extreamly confusing chemistry assigment (1 Viewer)

[leapordfist]

ok guys, im having this mind boggling chem assigment and the teacher has his lips sealed.....

maybe im retarded and u guys will see through this in a second. but lets see

ok in the assigment we are given a sample of MgSO4.7H2O (known as ipsom salt i think) in a mixture of NaCl

both are solouble in water....

we have to find the % water of crystalisation aswell as the % of the hydrated magnesium sulfate in the mixture containing NaCl...

we are supposed to do this in a lab

wat i though would be good to do was count up the total AMU of the hydrated magnesium sulfate and the 7H2O inside the hydrated magnesium sulfate and then heat the mixture..

the water will evaporate and then i can calculate the mass of hydrated magnesium sulfate using proportions...

this is where the problem is....no matter what the water of crystalisation is....ittl give me mass that is exactly in therotical ratio of the ammount of water of crystalisation in any sample of hydrated mgso4....

so what do i do? we cant have an experimental result that is exact...on the dot....in every case....so there has to be another option...ive tried moles...but tahts the same exact story...NaCl isnt in an exact ratio to hydrated mgso4...its simply a mixture...









heeeelpppppppppppppppppppppppppp

 

[brenton1987]

ok in the assigment we are given a sample of MgSO4.7H2O in a mixture of NaCl
both are solouble in water
we have to find the % water of crystalisation aswell as the % of the hydrated magnesium sulfate in the mixture containing NaCl

NaCl^.MgSO₄^.7H₂O --> NaCl^.MgSO₄ + 7 H₂O

Weigh the sample --> m_{NaCl.MgSO4.7H2O}.
Heat in excess of 100^oC.
Reweigh --> m_NaCl.MgSO4.
m_{NaCl.MgSO4.7H2O} - m_NaCl.MgSO4 = m_H2O.
m_H2O / F_H2O = n_H2O.
n_H2O / 7 = n_MgSO4.
n_MgSO4 * F_MgSO4 = m_MgSO4.
m_MgSO4 / m_{NaCl.MgSO4.7H2O} = % MgSO₄.
m_H2O / m_{NaCl.MgSO4.7H2O} = % H₂O.

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You could also find the mass of MgSO₄ by adding CaCl₂ and weighing the precipitate of CaSO₄.

 

[leapordfist]

sorry but what does the m and n stand for in youre reply

 

[study-freak]

in chemistry, n=number of moles
m=mass