topic 4 Flashcards
flame test procedure
place nichrome wire in conc HCL
place wire in roaring bunsen flame
place wire in sample then back into flame
observe colour
Li+
bright red
Na +
bright yellow
k+
lilac
Be 2+
no colour
mg2+
colourless
ca 2+
brick red
sr 2+
bright red
ba 2+
pale green
what could cause yello contamination
Na + presence
what causes colour
e excited to higher energy level
e relaxes back to lower energy level, emitting photon of light whose energy is equal to the energy difference between the shells e has moved from
thermal decomposition
breaking down using heat = lot of energy required to break strong bond between atoms
group 1 hydroxide solubility
soluble
group 1 sulfate solubility
soluble
group 1 nitrate solubility
soluble
group 1 carbonate solubility
soluble
group 2 hydroxide solubility
solubility increases down group
group 2 sulfate solubility
solubility decreases down group
group 2 nitrate solubility
soluble
group 2 carbonate solubility
insoluble
which chloride aren’t soluble
silver and lead chloride
which sulfates arent soluble
barium and lead sulfates
reactivity trend in group 2
reactivity increases down group
barium plus water observation
lots of bubbles
Mg plus water observation
nothing much occurs
calcium oxide plus water
CaO plus H2O —–> Ca(OH)2
why dont BeO and MgO react with water well
BeO is insoluble and
MgO isnt very soluble
Group 1 nitrates decomposition
partially decompose to form metal nitrate plus oxygen
exception lithium undergoes complete decomposition to form lithium oxide (white solid), NO2 (red brown gas) and oxygen
group1 carbonates decomposition
do not decompose
except lithium carbonate to give lithium oxide plus CO2
group 2 nitrates
all nitrates fully decompose to form metal oxide, NO2 and oxygen
becomes harder to decompose down group = more thermally stable
group 2 carbonates
decompose to form metal oxide and CO2
measuring rates of decomposition
change in mass
colorimetry
gas formation
positives and negatives of change in mass
+ = accuate measurements, mass balance to 2 d.p
- = non continuous measurement and toxic no2 produced, skin eye burns, fatal if inhaled
positives and negatives of colorimetry
+ = continous monitoring
- = product is involved in furhter reaction (2NO2 —-> N2O4)
positives and negatives of gas formation
+ = continous monitoring, toxic No2 captured
- = potential for NaOH solution to be drawn back into test tube after heating = pressure difference so glass could break
comparing MgCO3 and SrCO3 decomposition
Mg 2+ has higher charge density than sr2+
Mg 2+ strongly polarises the carbonate ion more than the sr2+
so the Mg- O bond is strengthened results in the C- O bond weakening
less energy required to break C- O bond so less energy to decompose MgCO3
group 7 MP trend and why
increases down group due to increased london forces as the molecules get larger
group 7 electronegativity trend and why
decrease as you go down the group due to increased shielding and atomic radius so weaker attraction to bonded electrons
Fluorine
pale yellow gas
chlorine
pale green gas
bromine
brown/red liquid
iodine
grey solid
violet vapour
astatine
black solid
colour of chlorine dissolved in water
pale green
colour of bromine dissolved in water
orange
colour of iodine dissolved in water
brown
colour of chlorine dissolved in organic solvent
pale green
colour of bromine dissolved in organic solvent
orange
colour of iodine dissolved in organic solvent
purple
Cl2 plus Br- —->? colour change
orange solution produced
Cl2 plus I- —->?
colour change
brown solution produced
Br2 plus I- ——>?
colour change
brown solution produced
oxidising agent strength trend group 7
decreases down group
chlorine strongest oxidising agent as it has smallest atomic radius and less shielding so able to attract incoming e more easily
reducing agent strength (donates e) trend
reducing agent strength increases down group as atomic radius get larger and increased shielding means there’s less attraction between valence e and nucleus so electrons lost more easily
test for halides procedure and results
dissolve sample
add nitric acid to remove carbonates
add silver nitrate (silver complex ions)
cl- white ppt
br- cream ppt
I- yellow ppt
how to test ppt from above
AgCl dissolves in dilute and conc NH3
AgBr dissolves in conc NH3 but not in Dilute NH3
AgI doesn’t dissolve in either dilute or conc NH3
chlorine plus water
Cl2 (g) + H2O —-> HClO (aq) + HCl (aq)
chlorine plus cold KOH
Cl2 (g) + 2KOH (aq) ——> KClO (aq) + KCl (aq) +H2O
chlorine plus hot KOH
3Cl2 (g) + 6KOH (aq) ——> KClO3 (aq) + 5KCl +5H20
HBr + NH3 —–>
HBr + NH3 —–> NH4Br
HBr +H20 —–>
HBr +H20 —–> H3O+ + Br-
metal plus halogen procedure
in fume hood so cl2 doesnt escape
iron is in wool not in blocks to increase surface area
iron heated to increase rate of reaction
halogen vapour is dry otherwise cl2 reacts with H20 to form acidic gas
excess gas allowed to escape so no pressure build up
does iodine with fe2+ ion
no bc iodine isnt strong enough oxidisng agent
Cl2 + H2 —–>
Cl2 + H2 —–> 2HCl violent reaction
Br2 plus H2
creates HBr react with calm pale blue flame
iodine plus hydrogen
produces HI and reaction is reversible
H2SO4 + NaBr —–>
H2SO4 + NaBr —–> Br2 (g) + SO2 (g) + H2O (g)
br2 is orange and so2 is acidic choking
H2SO4 + NaI —->
H2SO4 + 6NaI —-> 3 I2(s) + 2 H2O (s) + H2S(g) +NaHSO4
i2 is grey solid
s is yellow solid and H2s has egg smell
H2SO4 + NaCl —->
H2SO4 + NaCl —-> HCl + NaHSO4
test for carbonate ions
disslove carbonate
add hcl to solution
bubble gas through limewater
if carbonate present - limewater turns cloudy
equation for test carbonate
CO3- + H+ ——-> H20 + C02
test for sulphate ions
disslove compound and add dilute HCl to remove carbonate ions
add few drops of barium chloride
if sulphate ion present - white ppt of barium sulfate forms
equation for testing of sulphate ions
SO42- + Ba2+ —-> BaSO4(s)
testing for NH4+ ions
dissolve NH4+
add dilute NaOH
heat gently
IF ion present damp red litmus paper turns blue
