I am stuck on a question.
Place a small sample of the solid in a bunsen flame = Flame becomes a lilac colour.
Add 5cm3 of HCL acid = No change
Dissolve in water. Add a few drops of NaOH solution = No change
Dissolve in water. Add 2cm3 of dilute nitric acid followed by 2cm3 of silver nitrate solution. = A yellow precipitate is formed.
a) Which cation is present in compound Z? Explain how you know.
b) Which anion is present in compound Z? Explain how you know.
I gathered that the substance was potassium as potassium makes a flame go lilac. However how do i put that into these two forms?
Chemistry : Identifying Unknown Substances?
Well...
A lilac flame indicates that there are potassium ions in the substance...
Also, when a precipitate is formed from the silver nitrate test, it indicates the presence of halide ions...and the colour of the precipitate indicates the type of ions which are present.
Yellow precipitate - Iodide Ions
Creamy White Precipitate - Bromide Ions
White Precipitate - Chloride Ions
So in your case the compound you have is Potassium Iodide.
The Cation is the positively charged ions in the compound.
Anion is the negatively charged ions.
Because the bonding is ionic, electrons are effectively "transferred" from one to another. Potassium will donate its electrons to iodine, making it positively charged ions (The Cation).And iodine will now have more electrons than normal making it negative (The Anion).
Hope this helps. =]
Reply:A flame test which gives a lilac flame means that the Cation is Potassium+.
The Nitric acid and silver nitrate solution giving a yellow ppt means that the Anion is Iodide-.
Therefore the salt is Potassium Iodide (KI)
Reply:a) The cation is K+
b) The important bit to work out the anion is the last test - the adding nitric acid etc. this is the test for halide ions. As the ppte produced is yellow this indicates it is Iodide (I-)
So the compound would be : KI
beauty
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