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4.2 Classifying chemical reactions

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By the end of this section, you will be able to:
  • Define three common types of chemical reactions (precipitation, acid-base, and oxidation-reduction)
  • Classify chemical reactions as one of these three types given appropriate descriptions or chemical equations
  • Identify common acids and bases
  • Predict the solubility of common inorganic compounds by using solubility rules
  • Compute the oxidation states for elements in compounds

Humans interact with one another in various and complex ways, and we classify these interactions according to common patterns of behavior. When two humans exchange information, we say they are communicating. When they exchange blows with their fists or feet, we say they are fighting. Faced with a wide range of varied interactions between chemical substances, scientists have likewise found it convenient (or even necessary) to classify chemical interactions by identifying common patterns of reactivity. This module will provide an introduction to three of the most prevalent types of chemical reactions: precipitation, acid-base, and oxidation-reduction.

Precipitation reactions and solubility rules

A precipitation reaction    is one in which dissolved substances react to form one (or more) solid products. Many reactions of this type involve the exchange of ions between ionic compounds in aqueous solution and are sometimes referred to as double displacement , double replacement , or metathesis reactions. These reactions are common in nature and are responsible for the formation of coral reefs in ocean waters and kidney stones in animals. They are used widely in industry for production of a number of commodity and specialty chemicals. Precipitation reactions also play a central role in many chemical analysis techniques, including spot tests used to identify metal ions and gravimetric methods for determining the composition of matter (see the last module of this chapter).

The extent to which a substance may be dissolved in water, or any solvent, is quantitatively expressed as its solubility    , defined as the maximum concentration of a substance that can be achieved under specified conditions. Substances with relatively large solubilities are said to be soluble    . A substance will precipitate    when solution conditions are such that its concentration exceeds its solubility. Substances with relatively low solubilities are said to be insoluble    , and these are the substances that readily precipitate from solution. More information on these important concepts is provided in the text chapter on solutions. For purposes of predicting the identities of solids formed by precipitation reactions, one may simply refer to patterns of solubility that have been observed for many ionic compounds ( [link] ).

Solubilities of Common Ionic Compounds in Water
Soluble compounds contain
  • group 1 metal cations (Li + , Na + , K + , Rb + , and Cs + ) and ammonium ion ( NH 4 + )
  • the halide ions (Cl − , Br − , and I − )
  • the acetate ( C 2 H 3 O 2 − ) , bicarbonate ( HCO 3 − ) , nitrate ( NO 3 − ) , and chlorate ( ClO 3 − ) ions
  • the sulfate ( SO 4 2− ) ion
 Exceptions to these solubility rules include
  • halides of Ag + , Hg 2 2+ , and Pb 2+
  • sulfates of Ag + , Ba 2+ , Ca 2+ , Hg 2 2+ , Pb 2+ , and Sr 2+
Insoluble compounds contain
  • carbonate ( CO 3 2− ) , chromate ( CrO 4 2− ) , phosphate ( PO 4 3− ) , and sulfide (S 2− ) ions
  • hydroxide ion (OH − )
 Exceptions to these insolubility rules include
  • compounds of these anions with group 1 metal cations and ammonium ion
  • hydroxides of group 1 metal cations and Ba 2+

Questions & Answers

A golfer on a fairway is 70 m away from the green, which sits below the level of the fairway by 20 m. If the golfer hits the ball at an angle of 40° with an initial speed of 20 m/s, how close to the green does she come?
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Joseph Reply
Nevermind i just realied that the graph is the phons output for a person with normal hearing and not just the phons output of the sound waves power, I should read the entire thing next time
Joseph
Follow up question, does anyone know where I can find a graph that accuretly depicts the actual relative "power" output of sound over its frequency instead of just humans hearing
Joseph
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A string is 3.00 m long with a mass of 5.00 g. The string is held taut with a tension of 500.00 N applied to the string. A pulse is sent down the string. How long does it take the pulse to travel the 3.00 m of the string?
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Source:  OpenStax, Chemistry. OpenStax CNX. May 20, 2015 Download for free at http://legacy.cnx.org/content/col11760/1.9
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