Hydrochloric acid (HCl) is commonly sold as a pool additive, where it is used to lower the pH of the pool water if it is too high. Swimming pools are commonly kept between a pH of 7.0 - 7.6 to ensure the comfort of the swimmers. You find a bottle of HCl in the pool aisle at the hardware store which is labelled as having a concentration of 168 g/L. What is the pH of this solution, to 2 decimal places? The molar mass of HCl is 36.46 g/mol. Remember: pH = -log10[H3O+(aq)], pOH = -log10[OH-(aq)] and pH + pOH = 14.00
Question
Hydrochloric acid (HCl) is commonly sold as a pool additive, where it is used to lower the pH of the pool water if it is too high. Swimming pools are commonly kept between a pH of 7.0 - 7.6 to ensure the comfort of the swimmers. You find a bottle of HCl in the pool aisle at the hardware store which is labelled as having a concentration of 168 g/L. What is the pH of this solution, to 2 decimal places?
The molar mass of HCl is 36.46 g/mol.
Remember: pH = -log10[H3O+(aq)], pOH = -log10[OH-(aq)] and pH + pOH = 14.00
Solution
To find the pH of the solution, we first need to find the concentration of HCl in moles per liter (M).
- Convert the concentration from g/L to mol/L.
Given that the molar mass of HCl is 36.46 g/mol, we can use this to convert the concentration:
168 g/L ÷ 36.46 g/mol = 4.61 mol/L
So, the concentration of HCl is 4.61 M.
- Calculate the concentration of H3O+ ions.
In a solution of HCl, it dissociates completely into H+ and Cl- ions. Therefore, the concentration of H3O+ ions is equal to the concentration of HCl, which is 4.61 M.
- Calculate the pH of the solution.
We can now use the formula for pH, which is pH = -log10[H3O+(aq)].
pH = -log10(4.61) = -0.66
However, pH cannot be negative. The negative value indicates that our assumption of complete dissociation of HCl is not valid at such high concentrations. In reality, the pH of such a concentrated HCl solution would be less than 1, but the exact value would need to be determined experimentally.
So, the pH of the solution is less than 1.
Similar Questions
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