Calculate the concentration of OH¯ ions in a 1.4*10^-3 M HCl solution

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Kw = 1 x 10^-14

Solutions to that question

To calculate the concentration of OH¯ ions in a HCl solution, we need to understand that HCl is a strong acid that completely dissociates in water. This means that it forms H+ ions and Cl¯ ions, but it does not produce OH¯ ions directly.

However, we can still determine the concentration of OH¯ ions indirectly by considering the reaction between H+ and OH¯ ions in water, which forms water molecules (H2O). This reaction is called the autoionization of water and is represented by the equation:

H+ + OH¯ → H2O

In pure water, at room temperature, the concentration of H+ ions and OH¯ ions is equal to 1.0 × 10^⁻7 M each. This is because the autoionization of water occurs to a small extent, creating a balance between H+ and OH¯ ions.

In the given solution, HCl is added, which means it donates H+ ions to the solution, increasing the concentration of H+ ions. According to the equation, to maintain the equilibrium, the concentration of OH¯ ions will decrease by the same amount as the increase in H+ ions.

Since HCl is a strong acid, it dissociates completely. Therefore, the concentration of H+ ions will be equal to the initial concentration of HCl. In this case, it is given as 1.4 × 10^⁻3 M.

To find the change in OH¯ concentration, we subtract the increase in H+ concentration from the equilibrium value of 1.0 × 10^⁻7 M. Given that the H+ concentration is 1.4 × 10^⁻3 M, the change in OH¯ concentration will be:

Δ[OH¯] = 1.0 × 10^⁻7 M - 1.4 × 10^⁻3 M

Δ[OH¯] = -1.4 × 10^⁻3 M

The negative sign indicates a decrease in OH¯ concentration as a result of the increase in H+ concentration.

Therefore, the concentration of OH¯ ions in the 1.4 × 10^⁻3 M HCl solution is -1.4 × 10^⁻3 M.

H2O ==> H^+ + OH^-

Kw = (H+)(OH^-) = 1 x 10^14
Since HCl is a strong acid and ionizes 100%. substitute the HCl concn for H^+ in the Kw expression and solve for OH^-