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Mass-Mass Problems Solving Stoichiometry Problems
Major categories of stoichiometry problems are: 1.) mass-mass problems 2.) mass-volume problems 3.) volume-volume problems Types of Stoichiometry Problems
STOICHIOMETRY MASS A VOLUME A MASS B VOLUME B MOL “A” MOL “B”
In a mass-mass problem, you are given the mass of one substance and are asked to find the mass of another substance. STEP 1: Convert the given mass to moles using molar mass of given. Given mass of substance “A” ÷ molar mass of substance “A” = Mol “A” Solving Mass-Mass Problems
STEP 2: Determine the number of moles for the unknown by using molar ratio of the coefficients in the balanced equation. Mol “A” x molar ratio “B” = Mol “B” “A”
STEP 3: Convert the number of moles for the unknown into grams using molar mass of the unknown. Mol “B” x molar mass of unknown = Mass “B”
The average person drinks 2 L of water each day, yet eliminates about 2.5 L. Where do you think the extra water comes from? It is produced when food is metabolized in the body. Metabolism is the sum of all the chemical reactions that occur in the body. In one series of reactions, glucose (C6H12O6) is burned in oxygen to produce carbon dioxide and water. What mass of water is produced from 1.5 g of glucose? The balanced equation for this reaction is: C6H12O6 + 6O2 6CO2 + 6H2O EXAMPLE
Molar mass: C = 6 x 12 = 72 C6H12O6 H = 12 x 1 = 12 O = 6 x 16 = 96 180 g/mol Calculate the molar mass of the given substance: C6H12O6
0.0083 molC6H12O6 x 6 H2O = 0.050 molH2O 1 C6H12O6 Convert grams of glucose (C6H12O6) to moles of water (H2O). 1.5 g C6H12O6 180 g/mol C6H12O6
Molar mass: H = 2 x 1 = 2 H2O O = 1 x 16 = 16 18g/mol Calculate molar mass of unknown substance: H2O
0.090 g H2O 0.050mol x 18g/mol Convert moles of water (H2O) to grams of water (H2O).
1. In a thermite reaction, powdered aluminum reacts with iron (III) oxide to produce aluminum oxide and molten iron. What mass of aluminum oxide is produced when 2.3 g of aluminum reacts with iron (III) oxide? The balanced equation is: 2Al + Fe2O3 2Fe + Al2O3 Practice Problems
2. Determine the mass of sodium hydroxide produced when 0.25g of sodium reacts with water according to the following equation: 2Na + 2H2O 2NaOH + H2
3. What mass of bromine (Br2) is produced when fluorine reacts with 1.72 g of potassium bromide. The balanced equation is: 2F + 2KBr 2KF + Br2