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# Dilution - (moles/liter(liter =(moles/liter(liter moles =...

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Dilution For convenience, solutions are either purchased or prepared in concentrated stock solutions which must be diluted prior to use. When we take a sample of a stock solution we have a certain number of moles of molecules in that sample. Dilution alters the molarity (i.e. concentration ) of the solution but not the total number of moles of molecules in the solution (in other words, dilution does not create or destroy molecules). One of the standard equations for determining the effects of dilution upon a sample is to set up an equation comparing (concentration)*(volume) before and after dilution. Since (concentration)*(volume) gives us the total number of moles in the sample , and since this does not change , this value before and after dilution are equal: (concentration)*(volume) = (concentration)*(volume)
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Unformatted text preview: (moles/liter)*(liter) = (moles/liter)*(liter) moles = moles How much of a 5 M stock solution of NaCl will you need to make up 250 mls of a 1.5 M solution? X liters = 0.075 liters (or 75 mls) Thus, we would need 0.075 liters of our 5M NaCl stock solution. The rest of the 0.25 liter volume is made up by the addition of water: 0.25 liters - 0.075 liters = 0.175 liters So we would take 0.075 liters of stock 5M NaCl solution and add to that 0.175 liters of water for a final volume of 0.25 liters with a final concentration of 1.5 moles/liter (i.e. 1.5 M) What is the concentration of water? Molecular weight of H 2 O = 18.0g/mole Density of H 2 O = 1g/ml or 1000g/L Pure water is 55.6M H 2 O...
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