Improving upon the capabilities of indicator paper, pH meters are able to quanti

Question

Improving upon the capabilities of indicator paper, pH meters are able to quantitatively measure the acidity of a solution. All pH values that follow are measurements of 0.010 M solutions. For ions, the values represent solutions of the sodium salts of the ion. Drawing Lewis structures will help you see the structure–pH relationship more clearly. If uncertain of the atom attachments ask your instructor.

5.   Rank the bases by increasing base strength:

Species pH Species pH Species pH HClO4 2.00 SO32– 9.60 H2S 4.50 H2SO4 2.00 HCl 2.00 HPO42– 9.60 H3PO4 2.24 H2PO4– 4.60 HBr 2.00 ClO– 9.73 HI 2.00 SO42– 7.00 ClO4– 7.00 H2SO3 2.18 PO43– 11.89 HSO4– 2.88 CH3COOH 3.37 NaOH 12.00 HClO 4.73 HS– 9.50 HNO2 2.72 HSO3– 4.60 H2O 7.00 Cl– 7.00

Explanation / Answer

As pH values are given in the table along with the species at a particular concentration i.e. 0.010 Molar.

As we all know that stronger is the base, weaker will be its conjugate acid and vice-versa.

As pH= -log(H+) and pOH = -log(OH-)

where (H+) & (OH-) are the concentration of H+ and OH- at equilibrium.

Also pH +pOH =14(pKw) for aqueous solutions at 25 degree cetigrade.

At a particular concentration, higher the pH, lower will be the acidic strength or higher is the conjugate basic strength.

This is because higher the pKb, higher will be pH of solution ad lower will be the pOH of the solution where pKb is the equilibrium dissociation constant of the base.

Rank the bases by increasing base strength:

First, we have to choose the bases from the give species:

ClO–,   ClO4–,  HSO4–, HSO3–, SO32–, H2PO4–, HS–, H2O, HPO42–, SO42–, PO43–, NaOH, Cl–

Rank the bases by increasing base strength:

HSO4–< HSO3– = H2PO4– < Cl– = ClO4– = SO42– = H2O < HS– < SO32– = HPO42– < ClO– < PO43– < NaOH

Lower the basic strength of the base, higher is the stability may be due to large size, the presence of empty d orbitals and the resonance also.

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