Carbonate Analysis

PURPOSE

To determine the formula mass and identity of an unknown carbonate by back titration.

PROCEDURE

I.  Weigh out about 0.15 gram (±0.001g) of unknown group IIA carbonate into 250 mL Erlenmeyer flask.

A.   Pipet 10.00 mL standardized ~0.5 M HCl with volumetric pipet into 250 mL Erlenmeyer flask with unknown.

1.   Swirl flask until fizzing stops and solid is dissolved.

a)     Break up chunks with stir rod.

b)     Rinse off stir rod with D.I. water.

(1)   If fizzing does not stop add 10.00 more mL of HCl solution

2.     Add 3 drops of bromophenol blue indicator

a)     If indicator does not turn yellow add 5.00 more mL of HCl solution.

3.     Titrate with standardized 0.26 M NaOH solution to the endpoint ( solution goes from yellow to purple).

II. Repeat step I for 2 more samples of the unknown.

III.    Calculate the formula mass of the unknown carbonate

IV.   Determine the identity of the unknown carbonate.

CONSTANTS

DATA

CALCULATIONS

Moles HCL initially =

Moles NaOH added =  

Moles excess HCL = moles NaOH added = _________mol HCL excess

Moles HCL reacted with carbonate =

(___________mol HCl initially) - (_______mol HCL excess)

Moles carbonate ion =

Moles unknown = Moles IIA cation  = ______moles carbonate

Formula mass carbonate =

(_______g unknown initially)/(_______moles unkown) = _______g/mol

Mass carbonate = = ____g carbonate ion

Mass IIA cation =

(_______g unknown) - ( _______ g carbonate ion) = _______g IIA cation

Molar Mass IIA cation = (_______g IIA cation)/(_____moles IIA cation) = ______g/mol