Analyze Rough Titration Results

Calculations Overview

Now that you have finished the first titration, it's time to analyze the data. The information that we need for this analysis are the mass of the sodium carbonate, the initial buret volume, and the final buret volume. To calculate the molarity of the dilute HCl unknown solution, you need to calculate the number of moles of HCl that reacted with the sodium carbonate, which can be done through stoichiometry. You will also need to calculate the volume of dilute HCl solution used.

Moles HCl Reacted

Although it takes two moles of HCl to fully neutralize sodium carbonate, the indicator changes color to greenish-grey at the first end point. In other words, given how the titration was set up and performed, you will use a 1:1 stoichiometric conversion ratio.

N A 2 C O 3, aqueous, and H C L, aqueous, yield H N A C O 3, aqueous, and N A C L, aqueous.

To start, convert the mass of sodium carbonate into moles of sodium carbonate. This can be done by dividing by the molar mass of sodium carbonate (105.9888 g/mol) or by multiplying by the inverse (1 mol / 105.9888 g). The number of moles of sodium carbonate can then be converted into moles of reacted HCl by using the molar conversion ratio (1 mol Na₂CO₃:1 mol HCl).

Moles H C L reacted equals mass N A 2 C O 3 , times, 1 mole N A 2 C O 3 over 105.9888 g N A 2 C O 3, times, 1 mole H C L over 1 mole N A 2 C O 3.

Moles H C L reacted equals 0.0923 grams N A 2 C O 3 , times, 1 mole N A 2 C O 3 over 105.9888 g N A 2 C O 3, times, 1 mole H C L over 1 mole N A 2 C O 3.

Moles H C L reacted equals 8.71 times ten to the negative fourth power mols H C L.

Volume HCl Used

To calculate the volume of HCl used, take the final buret volume and subtract the initial buret volume.

Volume used equals volume final minus volume initial.

Calculating Molarity

To calculate molarity of the diluted HCl solution (the solution in the buret), take the moles of solute (HCl in this case) and divide by the volume of solution (volume used).

Molarity equals moles solute over volume of solution, in liters.

Molarity equals 0.109 moles over liters equals 0.109 molar.

Determining the Original Molarity

To calculate the molarity of the concentrated HCl unknown (the solution you added to the 250.00 mL volumetric flask), you can use the dilution equation,

M concentrated times v concentrated equals m dilute times v dilute.

where M corresponds to molarity and V corresponds to volume. Furthermore, V_concentrated corresponds to the intial volume (5.000 mL) of the original unknown that was used to make the diluted solution, and V_dilute corresponds to the volume that the solution was diluted to (250.00 mL).

M concentrated equals the quantity m dilute times v dilute divided by v concentrated.

M concentrated equals the quantity 0.109 molar times 250.00 milliliters divided by 5.000 milliliters

Additional Notes

Keep in mind that this first trial is a rough titration. It might not be an accurate result. Additionally, the solution eventually turned a pale yellow at the end. Ideally the indicator should change from blue to a green/greyish color. The fact that it turned yellow indicates that too much HCl solution was added to the flask and the endpoint was overshot. Given this information, it is likely that the true concentration of the original HCl unknown is less than 5.45 M.

Continue to precise titration

Page updated

Report abuse