Determination of Na2Co3 in an Unknown.

Purpose: The purpose of this was to determine the concentration of sodium carbonate in an unknown sample by titration. The solution of hydrochloric acid was prepared and standardized using Na2CO3.

Observations:

Week 1: Standardizing hydrochloric acid using sodium carbonate with bromocresol green indicator

Table 1: Titration of sodium carbonate using hydrochloric acid

Trial | Mass of Na2CO3 (g) | Burette Reading (mL) | Final Volume of HCl (mL) | | | Initial | Final | | 1 | 0.2123 | 0.00 | 42.34 | 42.34 | 2 | 0.2195 | 0.00 | 47.24 | 47.24 | 3 | 0.2049 | 0.00 | 26.65 | 46.65 | After Boiling | 1 | | 31.52 | 32.22 | 0.70 | 2 | | 29.34 | 30.61 | 1.27 | 3 | | 30.61 | 31.52 | 0.91 |

Week 2: Determination of Sodium Carbonate in the unknown via titrating using bromocresol indicator

Sample number: SC 8

Table 2: Titration of the unknown using hydrochloric acid

Trial | Mass of unknown (g) | Burette reading (before boiling) | Final Volume of HCl (mL) | | | Initial | Final | | 1 | 0.5065 | 0.00 | 30.25 | 30.25 | 2 | 0.5007 | 0.00 | 28.72 | 28.72 | 3 | 0.5026 | 0.00 | 29.01 | 29.01 | After Boiling | 1 | 29.01 | 29.49 | 0.48 | 2 | 29.49 | 29.91 | 0.42 | 3 | 29.91 | 30.21 | 0.30 |
Calculations:

Mass % of Na2CO3 in the unknown for trial 1

Na2CO3 + 2HCl ---> 2NaCl + H2O + CO2

Molar mass Na2CO3= 105.99g/mol

Mass of Na2CO3= 0.2123g

Moles of Na2CO3= 0.2123g/105.99g/mol

Moles of Na2CO3= 2.003 x 10-3 moles

Mole-to-Mole Ratio

1 Na2CO3: 2 HCl

Moles of HCl= 2 x 2.003 x 10-3moles

Moles of HCl= 4.006 x 10-3

Molarity of HCl= (4.006 x 10-3)/0.04304
Molarity of HCl= 0.09308M

Moles of HCl= 0.09308M x 0.03073L
Moles of HCl= 2.8601 x 10-3 moles

Moles of Na2CO3 = (2.860 x 10-3 moles) / 2
Moles of Na2CO3 = 1.4301 x 10-3

Mass of Na2CO3== 1.4301 x10-3 x 105.99g/mol
Mass of Na2CO3= 0.152g

Mass % Na2CO3= (0.1523g/0.5065) x100
Mass % Na2CO3= 30.07%

Results:

Trials | %

References: * http://antoine.frostburg.edu/chem/senese/101/acidbase/indicators.shtml * Analytical Chemistry 1 Lab Manual