I believe that the property referenced in 'like dissolves like" is polarity. Solvents are substances that dissolves solutes forming a solution. Solvents may be either polar or non polar; polar solvents contain bonds between atoms with very different electronegativities, such as oxygen and hydrogen, while non polar solvents have bonds between atoms with similar electronegativities such as hydrogen and carbon.
Any elements in the same periodic group as oxygen such as sulfur, as elements are grouped together through similar properties
H₃O ions are when water is protonated
H₂O + H⁺ --> H₃O⁺
HCl is a strong acid therefore complete ionisation takes place.
HCl ---> H⁺ + Cl⁻
1 mol of HCl dissociates to give out 1 mol of H⁺
since H⁺ together with water forms H₃O⁺ ions,
[HCl] = [H₃O⁺]
therefore concentration of [H₃O⁺] is 0.0005 M
