Final answer:
Soap contains water solutions with a higher concentration of hydroxide ions (OH-) compared to juice, as it has a pH greater than 7, which is characteristic of bases on the pH scale.
Step-by-step explanation:
The student asked which food item, juice or soap, contains water solutions with a higher concentration of hydroxide ions (OH-). In the pH scale, solutions with a pH higher than 7 are considered to be bases. Bases have a higher concentration of hydroxide ions compared to hydronium ions. Soap, typically being basic, would have a pH greater than 7 and thus a higher concentration of hydroxide ions. Juices, on the other hand, are usually acidic with a pH lower than 7, meaning they contain a lower concentration of hydroxide ions compared to soap.
Bases such as baking soda have a bitter taste and contain a lower concentration of hydronium ions and a higher concentration of hydroxide ions. Strong bases can harm organisms and damage materials. On the pH scale, the concentration of hydroxide ions increases as the solution becomes more basic, and soap being a base, has a pH that reflects a higher concentration of hydroxide ions.