Dec 2, 2013
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  1. Pre-Medical
I came across a question in my gen chem textbook where they want you to find the heat capacity of a calorimeter, because it isnt always negligible. Well, that is beside the point because I am stumped on part of the question that doesn't really deal with that. It says:

Consider an experiment in which we combine 50.0 mL of 0.250 M HCl (aq) with 50.0 mL of 0.250 M NaOH. The calorimeter and both solutions are initially at 23.50*C and the density and specific heat of both solutions are the same as that of water (1.000g/mL and 4.184 J/g*C, respectively). We can determine the amount of heat the reaction will generate using moles of reactant and heat of neutralization blah blah blah...

Guys, I CANNOt understand why the combined densities are the same as that of water. It makes sense intuitively because they will basically become water, but looking at it this way:

HCl: (0.250 M)(.050 L) = 0.0125 mol
NaOH: (0.250 M)(.050 L) = 0.0125 mol

0.0125 mol HCl = 0.456 g HCl
0.0125 mol NaOH = 0.5 g NaOH

0.456 + 0.5 = 0.956 g

This is 0.956 grams per 0.1 L, which is 10 g/L, or **0.01 g/mL** and this is NOT the density of water. PLEASE HELP ME HERE LOL



AdaptPrep MCAT
2+ Year Member
Jan 19, 2017
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  1. Pre-Medical
Hi, Slinquii.
I think you calculated mass/volume (1% m/v) which is not the same as density. 100 mL (0.1 L) of water weighs 100 grams. So the total solution would weigh 101 grams (roughly). But the volume would not increase much at all from the original 100 mL. So 101 grams/100 mL is still approximately 1.0 g/mL. Does that help?
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