JEE Advanced 2019 · Paper 1 · Chemistry Q1

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ChemistrySingle correct+3 / -1Question 19 of 54

The green colour produced in the borax bead test of a chromium(III) salt is due to

\ce{Cr(BO2)3}

\ce{Cr2(B4O7)3}

\ce{Cr2O3}

\ce{CrB}

Answer and worked solution

Official answer: A

On heating, borax loses water and gives sodium metaborate and boric anhydride:
$\ce{Na2B4O7 -> 2NaBO2 + B2O3}.$
The $\ce{B2O3}$ combines with the metal oxide to form the metaborate. For chromium(III) this is green $\ce{Cr(BO2)3}$ .

(A)

Topics:Flame and borax bead tests

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JEE Advanced 2019 · Paper 1, Chemistry question 1