5. Surface energy (2 pts). Let’s use the concept of surface tension as surface energy per unit area to see if we can estimate, at least to the correct order of magnitude, the surface tension of water.

a) Water has a molar mass of 18 g/mol and a density of 1000 kg/m3 (or 1 g/cm3). Based on this data, estimate the number of water molecules per unit surface area of water.

b) The coordination number of water (i.e., the average number of “neighbors” each water molecule has) in the liquid state is 4. Neighboring water molecules attract each other via hydrogen bonds, each of which has a binding energy of roughly 10–20 J (although this number depends relatively strongly on temperature). Use this information to estimate the surface tension of water. How does your estimate compare to the observed figure ( γ water = 0.072 N/m ) (hints: Keep in mind that we can think of surface tension as surface energy per unit area, and consider the energy needed to bring a molecule from the bulk to the surface)?

1. Explain why a packed fractionating column (steel wool inside the glass tube) is more efficient than an unpacked one for distillation? Explain in detail.

2. If 3 spots on a TLC, plates have the following Rfs, A= 0.43, B=0.89, and C=0.53 what would be the order that the spots came off a column? What would happen if you increased the polarity of the solvent?

1.A bucket of nails contains 348 nails. How many dozens of nails does the bucket contain? 1 dozen=12 objects 2.How many atoms are in 3.56 mol of pure aluminum? 3.For the given elements, convert the given mole amounts to grams. A.How many grams are in 0.0564 moles of lithium? B.How many grams are in 0.550 moles of cobalt? C.How many grams are in 0.790 moles of oxygen? 4.For the given elements, convert 1.00 gram of that element to moles. A.How many moles of beryllium are in 1.00 gram? B.How many moles of zinc are in 1.00 gram? C.How many moles of phosphorus are in 1.00 gram?

a. A 1.500 g sample of a mixture of solid Na3PO4 - 12H2O and BaCl2 - 2H2O was dissolved in water and formed 0.520g of Ba3(PO4)2 precipitate. If reagent tests demonstrated that Na3PO4 - 12H2O was the limiting reactant in the precipitation reaction, calculate the mass percent of each reactant in the original sample. b. Clearly demonstrate which reactant salt would be limiting if the experiment was performed with equal masses of each salt. Assume 0.500g of each salt, for instance.

Consider the data for the following reaction at 25 ^oC

                2 HgCl₂(aq) + C₂O₄^2-(aq) --------2 Cl^-(aq) + 2 CO₂ (g) + Hg₂Cl₂(s)    Where Rate = [C₂O₄^2-]/t

Determine the 'orders for each reactant.

Determine the rate constant for this reaction.

Determine the instantaneous rate of change for HgCl₂ when [HgCl₂] = O.l22 M and [C₂O₄^2- ] = 0.50 M.           

Experiment	[HgCl2] (M)	[C2O42-] (M)	Rate (M/s)
1	0.164	0.15	3.2 x 10-5
2	0.164	0.45	2.9 x 10-5
3	0.082	0.45	1.4 x 10-5
4	0.246	0.15	4.8 x 10-5

Excited H atoms have many emission lines. One series of lines, called the brackett series, occurs in the infrared region. It results when an electron changes from higher energy levels to a level with n=4. Calculate the wavelength and frequency of the lowest energy line of this series.

Modern pennies are composed of zinc coated with copper. A student determines the mass of a penny to be 2.480 g and then makes several scratches in the copper coating (to expose the underlying zinc). The student puts the scratched penny in hydrochloric acid, where the following reaction occurs between the zinc and the HCl (the copper remains undissolved):
Zn(s)+2HCl(aq)→H2(g)+ZnCl2(aq)
The student collects the hydrogen produced over water at 25 ∘C. The collected gas occupies a volume of 0.903 L at a total pressure of 786 mmHg .

Calculate the percent zinc in the penny. (Assume that all the Zn in the penny dissolves.)

The samples of cyclohexane and toluene you collected during distillation were kept in a fridge for a week before being analyzed by GC. Explain what would be different about the GC analysis results if they were kept out on a shelf in lab instead. Refer to each fraction collected

The dibasic compound B (pKb1 = 4.03, pKb2 = 8.06) was titrated with 1.18 M HCl. The initial solution of B was 0.118 M and had a volume of 100.0 mL. Find the pH at the following volumes of acid added: Va = 0.00, 2.00, 5.00, 9.00, 10.00, 11.00, 15.00, 19.00, 20.00, and 22.00 mL. (Assume Kw = 1.01 ✕ 10−14.)

Provide a desription of the Kreb's cycle in the biosynthesis of amino acid

Using the values of the effective molar absorptivities you determined from your slopes and the values of the absorption you obtained for the mixture at the spectral maxima of 434 nm and 618 nm, solve the 2x2 simultaneous linear equations for the concentrations of bromothymol blue and thymol blue.

The slope of thymol blue at 434nm is y=.0124x, and bromothymol blue at 434nm is y=.0053x.

The slope of thymol at 618nm is y=.0018x, and bromothymol blue at 618nm is y=.0296x.

Given that the absorbance of the unknown mixture is 0.524 at 434nm and 0.293 at 618nm, what is the concentration of bromothymol blue and thymol blue respectively?

Additionally, the undiluted molarity of the thymol is 61.6um and the molarity of the undiluted bromothymol blue is 23.2um.

Summarize 4th phase of water

Consider the following reduction potentials:

Mg2+ + 2e- → Mg

E° = -2.37 V

V2+ + 2e- → V

E° = -1.18 V

Cu2+ + e- → Cu+

E° = +0.15 V

Which one of the following reactions will proceed spontaneously?

• Mg2+ + V → V2+ + Mg

• Mg2+ + 2Cu+ → 2Cu2+ + Mg

• V2+ + 2Cu+ → V + 2Cu2+

• V + 2Cu2+ → V2+ + 2Cu+

1.) An unknown carbohydrate solution tested positive with molisch reagent, formed a red precipitate with barfoed's reagent within 3 minutes, and turned blue-green when mixed with bials reagent. what carbohydrate is this?

2.) Erythrose is a four-carbon aldose. Describe the results of testing it with the following reagents.

a.) Molisch

b.) Barfoed's

c.) Benedict's

d.) Seliwanoff's