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The limiting reagent (or limiting reactant or limiting agent) in a chemical reaction is a reactant that is totally consumed when the chemical reaction is completed. [ 1 ] [ 2 ] The amount of product formed is limited by this reagent, since the reaction cannot continue without it.
The limiting reagent is the reagent that limits the amount of product that can be formed and is completely consumed when the reaction is complete. An excess reactant is a reactant that is left over once the reaction has stopped due to the limiting reactant being exhausted.
Then an excess but fixed volume of sulfanilamide and N-(1-naphthyl)ethylenediamine dihydrochloride solution is added. With nitrous acid as the limiting reagent, the azo coupling reaction produces an azo dye quantitatively with respect to the nitrite ions: The diazo compound formed accounts for the red coloration typical for a positive result.
Stoichiometric equations are used to determine the limiting reagent or reactant—the reactant that is completely consumed in a reaction. The limiting reagent determines the theoretical yield—the relative quantity of moles of reactants and the product formed in a chemical reaction. Other reactants are said to be present in excess.
The color-change that occurs in the blue bottle experiment has features of a clock reaction, in which a visible change in the concentration of one or more reagents suddenly occurs upon the exhaustion of a limiting reagent. For example, the limiting reactant, oxygen, is consumed by another reactant, benzoin, with the help of safranin as a ...
For example, when preparing Grignard reagents, magnesium (the cheapest reagent) is often used in excess, which reacts to remove trace water, either by reacting directly with water to give magnesium hydroxide or via the in situ formation of the Grignard reagent which in turn reacts with water (e.g. R-Mg-X + H 2 O → HO-Mg-X + R-H).
An excess of phosphorus is used in order to prevent formation of PBr 5: [1] [2] P 4 + 6 Br 2 → 4 PBr 3. Because the reaction is highly exothermic, it is often conducted in the presence of a diluent such as PBr 3. Phosphorus tribromide is also generated in situ from red phosphorus and bromine. [3]
Tebbe's reagent, useful in organic chemistry, is an aluminium-containing derivative of titanocene that arises from the reaction of titanocene dichloride with trimethylaluminium. It is used for the "olefination" reactions. [17] Arenes, such as C 6 (CH 3) 6 react to give the piano-stool complexes [Ti(C 6 R 6)Cl 3] + (R = H, CH 3; see figure above).