experiment 7: determination of chloride and sulfate by precipitation titration Flashcards
title of the experiment
determination of chloride and sulfate by precipitation titration
avoid contact with _____ as it is a known carcinogen.
potassium chromate
it can can cause staining of skin and fabric.
silver nitrate
it is harmful by inhalation and toxic if swallowed.
barium chloride
what pipette will be used and the purpose
volumetric pipette
serological pipette
what are the reagents used
std. BaCl2· 2H2O
Pre-dried Std. AgNO3
Methanol
Unk. Chloride solution
Unk. Sulphate Solution
5% K2CrO4
5% HCl
0.20% Alizarin red S.
a titration which involves the formation of a precipitate
precipitation titration
how can anions be analyzed
anions - chloride and sulfate
analyzed by precipitating as silver chloride and barium sulfate
what indicator is used
chromate
what is the unknown sample
amt. of chloride ion present in an unknown sample
how can be the unknown sample can be determined
by titration with silver ions
this method:
The amount of chloride ion present in an unknown sample can be determined by titration with silver ions using chromate as the indicator. is called …
mohr method
what is the endpoint of the first appearance of precipitate
reddish-brown precipitate
how does silver ions form precipitate
with both chloride and chromate ions
it has a greater solubility
silver chromate
all of the _____ must be consumed first before a reddish-brown precipitate of silver chromate can be seen
chloride ions
why des the pH must be kept at 7 - 10 pH
to prevent formation of chromic acid and precipitation of silver hydroxide
the amount of sulfate ion in an unknown sample can be determined by titration with barium ions using _______
alizarin red S as the indicator
what is the end point of the unknown sample
pale pink
this method produces results which are comparable to that of gravimetry. the net ionic equation is:
Ba^2+ + SO4^2- ——-> BaSO4
what temp and for how long shld u dry primary standard silver nitrate at
110 degree Celsius
1hr
weigh how much of dry silver nitrate
1.1500g - 1.2000
after weighing the silver nitrate, where do u transfer it
to a 250ml volumetric flask and dissolved in water then invert the flask thrice
then transfer to cleared colored glass bottle
weigh how much of barium chloride dilhydrate standard
3.0500g - 3.0800g
after weighing the barium chloride dilhydrate standard, where do u transfer it
to a 250ml beaker
add 170ml distilled water
3-4 drops of 5% HCI
transfer to volumetric flask
invert thrice
transfer to clear bottle
how to adjust the pH to 3-4 of barium chloride dilhydrate
by adding 5% HCI
in the determination of chloride AND sulfate in the unknown sample, use what type of pipette to transfer ____mL of unknown chloride sample into a 250ml Erlenmeyer flask
volumetric pipette
25
titrate the solution with the standard silver nitrate until the first appearance of _______
reddish brown color
Rinse the burette twice with distilled water and twice with ____ mL standard silver nitrate solution.
5
Record the initial and final volume of silver nitrate solution and calculate the concentration of chloride in _____.
ppm
in Determination of Sulfate in the Unknown Sample,
add how much of
unknown sulfate sample:
distilled water:
methanol:
alizarin red S. indicator:
5% HCI:
into a ______
endpoint color:
unknown sulfate sample: 25mL
distilled water: 25mL
methanol: 40mL
alizarin red S. indicator: 2drops
5% HCI: dropwise until color of solution turns yellow
into a 250mL Erlenmeyer flask
endpoint color: pale pink
indicator for
silver ions:
barium ions:
silver ions: chromate
barium ions: alizarin red S
