GROUP VIB CHROMIUM GROUP

- Livy

False (high melting points*)

True or False
Cr, Mo, W and U are metals with low melting points, great hardness, and excellent resistance to corrosion

Chromium

this element under this group, exhibit +2,+3 and +6 valences

Molybdenum and Tungsten

these elements under this group, exhibit +2 to +6 valences

Cr(OH)3

this is amphoteric and will dissolve in acid to form Cr(III) ion or in alkali to form CrO2

Cr+3

Identification test:

• Reaction w/NaOH

• Formation of grayish green ppt. of Cr(OH)3 which will dissolve in excess of the alkali to form green solution (NaCrO2)

• Upon addition of an oxidizing agent (Na2O2), it turns yellow due to Na2CrO4

CrO4 -2

Identification test:

• Reaction with BaCl2 – yellow ppt. of BaCrO4

• AgNO3 – brownish red ppt. of Ag2CrO4

• Perchromic acid test or vanishing blue test - presence of blue ethereal layer due to perchromic acid