pH stands for the power of hydrogen. pH that ranges form 1-6.9 are acid substances. At pH 1 - 2.9, the substance is highly acidic. At pH 3 - 4, the substance is mildly acidic. At pH 4.1 – 6.9, the substance is weakly acidic. At pH 7, it is neutral. At pH 7.1-14, it is basic. At pH 7.1 - 10.9, the substance is weakly basic. At pH 11 - 13, the substance is mildly basic. At pH 13.1 – 14, the substance is highly basic.