CHEM TITRATION

bennyh1993

2010-03-27 5:21 am

‘10.0 cm3 of the acid was first diluted to 250 cm3 with distilled water. 25 cm3 of the diluted solution
waswithdrawn to a conical flask and titrated against 0.1 M sodium hydroxide solution with an addition
of a few drops of methyl orange. 18.2 cm3 of the sodium hydroxide was required to attain the end point.’

Determine the molarity of the sample of sulphuric acid!!
State the expected observation when the end point of the titration is attained.!

更新1:

how to know red to orange??

回答 (1)

胡雪8°

2010-03-27 9:29 am

✔ 最佳答案

Titration:
2NaOH + H2SO4 → Na2SO4 + 2H2O
Mole ratio NaOH : H2SO4 = 2 : 1

No. of moles of NaOH = 0.1 x (18.2/1000) = 0.00182 mol
No. of moles of H2SO4 = 0.00182 x (1/2) = 0.00091 mol
Molarity of diluted H2SO4 = 0.00091/(25/1000) = 0.0364 M
Molarity of sample of H2SO4 = 0.0364 x (250/10) = 0.91 M

At the end point, the solution changes from red to orange.

2010-03-29 01:41:18 補充：
At very acidic solution, methyl orange is red.
At very alkaline solution, methyl orange is yellow.
At the end point, the colour is the mixing of red and yellow, thus orange.

參考: 胡說八

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