Group 1, the alkali metals Flashcards
describe the physical appearance of alkali metals
soft, easily cut and shiny
what is the oxidation state of Group 1 metals in their compounds ?
+ 1
what is the reaction with water - lithium
reacts steadily with cold water given off
what is the reaction with water - sodium
melts and bubbles
what is the reaction with water - potassium
melts and bubbles
write the balanced equation for the reaction between lithium and water
2Li (s) + 2H2O -> 2LiOH (aq) + H2
(g)
write the balanced equation for the reaction between potassium and chloride
2K (s) + CI2 (g) -> 2KCI (s)
describe the trend in solubility of the hydroxides down Group 1
increases down the group
strong base - define
they are fully ionised in water giving solutions that contain OH-ions
what are the two unusual features of Group 1 carbonates
dissolve in water
do not decompose on heating except lithium carbonate
describe what happens when sodium and potassium nitrates are heated
first melt and then on stronger heating start to decompose, giving of oxygen, only decompose till nitrates
write the balanced equation for the thermal decomposition potassium nitrate and oxygen
2KNO3 (s) -> 2KNO2 (s) + O2 (g)
write the balanced equation for the thermal decomposition lithium nitrate into lithium oxide, nitrogen dioxide and oxygen
LiNO3 (s) -> 2LiO (s) + 4NO2 (g) + O2 (g)
give 3 reasons why compounds of sodium and potassium are widely used as chemical reagents
- ions of alkali metals are unreactive so they act as spectator ions
- most sodium and potassium compounds are soluble in water
- the ions of alkali metals are colourless in aqueous so they o not hide or interfere with colour changes
flame colours
lithium
sodium
potassium
lithium - crimson
sodium - yellow orange
potassium - lilac
describe how to conduct a flame test
- moisten a nichrome wire with concentrated HCI
- dip the wire into the sample
- hold the wire in a blue Bunsen burner flame
why do we dip the nichrome wire into HCI before dipping into the sample ?
solid salt is converted into more volatile metal chlorides - turns solid to gas so easier to observe
what does not burn during flame tests ?
ionic compounds such as NaCI
explain the origins of flame colour
thermal energy from excites the outer electrons of the metal ions promoting them to higher energy levels drop - radiation emitted in visible region of the spectrum
suggest why Be and Mg produce no flame colour
radiation emitted is not visible region of the spectrum
is group 1 carbonates more/less thermally stable than group 2 compounds ?
more
what does nitrates break down into in group 1 compounds ?
nitrates and oxygen except LiNO3 decomposes to form Li2O,NO2 and O2
nitrate ion
NO3-
Nitrite ion
NO2 -1
how do we get different colours ?
- electrons in the shells move to higher energy levels as they absorb energy from the flame
- when they drop back down to lower energy level light is released
- different colours in energy levels determines the wavelength of light released
