Using moles to figure out chemical equations

Pt + 4 HNO3 + 6 HCl → H2PtCl6 + 4 NO2 + 4 H2O

What difference does it make how many moles there are?

• Pt + 4 HNO3 + 6 HCl → H2PtCl6 + 4 NO2 + 4 H2O• The price of platinum is $47/g• The price of HNO3 is $0.47/g• Would it be wise to ignore mole ratios?

Multiply that to the industrial scale1 tonne of Pt = 47 million dollars

Stoichiometry: measuring the elements

• Stoichiometry – calculating the relative amounts of reactants and products in chemical reactions

Mole ratio• Mole ratio – the ratio of the amount in moles,

of reactants and products in a chemical reaction

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How to find a mole ratio

1. Start with a balanced equation• N2(g) + 3H2(g) → 2NH3(g)

2. Find the ratio of the coefficients• 1 molecule N2(g): 3 molecules H2(g): 2 molecules NH3(g)

3. Convert molecules to moles• 1 mole N2(g): 3 moles H2(g): 2 moles NH3(g) [mole ratio]

• Can write as 1:3:2

Review Question:

• How many molecules in a dozen molecules?• 12

• How many molecules in a mole of molecules?• 6.02x1023

What’s the mole ratio?

• A + 4 B + 6 C → 3 D• 1:4:6:3

Let’s balance an equation

• H2(g) + O2(g) → H2O(l)

Crossing the mole bridge: how to do mole calculations in 3 easy steps!!!

Crossing the mole bridge: how to do mole calculations in 3 easy steps!!!

• 1. Find the balanced equation• 2. Identify the knowns and unknowns• 3. Cross the mole bridge– Only moles are allowed on the mole bridge– To cross, multiply or divide

• Problem: If you burn 15 g of propane, C3H8(g) (the gas in barbecues), how much oxygen was needed? (hint burning hydrocarbons produces carbon dioxide and water)

C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(l)

C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(l)

C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(l)

2H2(g) + O2(g) → 2H2O(l)2 g x g