F4 Chem: Volumetric Analysis

1. (not too good at this part[stand. soln.]; if there are any mistake please point out)
H2SO4 -> absorb H2O
NaOH -> absorb CO2
NH3 -> volatile

2.
rinse by the solution only
as you will wash the apparatus
water left will dilute the solution u put in it
=> rinse by solution => keep molarity (conc.

3.
the point that u can observe the sharp colour change
=> usually already slightly acidic/alkaline
(we cannot recognize the equicalent point)

4.
Methyl orange: change colour in pH 3-4 (only can be meet by strong acid
Phenolphthalein: change colour in pH 8-10 (only can be meet by strong alkaline
=>my method: if u have strong acid in the reaction => methyl orange is ok
+ if u have strong alkaline in the reaction => phenolphthalein is ok

5.
u should know the mechanism first
in reaction
2NaOH + H2SO4 -> 2H2O + Na2SO4
there are 2 steps
1. H2SO4 + NaOH -> NaHSO4 + H2O
2. NaHSO4 + NaOH -> Na2SO4 + 2H2O
if there are excess H2SO4 -> not enough NaOH to form normal salt => mainly NaHSO4
if there are excess NaOH -> enough NaOH to form normal salt => mainly Na2SO4

2012-03-08 18:30:29 補充：
conical flask must not be rinsed by the solution!

the solution in conical flask can be calculated in this way...
Conc. x 25/1000 dm^3 = no of mole of substance in conical flask

if we use solution to rinse it
no. of mole will increase
the volume is no longer by 25cm^3 then

therefore
water only!

2012-03-15 22:39:56 補充：
thank you= =...

1.
NaOH can also absorb atmospheric CO2 readily.
NH3 is not volatile; it's a GAS at room conditions (which is readily liquefied by compression).