Flame Tests & Metal Hydroxides Flashcards
What are flame tests used for?
Indicate the presence of certain metal ions
How do you conduct a flame test?
Dip a clean wire loop into a sample of the compound being tested, then place the loop into the edge of a blue flame from a Bunsen burner
What colour do lithium ions turn the flame? (Li+)
Red
What colour do sodium ions turn the flame? (Na+)
Yellow
What colour do potassium ions turn the flame? (K+)
Lilac
What colour do calcium ions turn the flame? (Ca2+)
Orange-red
What colour do copper ions turn the flame? (Cu2+)
Blue-green
What is an ion?
Electrically charged particle, formed when an atom or molecule gains or loses electrons
What does adding dilute sodium hydroxide (NaOH) identify
certain positive ions in solution (cations)
What coloured precipitate do copper ions produce? (Cu2+)
Blue precipitate
What coloured precipitate do iron (|||) ions produce? (Fe3+)
Brown precipitate
What coloured precipitate do iron (||) ions produce? (Fe2+)
Green precipitate
Which ions produce a white precipitate?
Aluminium (Al3+), calcium (Ca2+), magnesium (Mg2+)
What happens when you add excess sodium hydroxide to aluminium hydroxide?
Redissolves
What happens when NaOH is warmed with ammonium ions (NH4+)
ammonia gas is produced, which is alkaline so it turns damp red litmus paper blue.
What is a precipitate?
A suspension of particles in a liquid formed when a dissolved substance reacts to form an insoluble substance
What happens when there is a mixture of metal ions in a flame test?
One ion will mask the other
Test for carbonates
Carbonates react with dilute acids to form carbon dioxide gas. Carbon dioxide can be identified with limewater.
Test for halides
Halide ions in solution produce precipitates with silver nitrate solution in the presence of dilute nitric acid. Silver chloride is white, silver bromide is cream and silver iodide is yellow.
Test for sulfates
Sulfate ions in solution produce a white precipitate with barium chloride solution in the presence of dilute HCI.
What are instrumental methods
Instrumental methods are accurate, sensitive and rapid.
What is flame emission spectroscopy
Flame emission spectroscopy is an example of an instrumental method used to analyse metal ions in solutions.
The sample is put into a flame and the light given out is passed through a spectroscope. The output is a line spectrum that can be analysed to identify the metal ions in the solution and measure their concentrations.
What is the ionic equation for metal ions with sodium hydroxide solution?
Cu2+(aq) + 2OH-(aq) → Cu(OH)2(s)
Change to 3+, 3, 3 for a 3+ metal ion
Change Cu to the element you are using
