Final answer:
The statement is true; at pH 4, the concentration of H+ ions is indeed 1x10^-4 molar, indicating an acidic solution with a pH less than 7.
Step-by-step explanation:
The statement that at pH 4, the concentration of H+ ions is 1x10^-4 molar is true. The pH scale is logarithmic and represents the hydrogen ion concentration of a solution. The pH of a solution is the negative logarithm of the hydrogen ion concentration.
Therefore, when the hydrogen ion concentration is given as 1.0 x 10^-4 M, the pH is calculated as -log(1.0 x 10^-4), which simplifies to 4 because the exponent matches the pH value when the molar concentration coefficient is 1.
This indicates that the solution is acidic, as a pH less than 7 denotes an acidic solution.
For comparison, a neutral solution, like pure water at 25°C, has a hydrogen ion concentration of 1.0 x 10^-7 M and thus a pH of 7.
In contrast, acidic solutions have higher hydrogen ion concentrations, resulting in a pH below 7, while basic solutions have hydrogen ion concentrations lower than 1.0 x 10^-7 M, leading to a pH above 7.