Unit1Topic9 - Tests For Ions Flashcards
Definition of a salt
A salt is a compound that consists of at least two ions, a positive ion (the cation) and a negative ion (the anion) e.g. NaCl and CuSO4
Describe the process of a flame test
(1) adjust regulating collar, light the Bunsen and ensure a hot Bunsen flame
(2) dip the nichrome wire into concentrated hydrochloric acid to clean it
(3) dip nichrome wire into a solution and hold it in a roaring Bunsen flame
(4) observe the colour of the flame and identify which cation is present
(5) repeat to identify the unknown solution
Colour of flame: sodium Na+
Yellow
Colour of flame: potassium K+
Lilac
Colour of flame: calcium Ca+
Brick red
Colour of flame: barium Ba2+
Apple green
Colour of flame: copper Cu2+
Green/blue
What are flame tests used for?
To indicate the presence of various metal ions as the flame will turn a characteristic colour
Definition of a precipitate
A precipitate is an insoluble substance which sometimes forms when two aqueous solutions are mixed
Sodium hydroxide solution will form ………, coloured ……… ……… precipitates when added to different salt solutions.
Gelatinous
Metal hydroxide
Salt: magnesium chloride Mg2+
Colour of precipitate: ……
Redissolve is excess NaOH: …
White
No
Salt: aluminium chloride Al3+
Colour of precipitate: ……
Redissolve is excess NaOH: …
White
Yes
Salt: zinc (ii) chloride Zn2+
Colour of precipitate: ……
Redissolve is excess NaOH: …
White
Yes
Salt: copper (ii) chloride Cu2+
Colour of precipitate: ……
Redissolve is excess NaOH: …
Blue
No
Salt: iron (ii) chloride Fe2+
Colour of precipitate: ……
Redissolve is excess NaOH: …
Green
No
Salt: iron (iii) chloride Fe3+
Colour of precipitate: ……
Redissolve is excess NaOH: …
Red-brown
No
Ionic equation for the formation of the precipitate formed when magnesium chloride reacts with sodium hydroxide solution.
Mg2+ (aq) + 2OH- (aq) -> Mg(OH)2 (s)
Ionic equation for the formation of the precipitate formed when aluminium chloride reacts with sodium hydroxide solution.
Al3+ (aq) + 3OH- (aq) -> Al(OH)3 (s)
Ionic equation for the formation of the precipitate formed when zinc (ii) chloride reacts with sodium hydroxide solution.
Zn2+ (aq) + 2OH- (aq) -> Zn(OH)2 (s)
Ionic equation for the formation of the precipitate formed when copper (ii) chloride reacts with sodium hydroxide solution.
Cu2+ (aq) + 2OH- (aq) -> Cu(OH)2 (s)
Ionic equation for the formation of the precipitate formed when iron (ii) chloride reacts with sodium hydroxide solution.
Fe2+ (aq) + 2OH- (aq) -> Fe(OH)2 (s)
Ionic equation for the formation of the precipitate formed when iron (iii) chloride reacts with sodium hydroxide solution.
Fe3+ (aq) + 3OH- (aq) -> Fe(OH)3 (s)
We can use ……… ……… ……… to detect the presence of the halide ions.
Silver nitrate solution
Solution: sodium chloride
Halide ion present: …
Colour of precipitate: …
Ionic equation of silver halide formation: …
Cl-
White
Ag+ (aq) + Cl- (aq) -> AgCl (s)
Solution: potassium bromide
Halide ion present: …
Colour of precipitate: …
Ionic equation of silver halide formation: …
Br-
Cream
Ag+ (aq) + Br- (aq) -> AgBr (s)
Solution: sodium iodide
Halide ion present: …
Colour of precipitate: …
Ionic equation of silver halide formation: …
I-
Yellow
Ag+ (aq) + I- (aq)->AgI (s)
Describe the test for halide ions
When silver nitrate solution reacts with salt solutions containing a halide ion, a characteristic coloured precipitate of the silver halide is produced
Describe the test for sulfate ions
If sulfate ions are present a white precipitate of barium sulfate will form when the sample is reacted with barium chloride solution. This is bc barium sulfate is insoluble in water.
Give the ionic equation when testing for sulfate ions
Ba2+ (aq) + SO42- (aq) -> BaSO4 (s)
Equation for testing for carbonate ions
acid + metal carbonate -> salt + water + carbon dioxide
The presence of carbon dioxide gas is tested by…
Bubbling it through limewater. If carbon dioxide is present the limewater will turn cloudy.
Observations when testing for carbonate ions
Bubbles of gas
Solid disappears
Limewater turns cloudy
