Student 3 : No need to restart, since NaOH is to be in
excess anyway.
Student 4 :
You need either the molarity (if ester solution was used)
or density (if pure ester was used), to work out the moles of ester
to be hydrolyzed.
The stoichiometry for base promoted hydrolysis of ester is 1 :
1.
From molarity and volume of NaOH used, you can determine if the
ratio of NaOH to the ester is more than one (ie. excess NaOH) or
less than one (ie. excess ester).
I asked a teacher for help, but they told me we didnt need to do
these 2 Q but I want to do them anyway.
QUESTION
-
a student 3 added 20cm3 of the
2moldm-3 NaOH instead of 10cm^3 by accident. should they have
started again? why
AND student 4 only added 5cm3 of the
NaOH instead of 10cm3. Show by calculation that student 4 did not
have an excess of sodium hydroxide
Hydrolsis ester -
PROCEDURE
1.Add 2cm3 of methylbenzoate flask,
record mass
Add 10cm3 dilute 2.0moldm-3 NaOH
solution (in excess), about 10cm3 of ethanol and anti bump
granules. fit the water condesner on
2. heat flask gently without allowing
contents to boil for about 5 min. and then boil gently under reflex
for futher 15 min
3. allow contents flask to cool
remove condenser and decant solution from antibump graniles into a
beaker. add 10 drops methyl orange indicator and acidify with 2.0
moldm-3 HCl. filter product under reduced pressure
4. recrstyallise product - dissolve
solid in minim amount of boiling water to allow to cool slowly,
when cool filter purified product under reduced pressure and allow
dry in air on filter paper
5. dry sample of product by pressing
between filter papers and determine mpt (which is greater than 100
degrees) record value
6. weigh dry product and record
mass