qualitative investigation Flashcards
Recording observations refers to
writing down what you can see, hear or smell or feel (e.g. temperature).
For example: “fizzing, bubbles or effervescence” is an observation whereas “gas given off” is not.
If asked to describe the appearance of a substance you should
describe both the colour and state (solid, liquid or gas).
Use key terminology such as “reacts more violently” or “produces a precipitate much quicker” to describe
gradation in reactions with similar observations.
Note that a precipitate is a
a solid that has been formed in the reaction between two solutions.
Test for Metal Cations
If a precipitate is formed from either NaOH or aqueous ammonia then the hydroxide is ….
Zinc for example reacts as such:
ZnCl2(aq) + 2NaOH(aq) →Zn(OH)2 + H2O(l)
Ca2+ ions can be distinguished from Zn2+ and Al3+ as….
Zn2+ ions can be distinguished from Al3+ ions as….
Most transition metals produce….
Test for Metal Cations
If a precipitate is formed from either NaOH or aqueous ammonia then the hydroxide is insoluble in water.
Zinc for example reacts as such:
ZnCl2(aq) + 2NaOH(aq) →Zn(OH)2 + H2O(l)
Ca2+ ions can be distinguished from Zn2+ and Al3+ as calcium hydroxide precipitate does not dissolve in excess NaOH but both zinc hydroxide and aluminium hydroxide do.
Zn2+ ions can be distinguished from Al3+ ions as ZnOH dissolves in excess aqueous ammonia but Al(OH)3 does not.
Most transition metals produce hydroxides with distinctive colours.
Be sure to distinguish between the term “colourless” and “clear”.
A solution that loses its colour has become…
A clear solution is one that….
Solutions can be clear and have colour e.g: dilute copper sulphate.
Be sure to distinguish between the term “colourless” and “clear”.
A solution that loses its colour has become colourless.
A clear solution is one that you can see through such as water.
Solutions can be clear and have colour e.g: dilute copper sulphate.
The flame test is used to…
The flame test is used to
A small sample of the compound is placed on an unreactive metal wire such as nichrome or platinum.
The colour of the flame is observed and used to identify the metal.
identify the metal cations by the colour of the flame they produce.
flame tests
A small sample of the compound is placed on an
The colour of the flame is observed and used to identify the
an unreactive metal wire such as nichrome or platinum.
metal.
Results
Red =
Yellow =
Lilac =
Orange-red =
Blue-green =
Bright white =
Results
Red = Li+
Yellow = Na+
Lilac = K+
Orange-red = Ca2+
Blue-green = Cu2+
Bright white = Mg2+
Sources of error in flame tests
It can be difficult to determine a colour in bright flames.
why
Impurities in metal ion solutions can alter results.
The solution must have a high concentration of the metal ions.
Test for Anions
Tests for Gases
It is easy to confuse the tests for hydrogen and oxygen.
Try to remember that a ligHted splint has a
while a glOwing splint has
It is easy to confuse the tests for hydrogen and oxygen.
Try to remember that a ligHted splint has a H for Hydrogen, an O for Oxygen.
