ACT Test Prep: pH scale

Please read the following passage and then answer the questions that follow:

A Science student placed a strip of blue litmus paper and a strip of pink litmus paper in a glass dish. Then she added a drop of dilute sulfuric acid to each strip of litmus paper. She observed that the blue litmus paper turned pink, but the pink litmuspaper did not change color. Next she placed a drop of sodium hydroxide (NaOH) on other strips of blue and pink litmus paper. This time, the pink litmus
paper turned blue, but the blue litmus paper did not change. Finally, she put a drop of distilled water on strips of blue and pink litmus paper. Neither strip changed color. She repeated the tests several times with the same results. The student concluded that acids turn blue litmus paper pink; bases, such as sodium hydroxide or Potassium hydroxide, turn pink litmus paper blue. As water did not affect either pink or blue litmus paper, she reasoned that water was not an acid or a base, but a neutral substance.

Keeping these results in mind, the student poured a little sodium hydroxide into a beaker containing pink and blue litmus paper. Then she added hydrochloric acid (HCl) drop by drop until the solution became neutral. She determined that a new, neutral substance had formed in the beaker. The substance was table salt, or sodium chloride (NaCl), which is one of many salts formed from an acid and a base.

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