Test of Essential Academic Skills (TEAS) Science Practice Test

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What is the concentration of hydrogen ions in water with a pH of 7?

Ten to the seventh power times M

Seven times M

Point seven times M

Ten to the negative seven times M

A pH of 7 indicates a neutral solution, which is characteristic of pure water at 25 degrees Celsius. The pH scale is logarithmic; specifically, pH is defined as the negative logarithm (base 10) of the hydrogen ion concentration. This means that a pH of 7 corresponds to a hydrogen ion concentration of 1 x 10^(-7) M (molar).

Thus, when the pH is 7, it directly translates to a concentration of hydrogen ions being 10 to the negative seventh power times M, reflecting a neutral state. This concept aligns with the understanding that each unit change in pH represents a tenfold difference in hydrogen ion concentration. Therefore, a pH of 7 signifies a hydrogen ion concentration of 0.0000001 M, or 10^(-7) M, confirming the accuracy of the answer provided.