a. If a salt with a polyatomic anion is dissolved in water, the salt tends to di

Question

a. If a salt with a polyatomic anion is dissolved in water, the salt tends to dissolve such that the cation and anionic groups separate but the elements in the anion are still strongly bound together. Even though the anion remains intact, this is still considered to be a process of dissociation. An example of this would be the dissolution of Epsom salt, which has the chemical formula MgSO4-7H20 (where the seven water molecules are part of the mineral structure and will also dissociate from the salt). Write out a balanced chemical equation for the dissociation of Epsom salt: b. Chalcanthite (CuSO4·5H2O) and bonattite (CuSO4·3H2O) are two copper sulfate minerals. If we have a solid sample of chalcanthite, put it into an oven, and ramp up the temperature, eventually it will lose water as vapor and form bonattite (though on cooling the reverse would happen!). Write a balanced chemical equation with the appropriate subscripts for the reaction that occurs when heating chalcanthite to make bonattite:

Explanation / Answer

a) The balanced chemical equation is given as

MgSO4.7H2O (s) ---------> Mg2+ (aq) + SO42- (aq) + 7 H2O (l)

b) The balanced chemical equation for the reaction is given as

CuSO4.5H2O (s) ---------> CuSO4.3H2O (s) + 2 H2O (g)

c) Carbonic acid is denoted as H2CO3; hence, the balanced chemical reaction is

H+ + NaHCO3 <=======> H2CO3 + Na+

d) The numerator represents the products of the reaction while the denominator gives the reactants. Therefore, the unbalanced equation is

NO2 --------> H+ + NO2- + NO3-

The superscripts denote the number of mole(s) of the reactants or the products. One of the reactants is missing (the source of H+) which is H2O. Since H2O is present in a large proportion in any chemical reaction, the concentration of H2O is usually omitted. Hence, we write the equation as

2 NO2 + H2O ----------> 2 H+ + NO2- + NO3-

All the atoms in the above reaction are balanced; hence, we write the balanced chemical equation (with states) as

2 NO2 (g) + H2O (l) --------> 2 H+ (aq) + NO2- (aq) + NO3- (aq)

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