1. Write the formulas of the principal molecular or ionic species present in an aqueous solution of each substance.
(a) Sodium Chloride, NaCl
Na+ + Cl-
(b) Hydrogen bromide, HBr
(c) Iron (III) sulfate, Fe2(SO4)3
(d) Ethanol, CH3CH2OH
(e) Glucose, C6H12O6
(f) Ammonium acetate, NH4CH3COO
HBr is a strong acid and ionizes 100%.
Fe2(SO4)3 is completely soluble in water and is present as the ions.
Same for CH3COONH4
The others are ok.
2. What are spectator ions in chemical reactions
The spectator ions are those that cancel when writing the net ionic equation. For example, an acid/base reaction between HCl and NaOH is
HCl(aq) + NaOH(aq) ==> NaCl(aq) + H2O(l)
We turn that into an ionic equation--you can add the aq part to each.
H^+ + Cl^- + Na^+ + OH^- ==> Na^+ + Cl^- + H2O
You see Cl^- is on both sides and those cancel.
You see Na^+ on both sides. Cancel them.
That leaves
H^+(aq) + OH^-(aq) ==> H2O(l) as the net ionic equation. The Na^+ and Cl^- are spectator ions.
To determine the formulas of the principal molecular or ionic species present in an aqueous solution of each substance, we need to break down the compounds into their individual ions or molecules.
(a) Sodium Chloride, NaCl:
In an aqueous solution, sodium chloride dissociates into sodium ions (Na+) and chloride ions (Cl-).
Formula: Na+ + Cl-
(b) Hydrogen bromide, HBr:
In an aqueous solution, hydrogen bromide dissociates into hydrogen ions (H+) and bromide ions (Br-).
Formula: H+ + Br-
(c) Iron (III) sulfate, Fe2(SO4)3:
In an aqueous solution, iron (III) sulfate dissociates into iron (III) ions (Fe3+) and sulfate ions (SO4^2-).
Formula: Fe3+ + 2(SO4^2-)
(d) Ethanol, CH3CH2OH:
Ethanol does not dissociate in water. Therefore, in an aqueous solution of ethanol, the principal molecular species is simply the ethanol molecule itself.
Formula: CH3CH2OH
(e) Glucose, C6H12O6:
Glucose also does not dissociate in water. In an aqueous solution of glucose, the principal molecular species is glucose.
Formula: C6H12O6
(f) Ammonium acetate, NH4CH3COO:
In an aqueous solution, ammonium acetate dissociates into ammonium ions (NH4+) and acetate ions (CH3COO-).
Formula: NH4+ + CH3COO-