What follows is an example of each way.Įxample #7: A 241.3 gram sample of CoCl 2 ⋅ 2H 2O is heated to dryness. There are three different ways you can approach this type of problem. When I realized the lack, I put three examples here (as opposed to their own separate file) and included another in the problems.
#CHEMLAB HYDRATE FORMULA FULL#
Determine the value of n.Ĥ) Determine smallest whole-number ratio:ĭuring the time I assembled the examples (and the problems) above and below, I never addressed the following type of problem, one in which the full formula of the hydrate is known and you are asked how much anhydrate remains after driving off the water. nH 2O is 322.1 g/mol, calculate the value of n.ġ) The molar mass of anhydrous Na 2SO 4 is:Ģ) The mass of water in one mole of the hydrate is:Įxample #6: 4.92 g of hydrated magnesium sulphate crystals (MgSO 4 ⋅ nH 2O) gave 2.40 g of anhydrous magnesium sulfate on heating to a constant mass.(1.864 g) (137.33 g/mol / 233.39 g/mol) = 1.0968 gĢ) Calculate mass of anhydrous BaCl 2 that contains 1.0968 g of Ba:ġ.0968 g is to 137.33 g/mol as x is to 208.236 g/molģ) Calculate mass of water in original sample:Ĥ) Calculate moles of anhydrous BaCl 2 and water:ĥ) Express the above ratio in small whole numbers with BaCl 2 set to a value of one:Įxample #5: Given that the molar mass of Na 2SO 4 nH 2O yields 1.864 g of anhydrous BaSO 4 after treatment with sulfuric acid, calculate n.
This means that the HCl reacted with 0.013722 mole of sodium carbonate.Ġ.013722 mol times 105.988 g/mol = 1.4544 gĢ.4723 g / 18.015 g/mol = 0.13724 mol of waterĦ) For every one Na 2CO 3, how many waters are there?Ĭomment: this is one of the three sodium carbonate hydrates that exist. We also assume that no CO 2 dissolves in the water.)Ġ.6039 g / 44.009 g/mol = 0.013722 mol of CO 2ģ) Use the 1:1 molar ratio referenced above: (Also, note that we assume that the gas is pure CO 2 and that there is no water vapor whatsoever. The key is that there is a 1:1 molar ratio between Na 2CO 3 and CO 2. Ignore the water of hydration for a moment. What is the number of water molecules bonded to Na 2CO 3 (value of n)?
Determine the formula of the hydrate and then write out the name of the hydrate.Ģ) Determine moles of Na 2CO 3 and water: After heating, the mass of the anhydrous compound is found to be 3.22 g. H 2O -> 8.09 g / 18.015 g/mol = 0.449 molĮxample #2: A hydrate of Na 2CO 3 has a mass of 4.31 g before heating. The original location of this document is here.Įxample #1: A 15.67 g sample of a hydrate of magnesium carbonate was heated, without decomposing the carbonate, to drive off the water.
Here's a worksheet with eight hydrate problems, all of which have (hand-written) solutions. Ten problems Calculate empirical formula when given mass data Fifteen problems Calculate empirical formula when given percent composition data A list of all the problems Determine identity of an element from a binary formula and a percent composition Mole Table of Contents Determine identity of an element from a binary formula and mass data ChemTeam: Determine the formula of a hydrate: fifteen examplesĭetermine the formula of a hydrate: fifteen examples
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