# How to predict colour of precipitate? [duplicate]

I am currently preparing for Junior science competitions and I am coming across many questions where colour of precipitate plays important role... Like

When compound $$\ce{Hg2(NO3)2}$$ reacts with $$\ce{Na2CrO4}$$ solution, the colour of the compound formed is--

The question is a bit long and the compound can be determined from a series of experiments given in question. the product is $$\ce{Hg2CrO4}$$ but guessing the colour is impossible. Is there any way to determine colour of compound i.e. precipitate.??

• Actually the question is a a bit long and from the question the compound is determined. Let's assume the product can be determined easily. Is there any way to know it's colour?? Oct 2 '21 at 17:46
• May be the solution is in the details (I am looking for the hints there). Please post the entire question. Oct 3 '21 at 0:34
• @Nilay Ghosh Looks perfect, Brilliant, Thanks Oct 3 '21 at 3:30

• the mercury(I) chromate $$\ce{Hg2CrO4}$$ is brown at room temperature, and turns red at $$100$$°C. It changes crystallization system at high temperature.
• the mercury(II) chromate $$\ce{HgCrO4}$$ is yellow at room temperature, and becomes red at $$100$$°C. This change is due to the formation of a basic salt.
• The dichromate ion $\ce{Cr2O7^{2-}}$ does not give a precipitate with $\ce{HgCl2}$, but is gives a brownish yellow precipitate with $\ce{Hg(NO3)2}$, according to Treadwell's Qualitative Analysis. Oct 3 '21 at 9:38