Experiment7Preparation and Properties of BuffersPurposes1.Grasp the properties of buffer solutions and effectfactors ofbuffercapacity2.Learn thepreparation of buffer solution and operation of themeasuringpipet3.Learn to determine the pH with colorimetry and pH-meter
Experiment 7 Preparation and Properties of Buffers Purposes 1. Grasp the properties of buffer solutions and effect factors of buffer capacity 2. Learn the preparation of buffer solution and operation of the measuring pipet 3. Learn to determine the pH with colorimetry and pH-meter
PrinciplesBuffer solution is defined as a solution that resists achange in pH when a small amount of acid or base isadded to it or when the solution is diluted. The buffersolution consists of a weak acid (HB) and its conjugatebase(B).The pH value of the buffer solution can becalculated by the following euationSB-pH =pKa + lgCHBK,istheacidionizationconstantFrom the equation above we can see that thepH value ofthe buffer solution depends upon the value of the ionizationconstant of conjugate acid and the concentration ratio ofthe conjugate acidto its conjugate base at equilibrium
Principles Buffer solution is defined as a solution that resists a change in pH when a small amount of acid or base is added to it or when the solution is diluted. The buffer solution consists of a weak acid (HB) and its conjugate base (B- ).The pH value of the buffer solution can be calculated by the following equation: HB B a pH p lg c c K − = + Ka is the acid ionization constant From the equation above we can see that the pH value of the buffer solution depends upon the value of the ionization constant of conjugate acid and the concentration ratio of the conjugate acid to its conjugate base at equilibrium
When the buffer solution is prepared by mixingequal concentrations of weak acid and its conjugatebase, the equation can be expressed asVBpH =pK, + lgVHB
When the buffer solution is prepared by mixing equal concentrations of weak acid and its conjugate base, the equation can be expressed as HB B a pH p lg V V K − = +
Buffer capacity is a quantitative measure of theability of the buffer solution to resist changes in pHit depends on concentrations and the ratio of B1/[HB]
Buffer capacity is a quantitative measure of the ability of the buffer solution to resist changes in pH, it depends on concentrations and the ratio of [B- ]/[HB]
pH value of a sample solution can be measured bypH-meter. There are two electrodes on a pH-meter,one is reference electrode which electrode potentialis a constant in some conditions: Another electrodeis sensitive to [H+l. When they are immersed in asolution,the potential difference between the twoelectrodes is related topH of the solution.The pHmeter is ordinarily used when an accuratedetermination of pHis needed
pH value of a sample solution can be measured by pH-meter. There are two electrodes on a pH-meter, one is reference electrode which electrode potential is a constant in some conditions; Another electrode is sensitive to [H+ ]. When they are immersed in a solution, the potential difference between the two electrodes is related to pH of the solution. The pH meter is ordinarily used when an accurate determination of pH is needed