Question

Limiting reactnt experiment

• What happens, if you will not stir the reaction mixture while heating on hot plate?
• What would be the effect, if you will add tap water instead of deionized water into the salt mixture?
• How will you identify the limiting reagent?
• What technique will you use to separate the un-reacted chemical from the reaction mixture?

Answer 1

1. If the reaction mixture is not stirred the temperature will not be uniformly maintained throughout the solution. If temperature is given to a system it will increase the kinetic energy of the particles and the reaction will takes place at a faster rate. Upon stirring the kinetic energy will be uniformly distributed to all the particles and the reaction will takes place at a constant rate. If not stirred the completion of reaction will take longer time or sometimes will not get complete at all as there is no diffusion of the reactants.

2. The tap water is nothing but impure water. Tap water is hard water. It contains of heavy metals, calcium carbonate and salt (NaCl) content in it. If tap water is added to the salt mixture, the salt mixture gets contaminates and the analysis will result in error.

3. A limiting reagent is the one that determines the amount of product formed in a reaction. The following steps are to be followed to determine the limiting reagent.

Step 1. First determine the chemical reaction involved and then write the balanced chemical equation.

Step 2. Always in stoichiometry it is necessary to express the concentration in terms of moles. So convert all the concentration given in terms of moles.

Step 3. Use stoichiometry to each individual reactant and calculate the mass of the product formed.

Step 4. The reactant which gives the less amount of product is the limiting reagent and the reactant which gave more amount of product is the excess reagent.

4. Distillation is the common technique used to separate the un-reacted reactant. Based on the difference in the boiling points the reactant it can be separated.

If it is a solid component then simple filtration or centrifugation technique can be used.

Other advanced technique which can be employed is chromatographic techniques like column chromatography, gas chromatography etc.