Acids, Bases, Indicators, and pH
Big idea: aqueous solutions can be acidic, neutral or basic. Indicators provide visible evidence, and the pH scale helps us compare these conditions.
You will classify teacher-prepared solutions, read a simple pH scale, use indicator evidence carefully, and follow safe testing rules.
1. Three kinds of aqueous conditions
pH below 7. Dilute lemon juice or vinegar is often acidic, but its exact pH varies.
pH about 7. Pure water is used as the introductory example under ordinary classroom conditions.
pH above 7. A mild soap solution is commonly basic. An alkali is a base that forms a basic aqueous solution.
2. Indicators turn evidence into colour
An acid-base indicator is a substance whose colour depends on whether a solution is acidic or basic. Litmus gives a broad acid/base distinction. Universal indicator uses a range of colours to estimate pH. The result must be compared with the chart supplied for that indicator; a colour by itself has no universal meaning.