# Viscosity of liquid interrupts accuracy of micropipette?

Does viscosity of liquid interrupt accuracy of micropipette?

I would like to dilute 85% $\ce{H3PO4}$ acid to $\pu{1.194 mol/dm3}$ so I had to pipette 366 microliter into 4.634 mL of water. Then, I adjusted the pH to 11 by dropping 25% $\ce{NH3}$ solution. I did 4 times but final volume was not equal (about 50, 50,100, 200 mL). I think the problem is viscosity of liquid when I pipetted concentration acid.

• Why error at microliter scale should give difference as high as about 50 or 100 ml? In addition for non routine multi samples work microsyringes are preferable. – Alchimista Jan 7 '18 at 9:52
• In general, using a micropipette to work with highly corrosive substances is usually discouraged. Aside from this, I don't really see the problem in higher viscosity. Acid shouldn't be stuck in the tip, and, if you took the probe slowly, the proper amount of acid can be transferred with no losses. I also agree with @Alchimista that you bring tremendous error if you dilute little quantities in a large portion of water. This works for homeopathy, but not really for chemistry. – andselisk Jan 7 '18 at 15:26
• Also, pipettes tend to be designed to leave a little drop in the end because people have had this problem before. – bon Jan 7 '18 at 16:53

## 1 Answer

I think you try to use glass pipette instead. It may decrease viscosity effect.

• What exactly is this "viscosity effect" you are talking about which can be reduced by switching to a glass pipette? – andselisk Jan 7 '18 at 15:21