4.7 Cation Tests
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what is a cation
a positive ion (in groups 1-3)
explain a flame test [3 points]:
• when heated, some electrons are excited to higher energy levels • when they fall back to their initial levels, energy is emitted • this energy is sometimes seen as visible light
what is the colour of a flame determined by
a combination of all the energy emissions
give an explanation for a flame test producing colour
electrons are excited by different amounts [1] into different energy levels [2] and they drop back at different times [3]
give
give the flame colour for Na+
yellow/orange
describe the type of flame when Na+ is heated
lasting
give the flame colour for K+
Lilac
give the flame colour for Ca2+
orange-red OR brick-red
give the flame colour for Li+
crimson red
give the flame colour for Ba2+
Pale/apple green
give the flame colour for Sr2+
Scarlet red
give the flame colour for Cu2+
blue-green
describe the method to carry out a cation flame test [4 points]
• dip nichrome wire in HCl • heat nichrome wire over bunsen • dip Nichrome wire in sample • heat at tip of inner blue cone of bunsen
why is a nichrome wire used [2 points]
• doesn’t produce a coloured flame • rather resistant to heat
why is the nichrome wire dipped in HCl
to make sure it is clean
describe the type of flame used when carrying out a flame test
non-luminous
why is a non-luminous flame used
as it is not coloured
give the name of the compound used in ppt tests to determine the sample
Sodium Hydroxide, NaOH
what colour does the ppt CuSO4 go when reacted with NaOH
blue
give the name of the PPT when CuSO4 and NaOH are reacted together
Cu(OH)2
what is the colour of the PPT Cu(OH)2
blue
what is the colour of the PPT Fe(OH)2
Green
what is the colour of the metal PPT Fe(OH)3
brown