What is the oxidation number of chromium in the ionic compound ammonium dichroma

Question

What is the oxidation number of chromium in the ionic compound ammonium dichromate, (NH_4)_2 CR_2 O_2? A) +3 B) +6 C) +4 D) +5 E) +7 The following reaction occurs in basic solution. Identify the reducing agent. A) H_2O(g) B) Zn(s) C) OH^- (aq) D) NO_3^- (aq) E) NH_3(aq) Which one of the following items does not characterize an oxidizing agent? A) An oxidizing agent gains electrons B) An oxidizing agent causes another species to be oxidized. C) The oxidation number of an oxidizing agent decreases. D) An example of a good oxidizing agent is an alkali metal, such as Na. E) A good oxidizing agent is a metal in a high oxidation state, such as Mn^7+ The standard reduction potentials have been determine using _____ A) A battery B) A standard hydrogen electrode C) A silver/silver chloride electrode D) A zine air battery E) The work done on a circuit The spontaneous redox reaction in a voltaic cell has ____ A) a negative value of Ecell and a negative value of Delta G. B) a positive value of Ecell and a negative value of Delta G. C) a positive value of Ecell and a positive value of Delta G E) a positive value of Ecell and a value of zero for Delta G. A voltaic cell is constructed based on the oxidation of zine metal and the reduction of silver metal. Solutions of silver nitrate and zine nitrate also were used. Locate the solution of Ag^+ on the diagram A) A B) B C) C D) D E) E about the cell reaction It is correct ___ A) The reaction at the cathode is Cu^2 + Cu B) The cell notation is Cu(s)|Cu^2 +(aq) ||Zn^2+ (aq)| Zn(s) (C) The electrons flow from the Cu half cell toward Zn half cell D) The reaction at the anode is Zn^2 + rightarrow Zn E) The flow of electron takes place at the bridge Electrolysis is defined as: A) The force pushing electrons through an electrical circuit B) System that converts chemical energy into electrical work C) A procedure to correct the calculation of cell potential for non-standard conditions D) A concentration cell E) Process in which electrical energy drives a non - spontaneous chemical reaction

Explanation / Answer

8) ammonium dichromate (NH4)2Cr2O7--->2NH4+ +Cr2O72-

Let the oxidation number of Cr in the ion Cr2O72- be x,

then adding up the oxidation number of all the atoms o fCr2O72- to give a net charge of -2 for the molecule,

2x+7(-2)=-2

2x-14=-2

2x=14-2=12

x=+6

so the oxidation number of Cr in Cr2O72- is +6 (correct optionB)

9) Zn(s) -2e ----->Zn2+ (Zn gets oxidized so Zn is the reducing agent)

Zn2+ + 4OH-----> Zn(OH)42-

correct option B

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