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

If i were to get the amount of heat transfer using constant pressure calorimetery, can I get the amount for the constant volume calorimetery using that value? Or vice versa?

A solution contains 0.003Mof sodium phenobarbital together with a buffer consisting of 0.20 M sodium acetate and 0.30 M acetic acid. Acetic acid is a weak electrolyte; its degree, or fraction, of dissociation, α, at this concentration is 0.008 and the undissociated species do not contribute to the ionic strength. What is the ionic strength of the solution?

pka for acetic acid = 4.8

At 85oC, the vapor pressure of pure o-xylene is 55 Torr and the vapor pressure of pure p-xylene is 85 Torr. When liquid o-xylene is mixed with liquid p-xylene, the solution formed is ideal at all compositions.

(a) Calculate ∆G, ∆H, and ∆S of mixing when liquid o-xylene and liquid p-xylene are mixed at 85oC, given that the mole fraction of p-xylene is 0.30 and the solution contains a total of 4.0 mol of material.

(b) What are the mole fractions of o-xylene and p-xylene in the vapor at equilibrium with this solution?

A 115.0 −mL sample of a solution that is 2.6×10⁻³ M in AgNO3 is mixed with a 230.0 −mL sample of a solution that is 0.14 M in NaCN .

After the solution reaches equilibrium, what concentration of Ag+(aq) remains?

Could you give me some tips on how to know how to identify chiral centers in a large molecule?

I know that a chiral center is surrounded by 4 different groups...but I'm finding it a little bit hard to recognize multiple chiral center in large structures.

If the dissolution of KCl (74.55 g/mol) is expected to absorb 17.2 kJ of energy per mole of KCl dissolved, then what is the expected change in temperature (in oC) if 2.11 grams of KCl are dissolved in 10.00 mL of water (density of 1.00 g/mL and specific heat capacity of 4.184 J/g•oC)? (Give answer as the absolute value of the temperature change; do NOT include negative sign if temperature decreases.)