Assuming that an ER signal peptide forms an alpha helix, is that helix likely to be amphipathic? Why or why not?

Yes, the alpha helix is likely to be amphipathic because it is made of amino acids that are combined to form a secondary structure of proteins. The properties of the amino acids and the joins that make the alpha helix form an amphipathic structure that means that it has a hydrophobic part and an amphiphilic part.