Question

1. A student carries out a back titration to determine the concentration of ammonium chloride in a solution. The student collects 10.80 mL of the original NH₄Cl solution and dilutes it to 250.0 mL (we will refer to this as the dilute NH₄Cl solution). Then 25.00 mL of the dilute NH₄Cl solution are transferred to an Erlenmeyer flask and 25.00 mL of 0.1963 M NaOH are added. Calculate the moles of NaOH added to this Erlenmeyer flask.

2. In the same back titration experiment described in the previous example, the student heats the solution of dilute NH₄Cl with excess NaOH to complete the first step of the reaction. The student then adds bromocresol green indicator and titrates the unreacted NaOH with 35.18 mL of 0.1015 M HCl to reach the endpoint. Calculate the number of moles of HCl added in this titration.

3. Based on the number of moles of HCl you have calculated in the previous step, determine the number of moles of NaOH that were remaining after heating the solution.

4. Using the values you have calculated for the number of moles of NaOH initially used and the moles of NaOH remaining in the solution after heating, determine the number of moles of NaOH that reacted in the first step with the 25.00 mL of dilute NH₄Cl.

5. Recall that the original NH₄Cl solution was diluted from 10.80 mL to 250.0 mL. 25.00 mL of this dilute solution were used in the titration. Using your answer in the previous question, determine the number of moles of NH₄Cl in the original solution.

6. Using the moles of NH₄Cl calculated in the previous question, determine the concentration of the original NH₄Cl solution (recall, the student collected 10.80 mL of this solution at the beginning of the experiment)?

Answer 1

MOlavil'Y volume 0.1963 moles x 0,025七 4.905 x i6 mo les 3 5x 10 moles unreac ed HC 4) A wunt of NaOH :4.405 xlo moles I3368 xio' mo les メー>w.elef x d mo.mgc/ 3368 x1o moles : con taiS cumtains 3369 x lo xID woles -1-336i xlo mdes 2. 1-3368 x 1o moles original NH C