Molar Conversions & Calculations
Transcript of Molar Conversions & Calculations
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Molar Conversions & Calculations
Ch. 11 – The Mole I
Moles
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A. What is the Mole?• A counting number (like a dozen)• Avogadro’s number (n)• 1 mol = 6.02 x 1023 items
C. Johannesson
A large amount!!!!VERY
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A. What is the Mole?
• 1 mole of pennies would cover the Earth 1/4 mile deep!
1 mole of hockey pucks would equal the mass of the moon!
HOW LARGE IS IT???
1 mole of basketballs would fill a bag the size of the earth!
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Mole Day Project
Mole Man!!.wmv Mole Out!!!.wmv
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A. What is the Mole?
the chemical formula indicates the moles of each element
examples:
calcium chloride
aluminum nitrate
aluminum sulfate
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B. Molar Mass• Mass of 1 mole of an element or compound.• Atomic mass tells the...
> atomic mass units per atom (amu)> grams per mole (g/mol)> Round to 2 decimal places
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B. Molar Mass Examples
• carbon
• aluminum
• zinc
• water
• sodium chloride
• sodium hydrogen carbonate
• sucrose
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C. Percentage Composition
• the percentage by mass of each element in a compound
Find the % composition of Cu2S.
• Find the percentage composition of a sample that is 28 g Fe and 8.0 g O.
• How many grams of copper are in a 38.0‐gram sample of Cu2S?
• Find the mass percentage of water in calcium chloride dihydrate, CaCl2•2H2O?
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D. Molar Conversions
molar mass
(g/mol)
MASSIN
GRAMSMOLES NUMBER
OFPARTICLES
6.02 x 1023
(particles/mol)“Particles”=atoms, ions, molecules, formula units, anything!
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D. Molar Conversion Examples• How many moles of carbon are in 26 g of
carbon?
• How many molecules are in 2.50 moles of C12H22O11?
• Find the mass of 2.1 x 1024 units of NaHCO3.
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E. Empirical FormulaSmallest whole number ratio of atoms in a compound
C2H6reduce subscripts
CH3
1. Find mass (or %) of each element.2. Find moles of each element.
‐go out about 4 or 5 decimals3. Divide moles by the smallest # to find subscripts.4. When necessary, multiply subscripts by 2, 3, or 4 to get whole #’s.
• Poem to help you remember…
Percent to massMass to mole
Divide by smallMultiply ‘til whole!
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E. Empirical Formula Example• Find the empirical formula for a sample of 25.9% N and 74.1% O.
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F. Molecular Formula• “True Formula” ‐ the actual number of atoms in a compound
CH3empiricalformula
molecularformula C2H6
1. Find the empirical formula.2. Find the empirical formula mass.3. Divide the molecular mass by the empirical mass.4. Multiply each subscript by the answer from step 3.
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F. Molecular Formula Example
• The empirical formula for ethylene is CH2. Find the molecular formula if the molecular mass is 28.1 g/mol?
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G. Hydrates
• Compounds with a certain number of water molecules attached
• CuSO4∙5H20 = copper (II) sulfate pentahydrate• Use a prefix to indicate number of water
molecules• CuSO4 without water is called anhydrous
• To determine the number of water molecules, find the mole ratio of the anhydrous compound to the water> Find the moles of each> Set up a ratio: moles water/moles salt> Whole number answer is the number that
goes in front of H2O
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G. Hydrates
• A 5g sample of a hydrate of Cu(NO3)2 was heated, and only 3.9g of the anhydrous salt remained. What is the formula and name of the hydrate?
• Step 1: determine moles of the salt and the water
• Step 2: determine ratio
• Step 3: formula and name
Attachments
Mole_Man!!.wmv
Mole_Out!!!.wmv