experiment 7: determination of chloride and sulfate by precipitation titration

Question 1

title of the experiment

Answer 1

determination of chloride and sulfate by precipitation titration

Question 1

avoid contact with _____ as it is a known carcinogen.

Answer 1

potassium chromate

Question 2

it can can cause staining of skin and fabric.

Answer 2

silver nitrate

Question 3

it is harmful by inhalation and toxic if swallowed.

Answer 3

barium chloride

Question 4

what pipette will be used and the purpose

Answer 4

volumetric pipette
serological pipette

Question 5

what are the reagents used

Answer 5

std. BaCl2· 2H2O
Pre-dried Std. AgNO3
Methanol
Unk. Chloride solution
Unk. Sulphate Solution
5% K2CrO4
5% HCl
0.20% Alizarin red S.

Question 6

a titration which involves the formation of a precipitate

Answer 6

precipitation titration

Question 7

how can anions be analyzed

Answer 7

anions - chloride and sulfate
analyzed by precipitating as silver chloride and barium sulfate

Question 8

what indicator is used

Answer 8

chromate

Question 9

what is the unknown sample

Answer 9

amt. of chloride ion present in an unknown sample

Question 10

how can be the unknown sample can be determined

Answer 10

by titration with silver ions

Question 11

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 …

Answer 11

mohr method

Question 12

what is the endpoint of the first appearance of precipitate

Answer 12

reddish-brown precipitate

Question 13

how does silver ions form precipitate

Answer 13

with both chloride and chromate ions

Question 14

it has a greater solubility

Answer 14

silver chromate

Question 15

all of the _____ must be consumed first before a reddish-brown precipitate of silver chromate can be seen

Answer 15

chloride ions

Question 16

why des the pH must be kept at 7 - 10 pH

Answer 16

to prevent formation of chromic acid and precipitation of silver hydroxide

Question 17

the amount of sulfate ion in an unknown sample can be determined by titration with barium ions using _______

Answer 17

alizarin red S as the indicator

Question 18

what is the end point of the unknown sample

Answer 18

pale pink

Question 19

this method produces results which are comparable to that of gravimetry. the net ionic equation is:

Answer 19

Ba^2+ + SO4^2- ——-> BaSO4

Question 20

what temp and for how long shld u dry primary standard silver nitrate at

Answer 20

110 degree Celsius
1hr

Question 21

weigh how much of dry silver nitrate

Answer 21

1.1500g - 1.2000

Question 22

after weighing the silver nitrate, where do u transfer it

Answer 22

to a 250ml volumetric flask and dissolved in water then invert the flask thrice
then transfer to cleared colored glass bottle

Question 23

weigh how much of barium chloride dilhydrate standard

Answer 23

3.0500g - 3.0800g

Question 24

after weighing the barium chloride dilhydrate standard, where do u transfer it

Answer 24

to a 250ml beaker
add 170ml distilled water
3-4 drops of 5% HCI
transfer to volumetric flask
invert thrice
transfer to clear bottle

Question 25

how to adjust the pH to 3-4 of barium chloride dilhydrate

Answer 25

by adding 5% HCI

Question 26

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

Answer 26

volumetric pipette
25

Question 27

titrate the solution with the standard silver nitrate until the first appearance of _______

Answer 27

reddish brown color

Question 28

Rinse the burette twice with distilled water and twice with ____ mL standard silver nitrate solution.

Answer 28

5

Question 29

Record the initial and final volume of silver nitrate solution and calculate the concentration of chloride in _____.

Answer 29

ppm

Question 30

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:

Answer 30

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

Question 31

indicator for
silver ions:
barium ions:

Answer 31

silver ions: chromate
barium ions: alizarin red S