Methyl red has a pKa of 5.0 and is red in its acid form and yellow in its basic form. If several drops of this indicator are placed in a 25.0-mL sample of 0.100 M HCl, what color will the solution appear? If 0.100 M NaOH is slowly added to the HCl sample, in what pH range will the indicator change color?

Video transcript

Hi everyone here we have a question telling us bromo final blue is an acid based indicator with a P. K. A. Of 4.0. Its color changes from yellow to blue, going from a specific form to its basic form. What color will the solution appear when several drops of this indicator are placed in a 50.0 millimeter of 0. moller hydra bronek solution. What ph range will the indicator change color when 0.150 molar potassium hydroxide is slowly added to the solution. So we have to remember that when the ph is less than the P. K. A. The acidic form is in greater quantity. When the ph equals the P. K. A. The acidic and basic form are in equal quantities and when the ph is greater than the P. K. A. The basic form is in greater quantity. So we have 0. Moeller hydro bronek solution. And that is an acid. So it is acidic. So R P H. Is going to equal the negative log of our hydrogen ions. So P H equals negative blog of 0.450 Which equals 0.347. So our indicator is yellow because it is acidic. Now to calculate for the ph range, the ph range is going to be the P K. A. Plus or minus one. So four minus one equals +34 plus one equals five. So our ph range is 3.0 5.0. So our final answers are our indicator is yellow And a ph range of 3.025.0. Thank you for watching. Bye.