Examples of equivalence point in the following topics:
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- Before you begin the titration, you must choose a suitable pH indicator, preferably one that will experience a color change (known as the "end point") close to the reaction's equivalence point; this is the point at which equivalent amounts of the reactants and products have reacted.
- Below are some common equivalence point indicators:
- You can estimate the equivalence point's pH using the following rules:
- You can determine the pH of a weak acid solution being titrated with a strong base solution at various points; these fall into four different categories: (1) initial pH; (2) pH before the equivalence point; (3) pH at the equivalence point; and (4) pH after the equivalence point.
- The number of equivalents of acid and base must be equal at the equivalence point.
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- This indicates the formation of a buffer system as the titration approaches the equivalence point.
- At the equivalence point and beyond, the curve is typical of a titration of, for example, NaOH and HCl.
- At the equivalence point, all of the weak acid is neutralized and converted to its conjugate base (the number of moles of H+ = added number of moles of OH-).
- However, the pH at the equivalence point does not equal 7.
- The endpoint and the equivalence point are not exactly the same: the equivalence point is determined by the stoichiometry of the reaction, while the endpoint is just the color change from the indicator.
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- As the equivalence point is approached, the pH will change more gradually, until finally one drop will cause a rapid pH transition through the equivalence point.
- In strong acid-weak base titrations, the pH at the equivalence point is not 7 but below it.
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- Diprotic and polyprotic acids show unique profiles in titration experiments, where a pH versus titrant volume curve clearly shows two equivalence points for the acid; this is because the two ionizing hydrogens do not dissociate from the acid at the same time.
- The titration curve of a polyprotic acid has multiple equivalence points, one for each proton.
- In carbonic acid's case, the two ionizing protons each have a unique equivalence point.
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- A pH indicator shows the equivalence point—the point at which the equivalent number of moles of a base have been added to an acid.
- What is the unknown concentration of a 25.00 mL HCl sample that requires 40.00 mL of 0.450 M NaOH to reach the equivalence point in a titration?
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- The following table lists some representative derivatives and their boiling points.
- An aldehyde and ketone of equivalent molecular weight are also listed for comparison.
- Boiling points are given for 760 torr (atmospheric pressure), and those listed as a range are estimated from values obtained at lower pressures.
- As noted earlier, the relatively high boiling point of carboxylic acids is due to extensive hydrogen bonded dimerization.
- The relatively high boiling points of equivalent 3º-amides and nitriles are probably due to the high polarity of these functions.
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- It is instructive to compare the boiling points and water solubility of amines with those of corresponding alcohols and ethers.
- Corresponding -N-H---N- hydrogen bonding is weaker, as the lower boiling points of similarly sized amines (light green columns) demonstrate.
- Alkanes provide reference compounds in which hydrogen bonding is not possible, and the increase in boiling point for equivalent 1º-amines is roughly half the increase observed for equivalent alcohols.
- Indeed, 3º-amines have boiling points similar to equivalent sized ethers; and in all but the smallest compounds, corresponding ethers, 3º-amines and alkanes have similar boiling points.
- In the examples shown here, it is further demonstrated that chain branching reduces boiling points by 10 to 15 ºC.
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- The four equivalent bonds point in four geometrically equivalent directions in three dimensions corresponding to the four corners of a tetrahedron; this is called tetrahedral coordination.
- In an AX6 molecule, six electron pairs will try to point toward the corners of an octahedron (two square-based pyramids joined base-to-base).
- The shaded plane shown in the figure is only one of three equivalent planes defined by a four-fold symmetry axis.
- In an octahedral molecule, six electron pairs will try to point toward the corners of an octahedron.
- In a tetrahedral molecule, four equivalent bonds point in four geometrically equivalent directions in three dimensions, corresponding to the four corners of a tetrahedron centered on the carbon atom.
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- The face playing card provides an example of a center or point of symmetry.
- Another way of describing a point of symmetry is to note that any point in the object is reproduced by reflection through the center onto the other side.
- In these two cases the point of symmetry is colored magenta.
- A plane of symmetry divides the object in such a way that the points on one side of the plane are equivalent to the points on the other side by reflection through the plane.
- The symmetry elements of a structure provide insight concerning the structural equivalence or nonequivalence of similar component atoms or groups.
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- Most of the simple hydrides of group IV, V, VI & VII elements display the expected rise in boiling point with molecular mass, but the hydrides of the most electronegative elements (nitrogen, oxygen and fluorine) have abnormally high boiling points for their mass.
- The data in the following table serve to illustrate this point.
- If this is an accurate representation of the composition of this compound then we would expect its boiling point to be equivalent to that of a C4H8O4 compound (formula weight = 120).
- A related principle is worth noting at this point.
- Comparison of Boiling Points of Methane, Ammonia, Water, and Hydrogen Fluoride