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# Cr and Mn reactions

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For reaction 3b provide a completely balanced reaction and do it for number 6 also, my response for 3b was:

Cr(s) + 2HCl--> H2(g) + CrCl2+(aq)

My reaction may not be correct but the CrCl2+ is based off my results for the observation I got, which I don't believe are correct... The other two questions are what was the role of H2SO4 in the chromium #11 reaction (I put an acid catalyst because CrO4 to Cr2O7 is not a redox reaction) and the last was what was the role of FeSO4 salt after the addition of H2SO4 to the Cr reagent.

My results for # 3 were no reaction initially, after heating the HCl and Cr(s) , the solution evolved H2 and turned light blue. I have no clue about the product of 6 because I don't believe I had the previous two correct. For reaction 4, the tubes turned dark green after being shaken, and the same happened for reaction 5. Upon adding the zinc powder it precipitated and turned lighter green. Please let me know what you think, I'm attaching the oxidation states sheet with observations. Let me know if you need anything else but I believe I included everything

https://brainmass.com/chemistry/transition-metals/cr-mn-reactions-528132

#### Solution Summary

The details of reactions of Cr and Mn in a lab are discussed.

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## Questions I am iffy on

I am completing this class now, reviewing the entire scope of classwork leading to the finals, and there are some review questions I am just real shaky on-and some I simply cannot find an applicable formula for.

Thank you!

1. The measured voltage of a cell in which the following reaction occurs is 0.96 V:

H2(g, 1.0 atm) + 2Ag+(aq, 1.0 M) &#8594; 2H+(aq, pH = ?) + 2Ag(s)

Calculate the pH of the H+(aq) solution.

2. How many coulombs would be required to electroplate 35.0 grams of chromium by passing an electrical current through a solution containing CrCl3?

3. How many coulombs (C) of electrical charge must pass through an electrolytic cell to reduce 0.44 mol Ca2+ ion to calcium metal?

4. When the following redox reaction is balanced, the coefficient for Cl2 will be _____, and ____ is the reducing agent.
KMnO4(aq) + KCl(aq) + H2SO4(aq) ----> MnSO4(aq) + K2SO4(aq) + H2O(aq) + Cl2(g).

5. What is the coefficient of the bromide ion when the following redox equation is balanced?
BrO- (aq) Fe(OH2) (s) Br-(aq)Fe(OH)3(s) (basic solution)

6. Which one of the following reagents is capable of transforming Cu2+ to Cu(s)?
A I- (aq) Ag(s) B. Ni(s) C Al3+(aq) D. F- (aq)

7. Silver chloride (AgCl(s)) will be most soluble in a solution of:
A. 0.10 M AgNO3
B. distilled water
C. 0.10 M NaCl
D. 0.10 M HCl
E. 0.10 M aqueous NH3

8. Calculate the minimum concentration of Cr3+ that must be added to 0.095 MNaF solution in order to initiate a precipitate of chromium (III) fluoride. For CrF3 , Ksp = 6.6 × 10-11.

A. 0.023 M
B. 0.032 M
C. 7.7 × 10-8 M
D. 2.9 × 10-9 M
E. 6.9 × 10-10 M

9. The equilibrium constant for the reaction:
AgBr(s) Ag(aq) Br(aq) +&#8722;&#8660;+
is the solubility product constant, Ksp = 7.7 × 10-13 at 25°C. Calculate &#916;G for the reaction when [Ag+] = 1.0 × 10-2 M and [Br-] = 1.0 × 10-3 M. Is the reaction spontaneous or nonspontaneous at these concentrations?

A. &#916;G = 69.1 kJ, nonspontaneous
B. &#916;G = -69.1 kJ, spontaneous
C. &#916;G = 97.5 kJ, spontaneous
D. &#916;G = 40.6 kJ, nonspontaneous
E. &#916;G = -97.5 kJ, nonspontaneous

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