indicator

Examples of indicator in the following topics:

• Acid-Base Indicators

  • In this reaction, adding acid shifts the indicator equilibrium to the left.
  • Conversely, adding a base shifts the indicator equilibrium to the right.
  • These commercial indicators (e.g., universal indicator and Hydrion papers) are used when only rough knowledge of pH is necessary.
  • Therefore, you would want an indicator to change in that pH range.
  • Common indicators for pH indication or titration endpoints is given, with high, low, and transition pH colors.

• Acid-Base Titrations

  • Below are some common equivalence point indicators:
  • strong acid-weak base titration: methyl orange indicator the base is off the scale (e.g., pH > 13.5) and the acid has pH > 5.5: alizarine yellow indicator
  • the acid is off the scale (e.g., pH < 0.5) and the base has pH < 8.5: thymol blue indicator
  • The end point is reached when the indicator permanently changes color.
  • (An indication of the approaching equivalence point is the appearance, and disappearance after stirring, of the color that the indicator assumes beyond neutralization.)

• Writing Chemical Equations

  • For example, a compound in the gas state would be indicated by (g), solid (s), liquid (l), and aqueous (aq).
  • This equation indicates that oxygen and CH4 react to form H2O and CO2.
  • Sometimes, different arrows are used to indicate something about the reaction.
  • $\rightarrow$ indicates where the forward reaction is favored: in other words, more of the product is being produced.
  • If the reaction requires energy, it is often indicated above the arrow.

• Naming Molecular Compounds

  • Molecular compounds are named using a systematic approach of prefixes to indicate the number of each element present in the compound.
  • When naming molecular compounds prefixes are used to dictate the number of a given element present in the compound. " mono-" indicates one, "di-" indicates two, "tri-" is three, "tetra-" is four, "penta-" is five, and "hexa-" is six, "hepta-" is seven, "octo-" is eight, "nona-" is nine, and "deca" is ten.

• Specialized Equilibrium Constants

  • As such, strong acids will have large values of Ka that are greater than one, which indicates that the forward reaction of dissociation is strongly favored.
  • Weak acids, on the other hand, will have small values of Ka that are less than one, indicating that the reverse reaction is strongly favored; weak acids dissociate only to a small extent.
  • As such, Ka acts a relative indicator of acid strength.
  • As with the acid dissociation constant, large values of Kb are indicative of a stronger base, while small values of Kb are indicative of a weaker base.

• Bond Order

  • Bond order indicates the stability of a bond.
  • A bond order of one is obtained by employing the formula above, indicating a stable bond.
  • A bond order of zero is obtained by placing the available electrons in the bonding and antibonding levels, indicating that dihelium does not exist according to valence bond and bond order theory.
  • Without the 1s electrons participating in bonding, the p electrons completely fill the bonding orbital; this leaves the antibonding orbital empty and gives a bond order of one, indicating a stable molecule (in this case, in the gas phase).

• Molecular Formulas

  • The simplest types of chemical formulas are called empirical formulas, which indicate the ratio of each element in the molecule.
  • The molecular formula indicates the exact number of atoms in the molecule.
  • A structural formula is used to indicate not only the number of atoms, but also their arrangement in space.
  • The chemical structure of butane indicates not only the number of atoms, but also their arrangement in space.

• Strong Acid-Strong Base Titrations

  • A strong acid-strong base titration is performed using a phenolphthalein indicator.
  • The indicator—phenolphthalein, in this case—has been added to the analyte in the Erlenmeyer flask.
  • 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.

• Redox Titrations

  • In this case, the use of KMnO4 as a titrant is particularly useful, because it can act as its own indicator; this is due to the fact that the KMnO4 solution is bright purple, while the Fe2+ solution is colorless.
  • In this case, starch is used as an indicator; a blue starch-iodine complex is formed in the presence of excess iodine, signaling the endpoint.
  • Another example is the reduction of iodine (I2) to iodide (I−) by thiosulphate (S2O32−), again using starch as the indicator.
  • Because of its bright purple color, KMnO4 serves as its own indicator.

• Molecular, Ionic, and Complete Ionic Equations

  • In the molecular equation, electrolytes are written as salts followed by (aq) to indicate that the electrolytes are completely dissociated into their constituent ions; the (aq) designation indicates that the ions are in aqueous solution.
  • Note that the remaining salt, Ca(NO3)2, is still designed with (aq) to indicate that the ions are dissociated in solution.