Whoever wrote the English sentence about buying "new soap" doesn't know what he or she is talking about. I am a native English speaker and there is no such thing as "new soap." And what in the world is "old soap?" I understand the concept but these are NOT English words or expressions or whatever you want to call them. You don't say "I went to the store and bought "new soap." No native speaker would say that unless they were referring to changing brands of soap (that what it sounds like). The "new" is redundant. You just simply say "I went to the store and bought soap." Same problem with "old soap." To say "the cat tossed the "old soap" out the window is not an English sentence. You say " the cat tossed the soap out the window." We don't distinguish between "old" and "new" soap unless you are talking about different brands. If you are trying to refer to a half used bar of soap, and one you just freshly opened, we don't waste time distinguishing between the two. Probably because it's not important.