Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: newbie! on September 23, 2011, 03:59:07 PM
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in my lab manual for a course i'm doing titled "basic solid state chemistry" (part of my honours) the experiment is on "preparation on transition metal ion doped glasses"
the procedure is as follows:
take a known weigh (about 10g) of glass and calculate the quantity of transition metal salt (say the hydrated sulphate or nitrate) required to make up a 0.5M (0.02M in the case of cobalt) "solution" of the transition metal in the glass. Assume the denstiy of the phosphate glass is 2.5gcm-3.
i'm not sure how to calculate this.
assuming i need to make CuSO4, CU(no3)2, CoSO4 and Co(NO3)2
i know for CuSO4 the a.m is 159.62 and Cu makes 39.8% of that.
i need to get 0.5M of Cu overall right...
but where does density come into the calculation?
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Molarity is per volume, but you are to weigh the glass.
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hmm so i need to work out the volume then?
i should use equation d=mass/v or mol=c/v ?
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Both in correct moments - first to calculate volume of the glass sample, then to calculate necessary amount of salt.
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so like this:
d=m/v
v=m/d
= 10g/2.5gcm-1
= 4cm-3
mol=c/v
= 0.5/4
= 0.125
mass = mol x atomic mass
= 0.125 x 159.62
= 19.95g
so for the CuSO4 i would require 19.95g.
is that correct?
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d=m/v
v=m/d
= 10g/2.5gcm-1
= 4cm-3
OK
mol=c/v
= 0.5/4
= 0.125
Correct approach, but invalid result. Watch your units.
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mol=c/v
= 0.5/4
= 0.125
Correct approach, but invalid result. Watch your units.
hmm so the 0.5M IS the moles NOT the conc?
but why would i need to work out the conc?
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0.5M is a concentration - expressed in moles per liter, but your volume is not 4 liters.
As I told you - watch your units and such things become obvious.
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ahhh so its 4cm-1 which is equal to 4ml?
but in the n=c/v eqn. v has to be in litres.
so it would be 0.004 then
making it
n=c/v
= 0.5/0.004
= 125
surley that cant be right? it seems awful high...?
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Sorry, my mistake. That is, I was right about mL vs L thing, but somehow I failed to spot that the equation you are using is wrong. n is not c/v.
To say the truth, if you were not so stubbornly avoiding unit checking - even after being told several times to do so - you would find the problem on yourself.
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ahh sorry n=cv.
erm i'm not avoiding checking the units...
the volume should be cm3 not cm-3, right?
but i need still need to convert it to litres. and 1cm3=1ml so i have 4ml, equals 0.004l.
n=cv
= 0.5 x 0.004
= 0.002
is that better?
i'm not sure what units your referring to.. the conc is 0.5M and the vol is 0.004L and i spotted the cm3/cm-3 error.