There are acid-base reaction methods or acid-base indicator methods.

1) Acid-base reaction method: Baking soda, vinegar, etc. can be used for measurement in daily life. The main component of baking soda is sodium bicarbonate, which reacts with acidic foods to produce carbon dioxide.

2) Acid-base indicator method: Use curry powder to test the acidity and alkalinity of the solution. Take a spoonful of curry powder, make a paste with 50% alcohol, and apply it on both sides of a white cloth. After leaving it for a period of time, the excess curry powder is washed away with water, and the white cloth is dyed yellow, thus making an acid-base indicator cloth that can be used repeatedly. It turns red when exposed to alkaline solutions and yellowish-brown when exposed to acidic solutions. After each use, rinse the acidic or alkaline substances on the cloth with water. The indicator cloth will return to its original yellow color and can be used next time.

3) Acid-base indicator method: Extract the acid-base indicator from rice amaranth. Wash and chop 250g of red rice amaranth. Place it in about 500g of water and heat and boil for about 10 minutes. Filter out the residue. A red acid-base indicator is obtained. Its discoloration range is: when the pH value is less than 2, it appears purple; when the pH value is 2 to 4, it appears rose red; when the pH value is 5 to 7, it appears magenta or wine red; when the pH value is 7 to 9, it appears yellow; When the pH value is between 9 and 13, it appears yellow-green; when the pH value is greater than 14, it appears bright yellow.