TM 15: Using english to Predict rendement of product a reaction

When cooking, it's frequently handy to predict what will happen when we mix a bunch of ingredients together. For example, if we're interested in making a delicious new salad dressing, we would have a very small chance of making anything edible if we had no way of knowing which ingredients would have the greatest chance of succeeding.

Likewise, it's often necessary for chemists to predict the chemical reactions that will take place when two chemicals are combined. For example, if we're adding a chemical to a tank of toxic waste to stabilize it, we'd be very unhappy if we failed to predict an explosive reaction..

An easy way to predict what reaction will take place when two chemicals are mixed is to identify the type of reaction that's likely to occur when the chemicals are combined. Of course, we mentioned before that these types of reaction are arbitrary, but they do sometimes have a useful purpose.

Here are some tips you may find handy in helping to predict the type of reaction that will occur if you know only the reactants. Keep in mind that not all combiations of chemicals will result in a chemical reaction these tips are handy only for helping to predict what would happen should they happen to react.

  The theoretical rendement is calculated based on the number of moles of the limiting reagent. For this calculation, it is usually assumed that there is only one reaction involved. The ideal chemical yield value (theoretical rendement) is 100%, a value highly unlikely to be achieved in its practice. Calculate the percentage of rendemen that is by using the following equations percent rendemen = weight yield / weight of yield divided by the sample weight multiplied by 100%.              

Hint when trying to predict products of chemical reactions  
                   
First look for obvious precipitation reactions - two aqueous salt solutions mixed together with one of the salts containing an ion that quite often is insoluble (such as Ca, Fe, Ag, Hg, Pb). Then looks for other possible precipitation reactions in which one of the above ions is present in an aqueous salt but the other solution is an acid which might provide an anion (like sulfate or chloride) that could precipitate with the above ion. Next identify easy acid/base reactions - in which you have an easily identifiable acid (nitric, sulfuric, hydrochloric) and a hydroxide salt as the base. Now look for easily identifiable redox reactions in which O2 is a reactant and probably an oxidizing agent and the other reagent is a hydrocarbon, a carbohydrate, a metal, etc. The hydrocarbon and carbohydrate will react to form carbon dioxide and water, and the metal will react to form oxides. Finally look for other redox reactions, such as when you have a pure metal interacting with a ion of another metal or an acid which could dissolve it to form a salt of the metal.

example: 

In 50 grams of urea fertilizer (CO (NH2) 2) there are 21 grams of nitrogen. The purity of urea fertilizer is ...
Answer:
If you find a question that asks for purity then all you have to compare facts with theory.
FACT in Problem:
In 50 grams of urea fertilizer (CO (NH2) 2) there are 21 grams of Nitrogen (N)

THEORY:

 

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