94260-Stoichiometry

# 94260-Stoichiometry - The Mole The quantity of a substance...

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The Mole The quantity of a substance is measured in metric units, called moles . A mole of a substance is the quantity of that substance that contains the same number of particles as Avagadro’s number . Avagadro’s number 6.023 · 10 23 = 1 mol. - atoms - particles - molecules - formula units - ions 6.023 · 10 23 is equal to 6.02300000000000000000. U N I T 1 : S T O I C H I O M E T R Y P A G E 1 O F 1 3

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Molar Mass Molar Mass is the mass of one mol of a substance. You determine molar mass using the atomic mass values in the periodic table. Example: What is the molar mass of Water – H2O? Hydrogen 2 · 1.01 = 2.02 Oxygen 1 · 16.00 = 16.00 = 18.02 Therefore, water (H2O) has a molar mass of 18.02 g. U N I T 1 : S T O I C H I O M E T R Y P A G E 2 O F 1 3
Percent Composition of Molar Mass To find the percent composition of molar mass, simply take the total of each element. Example: take 117.3g of Potassium, divide it by the overall total of molar mass (212.27g), and then multiply it by 100. This is the percent composition of molar mass for whichever element you are solving for. K 3 · 39.00 = 117.30 P 1 · 30.97 = 30.97 O 4 · 16.00 = 64.00 Total: 212.27g. K 117.30 ÷ 212.27 · 100 = 55.26% P 30.97 ÷ 212.27 · 100 = 14.59% O 64.00 ÷ 212.27 · 100 = 30.15% Ensure that all percent totals for each element equal a combined number of 100, or a number close to 100, and remember to round two places after the decimal. U N I T 1 : S T O I C H I O M E T R Y P A G E 3 O F 1 3

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The Empirical Formula The empirical formula shows the lowest whole number ratio of the elements in a compound (the simplest formula of a compound). 1. When you are given the percent composition, you assume that the percentage is grams (g). So 14.9% = 14.9 grams. 2. Convert the grams to mols. 14.9 g of H = 1 mol 1.01 g = 14.8 mols of H 3. Find the ratio. Example: H 14.8 O 2.0 4. Divide both sides by the lowest number that is visible. So 2.0 is the lowest number visible. Example: H 14.8 ÷ 2.0 O 2.0 ÷ 2.0 Total: H 7.4 and O 1 H7O is the final answer Things To Remember : You may have to multiply your “total” to obtain a final answer that does not have decimals. U N I T 1 : S T O I C H I O M E T R Y P A G E 4 O F 1 3
The Molecular Formula of a Compound The molecular formula, also known as the actual formula, describes the number of atoms of each element that make up a molecule. Molecular formula subscripts = n x Empirical formula subscripts. (n = 1, 2, 3.

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## This note was uploaded on 10/07/2009 for the course ALL 4567 taught by Professor Jhn during the Spring '09 term at CUNY Hunter.

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94260-Stoichiometry - The Mole The quantity of a substance...

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