Unit+3+-+Stoichiometry


 * __STOICHIOMETRY__**

__**Atomic Mass Unit (amu)-**__ ﻿ weight of an atom based on its mass relative to 1/12 an atom of Carbon-12

__**Avogadro's number:**__ 1 mole = 6.022 x 10^23

__**Isotopic abundances-**__ the fraction of atoms of a given isotope in a sample of an element. __Calculations:__ Ne-20 20(0.9029) = 18.184 Ne-21 21(0.0026) = 0.055 Ne-22 22(0.0882) = __+ 1.941__ Atomic mass of Neon = 20.18 amu
 * Isotope || Atomic Mass || Percent Abundance ||
 * Ne-20 || 20.00 amu || 90.92% ||
 * Ne-21 || 21.00 amu || 0.26% ||
 * Ne-22 || 22.00 amu || 8.82% ||

__**Mole-Gram Conversions:**__

__ex:__ How many grams is 6.3 moles of Oxygen?

6.3 moles x (16 g / 1 mole) = 100.8 g

**__Percent Composition__-** amount of an element in a chemical formula written as a percent

__ex:__ In a 100 g sample of water there are 11.19 g of hydrogen and 88.81 g of oxygen so:

__11.19 g H__ x 100% = 11.19% H 100.0 g  __88.81g O__ x 100% = 88.81% O  100.0 g
 * the subscrips in a formula represent not only the atom ratio in which the different elements are combined but also the mole ratio.

__**Simplest formula-**__ the simplest whole-number ratio of the atoms present.

Calculate the simplest formula:
 * if percents are given assume that the sample is 100g.

__ex:__ K: 26.6% Cr: 34.4% O: 38.0% The percent is equal to the grams in a 100g sample

mol of K = 26.6g x (1 mol / 39.10g)= 0.680 mol K

mol of Cr = 34.4g x (1 mol / 52.00g) = 0.661 mol Cr

mol of O = 38.0g x (1 mol / 16.0g) = 2.375 mol O

To find the mole to mole ratio, divide by the smallest number.

__.680 mol K__ = 1.02 which rounds to 1 mol of K 661 mol Cr

__2.375 mol O__ = 3.59 which rounds to 3.5 mol O .661 mol Cr

Mole ratios have to be whole numbers so we multiply by two K: 2 mol Cr: 2 mol O: 7 mol So, the simplest formula is K2Cr2O7

**__Theoretical yield-__** amount (mass) of product obtained from the complete conversion of the limiting reactant

percent yield = experimental yield / theoretical yield x 100%

**__Limiting reactant-__** least abundant reactant based on the equation for a reactio; dictates the max amount of product that can be formed.

[|Stoichiometry song!] (Mark Rosengarten)

"[|AMAZING" student video on stoichiometry!]

media type="youtube" key="q_rbjDGiyWM" height="349" width="425"