Buffering Action of Proteins

We did this experiment in class but I want to see if the results seem reasonable and, if so, why they were not more varied.

1) Beginning with 10 mL of unbuffered, demineralized water, add 2 drops of 0.1 M HCl at a time, checking the pH every two drops. Results were as follows:

# Drops of acid pH
0 7
2 5
4 4
6 3
8 3
10 3
WHY WERE THE LAST THREE UNCHANGING?

2) Beginning with 10 mL of 1% solution of serum albumen in water, add 2 drops of 0.1 M HCl at a time, checking the pH every two drops. Results were as follows:

# Drops of acid pH
0 6
2 7
4 5
6 4
8 4
10 4
AGAIN, WHY WERE THE LAST THREE UNCHANGING?

3) Beginning with 10 mL of unbuffered, demineralized water, add 2 drops of 0.1 M NaOH at a time, checking the pH every two drops. Results were as follows:

# Drops of base pH
0 7
2 10
4 10
6 11
8 11
10 11
WHY WERE THE LAST THREE UNCHANGING AND WHY WAS THERE NO GREATER RANGE IN pH?

4) Beginning with 10 mL of 1% solution of serum albumen in water, add 2 drops of 0.1 M NaOH at a time, checking the pH every two drops. Results were as follows:

# Drops of base pH
0 6
2 10
4 10
6 11
8 11
10 11
WHY WERE THE LAST THREE UNCHANGING AND WHY WAS THERE NO GREATER VARIATION IN pH? ALSO, WHY WERE THEY NEARLY IDENTICAL TO THE PLAIN WATER, IS IT BECAUSE THE pH of the WATER WAS SO SIMILAR TO THAT OF THE SERUM ALBUMIN SOLUTION?

5) What conclusions can be drawn from this on the effect of acid or base on a solution containng a dissolved protein?