HCl lahus (0)

Aim of the work
The determination of the concentrations of acid and base solutions through titration .
Used compounds
HCl solution with an unknown concentration . NaOH solution with a known accurate concentration, indicators phenolphthalein (ff/pp) and methyl red (mp/mr).
Equipment
Conical flasks (250 cm3), 2 burettes (25 cm3), pipette (10 cm3).
Procedure
A. Determining the concentration of a hydrochloric acid solution through titration
1. To determine the concentration of the acid solution take the NaOH solution with a known concentration (the standard solution) and pour it into the burette (α in figure 2.2). See that there are no air bubbles near the tip. Fill the burette until the 0-point of the scale .
When measuring the level of the solution keep your eyes at the same level with the liquid level. The lower edge of the liquid level has to be at the 0 calibration mark (see figure 2.1). Figure 2.1
Work solutions are the solutions which are going to be used for pipetting or added from the burette. This step is necessary to ensure that the measuring of concentration is not changed by water or solvent of another concentration.
2. Use the pipette pump (c) on the pipette (figure 2.2, b). With the pipette, measure 10 cm3 of acid into a clean conical flask and add 2-4 drops of indicator ff (phenolphthalein).
3. Next let the base (NaOH) solution drip dropwise from the burette into the acid (HCl) by pressing the glass ball in the rubber tube at the bottom of the burette. Do this until the colour of the solution turns red with the adding of one drop . Then the acid is neutralized. Figure 2.2
4. Read the level of the base in the burette with a 0.05 cm3 accuracy . This reading will show the amount of base needed to neutralize the acid solution in cm3. Repeat the experiment until the volumes of NaOH needed do not differ more than 0.1 cm3 (at least 3 times ). Find the arithmetic average from these results .
Calculation
1) Calculate the molar concentration (equation 2.2) of HCl through the amount of NaOH solution needed for titration.
B. Determining the concentration of the control solution through titration
1. The control solution is the base (NaOH) solution in the graduated volumetric flask. The burette for the hydrochloric acid (HCl) must be thoroughly rinsed with small portions of the acid solution. The concentration of the acid solution was determined in the first part of the experiment. After rinsing fill the burette with the same acid solution to the 0-point of the measuring scale.
2. To titrate the control solution pipette 10 cm3 of the control solution into a flask and add 2-4 drops of indicator mp (methyl red). Titrate with the HCl solution until the yellow solution (NaOH + indicator) turns red. Repeat the experiment three times. Find the arithmetic average from the results.

Results

Volumes of NaOH to neutralize the solution:
Volume of acid in experiment:
Concentration of used solutions:
Volumes of HCl till the change of colour of the solution ( controll solution no.2 + indicatior):
Volume of controll solution in experiments:
Actual molarity of controll solution:

Calculations

Reaction:
Calculations of part A:
1) Calculation of the molar concentration of HCl through the amount of NaOH solution needed for titration:
Calculations of part B:
1) Calculation of the molar concentration of the control solution:
2) Finding the mass of the dissolved NaOH in the graduated volumetric flask:
Molar mass of NaOH is:
3) Calculation of the systematic error for the experiment:

Conclution

Using titration we can calculate the consentrations of incredients (acid/base). Through this experiment I got the molar concentration. Systematic error of this experiment is 9,12%. As it is less than 10% we can consider it OK. To decrease the systematic error I should monitor more closely the titration process and read results more punctually.