3.13
완충: 완충액 용량
완충 용량은 pH 변화에 저항하는 완충액의 정량적 측정값입니다. 다음 방정식에서 볼 수 있듯이 '베타'로 표시되는 완충 용량은 1리터 완충 용액의 pH를 1 단위만큼 변화시키는 데 필요한 산 또는 염기의 몰수로 표현됩니다. 여기서 Ca와 C b는 각각 산과 염기의 몰수…
베타로 표시되는 완충액 용량은 산 또는 염기를 추가할 때 pH 변화에 대한 완충액의 저항을 정량적으로 측정한 것입니다. 단위 pH 변경 전에 1리터 완충 용액에 첨가된 산(C, a) 또는 염기(C, b)의 몰 수로 표시됩니다.
버퍼 용량이 높을수록 pH 변화에 저항하는 버퍼의 능력이 높아집니다.
pKa가 5인 산에 첨가된 염기의 몰 수가 pH에 대해 표시됩니다. 얻어진 곡선의 도함수는 pH가 pKa와 같을 때 가장 높은 완충 용량을 보여주며, 여기서 약산과 그 접합 염기의 농도는 완충 용액에서 동일합니다. 따라서, 완충액의 유효 pH 범위는 pka보다 1단위 크거나 작다.
3-10 pH 범위를 벗어나면 기존의 고농도의 H+ 또는 OH- 이온은 첨가된 산 또는 염기에 대한 pH 변화에 저항합니다.
완충 종의 농도는 비례적으로 완충 용량을 결정합니다.
Q1: What is buffer capacity and how is it measured?
Buffer capacity, represented as beta, quantifies a buffer's resistance to pH change when acid or base is added. It is expressed as the number of moles of acid or base needed to change the pH of a one-liter buffer solution by one unit. Higher buffer capacity indicates stronger resistance to pH changes.
Q2: Why is buffer capacity highest when pH equals pKa?
Buffer capacity reaches its maximum when pH equals pKa because the buffer solution contains equal concentrations of weak acid and its conjugate base. At this point, the buffer has maximum resistance to pH changes. The effective pH range of a buffer extends one unit above and below the pKa value.
Q3: How does buffer species concentration affect buffer capacity?
The concentration of buffer species proportionally dictates buffer capacity. Higher concentrations of weak acid and conjugate base in the solution increase buffer capacity. Therefore, selecting a buffer with appropriate species concentration is essential for achieving desired pH resistance in analytical applications.
Q4: What pH range should a buffer maintain for effective buffering?
A buffer's effective pH range is one unit more or less than its pKa value. Outside this range, high concentrations of H+ or OH− ions resist pH change from added acid or base. Buffers should be selected with pKa values within plus or minus one unit of the desired pH.
Q5: How is buffer capacity determined graphically?
Buffer capacity is determined by plotting pH versus moles of acid or base added to a buffer solution. The derivative of this curve yields a plot showing buffer capacity versus pH. This graphical method reveals that maximum buffer capacity occurs at pH equal to pKa, where solution composition during acid base titrations is most balanced.
Q6: What factors determine the choice of an effective buffer?
An effective buffer requires a pKa value within plus or minus one unit of the desired pH and sufficient concentration of weak acid and conjugate base species. Both the pKa and buffer species concentration proportionally influence buffer capacity. These factors together ensure maximum resistance to pH changes in the target pH range.
Q7: How do weak acid and conjugate base concentrations relate to buffer effectiveness?
Buffer capacity depends directly on the concentration of weak acid and its conjugate base in solution. When these species are present in equal concentrations at pH equal to pKa, the buffer achieves maximum capacity. Increasing either species' concentration proportionally increases the buffer's ability to resist pH changes.