Removing impurity from a touch screen phone

Q: I have a question regarding impurity and touch screen phones. I would like to know how invisible impurity such as urine traces or other invisible impurity may be removed from a cellphone as it cannot be washed as it would be ruined. Would wiping the dry invisible impurity with a dry cloth remove it from the smooth surface of a phone? Or how about a wet cloth that is wetted with isopropyl alcohol (as this does not harm the phone)?

Keeping textbooks containing words that may affect one's beliefs

Q: I am a science student and I have a bunch of math textbooks. These are strictly math textbooks as I understand. In one of the books, the author mentions solving equations in their multiple variable "incarnations". I assume the author means "form" because there is no religious meaning here as far as I can tell. In a different book, the author tells a short biography of a mathematician who was also an astrologer. The presence of such words disturbs me. I would like to know if there is something wrong with me continuing to read these textbooks and can I keep them or not. 

Hadith regarding people who will come with mountains of good deeds that will be turned into scattered dust on the Day of Judgement

Q: I have recently read this Hadith:

Thawbaan (May Allah Ta'ala Be Pleased with him) narrated that the Prophet (SallAllahu 'Alayhi Wa Sallam), (May Allah Ta'ala Exalt his mention) said: "Indeed I know a type of people from my nation who would come on the Day of Judgement with good deeds as big as the mountains of Tihaamah, pure, but Allah will turn them into scattered dust." Thawbaan (May Allah Ta'ala Be Pleased with him) asked in fear: "O Prophet of Allah! Describe them to us, we fear to be amongst them while we do not know." Thereupon, the Prophet (SallAllahu `Alayhi Wa Sallam) (May Allah exalt his mention) said: "Indeed they are your brothers, and they perform acts of worship by night [prayers] in the same way you do, but when they are alone, they transgress the Limits of Allah." [Ibn Maajah and At-Tabaraani]

My question is this that does this Hadith include all types of sins and not just zina? Does it include listening to music, seing a non-mahram accidentally twice in public?