Question

how does the ph of hydrochloric acid change when copper oxide is graduallt added to hydrochloric acid until excess?
does it increase? decrease?

Answer 1

Copper does not react with HCl acid, but copper oxide does react. A metal-acid reaction is always a redox reaction. Since copper has a higher reduction potential than hydrogen, it does not react with non-oxidising acids like HCl or dil.H2SO4.