Humboldt State University ® Department of Chemistry

Richard A. Paselk

Chem 107

Fundamentals of Chemistry

Fall 2009

Lecture Notes: 24 September

© R. Paselk 2005
 
     
PREVIOUS  

NEXT

Chemical Reactions, cont.

Net Ionic Equations, cont.

Let's look at a couple of more examples of net ionic equations:

Consider the reaction of 50.0 mL of 0.25 M hydrochloric acid with 25.0 mL of 0.50 M sodium hydroxide.

H+(aq) + Cl-(aq) + Na+(aq) + OH-(aq) right arrow H2O + Cl-(aq) + Na+(aq)

Giving: H+ + OH- right arrow H2O

Consider the reaction of calcium metal with hydrochloric acid. This is similar to the reaction of sodium and water, and hydrogen gas is given off.

H+(aq) + Cl-(aq) + Ca0(s) right arrow H2 (g) + Ca2+(aq) + Cl-(aq)

Balancing: 2 H+ + Ca0(s) right arrow H2 (g) + Ca2+

Notice that this net ionic equation also involves electron transfer, so it is a redox equation.

Oxidation/Reduction Reactions

In these reactions we see a transfer of electrons from one atom or molecule to another. Many of these reactions come under the description of combustion reactions in your tex. First let's look at some terms.

CH4(g) + 2O2(g) right arrow CO2(g) + 2H2O(l)

Notice that the methane is oxidized by the oxygen. We say that the carbon and hydrogen are both oxidized to give the new covalent products, water and carbon dioxide.

Examples:

KClO3(s) + heat right arrow KCl(s) + O2(g)

Balancing: 2KClO3(s) + heat right arrow 2KCl(s) + 3O2(g)

Fe(s) + O2(g) right arrow Fe2O3(s)

Balancing: 4Fe(s) + 3O2(g) right arrow 2Fe2O3(s)

Ag+ + NO3- + Cu0 right arrow Ag0 + NO3- + Cu2+

Balancing: 2Ag+ + Cu0 right arrow 2Ag0 + Cu2+

Cu2+ + SO42- + Fe0 right arrow Cu0 + Fe3+ + SO42-

Balancing: 3 Cu2+ + 2 Fe0 right arrow 3 Cu0 + 2 Fe3+

 

FYI

As another example we can look at a key oxidation reaction in glycolysis, the central pathway of metabolism. Don't worry about these reactions - they will not be on an exam. They are presented for your interest.

    • In this case we use a biological oxidizing agent, NAD+ to take electrons (in the form of a hydride ion, H:-)

chemical equation for the oxidation of Ga-3-P to 1,3-bisPGA by NAD+

    • Frequently organisms need to operate this reaction under anaerobic (oxygen free) conditions. For example the maximum power (energy/sec) you can get from your muscles is anaerobically. For this to occur you need to regenerate the oxidizer (NAD+) without the presence of oxygen. For this to occur we use another reaction:

chemical equation for the reduction of Pyruvate to L-lactate by NADH

The mechanism for this electron transfer is shown below:

simplified mechanism for the elctron transfer used in lactate dehydrogenase

Stoichiometry Revisited - Quantitative Chemical Equations (Chapter 6)

Theoretical Yield Problems

Another frequent question arising in chemical processes is the percent yield. This deals with the question of how effective was a given process in producing a product. Its an important consideration because chemical reactions rarely go completely to products. The maximum possible yield for a reaction is known as the Theoretical Yield.

Limiting Problems

Asking question of what is the maximum amount of something which can be produced from a given mixture of stuff. This is a fairly straight-forward sort of problem in the day-to-day world, but seems to cause a great deal of difficulty for lots of folks in chemistry. Let's start by looking at a non-chemical problem:

Consider you have to make a bunch of sandwichs for a party. The equation for the sandwichs (in slices) is:

2 Bread + 1 Cheese + 2 Meat right arrow 1 Sandwich

You have:

How many sandwichs can you make?

Look at how many sandwichs can be made from each ingredient:

Bread limits and we can make 27 sandwichs.


C107 Laboratory

C107 Home

C107 Lecture Notes

© R A Paselk

Last modified 24 September 2009