants to put 50.0L of hydrogen A student wants to put 50.0L of hydrogen gas at STP into a plastic bag by reacting gas at STP into a plastic bag by reacting excess aluminum metal with 3.00M sodium excess aluminum metal with 3.00M sodium hydroxide solution according to the reaction. hydroxide solution according to the reaction. What volume of NaOH solution is What volume of NaOH solution is required?required?

Step 1: Write out the EquationStep 1: Write out the Equation

Hydrogen gas = H2 (g) Hydrogen gas = H2 (g)

since hydrogen is a diatomic moleculesince hydrogen is a diatomic molecule

Al(s) + NaOH(aq) + H2O(l) Al(s) + NaOH(aq) + H2O(l) NaAlO2(aq) + H2(g) NaAlO2(aq) + H2(g)

reactantsreactants productsproducts

Step 2: Balance the EquationStep 2: Balance the Equation

2Al(s) + 2NaOH(aq) + 2H2O(l) 2Al(s) + 2NaOH(aq) + 2H2O(l) 2NaAlO2(aq) + 3H2(g) 2NaAlO2(aq) + 3H2(g)

Step 3: Find mole of given quantityStep 3: Find mole of given quantity

Given quantity: 50.0L Hydrogen gas at STP.Given quantity: 50.0L Hydrogen gas at STP.

Moles of H2 = 50.0L(1mol/22.4L) = Moles of H2 = 50.0L(1mol/22.4L) = 2.32 mol H22.32 mol H2

Step 4: Molar RatioStep 4: Molar Ratio

Moles of given quantity:Moles of given quantity: 2.32 mol of H2 2.32 mol of H2 Moles of wanted quantity:Moles of wanted quantity: ? Mol of NaOH ? Mol of NaOH

2Al(s) + 2Al(s) + 22NaOH(aq) + 2H2O(l) -> 2NaAlO2(aq) + NaOH(aq) + 2H2O(l) -> 2NaAlO2(aq) + 33H2(g)H2(g)

2 : 3 ratio (mol of NaOH: mol of H2)2 : 3 ratio (mol of NaOH: mol of H2)2:3 = 2/32:3 = 2/3

Mol(NaOH)= 2.32 mol H2 (2 mol NaOH/3 mol H2)= Mol(NaOH)= 2.32 mol H2 (2 mol NaOH/3 mol H2)= 1.49 mol NaOH1.49 mol NaOH

What What volumevolume of NaOH solution is of NaOH solution is required?required?

1.49 mol NaOH1.49 mol NaOH (step 4 answer) (step 4 answer)

3.00M3.00M sodium hydroxide (NaOH) solution (given) sodium hydroxide (NaOH) solution (given)

Volume(v) = Mole(n)/ Concentration(c)Volume(v) = Mole(n)/ Concentration(c) (Rearranged Molarity equation)(Rearranged Molarity equation)

Volume of NaOH = (1.49 mol) / (3.00mol/L) = Volume of NaOH = (1.49 mol) / (3.00mol/L) = 0.496L NaOH0.496L NaOH

You Are Done!You Are Done!Answer: Answer: 0.496L0.496L of Sodium Hydroxide of Sodium Hydroxide

(NaOH) solution was required.(NaOH) solution was required.

ALL IT TAKES IS THESE 5 ALL IT TAKES IS THESE 5 SPECIAL STEPS!SPECIAL STEPS!

Still having troubles Still having troubles remembering how to do remembering how to do

these questions? these questions?

NO WORRIES!NO WORRIES!

We have a song to help you!We have a song to help you!

If I were a Mole LyricsIf I were a Mole Lyrics*Tune: ‘If I were a Boy’ by *Tune: ‘If I were a Boy’ by

Beyonce KnowlesBeyonce Knowles

If I were a mole even just for a If I were a mole even just for a day day

I’d get up every morning just to I’d get up every morning just to

Do stoichiometry problems…Do stoichiometry problems…

I love those questionsI love those questions

With molar concentrationWith molar concentration

Except I always had a Except I always had a

Secret to solving all these tricky Secret to solving all these tricky ones. ones.

If I were a mole If I were a mole

I could always understandI could always understand

How you could solve this How you could solve this questionquestion

With five really ea-s-y stepsWith five really ea-s-y steps

Remember tha-atRemember tha-at

Molar ConcentrationMolar Concentration

Is c equals n over vIs c equals n over v

It’s also called molarityIt’s also called molarity

And you can use STP to solveAnd you can use STP to solve

If I were a moleIf I were a moleThe first big step is to The first big step is to Write out a proper Write out a proper

equation equation With all the right element With all the right element

symbolssymbols

Step two is to-ooStep two is to-ooBalance the equation Balance the equation

both sidesboth sides‘‘cause all elements need cause all elements need

to have to have same number of atoms on same number of atoms on

both sidesboth sides

If I were a moleIf I were a moleI could always understandI could always understandHow you could solve this How you could solve this

questionquestionWith 5 very eas-s-y stepsWith 5 very eas-s-y steps

Now let’s move on Now let’s move on For step three I wouldFor step three I wouldUse STP to change litres Use STP to change litres

to moleto moleBecause you need moles Because you need moles

for step 4for step 4

Use coefficients formula Use coefficients formula to getto get

The molar ratioThe molar ratio

We are almost at the We are almost at the endend

Recall mol of first Recall mol of first elementelement

And molar ratioAnd molar ratio

To find mol of what you To find mol of what you want want

Next use molarity to Next use molarity to

Find the volume in Find the volume in litres. litres.