Random chemistry quiz questions!?

Question

1. why is it necessary to use a buret for measuring standard solutions?

2. reaction between NaHCO3 and any acid? give the equation.

3. purpose of adding MgCl2·H20 to EDTA?

Answer 1

1. A buret (or burette) is used for creating standard solutions because it allows a very accurate measurement of how much solution is dispensed from the bottom, which is very important in determining molarity and ion concentrations of the standard solution (along with each  individual solutions' volume).

2. NaCO3 + 2H+ --> Na+ + H2CO3 --> Na+ + H2O + CO2

The sodium will dissociate from the bicarbonate ion (CO3-) in aqueous solution, and with two hydrogen ions from the aqueous acid, it will combine to form carbonic acid, which will quickly disassociate to form water and carbon dioxide.

3. EDTA forms an octahedral complex with most 2+ metal cations, M2+, in aqueous solution (in this case Mg2+ since MgCl2 is highly hygroscopic or water absorbing). The main reason that EDTA is used so extensively in the standardization of metal cation solutions is that the formation constant for most metal cation-EDTA complexes is very high, meaning that the equilibrium for the reaction:

    M2+ + H4Y → MH2Y + 2H+

lies far to the right. Carrying out the reaction in a basic buffer solution removes H+ as it is formed, which also favors the formation of the EDTA-metal cation complex reaction product. For most purposes it can be considered that the formation of the metal cation-EDTA complex goes to completion, and this is chiefly why EDTA is used in titrations/standardizations of this type.