[[[急]]]]如何把牛奶中的鈣含量(準確的驗出數量)

As mentioned by 黑白灰_唯物主義者, calcium sulfate is not completely insoluble.


圖片參考：http://imgcld.yimg.com/8/n/HA00075708/o/701202020009413873433770.jpg


圖片參考：http://imgcld.yimg.com/8/n/HA00075708/o/701202020009413873433771.jpg


圖片參考：http://imgcld.yimg.com/8/n/HA00075708/o/701202020009413873433772.jpg


Look at the attached link for a manual.
http://www.chemteach.ac.nz/investigations/documents/magnesium_calcium.pdf

calcium sulphate is not really insoluble but is slightly soluble
so, ppt. produced will only be part of the calcium
which makes the result inaccurate

2012-02-03 23:31:01 補充：
besides, most of the calcium-containing compounds are slightly soluble in water
so, the method of precipitation is not feasible

Add excess sulphuric acid into the milk
Calcium ion reacts with sulphate ion to form calcium sulphate , which is a insoluble precipitate
You can find out the mass of calcium by the following steps

1. Add excess sulphuric acid into milk , a white precipitate is formed
2. Weight a piece of filter paper
3. Filter the solution by using funnel and filter paper
4. Wash the precipitate to extract pure calcium sulphate
5. Place the filter paper and the precipitate into oven
6. Heat the filter paper and the precipitate about 30 minutes
7. Weight the filter paper and the precipitate
8. Calculate the mass of calcium by the following steps

Mass of filter paper and the precipitate - Mass of filter paper = Mass of the precipitate ( Calcium sulphate )

Mass of Calcium = Mass of the precipitate x ( 40.1 / 40.1+32.1+16x4)

鈣含量測定包括氧化還原法、以NN指示劑與鈣離子作用的呈色法等.
但需要特別的原料器材, 普通人不容易自己測量.
而且誤差度高.

如果閣下有確實需要, 建議花點錢呈往化驗公司檢測.