Compounds of the alkali metals
2 marks · EasyExplain why potassium dichromate(VI) is orange, while most compounds of sodium are white or colourless.
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Potassium dichromate(VI) is orange because the dichromate(VI) ion is coloured. Most sodium compounds are white or colourless because both the sodium ion and most common negative ions (except coloured ones) are colourless.
Must show: Mention of coloured negative ion (dichromate(VI)), Sodium compounds are colourless due to colourless ions
Also accept: The dichromate(VI) ion causes the orange colour in potassium dichromate(VI); sodium compounds are white or colourless because the ions present are usually colourless.
Common mistakes: Saying potassium ion itself is orange; Saying the sodium ion is coloured
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Marking points
B1 · 1 mark · States that the dichromate(VI) ion is coloured and causes the orange colour.
B1 · 1 mark · States that sodium compounds are white or colourless because their ions are usually colourless.
Worked solution
Potassium dichromate(VI) is orange because the dichromate(VI) ion is orange-coloured. Most sodium compounds are white or colourless because both sodium ions and their common negative ions are colourless.