Saransh Posted February 23, 2010 Report Share Posted February 23, 2010 So, I am designing my own procedure on how the concentration of substances affects the voltage in a voltaic cell. I am given two substances: 1) CuO4S.5H2O and the molecular weight is 249.68g/mol.2) Mg(NO3)2.6H2O and the molecular weight is 256.41g/mol. I have chosen my dependent variable to be the voltage and the independent variable being the concentration of solutions. I have to investigate how the change in the concentration in one of the substances affects the voltage. I am told to find out what mass I should be using in order to come up with different concentrations to use...I am confused about this bit...how do I find out which masses to use?? Oh, and I am going to be using 50mL of each solution. Reply Link to post Share on other sites More sharing options...
sweetnsimple786 Posted February 23, 2010 Report Share Posted February 23, 2010 There might be some safety parameters [ I haven't worked with those substances], but basically, you can decide which concentrations you want by saying molarity [the concentration] = moles / liter. So if you're going to use 50mL of water [if the adding substance won't add noticeable volume], then Molarity = moles/.050L. & to find moles, you'd say molar mass [molecular weight] for CuO4S.5H2O is 249.68g/mol. So rearranging from before, moles = molarity*(.05L) = mass/molecular weight because mass = molecular weight*number of moles.So if you want a molarity of .2mol/L and .4mol/L, then you'd say mass=molecular weight*molarity*volume of solvent [and the vol is .05L in this case]. And now that I look over this, there's probably a simpler way to do this. If it's confusing, sorry. I'm running on a low battery & I don't want to recharge. Reply Link to post Share on other sites More sharing options...
Sandwich Posted February 23, 2010 Report Share Posted February 23, 2010 Well you need to work out how you're going to make the solutions of different concentrations -- i.e. how much of substance X do you need to stick in to ensure a solution of Y molarity?You need to work out the molar mass of the crystals you're using and then, allowing for the size of your flask (e.g. 1M in a 1L flask would equate to 0.1M in a 100ml flask), work out how much of it to weigh out and then mix in in order to achieve the concentrations you need. This requires simple use of Mass = Moles x Molar Mass.So if you wanted 0.1M of whatever it is, you'd say the mass you need to dissolve is equal to 0.1 x Molar Mass.Just don't forget that the H2O counts as part of the molar mass when you're working that out for your substances. Reply Link to post Share on other sites More sharing options...
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