Alkali is a chemical substance, and its common feature is that it can be dissolved in water to form hydroxide ions (OH? )。 Alkali is usually bitter, slippery and corrosive.
In junior middle school chemistry, the definition of alkali is closely related to its acid-base properties and the concentration of hydrogen ions and hydroxide ions. The following are some important concepts and definitions related to alkali:
1. Reaction between alkali and water: The reaction between alkali and water will produce hydroxyl ions (OH? )。 This reaction process is called hydrolysis reaction. For example, when sodium hydroxide (NaOH) is dissolved in water, it will generate hydroxide ions and sodium ions.
2.pH value: pH value is an index used to quantify the pH value of the solution. A solution with a pH less than 7 is considered acidic, and a solution with a pH greater than 7 is considered alkaline. The pH value of alkaline solution is usually higher than that of neutral solution (pH 7).
3. Acid-base indicator of alkali: alkali can be used to test or determine the acid-base properties of solution. Commonly used alkaline indicators are phenolphthalein and methyl orange, which are red or orange in alkaline solution.
4. Some common alkalis: In junior high school chemistry, students usually learn some common alkalis, such as sodium hydroxide (NaOH), potassium hydroxide (KOH) and calcium hydroxide (Ca(OH)? ) and so on. These substances are common alkaline substances.
It should be noted that this is only a simple definition of alkali in junior high school chemistry. In more advanced chemistry courses, more complex concepts and definitions of alkalinity will be involved. Chemistry is a broad and profound subject, which needs further study and practice to deepen the understanding of chemical concepts such as alkali.