Which of the following cn be observed when 20,0 of 1.0 m naoh (aq), 10.0 ml of 1.0 m hcl(aq), and a few drops of phenolphthalein are combined and react?

The final solution will be clear and colorless.

Explanation:

The balanced reaction equation is:

NaOH + HCl ⇒ H₂O + NaCl

The amount of NaOH that is added is calculated as follows:

(20.0mL)(1.0mol/L) = 20 mmol NaOH

Similarly, the amount of HCl that is added is as follows:

(10.0mL)(1.0mol/L) = 10 mmol HCl

Since HCl and NaOH react in 1:1 proportions, the HCl is the limiting reaction. 10 mmmol of HCl will neutralize 10 mmol of NaOH, leaving 10 mmol of NaOH. The volume of the mixed solution is 30.0 mL, so the concentration of NaOH in the final solution is:

(10 mmol)/(30.0mL) = 0.3333 M NaOH

The pOH of the final solution is:

pOH = -log([OH⁻) = -log(0.3333) = 0.477

The pOH is related to the pH as follows:

pH = 14 - pOH = 14 - 0.477 = 13.5

At a pH of 13.5, phenolphthalein is colorless. The final solution will be observed as clear and colorless.