Chem 1C – Chapter 16 – CLAS – Key

1. Indicate the types of forces present and the type of solid for each of the following substances:a. CCl4 ⇒ Covalent intra – LDF inter – molecular solidb. HF ⇒ Covalent intra – HB, DD, and LDF inter – molecular solidc. NH4Br⇒ Ionic and covalent intra – Ionic solidd. F2⇒ Covalent intra – LDF inter – molecular solide. CH3OH⇒ Covalent intra – HB, DD and LDF inter – molecular solidf. Ca ⇒ Metallic bonds intra – metallic solidg. H2S ⇒ Covalent intra – DD and LDF inter – molecular solidh. KOH⇒ Ionic and covalent intra – Ionic solidi. BH3⇒ Covalent intra – LDF inter – molecular solidj. H2CO⇒ Covalent intra – DD and LDF inter – molecular solidk. SiO2 ⇒ Covalent intra – Covalent Network solidl. Ar⇒ LDF inter – Atomic solidm. P⇒ Covalent intra – Covalent Network solidn. S8⇒ Covalent intra – LDF inter – molecular solid

2. Using intermolecular forces predict the following:a. highest melting point F2 or Br2

b. highest melting point HF or HClc. highest boiling point HOCH2CH2OH or CH3CH2OHd. highest boiling point CH3CH3 or CH3CH2CH3

e. highest vapor pressure CH3CH2OH or CH3OCH3

f. highest vapor pressure CCl4 or CH2Cl2

g. highest freezing point MgO or H2Oh. highest surface tension C14H30 or C24H50

3. Consider the following phase diagrams for water and carbon dioxide respectively – which phase is the most dense for each substance? How does pressure affect the MP and BP for each substance? For water ⇒ the slope of the solid/liquid line is negative telling you that the liquid is the most dense phase ⇒ as the P↑BP↑MP↓ For carbon dioxide ⇒ the slope of the solid/liquid line is positive telling you that the solid is the most dense

phase ⇒ as P↑BP↑MP↑

4. Pure compound Z has a triple point at 18 ° C and 72 torr, a normal melting point at 21 °C, and a normal boiling point at 87 °C. Which of the following statements regarding compound Z is/are correct?a. The density of the solid is greater than that of the liquid. Trueb. Sublimation occurs if starting with a solid at a constant temperature of 17 °C the pressure is decreased until a

phase change occurs. Truec. Condensation occurs if the temperature is decreased from 55 °C to 13 °C at a constant pressure of 1.00 atm.

False5. The enthalpy of vaporization for water is 44 kJ/mol. What is the boiling point if the atmospheric pressure were 0.33

atm?

ln (P2P1 ) =

- ΔH vapR (1T 2

– 1T 1 )⇒ ln (0.33 atm

1atm ) = −44,000 J /mol8.3145 J/molK (1T 2

– 1373 K ) ⇒ T2 = 346

K or 73 °C

6. How much heat does is required to take 10 g of ice at -31 °C to vapor at 155 °C? (Csolid = 2.03 J/g°C , Cliquid = 4.18 J/g°C , Cgas = 2.02 J/g°C, ΔHfus = 6.01 kJ/mol, and ΔHvap = 40.7 kJ/mol)This is a 5 step process => 3 changes in temperature (q=mC Δ T) and 2 phase changes (q=n ΔH)q1=(10g)(2.03 J/g°C)(+31°C) = 629.3J or 0.629kJq2=(10g/18g/mol)(6.01kJ/mol) = 3.34kJq3=(10g)(4.18 J/g°C)(+100°C) = 4180J or 4.18kJq4=(10g/18g/mol)(40.7 kJ/mol) = 22.6kJq5=(10g)(2.02 J/g°C)(+55°C) = 1.11kJqtotal = 31.86kJ

7. Determine the final temperature if a 25 g cube of ice at -7 °C is placed in 180 mL of water at 64 °C and allowed to come to equilibrium. (Csolid = 2.03 J/g°C , Cliquid = 4.18 J/g°C , Cgas = 2.02 J/g°C, ΔHfus = 6.01 kJ/mol, and ΔHvap = 40.7 kJ/mol)Heat is transferred from the hot water into the cold water ⇒ q total = 0

0 = mCΔT(warm water) + mCsolid Δ T(ice cube) + nHfus (ice cube) + mCliquidΔ T(ice cube) 0 = (180g)(4.18J/g°C)(Tf-64°C) + (25g)(2.03J/g°C)(7°C)+(25g/18g/mol)(6010J/mol)+(25g)(4.18J/g°C)(Tf-0°C)

Tf = 46°C8. Copper has an inter-planar spacing of 1.36 Å. Calculate the wavelength of the X ray that should be used if θ is 15°

(assume n=1). nλ = 2dsinθ ⇒ (1)(λ) = 2(1.36 Å)(sin(15°)) ⇒ λ = 0.7 Å

9. Zinc crystallizes in a cubic closest packed structure. The radius of a zinc atom is 135 pm. Calculate the density in

g/mL for solid zinc. D = mass(g)

volume (mL) ⇒ since CCP solids have 4 atoms/unit cell we can get the mass ⇒

mass = 4 Zn atoms 1mole Zn

6.022 x 1023atomsx

65.38 g Zn1 mole Zn

=4.34 x 10−22 g Zn

The volume of a cube = e3 ⇒ The edge of a CCP = r√8 ⇒ e = 135pm√8 = 381.8 pm ⇒

381.8 pm 102 cm1012 pm

= 3.818x10– 8cm ⇒ volume = (3.818x10– 8cm)3 = 5.57x10 – 23 cm3

Density = 4.34 x 10−2222 g Zn5.57 x 10 – 23 cm3

= 7.8 g/mL

10. Titanium metal has a body-centered cubic unit cell. The density is 4.50 g/cm3. Calculate the atomic radius in

angstroms of titanium. (1010Å= 1m) The edge of a BCC = 4 r√3

⇒ you can find the edge of the cube because the

volume of a cube is e3 ⇒ to get the volume you can use the density equation D = mass(g)

volume (mL) ⇒ there are 2

atoms per unit cell for BCC ⇒ mass = 2 Ti atoms 1 mole Ti

6.022 x 1023atomsx

47.88 gTi1mole Ti

=1.59 x10−22 gTi ⇒

V = massdensity

=1.59 x 10−22 g Ti4.5 g /cm3 =3.53 x 10−23 cm3⇒ edge = 3√3.53 x 10−23 cm3= 3.29x10−8cm

⇒ r= e√34

r = 1.42x10−8cm

11. The unit cell in this two-dimensional crystal contains ______1____ Xs and _____1_____ Os.a. 1, 1 X X X X Xb. 2, 1 O O O O c. 1, 2 X X X X X d. 4, 1 O O O Oe. 1, 4 X X X X X

12. Assume the two-dimensional structure of an ionic compound MxAy is

What is the empirical formula of this ionic compound? MA2

13. Consider the following cubic closest packed structures. For each compound determine where the ions are in the lattice.a. NaCl (Na+ = 95 pm, Cl– = 181 pm ) ⇒ Since chloride is the larger ion it will reside in the lattice points of the

CCP ⇒ and since the ratio of the radii = 95 pm

181 pm=0.52 ⇒ the sodium ions will go into all 4 of

the octahedral holes b. ZnS (Zn2+= 74 pm, S2– = 184 pm) ⇒ Since sulfide is the larger ion it will reside in the lattice points of the

CCP ⇒ and since the ratio of the radii = 74 pm

184 pm=0.4 ⇒ the zinc ions will go into 4 of the 8

tetrahedral holesc. CaCl2 (Ca2+ = 99 pm, Cl– = 181 pm) ⇒ Since chloride is the larger ion it will reside in the lattice points of the

CCP ⇒ and since the ratio of the radii = 99 pm

181 pm=0.55 ⇒ the calcium ions will go into 2 of the

4 octahedral holes

14. Identify the type of doping in each of the following.a. Gallium doped with tin n typeb. Antimony doped with germanium p typec. A material is made from Al, Ga, and As. The mole fractions of these elements are 0.15, 0.26, and 0.59,

respectively.