Given:3.40g sample of the steel used to produce 250.0 mLSolution containing Cr2O72−
Assuming all the Cr is contained in the BaCrO4 at the end.
(0.145 g BaCrO4) / (253.3216 g BaCrO4/mol) x (250.0 mL / 10.0 mL) x (1 mol Cr / 1 mol BaCrO4) x (51.99616 g Cr/mol / (3.40 g) = 0.219 = 21.9% Cr
B. When electrons gain energy, they have the power to move up to a higher energy level in an atom.
Balancing redox reactions:
Oxygen should be balanced by adding 
as needed, while hydrogen should be balanced by adding 
.
What is a redox reaction?
Redox reactions, also known as oxidation-reduction reactions, involve the simultaneous oxidation and reduction of two different reactants.
The Half-Equation Method is one technique used to balance redox processes. The equation is divided into two half-equations using this technique: one for oxidation and one for reduction.
By changing the coefficients and adding , , and 
in that order, each reaction is brought into equilibrium:
- By putting the right number of water () molecules on the other side of the equation, the oxygen atoms are brought into balance.
- By adding ions to the opposing side of the equation, one can balance the hydrogen atoms (including those added in step 2 to balance the oxygen atom).
- Total the fees for each side. Add enough electrons () to the more positive side to make them equal. (As a general rule, and are nearly always on the same side.)
- The on either side must be made equal; if not, they must be multiplied by the lowest common multiple (LCM) in order to make them equal.
- One balanced equation is created by adding the two half-equations and canceling out the electrons. Additionally, common terms should be eliminated.
- Now that the equation has been verified, it can be balanced.
Learn more about redox reaction here,
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Mass of this substance = 9.928 g
<h3>Further explanation</h3>
Molarity is a way to express the concentration of the solution
Molarity shows the number of moles of solute in every 1 liter of solute or mmol in each ml of solution
Where
M = Molarity
n = Number of moles of solute
V = Volume of solution
So to find the number of moles can be expressed as
mol of substance -Lithium nitrite - LiNO₂ :
V = 250 ml = 0.25 L
M = 0.75 M
So mass of this substance - LiNO₂ (MW=52,947 g/mol) :
Answer:
D. Ni²⁺
Explanation:
We know at once that the answer cannot be A or C, because Ni and Cu are already in their lowest oxidation states.
The correct answer must be either B or D.
An electrolytic cell is the opposite of a galvanic cell. In the former, the reaction proceeds spontaneously. In the latter, you must force the reaction to occur.
One strategy to solve this problem is:
- Look up the standard reduction potentials for the half reaction·
- Figure out the spontaneous direction.
- Write the equation in the reverse direction.
1. Standard reduction potentials
E°/V
Cu²⁺ + 2e⁻ ⟶ Cu; 0.3419
Ni²⁺ + 2e⁻ ⟶ Ni; -0.257
2. Galvanic Cell
We reverse the direction of the more negative half cell and add.
<u>E°/V
</u>
Ni ⟶ Ni²⁺ + 2e⁻; 0.257
<u>Cu²⁺ + 2e⁻ ⟶ Cu; </u> 0.3419
Ni + Cu²⁺ ⟶ Cu + Ni²⁺; 0.599
This is the spontaneous direction.
Cu²⁺ is reduced to Cu.
3. Electrochemical cell
<u>E°/V</u>
Ni²⁺ + 2e⁻ ⟶ Ni; -0.257
<u>Cu ⟶ Cu²⁺ + 2e⁻; </u> <u>-0.3419</u>
Cu + Ni²⁺ ⟶ Ni + Cu²⁺; -0.599
This is the non-spontaneous direction.
Ni²⁺ is reduced to Ni in the electrolytic cell.
