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Friday, May 20, 2016

Magical precipitate of Chemistry

SHOW of PRECIPITATIONS in the beautiful metallic Hydroxides XIV ,we find a parade of metallic hydroxides precipitates from the addition of sodium hydroxide solution (NaOH) to several test tubes containing each a metal nitrate. The bulky texture characteristic of the hydroxides is very noticeable.

This type of reaction is used to discover the identity of the metal ion present in the solution being analyzed based on the colors and textures unique to each of the precipitates.
It is worth noting that the cobalt hydroxide precipitates with distinct color of solution: in the precipitate, Co2 + ion has no water molecules in their sphere of coordination, while in solution have exactly the ion [Co (H2O) 6] 2 +, hexa-aquocobalto (II).

The precipitate of Mn (OH) 2, white, rust quickly aired the MnO2 (or MnO (OH) 2). The solution of Fe (II) must be freshly prepared to prevent the precipitate contains a mixture of hydroxides of Fe (II) and Fe (III).
Avoid excess NaOH because some hydroxides may redissolve due to the formation of hidroxicomplexos (case of lead, zinc, chromium and aluminum in this posting).
So, with this show that only the chemistry can provide, we wish you all a superbv morning , thanks for your company

Precipitation Titration
Precipitation titration known as Mohr's Method that is was used to determine the chloride concentration .
This method is based on two reactions that yield ionic compounds of limited solubility.
First, the sample solution is titrated with silver nitrate, which upon addition, forms a white precipitate of silver chloride (AgCl).
The endpoint occurs when all the chloride ions have precipitated. Any additional silver ions then react with the chromate ions of the indicator, potassium chromate, to produce a red-brown precipitate of silver chromate, seen in the photo (Ag2CrO4).

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