A3 - group 2,7 qualitative analysis Flashcards
what is the trend in reactivity of group 2
atomic radius increases
shielding increases
nuclear attraction decreases
easier to remove to outer shell electrons
what is the trend in melting points down group 2
melting point decreases
ionic radius increases
charge density decreases
electrostatic attraction between ions and delocalised electrons decrease strength of metallic bonds
the trend in first ionisation energy down group 2
atomic radius increases
attraction between nucleus and valence electrons decreases
first ionisation energy decreases
what are the observations group 2 metals reacting with water
bubbles
increasingly vigorous bubbling
why is the 2nd ionisation energy larger than the 1st ionisation energy
larger because its removing the electron from an ion rather than then an atom
ions have a larger attraction between the electrons and nucleus
more energy needed
what is the use of Magnesium hydroxide
treat excess stomach acid
milk of magnesia
neutralise mouth acids in toothpaste
what is the use of calcium hydroxide
add to fields to make fields more alakaline
test for carbon dioxide
what is the use of calcium carbonate
treat excess stomach acid
what is the use Barium chloride
test for sulphate ions
what is the order for testing an unknown substance
CASH
carbonates
sulfates
halides
what is the test for ammonium
add sodium hydroxide
warm the solution
place red litmus paper near tube
litmus will blue
test for carbonate ions
add nitric acid
if carbonate ions are present bubbling will occur
test for sulphate ions
add nitric acid
add barium chloride aq
white ppt forms
test for halide ions
add nitric acid
add silver nitrate
Cl - white ppt
Br - cream ppt
I - yellow ppt
what block are halogens in
p block
what type of molecules are halogens
diatomic
describe the trend of boiling points down group 7
- down the group the group 7 molecules increase the number of electrons
- stronger london forces between molecules
- more energy is required to break them
describe why electronegativity decreases down the group
- number of protons increases down the group
- shielding increases
- atomic radius increases
- attraction between the nucleus and shared pair of electrons is weaker
why are halogens good oxidising agents
ability to donate its electrons to other species
what is the equation between water and chlorine
Cl2 + h20 —> HClO + HCl
what are the advantages of sterilising water with chlorine
prevents waterborne diseases
kills bacteria
disadvantages of sterilising water with chlorine
chlorine is toxic
can react to hydrocarbons to produce carcinogenic chlorinates hydrocarbons
what is the equation to produce bleach
NaOH with Cl2
2NaOH + Cl2 —-> NaCl + NaClO+ H2O
