Search results
Results from the WOW.Com Content Network
Titrations between a weak acid and a weak base have titration curves which are very irregular. Because of this, no definite indicator may be appropriate and a pH meter is often used to monitor the reaction. [24] The type of function that can be used to describe the curve is termed a sigmoid function.
Three different points in an acid-base titration using phenolphthalein as the indicator Phenolphthalein is widely recognized as one of the most commonly used acid-base indicators in chemistry. [ 12 ] Its popularity is because of its effectiveness in a broad pH range and its distinct colour transitions. [ 12 ]
In and of themselves, pH indicators are usually weak acids or weak bases. The general reaction scheme of acidic pH indicators in aqueous solutions can be formulated as: HInd (aq) + H 2 O (l) ⇌ H 3 O + (aq) + Ind − (aq) where, "HInd" is the acidic form and "Ind −" is the conjugate base of the indicator. Vice versa for basic pH indicators ...
Phenolphthalein is often used as an indicator in acid–base titrations. For this application, it turns colorless in acidic solutions and pink in basic solutions. It belongs to the class of dyes known as phthalein dyes. Phenolphthalein is slightly soluble in water and usually is dissolved in alcohols in experiments.
The indicator may be present in another liquid phase in equilibrium with the titrated phase, the indicator is described as extraction indicator. Some complexometric indicators are sensitive to air and are destroyed. When such solution loses color during titration, a drop or two of fresh indicator may have to be added.
The iodometric titration is a general method to determine the concentration of an oxidising agent in solution. In an iodometric titration, a starch solution is used as an indicator since it can absorb the I 2 that is released, visually indicating a positive iodine-starch test with a deep blue hue. This absorption will cause the solution to ...
Complexometric indicator, a chemical detector for metal ions in complexometric titrations. Humidity indicator card, a card impregnated with chemicals that change colour when a particular humidity is exceeded. pH indicator, a chemical detector for protons in acid-base titrations. Redox indicator, a chemical detector for redox titrations.
When used as an indicator in an EDTA titration, the characteristic blue end-point is reached when sufficient EDTA is added and the metal ions bound to the indicator are chelated by EDTA, leaving the free indicator molecule. Eriochrome Black T has also been used to detect the presence of rare earth metals. [2]