{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

Ch10_GilbertChem2E_StudentSolutions

# Ch10_GilbertChem2E_StudentSolutions - CHAPTER 10 | Forces...

This preview shows pages 1–3. Sign up to view the full content.

542 CHAPTER 10 | Forces between Ions and Molecules and Colligative Properties 10.1. Collect and Organize In Figure P10.1, two similarly sized spheres of opposite charge represent KF. In KI, the iodide ion is shown negatively charged and larger than the K + ion. We are to determine which substance would have a higher melting point by virtue of having stronger ion–ion forces. Analyze Coulomb’s law describes the strength of the ion–ion interactions in these substances as E ~ Q 1 Q 2 d In the case of KF and KI, Q 1 and Q 2 are the same ( Q K + = +1, Q F and Q I = –1). What does change is the distance between the ion centers. Solve Coulomb’s law states that as distance between the ions increases, the energy of the interaction decreases. Because I is larger than F , the KI interaction is weaker. Therefore, the stronger ion–ion interaction results in a higher melting point for KF than KI. Think About It The strength of the ion–ion interaction is even more influenced by the charge on the ions. The melting point of CaF 2 (where Q 1 = +2 and Q 2 = –1) would be predicted to be even higher than that of KF. 10.3. Collect and Organize Given the boiling points of two trigonal pyramidal molecules, we are to determine which substance is NH 3 and which is PH 3 . Analyze Both molecules might be polar due to their pyramidal geometry. The more polar molecule has the stronger intermolecular forces. The dipole strength may be estimated using electronegativity values for N (3.0), P (2.1), and H (2.1). Solve Because the electronegativity of P is equal to that of H, the phosphine, PH 3 , is predicted to be less polar. Ammonia, NH 3 , on the other hand, is more polar; morever, because H is bonded to the very electronegative N atom, it forms strong hydrogen bonds with other NH 3 molecules. Ammonia therefore has the higher boiling point (–33 ˚C YH 3 in Figure P10.3). Phosphine, with only weaker forces between its atoms, has a low (–88 ˚C) boiling point and is represented as XH 3 in Figure P10.3. Think About It The phosphine molecule is not strictly nonpolar. The lone pair will “pull” differently than the N atoms do on the electrons on the phosphorus atom, so PH 3 is slightly polar. 10.5. Collect and Organize From the boiling points for X and Y that are read from the plot in Figure P10.5, we are to predict which substance has stronger intermolecular forces between its molecules. Analyze The normal boiling point is defined as the temperature at which the vapor pressure of a substance is equal to 1.00 atm.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Forces between Ions and Molecules and Colligative Properties | 543 Solve From Figure P10.5, we see that the boiling point for X is about 5 ˚C and that the boiling point for Y is about 20 ˚C at 1.00 atm. The substance with the stronger intermolecular forces has the higher boiling point, so Y has the stronger intermolecular forces.
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

### What students are saying

• As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

Kiran Temple University Fox School of Business ‘17, Course Hero Intern

• I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

Dana University of Pennsylvania ‘17, Course Hero Intern

• The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

Jill Tulane University ‘16, Course Hero Intern