Acid-base theory


Exercise 1


$20.0 mL$ $NH_3$ $0.1 M$ are titrated by $H Cl$ $0.1 M$ . Let's call $x$ the volume of $H Cl$ already added at a given moment.

a) Theoretically establish the function $pH = f(x)$ .

$x = 0$: Weak base: $pH = 11.10$ $0\lt x \lt 20$: Buffer: $pH$ $=$ $9.20$ $ +$ $ log\frac{20 - x}{ x}$ $x = 20$: Weak acid: $pH$ $=$ $5.25$ $x \gt 20$: Strong acid in excess: $pH$ $=$ $-log(0.1 \frac{x - 20}{20+x})$

b) Give a table of values of the function by searching images (1 mL intervals of x). Graph on graph paper please!

c) Choose a suitable indicator for this titration.

Methyl red

d) Search graphically in what time interval during addition (between which $x$) we observe the color change of phenolphthalein, if that was the indicator chosen. Is this a suitable indicator?

Interval: $2 \lt x \lt 19$ Phenolphthalein is not suitable!!