Hydrochloric acid (HCl) is a common acid used in the laboratory to make acidic solutions. Aqueous HCl solutions show low pH values because HCl is a strong acidic compound. You can easily check this by using a pH meter. In theoretically, pH value can be found by substituting concentration of HCl in the pH equation.
In this tutorial we will cover following sections.
|Concentration (mol dm-3)||pH|
According to the data you know, you can use a suitable calculator to calculate pH value.
you can enter the concentration of HCl acid in mol dm-3 and check the pH value.
Note: This online calculation is not suitable for very dilute solutions of HCl (such as 0.0000005 mol dm-3) because, those solutions give very low H+ ion concentrations. In those cases, pH value is very close to the neutral value of seven.
Because HCl is a strong acid, it dissociates completely to H+ and Cl- ions in the water.
According to the stoichiometric ratios, H+ concentration equals to the HCl concentration. Therefore, we can directly substitute HCl concentration to pH equation.
We can write above equation for HCl as below.
pH = -log10[HCl(aq)]
You can see, 0.1 mol dm-3 HCl solution is strong acidic solution because pH value is well below seven.
In the lab, there are concentrated HCl bottles. H+ concentration is very high in those solution. Therefore, pH value of these concentrated HCl bottles are very low values (negative pH values).
Concentration of laboratory concentrated HCl bottles is expressed as weight percentage (w/w%) as 36% , 36.5%, 37.
Because volume is not given, we can take volume as 1 dm3. As the next step, find the mass of that solution (1 dm3).
Now, mass of HCl in 1 dm3 is found. Weight fraction (w/w%) data is used.
Next, amount of HCl is determined by dividing HCl amount from molar mass of HCl.
Because HCl amount is found in 1 dm3 solution, that HCl amount become the concentration of HCl. Therefore, concentration of HCl is 11.8 mol dm-3.
If HCl solution has a high concentration such 0.1, 0.01 mol dm-3, pH value is increased by 1 when concentration is reduced from 10 times. When HCl concentration is too low like 0.00000001, 0.000000001 mol dm-3, pH value is not effected very much due to dilution of HCl acid. If HCl concentration is very low, pH value is close to the seven (neutral solution)
When you add 1 cm3 of drop of HCl to the 999 cm3 distilled wate volume, total volume become 1000 cm3. Therefore, HCl concentration is reduced by 1000 times. Therefore, HCl concentration relative to the HCl is 1 * 10-8 mol dm-3. Distilled water can give 1 * 10-7 mol dm-3 H+ concentration. Therefore, HCl does not effect for the water dissociation and H+ concentration can be considered as 1 * 10-7 mol dm-3 in aqueus solution.
Therefore, pH value is increaded from 5 to 7.