胡椒 = Hújiāo = pepper
护照 = Hùzhào = passport

城市 = Chéngshì = city
诚实 = Chéngshí = honest

山西 = Shānxī = (the province near Beijing, in which Taiyuan is located)
陕西 = Shǎnxī = (the province in which Xi'an is located; sometimes romanized as Shaanxi in order to trigger the 3rd tone)

西安 = Xī'ān = the aforementioned city
先，现 = Xiān, xiàn = first, now

机长 = Jī zhǎng = captain/pilot
机场 = jīchǎng = airport

苏州 = Sūzhōu = famous city in Jiangsu
宿州 = sùzhōu =unimportant city in Anhui
肃州 = sùzhōu = unimportant city in Gansu
徐州 = xúzhōu = city halfway between Beijing and Shanghai in the north of Jiangsu

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You, as an adult, can employ theoretical "pinyin" principles until the cows come home, but are almost guaranteed to strike out. Meanwhile, your kids, and singers that memorize songs will excel in all of the above sample cases, with the possible exception of the last (i.e. only half of my Chinese friends can differentiate between 宿州 and 肃州 out of context).

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Going back to the singing theme, if you (or anyone else) spends 2 hours learning 月亮代表我的心 (really easy!), you'll be in far greater shape than the pinyin crowd because you will have established a connection between music and Mandarin.