Final answer:
An alkaline substance is characterized by providing hydroxide ions or accepting hydrogen ions, resulting in a higher pH value above 7. Baking soda is a common example with a pH of about 9.0. Small pH changes indicate significant shifts in hydrogen ion concentration in a solution.
Step-by-step explanation:
An alkaline (basic) substance is defined by its ability to increase the pH of a solution, typically by providing hydroxide ions (OH-) or accepting hydrogen ions (H+). The pH scale, which ranges from 0 to 14, measures this alkalinity or acidity. Alkaline substances have a pH value greater than 7.0. When an alkaline substance such as sodium hydroxide is dissolved in water, it releases OH- ions, which combine with H+ ions to form water, therefore increasing the solution's pH. A real-world example of an alkaline substance is baking soda (sodium bicarbonate), which has a pH of approximately 9.0.
On the pH scale, a pH above 7 indicates a basic or alkaline environment, with an increased concentration of hydroxide ions and a decreased concentration of hydrogen ions compared to neutral water. Small changes in pH can represent large changes in ion concentration; for example, a substance with a pH of 8 has ten times fewer hydrogen ions than one with a pH of 7.