chemistry topic 3 - the mathematics of formulas and equations
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Chemistry Topic 3
The Mathematics of Formulas and Equations
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• Mass of atom is based on the mass of a Carbon-12 atom
• Formula Mass – sum of the atomic masses of all the atoms present.
• Gram Formula Mass – formula mass expressed in grams instead of atomic mass units.
• Use 35.5 for Cl
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Find the Gram Formula Masses
• Na
• O2
• NaCl
• HBr
• NaOH
• Mg3N2
• Al2(SO4)3
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• Percent Composition – composition as a percentage of each element compared to the total mass of the compound.
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Find the Percent Composition
• Na
• O2
• NaCl
• HBr
• NaOH
• Mg3N2
• Al2(SO4)3
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• Hydrates – crystals that contain water.
• Anhydrous – substances without water
• To calculate % water, treat the water molecule as a single unit.
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Calculate % Water
• CuSO4∙5H2O
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11/6 Chemistry
Aim: What calculations can we perform with formulas?
Obj: SWBAT calculate moles, find molecular formulas, and set up mole ratios
Do Now: What is the formula mass of NaOH?
Homework: Worksheet
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Moles
• Mole = number of atoms of carbon present in 12.000 g of C-12
• Avogadro’s number = 6.022 x 1023
– Number of particles in a mole of a substance
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• Moles = grams / gram formula mass
• Grams = moles x gram formula mass
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• What is the mass in grams of a 8.4 mole sample of iron?
• Convert 0.45 g of sodium hydroxide, NaOH to moles.
• How many moles of potassium nitrate, KNO3 are present in a sample with a mass of 85.2 g.
• What is the mass in grams of 0.94 moles of sodium bicarbonate, NaHCO3?
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Finding Molecular Formulas from Empirical Formulas
• Find the formula mass of the empirical formula
• Divide mass of compound by the mass of the empirical formula.
• Multiply your empirical by that answer.
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• A compound has an empirical formula of CH2 and a molecular mass of 56 amu. What is its molecular formula?
• A compound has an empirical formula of CH and a molecular mass of 78 amu. What is the molecular formula?
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Mole Relations in Balanced Equations
• Set up ratios
• Also works for volumes of gases
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