q's on Heinemann

[khalil]

" A student noted that her 50 ml burette was dirty and that droplets of liquid stuck to the inside surface of the tube. She decided to investigate if this would effect the burette's accurarcy. She filled the burette to the zero mark and drained a 50 ml titre into a flask that had previously been weighed. the flask was weighed again and the mass of water calculated. The student then calculated the volume of water by assuming that the density of water is 1 g mL(-1). This procedure was repeated another four times. The masses of water for the five trials were 49.95g 49.93g 49.9g 49.93g 49.92"

(A)  What is the average mass of the five water samples?

what i did was....add them all and divide by 5..= 49.926g however in book it says "49.63g"

(b) calculate the average volume of these samples

for this part i did 1g\ml =49.926g which gives mL = (1)\ (49.926) however books says "49.63mL"... the reason i did g divided my mL is because in the density mL has (-1) on top of it.. hence puting it on the botton so it coud be positive.... ...

Also...

"Another burret was selected. Before tesing it was cleaned thoroughly. The same procedure was used and the average titre was found to be 49.5 rather than 50 g. . the error was thought to be due to a poor standard of calibration

(h) how should measurements taken from this burette be adjusted.

can sum1 pls explain this.. the answer says " add .5 mL for every 50 mL or 0.01 mL for every 1 mL delivered by the burette.

 (i) and also wat does "standard of calibration " mean???

(j) wat does concordant mean?

(k) "rough" titration carried out before first accurate titration.. wat does it mean.. and why used??

(l) for titration values 25.32, 25.3, 25.34 mL wat sort of errrors explains difference.. random or systematic.. explain..

thx.. if u can answer all. ....