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Chemistry Forums for Students => Inorganic Chemistry Forum => Topic started by: smithgabriel on June 13, 2014, 02:54:17 PM

Title: Tungstic Acid color changes
Post by: smithgabriel on June 13, 2014, 02:54:17 PM

I have some tungstic acid that is yellow, and when I use a spatula to push down on the powder or move it around, it turns a blue color.  I know that there are tungsten blue oxides, but has anyone ever seen tungstic acid change color from a stainless steel spatula?  Is this reversible?

Title: Re: Tungstic Acid color changes
Post by: Radu on June 14, 2014, 10:47:54 AM

 Are you sure it's a stainless steel spatula? What if it's a Zn based alloy? W⁵⁺ is fairly blue, so your spatula's metal may reduce WO₃*nH₂O

Title: Re: Tungstic Acid color changes
Post by: Arkcon on June 14, 2014, 02:00:05 PM

I don't really understand the chemistry at work here, although Radu: seems to be on the right track -- the spatula may have reduced the sample, either because of what it was made of, or.  You really shouldn't use a metal spatula with reactive reagents.  You can try a disposable plastic spatula.  My favorite thing is to cut the bulb of a polypropylene dropper in half.  That give me a spoon that I know has never touched another reagent ... because it was never a spoon in the first place.

Title: Re: Tungstic Acid color changes
Post by: smithgabriel on June 17, 2014, 03:59:13 PM

Thanks for the info.  I did find an old paper that describes the dry testing for tungstic acid using a spatula.  It involves rubbing a spatula onto the Tungstic acid sample and looking for a blue/grey color that indicates reduction.