Question

a. The concentration of OH- ions in a sample of seawater is 5.0 x 10-6M. Calculate the concentration of H+ ions and determine the pH and pOH of this solution. Is it neutral, acidic, or basic? b. The concentration of H+ ions in a sample of lemon juice is 2.5 x 10-3M. Calculate the concentration of OH- ions and determine the pH and pOH of this solution. Is it neutral, acidic, or basic?

Answer 1

To calculate the concentration of H+ ions in a seawater sample with a concentration of 5.0 x 10^-6M OH-, you can use the equation H+ concentration = Kw / OH- concentration. The pH and pOH can be calculated using the equations pH = -log[H+] and pOH = -log[OH-]. To determine if the solution is neutral, acidic, or basic, examine the pH value. The concentration of H+ ions in lemon juice with a concentration of 2.5 x 10^-3M can also be calculated using similar equations.

Step-by-step explanation:

(a) To calculate the concentration of H+ ions, we can use the equation:

H+ concentration = Kw / OH- concentration

Given that the OH- concentration is 5.0 x 10^-6M, we can substitute this value into the equation and use the value of Kw at 25 °C (1.0 x 10^-14) to calculate the concentration of H+ ions.

To determine the pH, we can use the equation:

pH = -log[H+]

And to calculate the pOH, we can use the equation:

pOH = -log[OH-]

To determine if the solution is neutral, acidic, or basic, we can examine the pH value. If the pH is less than 7, the solution is acidic. If the pH is greater than 7, the solution is basic. If the pH is equal to 7, the solution is neutral.

(b) Using a similar process for the concentration of OH- ions in lemon juice, we can calculate the concentration of H+ ions using the equation:

H+ concentration = Kw / OH- concentration

Given that the H+ concentration is 2.5 x 10^-3M, we can substitute this value into the equation and use the value of Kw at 25 °C (1.0 x 10^-14) to calculate the concentration of OH- ions.

Once we have the concentration of OH- ions, we can determine the pOH using the equation:

pOH = -log[OH-]

And to calculate the pH, we can use the equation:

pH = 14 - pOH

To determine if the solution is neutral, acidic, or basic, we can examine the pH value. If the pH is less than 7, the solution is acidic. If the pH is greater than 7, the solution is basic. If the pH is equal to 7, the solution is neutral.

Answer 2

To solve this problem we need to keep in mind the definitions of pH and pOH:

• pH = -log[H⁺]

• pOH = -log[OH⁻]

• pH + pOH = 14

a. [OH⁻] = 5.0 x 10⁻⁶ M

With that value we can calculate pOH:

• pOH = -log (5.0 x 10⁻⁶) = 5.3

With pOH we calculate pH:

• pH = 14 - pOH = 14 - 5.3 = 8.7

With pH we calculate [H⁺]:

• 8.7 = -log [H⁺]

• 
  `10^(-8.7)` = [H⁺] = 2.0 x 10⁻⁹ M

The pH in the sample is higher than 7.0, so it is basic.

b. [H⁺] = 2.5 x 10⁻³ M

With that value we can calculate pH:

• pH = -log(2.5 x 10⁻³) = 2.6

With pH we calculate pOH:

• pOH = 14 - pH = 14 - 2.6 = 11.4

With pOH we calculate [OH⁻]:

• 11.4 = -log[OH⁻]

• 
  `10^(-11.4)` = [OH⁻] = 4.0 x 10⁻¹² M

The pH in the sample is lower than 7.0, so it is acid.