3. A calibration curve plotting E vs. pNi is used to measure the concentration of Ni2+ in solution at 25 °C using a solid Ni electrode. What is the slope of the calibration curve?

the slope of the calibration curve is - 0.0295

Explanation:

as things are not under standard conditions that is;  1M of each reactants at T = 25°C and P = 1 atm; therefore we will use the Nernst Equation.

E = a × pNi + b

a is the slope

pNi = -log [Ni²⁺] = log 1/[Ni²⁺]

therefore the Half reaction;

Ni²⁺ (aq) + 2e⁻ = Ni (s)

here; E = E₀ + RT/zF ln[Ni²⁺]

we know that;

gas constant R = (8.31 J/mol-K)

absolute temperature T =25°C =  298 K

number of moles of electrons transferred by the cell's reaction z  = 2

F is Faraday constant, = 9.64853399(24)×10⁴ C mol−1

E₀ = b

RT/zF ln[Ni²⁺] = alog 1/[Ni²⁺]

Logx = Ln x / Ln 10 = Ln (x/2.3)

so

a = (RT/zF ln[Ni²⁺])/log 1/[Ni²⁺]

= (RT/zF ln[Ni²⁺]) / ((ln 1/[Ni²⁺]) / 2.3)  

= (2.3RT/zF ln[Ni²⁺]) / (ln 1/[Ni²⁺])

= (2.3RT/zF ln[Ni²⁺]) / (-ln [Ni²⁺])

= -2.3RT/zF

so we substitute

= (-2.3 × 8.31 ×298 ) / (2 × 9.64853399(24) × 10⁴)

= - 0.0295

therefore the slope of the calibration curve is - 0.0295

answer is a

explanation:

answers: to make sure that all of the broken pieces of tablet were added to the water, to allow for fair comparison of all three trials, with different particle sizes to avoid experimental error