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# Need help with chemistry problems

Registered User regular
edited April 2009
Hi, H/A, it turns out that I forgot everything from the beginning of the semester in my chem lab.

And so, I require your aid in solving these here problems:

1.
A 50.0 mL sample of 0.400 M copper(II) sulfate solution at 23.35 degrees Celsius is mixed with 50.0 mL of 0.600 M sodium hydroxide solution, also at 23.35 degrees Celsius, in a calorimeter. After the reaction occurs, the temperature of the resulting mixture is 25.23 degrees Celsius. The density of the final solution is 1.02 g/mL. Calculate the heat of reaction. Assume the specific heat of the solution is the same as that of pure water 4.184 J/(g*degrees Celsius).

2.
75.0 mL of a 20.0 M solution of HIO (Ka= 2.3E-11) is titrated with 0.20 M solution of KOH. Determine the pH at the following points along the titration and draw the curve and label the points.

a) initial pH and [H+] of the weak acid prior to addition to the base
b) pH of the solution after 20 mL of KOH is added
c) pH at the 1/2 equivalent point
d) pH at the equivalent point
e) pH after a total of 100.0 mL of KOH are added to the acid

3.
Balance the Redox reactions

a) Iron reacts with hydrochloric acid to form aqueous iron(II) chloride and gaseous hydrogen
b) Chromium reacts with sulfuric acid to form aqueous chromium(III) sulfate and gaseous hydrogen
c) Tin reacts with concentrated nitric acid to form tin(IV) oxide, nitrogen dioxide and water

4.
Draw a schematic showing electron flow and find E naught, E, delta G naught, oxidizing agent, reducing agent, for the voltaic cell below.

Li(s), [Li+] = 0.25 || Au(s), [Au 3+] = 0.050

Take a stab at any of these you feel confident in explaining. I'm not looking for answers, in fact, I'd rather you just tried to explain how to do these.

Tam on

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Registered User regular
edited April 2009
What parts of these problems exactly are you having trouble with?

4U2NV on
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Registered User regular
edited April 2009
I don't even know how to start with 3 and 4 and I strongly suspect I'm doing 1 and 2 wrong. On number one, all I did was to calculate mass by multiplying the density by the total volume and then I ran the numbers through the Q = mCdeltaT equation and that's it.

I can do the first part of two, but I forgot which equations and formulas are appropriate for the rest of the parts.

Tam on
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Dr. Robot King Registered User regular
edited April 2009
for 3 essentially you :

Fe + HCl=FeCl + H+

then you need to balence the charges with molar equivilants and charges. i think. its been a while since i had to balance . but thats the jist of it. make sure you actually check that that is the actual things for the components though

mts on
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Registered User regular
edited April 2009
Ok, thanks. I'll keep working on these.

Tam on