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原理:向饱和 Na_2SiO_3溶液中逐渐滴加较浓盐酸,边滴边振荡,当溶液 pH 在7～8时,静置两三分钟,有白色胶状沉淀硅酸生成。方程式可以简写为:Na_2 SiO_3+2HCl=H_2 SiO_3+2NaCl但在实际操作中,因嫌测量溶液的 pH 比较麻烦,常常省掉这一步,使得盐酸过量或不足。而盐酸过量或不足,胶体都不能生成,因此实验常常失败。现在的普通高中课程标准实验教科书化学必修1对此做了修改。具体操作如下:在小试管中取适量的饱和溶液,滴一滴酚酞试液,呈红色。再逐渐滴入较浓盐酸,同时振荡,当观察到红色刚好褪去时,停
Principle: The solution of saturated Na_2SiO_3 gradually dripped concentrated hydrochloric acid, while dropping edge oscillation, when the solution pH at 7 ~ 8, let stand for two or three minutes, a white colloidal precipitate silicate generated. The equation can be abbreviated as: Na_2SiO_3 + 2HCl = H_2SiO_3 + 2NaCl But in practice, due to the measurement of the pH of the solution is too cumbersome, often save this step, making the hydrochloric acid excess or deficiency. However, too much or too little hydrochloric acid can not form colloids, so experiments often fail. Now the general high school curriculum standard textbook chemistry compulsory 1 has been modified. The specific operation is as follows: Take a suitable amount of saturated solution in a small test tube, dropping a drop of phenolphthalein test solution, red. Then gradually into the more concentrated hydrochloric acid, while shaking, when observed just faded red, stop