Stoichiometry Involving Molar Concentration

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Stoichiometry Involving Molar Concentration

• By, Abby Leung Peggy Fung
• Block A

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What is Stoichiometry?

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

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Confused when stoichiometry involves molar
concentration?

• MOLARITY?
• MOLES?!
• STOICHIOMETRY!

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Just Remember This!

• We
• Bake
• Fresh
• Magnificent
• Muffins!

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5 REALLY EASY STEPS

• 1. Write an Equation
• 2. Balance the Equation
• 3. Find the mole of the given quantity
• 4. Molar Ratio
• 5. Molarity- Use equation to Solve Your Question

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FACTS YOU SHOULD KNOW

• STP 22.4 L/mol
• Molar Concentration Molarity
• c n/v
• -or-
• Molarity mole/volume (in L)
• KEEP TRACK OF SIG FIGS DURING YOUR CALCULATIONS!

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1. Write the Equation

• Put reactants on the left side of equation
  products on the right side.
• Reactants ? Products

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2. Balance Equation

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

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3. Find mole of given quantity

• Convert given quantity to of mol of quantity
• If given quantity in L use STP to convert
• STP 1 mol/ 22.4 L
• If given quantity in particles Use Avogadros
  Number to convert
• 6.02 1023

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4. Molar Ratio

• Use molar ratio to convert moles of given
  quantity to wanted quantity
• Note Coefficients in balanced equation
  represent molar ratio.
• Molar ratio used in fraction form
• E.g. 34 3/4

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Which mol quantity in molar ratio is the
denominator?

• Denominator mole ratio of the given quantity
• Numerator mole ratio of wanted quantity

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5. Molarity

• Use step 4s answer molar concentration to
  answer question.
• This step turns mol of a quantity to the answer
  of the question.
• Molarity given in form ? M (mol/L)
• Depending on question, you may need to rearrange
  molarity equation.
• cm/v equals vm/c equals mcv

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Lets Try It Together!

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

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Step 1 Write out the Equation

• Hydrogen gas H2 (g)
• since hydrogen is a diatomic molecule
• Al(s) NaOH(aq) H2O(l) ? NaAlO2(aq) H2(g)
• reactants products

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Step 2 Balance the Equation

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

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Step 3 Find mole of given quantity

• Given quantity 50.0L Hydrogen gas at STP.
• Moles of H2 50.0L(1mol/22.4L) 2.32 mol H2

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Step 4 Molar Ratio

• Moles of given quantity 2.32 mol of H2
• Moles of wanted quantity ? Mol of NaOH
• 2Al(s) 2NaOH(aq) 2H2O(l) -gt 2NaAlO2(aq)
  3H2(g)
• 2 3 ratio (mol of NaOH mol of H2)
• 23 2/3
• Mol(NaOH) 2.32 mol H2 (2 mol NaOH/3 mol H2)
  1.49 mol NaOH

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What volume of NaOH solution is required?

• 1.49 mol NaOH (step 4 answer)
• 3.00M sodium hydroxide (NaOH) solution (given)
• Volume(v) Mole(n)/ Concentration(c)
• (Rearranged Molarity equation)
• Volume of NaOH (1.49 mol) / (3.00mol/L)
  0.496L NaOH

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You Are Done!

• Answer 0.496L of Sodium Hydroxide (NaOH)
  solution was required.
• ALL IT TAKES IS THESE 5 SPECIAL STEPS!

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• Still having troubles remembering how to do these
  questions?
• NO WORRIES!
• We have a song to help you!

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If I were a Mole Lyrics

• Tune If I were a Boy by Beyonce Knowles
• If I were a mole even just for a day
• Id get up every morning just to
• Do stoichiometry problems
• I love those questions
• With molar concentration
• Except I always had a
• Secret to solving all these tricky ones.

• If I were a mole
• I could always understand
• How you could solve this question
• With five really ea-s-y steps
• Remember tha-at
• Molar Concentration
• Is c equals n over v
• Its also called molarity
• And you can use STP to solve

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• If I were a mole
• The first big step is to
• Write out a proper equation
• With all the right element symbols
• Step two is to-oo
• Balance the equation both sides
• cause all elements need to have
• same number of atoms on both sides

• If I were a mole
• I could always understand
• How you could solve this question
• With 5 very eas-s-y steps
• Now lets move on
• For step three I would
• Use STP to change litres to mole
• Because you need moles for step 4

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• Use coefficients formula to get
• The molar ratio
• We are almost at the end
• Recall mol of first element
• And molar ratio

• To find mol of what you want
• Next use molarity to
• Find the volume in litres.