A Lewis acid is a compound that is in position to be an electron pair acceptor. The fact that the sodium bromide is ionized (NaBr-) suggests that it is the compound with the electron pair to donate. That would mean the other compound, aluminum bromide (AlBr3) would be the electron pair acceptor, hence it would be the Lewis acid. Acids, by definition, are substances that produce hydrogen ions (H+) upon dissociation, when mixed with water. Stronger acids dissociate more, producing large amounts of hydrogen ions, and weaker acids dissociate less, producing less hydrogen ions. Acids have a sour taste, and tend to fall somewhere to the left of the "7" on the pH scale. The pH scale is a scale from 0 to 14, with 7 representing neutral terrritory in the middle. Substances with a pH less than 7 are acidic, while substances with a pH of more than 7 are basic.