hydrates “a solid compound containing water molecules combined in a definite ratio as an integral...
TRANSCRIPT
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HYDRATES
“A solid compound containing water molecules combined in a definite ratio as an integral part of the crystal”
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What is a Hydrate?
• Any salt that has water chemically bonded to the ions in the crystal structure is a hydrate or hydrated crystal.– Copper(II) sulfate is a
hydrate.– Hydrated copper(II) sulfate is
deep blue in color.
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What does the Chemical Formula of A Hydrate Look Like?
• BaCl2•2H2O
• FeSO4•6H2O
• Na2CO3•10H2O
• CuSO4•5H2O
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How are Names of Hydrates Written?
• BaCl2•2H2O•
• FeSO4•6H2O•
• Na2CO3•10H2O•
• CuSO4•5H2O•
• BaCl2•2H2O• barium chloride dihydrate
• FeSO4•6H2O• iron(II) sulfate hexahydrate
• Na2CO3•10H2O• sodium carbonate decahydrate
• CuSO4•5H2O• copper(II) sulfate pentahydrate
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What prefixes are used?
0.5 hemi 7 hepta
1 mono 8 octa
2 di 9 nona
3 tri 10 deca
4 tetra 11 undeca
5 penta 12 dodeca
6 hexa 13 triskaideca
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Practice Naming
• http://www.chem.purdue.edu/gchelp/nomenclature/hydrates_2009.htm
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How can the water be removed?
• Heat the crystal. The water is loosely bound, and will come away as water vapor.
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What is the compound called after the water has been removed?
• Anhydrous (adjective)= NO WATER!
– Anhydrous copper(II) sulfate is left in the test tube after heating.
BaCl2•2H2O BaCl2(s) + 2H2O (g)
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Example hydrate problem
Let’s make things a little more clear
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Example #1 • A 3.34 g sample of a hydrate has the formula
SrS2O3 ● xH2O and contains 1.04 g of water. What is the chemical formula for this hydrate?
Compound Mass (g) Moles (mol)n=m/MM
÷ by the lowest n
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• A hydrate of zinc chlorate, Zn(ClO3)2 ● xH2O, contains 21.5% zinc by mass. Find the value of x to determine the chemical formula of the hydrate.
Example #2
Compound Mass (g) Moles (mol)n=m/MM
÷ by the lowest n
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• A hydrate of barium hydroxide, Ba(OH)2 ● xH2O is used to make barium salts and to prepare certain organic compounds.
a) A 50.0 g sample of the hydrate contains 27.2 g of Ba(OH)2. Calculate the percent, by mass, of water in Ba(OH)2 ● xH2O
Example #3
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b) Find the value of x in Ba(OH)2 ● xH2O
Compound Mass (g) Moles (mol)n=m/MM
÷ by the lowest n
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How is a hydrate formed?
• A substance that absorbs water from the air is said to be hygroscopic.
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How to find the formula of a Hydrate
• To determine the water content of an ionic hydrate sample, we measure the mass of the sample before and after heating.
• Based on the analysis, we can express the water content of the hydrate
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Finding Formula of a hydrate
• calculate the mass % of water in the hydrate.
• mass of water in the hydrate sample equals the mass lost upon heating.
• Based on the mass of water and total sample mass, we can calculate the mass percent of water
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• Mass percent of water, % = (mass of water/ mass of original sample) x 100
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Determine number of moles
• Mass of anyhdrous portion = mass of substance left after heating
• Figure out how many moles there are of water and of anhydrous portion
• Divide number of moles of water by the number of moles of anhydrous portion – this gives you the number of moles of hydration
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Finding Moles of Water of Hydration
• Number of moles of waters of hydration = moles of water/ moles of anhydrous compound
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Writing the formula
• Once we have determined the number of moles of the water of hydration, we can write the chemical formula for the anhydrous compound, followed by a raised dot, followed by the number of waters of hydration obtained by calculation.