① Measure the mass of a bottle of raw vinegar M 1 with a balance;

② Pour the vinegar in the bottle into a beaker, and measure the mass m2 of the empty vinegar bottle with a balance;

(2) The mass of vinegar is m=m 1-m2,

Density of vinegar:

ρ= mV = m 1-m2v 0；

(3) When the vinegar in the cup is poured out, some vinegar will remain in the vinegar bottle, so the measured quality is inaccurate and the calculated density will be wrong.

In order to reduce the measurement error, it is necessary to replace the beaker with a measuring cylinder, pour a proper amount of vinegar into the measuring cylinder, and then measure the mass of the remaining vinegar and the bottle, so as to make the volume and quality of vinegar in the measuring cylinder accurate.

So the answer is:

(1)① Measure the quality of a bottle of raw vinegar with a balance M 1;

② Pour the vinegar in the bottle into a beaker, and measure the mass m2 of the empty vinegar bottle with a balance;

(2)ρ= m 1-m2v 0；

(3) vinegar is not clean; measuring cylinder