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rivatayah rivatayah
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12 years ago
How do you determine the molarity of the following solution:
35.0g NaOH in 100ml H2O

And the Molality of the following solutions:
258g HCl in 453g H2O
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wrote...
12 years ago
M = mol/L
m = moles of solvent/kilograms of solvent

For the first one, convert grams to moles and then use the first formula
For the second one, convert both values to kilograms and use the second formula
wrote...
12 years ago
right, lets take the 1st example and do it..

you need to find the number of mols of NaOH to find the molarity, and so need the equation n=mass/Mr    

the mass = 35g  and the Mr of NaOH = 40             (40 because O = 16, H= 1 & Na = 23)

so; 35/40 = 0.875mols of NaOH.

Now you need to find the molarity(concentration) of the NaOH in solution, for this you need the equation n = MV/1000      where M = molarity (what you want), n = number of mols, & V = Volume, rearrange equation to get;

M =  n x 1000 / V              we know n = 0.875 (as calculated above) and V = 100ml (as you said in your question).

therefore; M = 0.875 x1000 / 100 =  8.75M  concentration Slight Smile simple as that. I won't do the next one as an example, but the answer I got was 15.6M - oh..and a little hint, you need the density of water..1g for 1 ml...thus 453g = 453 ml, crafty devils try and catch you out.

Best of luck Slight Smile
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