5.13
단원: 강수량 적정 곡선: 분석
침전 적정 곡선은 첨가된 적정제의 부피에 따른 한 반응물의 농도 변화를 보여줍니다. 질산은을 사용하여 염화물 이온을 적정하는 동안 침전 적정 곡선은 당량점 이전, 당량점 및 이후의 세 영역으로 나뉩니다. 당량점 이전에 난용성 염화은 침전물의 낮은 재용해는 낮은 은 이온…
질산은을 사용한 염화물의 적정에서, 초기은 이온 농도는 드물게 용해되는 염화은 침전물의 제한된 재용해로 인해 낮습니다.
염화물은 당량점에서 완전히 소비되고은 농도가 급격히 상승합니다.
당량점을 넘어서면, 높은 은 농도는 주로 과도한 적정제에서 비롯됩니다.
적정 곡선의 모양은 침전물의 용해도 생성물에 의해 영향을 받습니다.
요오드화은 용해도가 낮다는 것은 은 농도가 낮고 당량점에서 더 큰 파단을 시사합니다.
더 큰 염화은 용해도 생성물은 더 높은 은 농도와 당량점에서 더 작은 파손을 시사합니다.
요오드화물과 염화물의 혼합물을 질산은에 대해 적정하면 요오드화은은 낮은 용해도 생성물로 인해 먼저 침전됩니다.
첫 번째 당량점에 가까우면 요오드화물이 거의 완전히 소모됨에 따라 염화은의 용해도 생성물에 도달할 때까지 은 농도가 증가합니다. 모든 염화물이 침전되면 두 번째 당량점이 관찰되고 은 농도가 다시 상승합니다.
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Q1: Why is the silver ion concentration low before the equivalence point in a chloride titration?
Before the equivalence point, silver ion concentration remains low because silver chloride is a sparingly soluble precipitate. Limited redissolution of this precipitate keeps silver ions in solution at minimal levels. As titrant is added, most silver ions are consumed forming the solid precipitate rather than remaining dissolved.
Q2: What causes the sharp increase in silver ion concentration at the equivalence point?
At the equivalence point, chloride ions are completely consumed, so silver ions are no longer being removed from solution by precipitation. This sudden shift causes silver ion concentration to rise sharply. Beyond this point, excess silver nitrate titrant directly increases the silver ion concentration in solution.
Q3: How does the solubility product affect the shape of a precipitation titration curve?
The solubility product determines the magnitude of the concentration break at the equivalence point. Silver iodide, with a lower solubility product than silver chloride, produces a larger break because less silver remains dissolved. Conversely, silver chloride's higher solubility product results in a smaller break and higher silver concentration before the equivalence point.
Q4: Why does silver iodide precipitate before silver chloride in a mixed halide titration?
Silver iodide precipitates first because it has a much lower solubility product than silver chloride. This means iodide ions are removed from solution at lower silver ion concentrations. Once iodide is nearly consumed, silver concentration rises until it reaches the solubility product threshold for silver chloride precipitation.
Q5: What are the two equivalence points observed when titrating a mixture of iodide and chloride?
The first equivalence point occurs when all iodide ions are consumed. After this point, silver concentration increases until silver chloride begins to precipitate. The second equivalence point marks complete consumption of chloride ions, after which silver concentration rises again due to excess titrant.
Q6: How does the titration curve change in the region after the equivalence point?
After the equivalence point, the silver ion concentration is high and increases linearly with added titrant volume. This region is dominated by excess silver nitrate, which directly contributes silver ions to the solution. The curve shows a steep positive slope as no precipitation reaction consumes the added silver ions.
Q7: What role does reactant concentration play in determining the precipitation titration curve shape?
Reactant concentration influences the overall magnitude and steepness of the titration curve. Higher concentrations of chloride or other halides affect how quickly the equivalence point is reached and the degree of concentration change observed. Combined with the solubility product, reactant concentration determines the curve's characteristic shape and break magnitude.