why do we perform tritation many times ?

Answer 1

If you're speaking of titrating the same method more than once it's because you want to know something about the precision. It is rare for the ratio to be EXACTLY the same time after time; we generally take the average. If you are speaking of titrating in different procedures it's because it is usually easier to measure a volume (with a buret) than using other methods. By the way, when you do these ratios you are looking at two places (10.0/20.0) = 0.50. In quantitative work of higher orders, we try to get four places; i.e., 0.5000. If we are determining Fe or Si or something like that we want to be able to report something like 29.12%.

Answer 2

thank you that helped a lot :)