Acids Taste: Sour. Touch: Like water. Tested with litmus paper: Turn blue litmus red. pH value: From 0 to less than 7. Reaction with metals: Form hydrogen and a salt. Reaction with carbonates: Form a salt, water and carbon dioxide. Reaction with ammonium compounds: No reaction. Alkalis Taste: Bitter. Touch: Soapy. Tested with litmus paper: Turn red litmus blue. pH value: From above 7 to 14. Reaction with metals: No reaction. Reaction with carbonates: No reaction. Reaction with ammonium compounds: Give off ammonia gas. Note: Strong acids and alkalis are corrosive and dangerous.