Waec Model Questions Vol1 2018 Chemistry Question 7

Practice essay / theory question 7 from the 2018 Waec Model Questions Vol1 Chemistry examination. This question covers Acids Bases and Salts .

Waec Model Questions Vol1 2018 Chemistry Essay / Theory

Topic: Acids Bases and Salts

Question 7 WAEC_MODEL_QUESTIONS_VOL1 • 2018 • CHEMISTRY • essay

A buffer solution is prepared by mixing a weak monoprotic acid HA (pK_a = 4.75) with its sodium salt NaA. The total volume of the solution after mixing is 1.00 L.

Question Parts

( a )

Write the expression for the acid dissociation constant K_a of HA and derive the Henderson–Hasselbalch equation relating pH, pK_a and the ratio [A⁻]/[HA].

( b )

Calculate the pH of the buffer when 0.250 mol of HA and 0.150 mol of NaA are dissolved in the 1.00 L solution.

( c )

If 0.050 mol of a strong acid (HCl) is added to the buffer, calculate the new pH, assuming the volume remains 1.00 L.

( d )

Determine the buffer capacity (β) for the addition of a small amount of strong acid, defined as β = Δn/ΔpH, where Δn is the number of moles of H⁺ added. Use the data from part (c) with Δn = 0.010 mol of HCl added to the original buffer (before any acid was added).

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About This Question

This is Waec Model Questions Vol1 2018 Chemistry Question 7. It is one of the essay questions from the 2018 Waec Model Questions Vol1 Chemistry examination.

The question covers Acids Bases and Salts .

View More Waec Model Questions Vol1 2018 Chemistry Questions More Waec Model Questions Vol1 Practice Questions Back to Questions

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