8B.6 Flashcards
what is a flame test
a very simple chemical test used to identify a cation (charged) in chemical compounds
how do you run a flame test
- wear a lab coat and safety goggles, within a fume cupboard light a bunsen flame
- using a dropper add a few drops of HCl into the metal compound and mix them together for them to begin to dissolve.
- take a clean metal wire (platinum and nichrome) or a silica rod and dip it into the mixture to obtain a sample of the compound
- hold the end of the wire above the flame and observe the colour
what is the reason for using HCl in the compound
because metal chlorides are more volatile than any other salt so we would have better results
what is the problem with flame tests
- many compounds contain small sodium compound as an impurity, the intense light of sodium can hide other colours
- describing colours with words is subjective
what colour does Li form
red
what colour does Na form
yellow/orange
what colour does K form
lilac
what colour does Rb form
red/purple
what colour does Cs form
blue/violit
what colour does Mg form
no colour
what colour does Be form
no colour
what colour does Ca form
brick red
what colour does Sr (strontium) form
crimson red
what colour does Ba form
apple green
what colour does Cu form
blue-green (even thou transitional metal)
what does groud state mean?
it is a term used to describe an atom with all its electrons in their lowest possible energy level
what is an exited state
when an electron in a ground state is heated and goes up to a higher energy level
how are colours shown during flame tests
when a cation is heated the electrons would absorb energy and go to a higher energy level and become in an excited state, but the electron then returns to its original state. and energy is released, if the energy corresponds to specific radiation in the visible light spectrum the characteristics of that light is shown
why does Mg have no colour
because the electron transition in Mg corresponds to a wavelength outside the visible light spectrum
what are the tests for ammonium ions s
- add sodium hydroxide solution plus warmth to an ammonium mixture the earth causes ammonia gas to be released, ammonia can be detected by smell but using a damp litmus paper turns blue is an easy chemical test
- we can add hydrogen chloride gas (from concentrated HCl acid) to ammonia mixture and white smoke of ammonium chloride forms
what is the net ionic equation for ammonium and sodium hydroxide
NH4^+ + OH^- ——–> NH3 + H2O
what is the equation between ammonia and hydrogen chloride gas
NH3 + HCl ——> NH4Cl
