The method and the results are on the vsepr theory lab. Do the analysis yourself first, then check the answers below.
Quick answer: A Lewis structure shows how valence electrons are shared as bonds and lone pairs, and formal charges help choose the best one. These answers go with the AP Chemistry lab on vsepr theory: the graph, the calculations, the uncertainties and the conclusion explained, for all 7 analysis questions.
Model answers use the sample table. Deflection depends on the stream and the rod, so expect your numbers to differ but the zero results for nonpolar liquids to be the same.
The liquids with a dipole moment of zero show no deflection, and larger dipole moments tend to give larger deflections (propanone is largest, ethanol smaller).
Question 2 Why a stream bends
The rod induces an arrangement of the molecules: the end of each polar molecule with opposite charge turns toward the rod. Either sign of charge attracts the oppositely charged end, so the stream bends toward the rod.
Question 3 Nonpolar liquids
Hexane is made of C–C and C–H bonds, which are nearly nonpolar, and its shape is symmetric overall. It has no permanent dipole, so the rod has nothing to align.
Question 4 Shape of water
H–O–H with two lone pairs on O. The two O–H bonds are polar (O is δ⁻) and the shape is bent at about 104.5°, so the dipoles do not cancel.
Question 5 Propanone
The carbonyl carbon has three domains, so the shape is trigonal planar (sp²). The C=O bond is strongly polar and the dipoles of the two CH₃ groups do not cancel it.
Question 6 Reliability
The stream wobbles, so the reading is uncertain: use a thin, steady stream and a video to read the deflection. Humidity changes the rod’s charge: keep the same rubbing routine each time. Repeat three times and average.
Question 7 Limits of the test
Deflection depends on the stream’s thickness, speed and density, and on how freely molecules rotate, which differ for each liquid. Hydrogen bonding in ethanol also affects it. It is a rough indicator, not a measurement of dipole moment.
