[newbie!]

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?

[Borek]

Molarity is per volume, but you are to weigh the glass.

[newbie!]

hmm so i need to work out the volume then?

i should use equation d=mass/v or mol=c/v ?

[Borek]

Both in correct moments - first to calculate volume of the glass sample, then to calculate necessary amount of salt.

[newbie!]

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?

[Borek]

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.

[newbie!]

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?

[Borek]

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.

[newbie!]

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...?

[Borek]

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.

[newbie!]

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.