1. a sample of sodium hydroxide, NaOH, is known to have become contaminated with sodium carbonate, Na2Co3, by reaction with CO2 in the air. A 1.00g sample is titrated with 0.500M HCI, and it is found that 46.5 ml of HCI are required for neutralization. Calculate the percentage by mass of Na2CO3 in the sample. ( Hint: Let mass of Na2CO3 = xg)
2.There are some titrations in which the endpoint is obtained by measuring the electrical conductivity of the solution and watching for the point at which the conductivity is at a minimum. Such a titration is called an electrometric titration. An example is the reaction of Ba(OH)2 solution with sulfuric acid, H2SO4 .Write the net ionic equation for the reaction (remembering the solubility table!), then explain why the conductivity reaches a minimum.
Thanks!
Chem question!! acid/base 20 分
2009-04-12 8:10 pm
回答 (2)
2009-04-12 10:54 pm
✔ 最佳答案
1) Mass of Na2CO3: x g and mass of NaOH: ( 1 - x ) gNa2CO3 + 2HCl ---> 2NaCl + H2O + CO2 --- (1)
NaOH + HCl ---> NaCl + H2O --- (2)
No. of moles of HCl used in (1):
2x / ( 2 x 23.0 + 12.0 + 16.0 x 3 ) = x / 53
No. of moles of HCl used in (2): ( 1 - x ) / ( 23.0 + 16.0 + 1.0 )
= ( 1 - x ) / 40
So, x / 53 + ( 1 - x ) / 40 = 0.5 x 46.5 / 1000
x = 0.2854
Hence % by mass = 0.2854 / 1.00 x 100% = 28.5%
2) Ba(OH)2(aq) + H2SO4(aq) ---> BaSO4(s) + 2H2O(l)
Net ionic equation: Ba2+(aq)+ SO42-(aq)---> BaSO4(s)
The mobile ions ( Ba2+ and SO42- ) for electrical conductivity have been precipitated out as insoluble barium sulphate. Therefore the conductivity reaches a minimum at the end - point of titration.
參考: My Chem Knowledge
2009-04-12 8:29 pm
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加蜂蜜清熱解毒、氣管敏感、腸胃健康都改善，鐘意飲牛奶、豆漿、咖啡亦可加入改變口味，平過食西式早餐好多。
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一杯相當於33種蔬菜, 6種水果, 內含200多種養養素,蛋白素相等於5 錢燕窩、2 份蔬菜、1 份水果、1 塊牛扒同半杯鮮奶！
我做文職133磅減咗22磅,改善頭痛,胃痛,暈車浪, 靜脈曲脹.
個女14歲三個月減20磅，改善鼻敏感, 流鼻血,暗瘡問題，讀書好咗仲拿第一添.
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原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20090412000051KK00564