How can scientist measure the standard reduction potential of a half cell

It is possible to determine the standard reduction potential of half cell by using hydrogen electrode as a reference electrode.

The standard oxidation potential of hydrogen half cell, under standard conditions, is 0 v. Hence, when an unknown half cell (say X/X-) is clubbed with hydrogen half cell, it directly gives the half cell potential of electrode of interest. 

Such electrochemical cell can be represented as follows:

                                                     Pt/H2/H+//X-/X

Here, Eo cell = Eo X/X-  -   Eo H2/H+

But,  Eo H2/H+ = 0 V

∴ Eo cell = Eo X/X-

Pair It with a hydrogen half-cell

Explanation:

Gradpoint

 the total volume  of   gas is 1687.75 L

Calculation

2NH4NO3→ 2N2(g) +O2(g) + 4 H2O(g)

Volume of a gas is calculated using ideal gas equation

that is Pv=nRT

P(pressure)= 749 mm Hg

V(volume)=?

n (no of moles)

to  calculate the  number  of  moles  of  gas.

  find  the  moles of NH4NO3

  moles=mass/molar  mass

  mass=1.56 kg = 1.56 x 1000 = 1560 g

 molar mass of NH4NO3 =14+(1 x4) + 14 +( 16  x3) = 80 g/mol

moles= 1560 g/80 g/mol=19.5 moles

by use of mole ratio of NH4NO3 : total number of  mole of a gas  from equation above  which is = 2:7 therefore the moles of gas = 19.5 x7/2 =68.25 moles

therefore n=68.35 mole

R( gas  constant)  =62.36367  L.mmhg/mol.K

T(temperature) =24°c into k = 24 +273=297K

by  making V the subject of the formula

v=nRT/P

V= (68.25  mol  x 62.36367 L.mmhg/mol.k  x 297 k) / 749  mmhg = 1687.75 L