Chem 130 WN26 Exam 3 Review

Solutions + IMFs

100

Define a Hydrogen Bond (what is necessary to form a hydrogen bond)

A hydrogen bond is a dipole-dipole interaction with especially strong covalent character. It has a) a donor proton thats bound to N,O, or F and b) an acceptor lone pair thats present on a N,O, or F atom

200

What is the formula for parts per billion (ppb)

g solute/g solution x 10^9

300

Daniel needs to dilute a stock for his experiment. The stock is currently at 500 nM, and he needs 1 mL at 10 nM. How much of the stock does he need?

0.02 mL or 20 microliters

400

Daniel is making a buffer that calls for 200 mM NaCl, 50 mM NaCH₃COO, and 20 mM Na₃PO_4. If he makes 1 L of buffer, what is the concentration of sodium ions in the buffer? 

200 mmol of NaCl = 200 mmol of Na+

50 mmol of NaCH₃COO = 50 mmol of Na+

20 mmol of Na₃PO_{4 =} 60 mmol of Na +

310 mmol/ 1 L = 310 mM Na+ or .310 M Na+

500

Scientists think they've discovered life on another planet. The planet doesn't seem to have any water, however, and instead seems to be based on Dihydrogen Sulfide (H₂S). Would H₂S be more likely to be a gas or a liquid at room temperature?

A gas. H₂S is a small polar compound, meaning it has weak IMFs and at room temperature is more likely to be in gas form.

Precipitation + Redox

100

What is the oxidation state of Bromine in Br₂

0. Br₂ is the elemntal form of Bromine

200

What is so special about a net ionic equation?

The net ionic equation details the actual chemical change that occurs. When two dissolved ionic compounds interact, if a solid (precipitate) forms, then an actual new substance is acquired vs the other ions that remain floating around in solution.

300

Predict the products: KCl (aq) + LiOH (aq) = ?

No Reaction. KOH and LiCl are both soluble 

400

In this reaction, Fe is being?

10 FeSO₄ + 2KMnO₄ + 8H₂SO₄ = 5Fe₂(SO₄)₃ + 2MnSO₄ + K₂SO₄ + 8H₂O

Oxidized. It goes from Fe²⁺ to Fe³⁺

500

Rank these molecules in terms of Nitrogen oxidation state (lowest to highest)

NO₂^-, NO₃^-, NH₃, N₂

NH₃,N_2,NO₂^-,NO₃^-

Thermodynamics

100

What is the first law of thermodynamics?

The energy of the universe is constant, so energy can neither be created nor destroyed

200

Name a path function

heat or work

300

A bomb calorimeter has a heat capacity of 1.12 kJ/ºC. If 3.46 moles of a hydrocarbon are burned, how much does the calorimeter change in temperature? dH = - 5.69 kJ/mol

q_comb=-q_cal

(5.69)(3.46)=-(1.12)(dT)

17.6 º C

400

Estimate the enthalpy change for the following reaction using the bond enthalpies provided:

H₂ (g) + Cl₂ (g) = 2HCl (g)

Bond Enthalpies:

• H-H: 436  kJ/mol

• Cl-Cl: 242 kJ/mol

• H-Cl: 431  kJ/mol

dH= (broken)-(formed)

dH= (436+242)-(2*431)

dH= -184 kJ/mol

500

Solve this Hess's law question:

1. 2 B (s) + 3/2O₂ (g)= B₂O₃ (s) dH = -1273  kJ/mol

2. B₂H₆ (g) + 3O₂ (g) = B₂O₃ (s) + 3H₂O (g)    dH= -2035 kJ/mol

3. H₂ (g) + 1/2 O₂ (g) = H₂O (g)                      dH= -242 kJ/mol
   
   

Target Equation: 2B (s) + 3H₂ (g) = B₂H₆ (g)

(-1273) + (-1)(-2035) + (3)(-242) = +36 kJ/mol

Phase Transitions (w some thermodynamics)

100

Define the triple point

The combination of pressure and temperature at which all three phases are in equilibrium

200

Why does stronger IMFs correlate with lower vapor pressure at the same temperature

Vapor pressure is the pressure of gas molecules above a liquid surface. If you have more molecules that can espace into the gas phase, you'll have more vapor pressure. If you have stronger IMFs, it's harder for molecules to transition from liquid to gas

300

100 g of ice initially at -10 ºC is heated to water at 34 º C. How much heat, in kJ, is associated with this process? 

Specific heat capacity of ice = 2.09 J/g ºC;

Heat of fusion = 334 J/g 

Specific heat capaticy of water = 4.184 J/g ºC

2.09 kJ + 33.4 kJ + 14.23 kJ =

49.72 kJ

400

52.7 mmols of water condense on a 75.0 g block of solid metal initially at 22 ºC. If the heat of condensation is used to warm up the block, what is the final temperature of the block? Heat of vaporization = 44.0 kJ/mol; C_metal = 0.449 J/g ºC

q_H2O=-q_metal

(-44,000 kJ/mol)(.0527 mol) = -(75g)(0.449 J/g ºC)(Tf -22ºC)

Tf= 91 º C

500

A 25.0 g ice cube at 0 º C is dropped into an insulated calorimeter containing 150.0 g of liquid water at 45.0 º C. Calculate the final temperature of the system once it reaches thermal equilibrium. Heat of fusion = 334 J/g; C_water= 4.184 J/g ºC

q_melt + q_warm-up=-q_cool-down

(334)(25) + (4.184)(25)(T-0)=-(4.184)(150)(T-45)

T= 27.2 º C