The purpose of williams’s a key into the language of america was

A Key into the Language of America (1643) is the first and best book written by the political and religious leader Roger Williams. It was written at a time where English settlers saw Native Americans as "savages" and inferiors in all sense. With this work, William wanted to prove something different. Thorough the book, Williams explained a variety of topics related to the daily life o  Narragansett Indians, such as their eating, entertaining activities, sleep, sickness, death, burial, familiar phrases, vocabulary, among others. Its main purpose was to provide insight into Native Americans cultures.

type of error:

the error in the sentence is a "dangling modifier". a dangling modifier is a phrase, word or clause that "dangles" because there is not target to modify. in this case, "after mopping the floor" is the dangling modifier since it has no word to modify. the noun "house" cannot mop the floor; therefore there is a mistake in the writing of the sentence.