Name_________________________Date___________________Per



Notes: Section 7.3Percentage Composition:Percentage Composition is the percent by mass of an element in a compound. The formula to calculate percentage composition is: Percent by mass of element = Mass of elementX 100Mass of compoundPercent element in compound = Mass of element in 1 mol of compoundX 100Molar mass of compoundBecause percent means parts per 100, the percent by mass of all the elements of a compound must always total 100%.Examples: A sample of a compound contains 55 g of Element X and 45 g of Element Y. What is the percentage composition of each element in the compound?% X = 55X 100100% X = 55% element X% Y = 45X 100100% Y = 45% element YFind the percentage composition of a pure substance that contains 7.22g nickel, 2.53g phosphorus, and 5.25g oxygen.7.22 + 2.53 + 5.25 = 15 grams% Ni = 7.22X 10015% Ni = 48.13% 48.1% Nickel% P = 2.53X 10015% P = 16.86% 16.9% Phosphorus% O = 5.25X 10015% O = 35.0% Oxygen Find the percentage composition of each element in Aluminum Sulfate.Al2(SO4)3 = 53.96 + 96.21 + 192 = 342.17 grams% Al = 53.96X 100342.17% Al= 15.769% 15.77% Aluminum% S = 96.21X 100342.17% S = 28.117% 28.12% Sulfur% O = 192X 100342.17% O = 56.11% OxygenFind the percentage composition of oxygen in Magnesium CarbonateMgCO3 = 24.31 + 12.01 + 48 = 84.32 grams % O = 48X 10084.32% O = 56.925% 56.93% Oxygen7.3 Formulas of HydratesHydrates are solid ionic compounds in which water molecules are trapped.A hydrate is a compound that has a specific number of water molecules loosely bound to its atoms. When a hydrate is heated, water molecules are driven off leaving an anhydrous compound, or one “without water”.Uses of hydratesCommercially the anhydrous form of the hydrate is used to keep moisture out of electronic equipment, clothing, shoes, etc. Packets called desiccants are often inserted in these items when they are packaged and shipped, to absorb any moisture that may enter the packing of such items.The formula for a hydrate includes:The chemical formula for the ionic compoundA raised dot (?)The coefficient of the number of water molecules attachedThe formula for waterThe raised dot (?) in the formula indicates that the water molecule is loosely attached and can be removed. Practice Examples:Give the correct formula for the following hydrates:1) ammonium carbonate monohydrate(NH4)2CO3 ? H2O2) sodium hydroxide decahydrateNaOH ? 10 H2O3) iron (III) phosphate tetrahydrateFePO4 ? 4 H2OGive the correct name for the following hydrates:4) CuSO4 ? 5 H2OCopper (II) sulfate pentahydrate5) Ba(OH)2 ? 8 H2OBarium hydroxide octahydrateNi(NO3)2 ? 3 H2ONickel (II) nitrate trihydratePercent composition of a Hydrate:What percentage of the hydrate copper (II) hydroxide pentahydrate is water?Cu(OH)2 ? 5 H2O = 63.55 + 32 + 2.02 + 90.1 = 187.67% H2O = 90.1X 100187.67% H2O = 48.01% H2OCalculate the percent composition of water in FeCl2 ? 2H2O.FeCl2 ? 2H2O = 55.85 + 70.9 + 36.04 = 162.79% H2O = 36.04X 100162.79% H2O = 22.138% 22.14%Determining the Formula of a HydrateSuppose you know the formula of the hydrate is BaCl2 ? x H2O. You must determine the x, coefficient of the H2O in the formula.In a laboratory situation you would need to heat up the hydrate to remove all the water. You must first measure the mass of the hydrate (this means with the water attached). The hydrate would then be heated to drive off the water thus forming a/an anhydrous compound. Then measure the resulting substance.What’s next? Subtract the two masses. Mass of Hydrate – Mass of Anhydrous = Mass of waterConvert mass of Anhydrous to molesConvert mass of water to molesSolve for x using the following equation:x =Moles of waterMoles of anhydrousHydrate Practice Examples:A mass of 2.50 g of blue, hydrated copper (II) sulfate is placed in a crucible and heated. After heating, 1.59 g of white anhydrous copper (II) sulfate remains. What is the formula for the hydrate? 2.50 – 1.59 = 0.91 grams H2O1.59 g CuSO41 mol CuSO4= 0.009961 0.00996 mol CuSO4 159.62 g CuSO40.91 g H2O1 mol H2O= 0.05049 0.0505 mol H2O 18.02 g H2Ox =0.05050.00996x = 5.07 ≈ 5What is the name of the hydrate?Copper (II) Sulfate pentahydrate (CuSO4 ? 5 H2O)The mass of the hydrate CoCl2 ? x H2O is 1.62g. After heating a residue of 0.88 g was recovered. Calculate the formula for the hydrate.1.62 – 0.88 = 0.74 grams H2O0.88 g CoCl21 mol CoCl2= 0.006778 mol 0.0068 mol CoCl2 129.83 g CoCl20.74 g H2O1 mol H2O= 0.04106 0.041 mol H2O 18.02 g H2Ox =0.0410.0068x = 6.029 ≈ 6What is the name of the hydrate? Cobalt (II) chloride hexahydrate (CoCl2 ? 6 H2O)An 8.3 g sample of a hydrate of CaCO3 was heated, and only 6.8 g of the anhydrous salt remained. What percentage of this hydrate was water?8.3 – 6.8 = 1.5 grams H2O% H2O = 1.5X 1008.3% H2O = 18.07% 18% H2O ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download