Experiment3E

Question 1

Soda Ash

Answer 1

o For adjusting and controlling pH of water, neutralizes the acids in the water
Ex: in treatment plants and swimming pools
o Active ingredient is sodium carbonate
o Benign weak base, neutralizes acids without leading to high alkalinity of water
o Its base strength is expressed as sodium carbonate content

Question 2

Back titration requires two standard solutions

Answer 2

1. Precisely known amount of the strong acid: sulfuric acid (in stoichiometric excess)
2. Standard strong base titrant (NaOH)

Question 3

o Sulfuric acid will neutralize…

Answer 3

o Sulfuric acid will neutralize the carbonate content quantitatively upon boiling

Question 4

o The amount of residual sulfuric acid is determined by…

Answer 4

o The amount of residual sulfuric acid is determined by titrating with standard sodium hydroxide.

Question 5

• Determining Amount of Sodium Carbonate….

Answer 5

o 1. Mmols in sample: Molarity/Volume of Aliquot
o 2. Mmol in excess: molarity/endpoint volume of NaOH
o 3. 2-1= molar amount of sulfuric acid needed
o Mass in mg= n(MM)

Question 6

• Back titration is more tedious but…

Answer 6

• Back titration is more tedious but can always use a strong acid and strong base, which gives the sharpest results.

Question 7

• pH of equivalence point ____, because _____ titration

Answer 7

• pH of equivalence point ~7, because strong acid-strong base titration

Question 8

Bromocresol green

Answer 8

oFrom light yellow acid to deep blue base
oColour transition pH is from 4-6
oMinute amount of co2 will not delay the endpoint, but don’t swirl excessively because dissolving atmospheric CO2 can return indicator to yellow

Question 9

Soda ash is hygroscopic…this means?

Answer 9

• tending to absorb moisture from the air.
• must be kept in the desiccator at ALL times.
• Exposure to atmosphere must be kept at a minimum