# Finding the Density of a Pipette

Purpose: To find the density of a pipette with less than 5% error.

Procedure:
1. Use a permanent marker to mark one of two pipettes and set it aside.
2. Weigh the non-marked pipette on the lab balance.
3. Record the mass of the pipette.
4. Fill the 50 ml beaker with water.
5. Pour the water from the beaker into the 50 ml graduated cylinder until it is near the 40ml line.
6. Use the marked pipette to adjust the amount of water in the graduated cylinder so that it is exactly 40ml.
7. Push the stem of the previously weighed pipette about 1 cm under the water.
8. Squeeze the bulb of the pipette to remove air from the pipette.
9. Release the bulb of the pipette to allow it to fill with water.
10. Still holding the pipette stem under the water, bend the stem so that the top of the water-filled bulb faces down.
11. Squeeze the bulb of the pipette to remove all air from the bulb and stem.
12. Keeping the tip of the pipette stem submerged, bend the bulb around so that the pipette ends up bent in half with both ends facing down inside of the graduated cylinder.
13. Use the glass stirring rod to push the pipette completely under the water.
14. Remove the glass stirring rod making sure to tap any water droplets on it back into the 50 ml graduated cylinder.
15. Record the amount of water in the 50 ml graduated cylinder.

Data Table:
 T1 T2 T3 T4 T5 T6 T7 T8 T9 Mass of pipette (g) 0.89 0.77 0.90 0.85 0.94 0.89 0.86 0.93 0.93 volume of water (ml) 40 40 40 40 40 40 40 40 40 volume with pipette 41 41 40.9 41.1 41.2 41 41.1 41 41.1 Volume of pipette (ml) 1 1 0.90 1.1 1.2 1.0 1.1 1.0 1.1 Density of pipette (cm3) 0.89 0.77 1.0 0.77 0.78 0.89 0.78 0.93 0.85 Average pipette density 0.85 0.85 0.85 0.85 0.85 0.85 0.85 0.85 0.85 Accepted (g) 0.91 0.91 0.91 0.91 0.91 0.91 0.91 0.91 0.91 % Error (%) 2 15 10 15 14 2 14 2 7

Calculations:

d = m / v
d = 8.9g / 1 ml
d = 8.9 g/ml

% Error = E - A x 100%
A

% Error = 0.89 - 0.91 x 100%
0.91

% Error = 0.02 x 100%
0.91

% Error = 0.02 x 100%

% Error = 2%

Pipette volume = V1 - V2
Pipette volume = 40 ml - 41 ml
Pipette volume = 1 ml

Error Analysis: Possible errors in measurement could have come from an inexact amount of water in the graduated cylinder or a pipette with an abnormal density due to a factory error could have been used. Air bubbles in the pipette were avoided in this experiment by making the hole at the top of the pipette, but if any unseen air pockets remained in the shaft they may not have been noticed. Another variable could have been an inexact reading of the amount of water in the graduated cylinder after the pipette was placed in it.