lake - Al(OH)3 precipitate)

[giuliano]

Hello,
I have started making some Madder Lake, by precipitating aluminium
hydroxide from a K2CO3 + AlK 2(SO4) 12H20 solution (I ignore the
presence of the madder roots in the initial K2CO3 solution).

I have done some stoichiometry to evaluate the correct proportion of the
two salts, but my chemistry knowledge lacks... Could someone check my
estimated reaction?

2 (AlK 2(SO4) 12H20) + 3 (K2 CO3) = 2 (Al (OH)3) + 4 (K2 SO4) + 18 H2O +
3 (H2 CO3)

that gives a mass ratio of approx. 2.29 parts alum/ 1 part potassium
carbonate.

1) Is the above formula correct?
2) as the solution is kept between 30 and 40C, I suppose that all the
H2CO3 will leave the solution as CO2, is then the result a neutral
solution?

note that point (2) would give me a better way of evaluating the amount
of alum to add to the solution, as after filtration of the potassium
carbonate/madder root solution, I do not really know how much carbonate
has been discarded.

Thanks

Giuliano

[jack]

Post by giuliano
Hello,
I have started making some Madder Lake, by precipitating aluminium
hydroxide from a K2CO3 + AlK 2(SO4) 12H20 solution (I ignore the
presence of the madder roots in the initial K2CO3 solution).
I have done some stoichiometry to evaluate the correct proportion of the
two salts, but my chemistry knowledge lacks... Could someone check my
estimated reaction?
2 (AlK 2(SO4) 12H20) + 3 (K2 CO3) = 2 (Al (OH)3) + 4 (K2 SO4) + 18 H2O +
3 (H2 CO3)
that gives a mass ratio of approx. 2.29 parts alum/ 1 part potassium
carbonate.
1) Is the above formula correct?
2) as the solution is kept between 30 and 40C, I suppose that all the
H2CO3 will leave the solution as CO2, is then the result a neutral
solution?
note that point (2) would give me a better way of evaluating the amount
of alum to add to the solution, as after filtration of the potassium
carbonate/madder root solution, I do not really know how much carbonate
has been discarded.
Thanks
Giuliano

sorry. what is the meaning of LAKE. i heared that lake substances does
not dissolove in water.

[giuliano]

Post by jack
sorry. what is the meaning of LAKE. i heared that lake substances does
not dissolove in water.

Lake as in the pigment made from an (organic) dye (presumably)
ad/absorbed by some inorganic binder. I think historically it is always
aluminium hydroxide, sometimes mixed with other insoluble salts. For
instance the precipitation from potassium aluminium sulphate plus
potassium carbonate gives this, but in cases where a less transparent
lake was preferred chalk was used instead of potassium carbonate, so
that some calcium sulphate was also precipitated.

I got an answer for my original question in the analytical chemistry
forum at http://www.chemicalforums.com/.

g

[jack]

Post by giuliano

Post by jack
sorry. what is the meaning of LAKE. i heared that lake substances does
not dissolove in water.

Lake as in the pigment made from an (organic) dye (presumably)
ad/absorbed by some inorganic binder. I think historically it is always
aluminium hydroxide, sometimes mixed with other insoluble salts. For
instance the precipitation from potassium aluminium sulphate plus
potassium carbonate gives this, but in cases where a less transparent
lake was preferred chalk was used instead of potassium carbonate, so
that some calcium sulphate was also precipitated.
I got an answer for my original question in the analytical chemistry
forum athttp://www.chemicalforums.com/.
g

I have benifited by your post and find chemical fourms address thanks
sir