Aug 1, Related questions Question 5c3cd. What are some common mistakes students make with stoichiometry? What is an example of a stoichiometry practice problem? What are some examples of acid and base dissociation? What is an example of an acid and base dissociation practice problem? Ion-dipole forces attract the positive hydrogen end of the polar water molecules to the negative chloride ions at the surface of the solid, and they attract the negative oxygen ends to the positive potassium ions.
The reduction of the electrostatic attraction permits the independent motion of each hydrated ion in a dilute solution, resulting in an increase in the disorder of the system as the ions change from their fixed and ordered positions in the crystal to mobile and much more disordered states in solution.
This increased disorder is responsible for the dissolution of many ionic compounds, including KCl, which dissolve with absorption of heat. In other cases, the electrostatic attractions between the ions in a crystal are so large, or the ion-dipole attractive forces between the ions and water molecules are so weak, that the increase in disorder cannot compensate for the energy required to separate the ions, and the crystal is insoluble.
Such is the case for compounds such as calcium carbonate limestone , calcium phosphate the inorganic component of bone , and iron oxide rust.
Water ionizes when one molecule of water gives up a proton to another molecule of water, yielding hydronium and hydroxide ions. In some cases, we find that solutions prepared from covalent compounds conduct electricity because the solute molecules react chemically with the solvent to produce ions.
For example, pure hydrogen chloride is a gas consisting of covalent HCl molecules. This gas contains no ions. However, when we dissolve hydrogen chloride in water, we find that the solution is a very good conductor. The water molecules play an essential part in forming ions: Solutions of hydrogen chloride in many other solvents, such as benzene, do not conduct electricity and do not contain ions.
Likewise, weak acids and bases that only react partially generate relatively low concentrations of ions when dissolved in water and are classified as weak electrolytes. The reader may wish to review the discussion of strong and weak acids provided in the earlier chapter of this text on reaction classes and stoichiometry. Substances that dissolve in water to yield ions are called electrolytes.
Electrolytes may be covalent compounds that chemically react with water to produce ions for example, acids and bases , or they may be ionic compounds that dissociate to yield their constituent cations and anions, when dissolved.
Dissolution of an ionic compound is facilitated by ion-dipole attractions between the ions of the compound and the polar water molecules. Note that there are ambiguities here starting in Step 4. That's just the way it is. To determine whether a substance is a weak acid or weak base you have to know more than the molecular formula, especially for compounds containing carbon. A structural formula, which shows the detailed connections of atoms is often necessary.
Summary In summary, know the more common element names and symbols, memorize the seven strong acids, be able to spot a metal know at least where they are on the periodic table , memorize at least a few of the more common weak acids and weak base, and you will be in good shape.
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