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Making_Solutions

Making_Solutions - Andreas Help Sheet on Preparing...

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Andrea’s Help Sheet on Preparing Solutions There are several types of stock solutions made in the research lab: Percent (%) solutions, Molar (M) solutions, X solutions, and mg/ml solutions. First are instructions on how to make % solutions. First, know the definition of a % solution: 1% = 1g/100ml That’s the basic formula, and it is logical because “per cent” means “per hundred”. So, let’s say you are assigned the task of making 1 liter of 20% SDS stock solution, a lab basic. (On quizzes, you may be told the MW of the chemical; it is not used in % solutions, so ignore it.) The three steps are: 1: write out the formula: 1% = 1g/100ml 2: scale it up on the percentage: 20% = 20g /100ml 3: scale to the final volume by multiplying by 10: 20% = 200g/1000ml Write out the description in the following manner: Place 200g of SDS powder a 1L beaker and add H 2 O up to 900ml. When dissolved, transfer solution to a 1L graduated cylinder and add H O to 1000ml. This works whether for a % w/v solution (as exampled above) or a % v/v solution. Suppose you need 100ml of 20% EtOH: 1% = 1ml/100ml 20% = 20ml/100ml Mix 20ml EtOH with 80ml H O for a final volume of 100ml. Next, let’s look at Molar (M) solutions. First, know the definition of a Molar solution: 1M = 1MW(in grams)/Liter (MW = molecular wt.) That’s the basic formula, and is logical because Molar is defined as a solution concentration having one mole of solute per liter of solution. So, lets say you are assigned the task of making 100ml of 5M NaCl . Here, you will need the molecular wt for NaCl; it is 58.44. The three steps are: 1: write out the formula: 1M = 1MW(g)/1000ml 2: plug in the numbers & scale it up on the Molarity: 5 M = (58.44)g /1000ml & work out the calculations: 5M = 292.2g/1000ml 3: scale to the final volume by dividing by 10: 5M = 29.22g/100ml Write out the description in the following manner: Dissolve 29.22g of NaCl in 90ml H O in a 100ml beaker. Transfer solution to a 100ml graduated cylinder and add H O to 100ml.

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Making_Solutions - Andreas Help Sheet on Preparing...

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