"Plural of Masculine Personal Nouns"
"Masculine personal nouns often take special endings in the plural. If the stem consonant is hard, the ending is usually -i/-y and the preceding consonant is softened: student student → studenci, Polak Pole → Polacy. If the stem consonant is soft, the ending is usually -e, that is, like non-personal nouns: nauczyciel teacher → nauczyciele."
Swan, Oscar (2008-10-12). Polish Verbs & Essentials of Grammar, Second Edition (Verbs and Essentials of Grammar Series) (Kindle Locations 253-258). McGraw-Hill Education. Kindle Edition.
Here the stem consonant is soft ("c"), so if it were a regular plural we would have "chłopce" but I'm starting to see that most personal masculine (and some feminine) plurals are irregular, so I guess here is another one. There are a limited number and we just gotta learn 'em. There is a list of about 30 in the above mentioned book.
The quote above does indeed start with the disclaimer "Masculine personal nouns often take special endings in the plural."
I make this note for others like myself who are learning the grammar rules and then go back to the easier examples and try and retrofit them lol
Dear learners. Don't even try to distinguish between 'ch' and 'h'. Nowadays, it is very (I would even say, extremely) rare and used basically in the very east of Poland, in the mountains and in Kresy (eastern lands that formerly belonged to Poland). One of the examples can be the dialect of Podhale. Another problem is if you distinguish between these two letters, the declination has to be changed. And most of Polish would consider it very confusing :)
I see now :) I was talking about the way of speaking when the difference is obvious to notice (mostly in Kresy, quasi-Ukrainian way) - then, for example, if you pronounce "Sapieha" with a 'hard h' you have to say "Sapieże" (famous Polish nobleman) instead of "Sapiesze" as you have the voicing there. But this is not really a typically Polish manner, rather an eastern influence.
Learning the international phonemic alphabet (IPA) makes prounouncing anything easier. It should be /ˈxwɔp.t͡sɨ/. /x/ is like saying k but letting air pass through, like russian-cyrillic X, /w/ is moving your lips together while saying /x/, like in "what", /ɔ/ and /ɨ/ are vowels that are basically oh and ee, /p/ is litterally p, and /t͡s/ is saying t and then s immidiately after.