Why is the end point of titration so steep? plz help me!

Question

i find it really hard to picture why the end point for a titration is so steep. Lets say its a strong acid strong base titration. How come 1 drop of alkali would make the ph rise by so much, and so steeply? alot of textbooks say its cos all the acid has been neutralized..... but so what? thx alot for ur help!

Answer 1

Let's say you neutralize HCl with a standard solution of NaOH. As you should know the pH will be 7 at the equivalence point.

The reason the point of titration is so steep is because the equivalence point (the point in the middle of the steep) is almost always over passed even by the most experienced chemists. There is a large spike in pH because the equivalence point is passed. The beginning of the steep is acidic pH<7 and the top of the steep is basic pH>7 and in between would be pH=7 for a strong acid strong base titration. Besides this point it's always good to have extra points on your titration graph and go past the equivalence point. Most raw titrations are carried out by simply using an indicator and not a pH meter for this very reason despite the inaccuracy of a color change as oppose to the use of a digital readout of the pH.  

Answer 2

The slope of your titration curve represents the change in pH with respect to the volume of strong base (or acid) titrated into the other.  The amount of change produced by each unit of volume is not the same every time.  Say you have 0.005 moles of hydrogen cation in 1 liter of solution, or a 0.005 M solution, yielding a pH of  ~2.30.  

You then add 1 mL of a solution containing 0.00005 moles of hydroxide anion.  The hydrogen ion concentration is now (0.005 - 0.00005 mol)/(1 + .001 L) = or ~0.004945 mol/L, yielding a pH of ~2.31 for a change in pH of of ~0.01.

Each time you add another volume unit of base you are decreasing the numerator (subtracting more from the initial concentration) and increasing the denominator (adding more to the initial volume).  Mathematically, doing either of these will give you a smaller number.  As the hydrogen ion concentration decreases, the pH (-log10(H+)) increases, and it will increase by more with each addition because the effect is magnified.  Each drop (or milliliter or gallon or any unit of volume) further decreases the numerator and increases the denominator.  

Answer 3

in acid base titration oh ions react with h ions when either one is completely finished the addition of further H OR OH ions will causew the ph to rise ,there are millions of ions in one drop