How the concentration of acid (HCl) can be determined by titrating it using base (NaOH)?
1- Phenolphthalein (color indicator).
2- Sodium hydroxide (NaOH) concentration of 0.5 molar.
3- Hydrochloric acid (HCl), with unknown concentration.
2- Pipette (uncertainty ï¿½0.05cm3).
3- Burette (uncertainty ï¿½0.05cm3).
4- PH meter.
5- Gloves, lab coat and plastic eye protection.
1- Add a known volume of HCl using pipette in the flask.
2- Add 2 drops of phenolphthalein in the flask using the pipette.
3- Shake the flask until the color changes to red.
4- Start to add NaOH on the HCl, drop by drop.
5- After each drop shake the flask to accomplish the mixing of the acid with the base.
6- Take readings of PH value using the PH meter, after each drop.
7- When HCl color turns to blue, immediately stop adding NaOH, this indicates the neutralization point.
8- To be sure that HCl is neutralized add few drops of NaOH on HCl.
9- Repeat the experiment to obtain more accurate data.
Data collection and processing:
The table below shows the values of PH recorded over the five trials and indicates the neutralization point at a specific volume of NaOH added:
(1.0) table shows the data collected during the trials
Below is the table produced after changing the volume of NaOH to the better measurable unit, also after adding the PH values for each volume added of NaOH then divide them by the number of trials to come out with the average PH value.
(1.1) table showing the processed data
Average PH value
The graph below shows the graphical relationship between volume of NaOH added in dm^3 versus average PH value:
As calculated at the neutralization point which is nearly equal to 7, the volume of NaOH added is approximately 0.0250 ï¿½ (0.0000450) dm^3
To calculate the concentration of base, it is most desirable to use the equation below:
Now substituting the concentration, also volume of the acid (HCl) and the volume added of the base (NaOH), then:
Conclusion and evaluation:-
– It is concluded that the concentration of HCl in the lab that all the trials occurred in is 0.6 Molar.
– It is concluded that titration of acid using base must be repeated many times to accomplish more accurate results.
– The usage of a digital PH meter may affect the accuracy of the data, as it produces systematic errors.
– The volume of phenolphthalein may play a role on the volume of HCl in the flask.
– Concentration of NaOH may not be exactly 0.5 molar as there might be impurities.
– The PH value as shown from the data collected is changing at a high manner near to the neutralization point; therefore it is not easy to know the precise concentration of NaOH.
– Calculating the PH value to indicate the rate of reaction, is not precise, because the PH has a logarithmic function not a linear function, then there will be a small change in the PH value while there will be big change of H+.
– Using a digital instrument to drop exactly 1.0 cm^3 in each drop.
– Using a base with primary standard to titrate HCl may be more accurate to indicate the value of it is concentration.
– Using a pipette with less uncertainty may help in improving the data collected.
– Using a burette with less uncertainty can determine more accurate results.