Buffer capacity, represented as beta, is the quantitative measure of a buffer's resistance to pH change upon adding an acid or base. It is expressed as the number of moles of acid (Ca) or base (Cb) added to a one-liter buffer solution before a unit pH alteration. The higher the buffer capacity, the higher the buffer's ability to resist the pH change. To an acid with pKa equal to 5, the number of moles of base added is plotted versus pH. The derivative of the curve obtained shows the highest buffer capacity when pH equals pKa, where the concentration of weak acid and its conjugate base are equal in the buffer solution. So, the effective pH range of a buffer is one unit more or less than the pKa. Outside the 3-10 pH range, the existing high concentration of H+ or OH− ions resists the pH change to the acid or base added. The concentration of the buffer species proportionally dictates buffer capacity.