teachbio

A 10.00mL sample of saturated Ca(IO3)2 is titrated with 0.0210M Na2S2O3 solution in the presence of excess KI and H2SO4. The reaction occurs according to equation:

IO3- + 6 S2O3^2- --> I- + 3 S4O6^2- + 9 H2O

a. If 32.10mL of Na2S2O3 is used to completely react with all of the IO3- in the 10.00mL sample of saturated Ca(IO3)2 solution, determine the molar concentration of IO3- in the saturated solution?

32.10mL x (0.0210 mol Na2S2O3/1000mL) x (1 mol IO3-/6 mol Na2S2O3) =

1.12 x 10-4 mol IO3-

1.1235 x 10-4 mol IO3-/0.010L= 0.0112 M IO3-

b. What is the molar concentration of Ca2+ in the solution?

Starting with the calculation in part a

(0.0112 moles Ca(IO3)2/1 L) x (1 mol Ca2+/2 mol (IO3)-) = 0.00560M Ca2+

c. Calculate the molar solubility and the Ksp of calcium iodate. The solubility equilibrium equation is

Ca(IO3)2 <-----> Ca2+ + 2 IO3- Ksp = [Ca2+][IO3-]^2

Ksp = [0.00560] x [0.0112]2 = 7.02 x 10-7

Molar solubility: 7.02 x 10-7 = (x) (2x)2 and then solving for x, x= 5.60 x 10-3 M

The question reads:

Quinine (an old drug used to treat malaria, and the characteristic flavoring in tonic water) is an example of a fluorescent compound. It absorbs ultraviolet light with a wavelength of 350 nm, and converts it into visible light with a wavelength of 450 nm.

A second photon is given off in this process. Calculate its wavelength.

My logic (be nice if I am way off, please ;):

1. The energy of a photon is inverse to it's wavelength. If we know the wavelength, we can calculate the energy.

2. Energy cannot be created or destroyed. If a 'visible light' ray and a 2nd photon are released, the sum of their emission energies should equal the energy of the absorption energy.

3. An electron absorbs the energy associated with a wavelength of 350nm.

4. Two photons are released. One photon has a total energy of a 450nm so the other photon has the energy of a 100nm wavelength.

350nm + x nm = 450nm --> x = 100 nm

Therefore, to 'calculate' the wavelength of the second photon, subtract the energy released from the energy absorbed.

Any help in logic would be appreciated.

The question:

Quinine (an old drug used to treat malaria, and the characteristic flavoring in tonic water) is an example of a fluorescent compound. It absorbs ultraviolet light with a wavelength of 350 nm, and converts it into visible light with a wavelength of 450 nm. A second photon is given off in this process. Calculate its wavelength.

I don't understand where to start....do I calculate energies for both the 350 and 450nm, subtract the difference and then solve for the new wavelength associated with that energy?

Thanks for any help....feeling really stupid right now :(

A 10.00mL sample of saturated solution of calcium iodate is titrated with 0.0210M Na2S2O3 in the presence of excess KI and H2SO4, using starch as an indicator. The reaction occurs according to the following equation:

IO3- + 6 S2O3 2- + 6 H3O+ --> I- + 3 S4O6 2- + 9 H2O

a. If 32.10mL of Na2S2O3 were needed to completely react with all of the IO3- in the 10.00mL sample of saturated Ca(IO3)2 solution, determine the molar concentration of IO3- in the saturated solution.

a. 32.10mL x (0.0210 mol Na2S2O3/1000mL) x (1 mol IO3-/6 mol Na2S2O3) =

1.1235 x 10-4 mol IO3-

Now divide by the 10.00mL: 1.1235 x 10-4 mol IO3-/0.010L= 0.01124 M IO3- is my answer

b. What is the molar concentration of Ca 2+ in the solution? I am assuming they are asking after titration?????

10.00mL Ca(IO3)2 x (0.0210 moles Ca(IO3)2/1000mL) x

(1 mol Ca2+/1 mol Ca(IO3)2) = 2.100 x 10-4 moles Ca2+

Now divide by the total 42.10mL:

2.100 x 10-4 moles Ca2+/0.04210L= 5.122 x 10-3 M Ca2+ is my answer

The answer is supposed to be 50.3 kg Al, but I keep getting 503 kg. Can you spot my error?

The production of aluminum metal by electrolysis of molten Al2O3-Na3AlF6 mixture uses electrolytic cells that operate at 3.5 V and 1.5 x 10^6 Amp. (a) How many kilograms of Al can be produced in 1.00 hour?

Al3+ + 3 e- → 3 Al

C= amp x sec → 1.5 x 106 Amp x (1.00 hr) x (3600 sec/hr) = 5.4 x 109 C

Moles e- = 5.4 x 109 C x (1 mol e-/96,485 C) = 5.6 x 104 mol e-

5.6 x 104 mol e- x (1 mol Al/3 mol e-) x (26.98 g Al/1 mol) x (1 kg/1000g) = 503 kg Al

I would appreciate any help you can give.

I know to break into 2 half-equation, but they seem to be opposite of each other:

Cl2 Ox number is 0, Cl ox number in NaOCl is +1, and in NaCl Cl ox number is -1

So I have: 2e- + Cl2 --> 2 Cl- and Cl2 --> 2Cl+ + 2e-

Na, O and H have not changed ox state so I can't use them for electrons.

Help!

OCl- + Cl- --> Cl2 + H20 must be balanced in acid

I came up with

4H+ + Ca(OCl)2 + 2 NaCl --> 2Cl2 + 2H20 + CaCl2

2x^2 - 13y^2 + 5 = 0

My process: 1. subtract 5 from both sides. 2. divide both sides by -5???

Tried dividing by -5, by GCF, etc.

Explanation would be appreciated.

How many ways are there to draw a 4, 5, 6, 7 and 8 from a deck of 52 standard cards, with the condition that not all the cards are the same suit?

I think this is combinations problem, with 5 separate 4C1 equations that I multiply together. But how do I account for the suits not all being the same?

How would I calculate the pH of a solution of a weak acid if I only know the molarity of the acid? Don't I need a Ka value? Ex: Determine the pH of a 0.531M HF solution.

Based on formal charge, the best structure for SO2 would be O=S=O with an unbonded pair of e- on the sulfur. This does disobey the octet rule, however. Based on octet rule, SO2 would have a single and a double bond (resonance structures) with +1 formal charge on S and -1 formal charge on single bonded O.

Bond measure for SO2 is 1.43A and for SO is 1.48A. Which structure is correct and why????

The BP of methylacetylene is -23C and that of 1,2-propadiene is -34C. I am not sure how to explain what IMFs explain this difference. My guess is that methylacetylene will have higher LDFs due to triple bond in structure, but I am not sure.

Thanks for any insight!

Which of these elements (Mg, S, Cl, N or B) forms a gaseous molecule with the formula XF2? And then please explain why. I know I can eliminate Mg because MgF2 is a solid.