Question

What are the properties of acids? List some foods that contain acids.

Short answer

Acids taste sour, have a pH less than 7, turn blue litmus paper red, react with metals to produce hydrogen gas, react with bases to form water and salt, and conduct electricity in solution. Foods with acids include citrus fruits, vinegar, apples, and yogurt.

Step-by-step solution

Identifying Properties of Acids

List the general chemical and physical properties of acids. Characteristics include: sour taste, pH less than 7, turn blue litmus paper red, react with metals to produce hydrogen gas, react with bases to form water and a salt, and conduct electricity when dissolved in water.

Listing Foods Containing Acids

Identify common foods that contain acids. Examples include: citrus fruits like lemons and oranges (contain citric acid), vinegar (contains acetic acid), apples (contain malic acid), and yogurt (contains lactic acid).

Key concepts

Understanding the pH Scale

The pH scale is a numerical representation of acidity and alkalinity in substances. It ranges from 0 to 14, where a pH of 7 is considered neutral—neither acidic nor basic. Substances with a pH value less than 7 are called acids, with a lower number indicating stronger acidity. Conversely, substances with a pH above 7 are known as bases or alkaline substances, and the higher the number, the stronger the base.

For example, common household vinegar has a pH around 2.5, demonstrating its acidic nature, whereas baking soda has a pH near 9, indicating it is basic. This scale is valuable because it gives us a precise and standardized way to compare the acidity of different materials, including those found in food. The pH level of food can affect its flavor, preservation characteristics, and how it interacts with our body.

Acidic Substances in Food

Many foods contain natural acids which are integral to their taste and preservation qualities. Citrus fruits, for instance, owe their tangy flavor to citric acid. Apples contain malic acid, giving them their slightly sour taste. Vinegar, used in salad dressings and pickling, is acidic because of acetic acid. Yogurt and other fermented dairy products have lactic acid, which is both a byproduct of fermentation and a contributor to the tangy flavor.

Acids in foods play a significant role in the way we experience taste. They stimulate saliva production and can make the mouth water, a familiar sensation when eating sour foods like lemons. Not only do these acids affect the sensory aspects of food, but they also act as natural preservatives by creating an environment that inhibits the growth of many microorganisms.

Acid-Base Reactions in Everyday Life

Acid-base reactions are chemical processes where acids react with bases to create water and a salt. This neutralization reaction is significant in many everyday life applications. For example, antacid tablets neutralize excess stomach acid to alleviate heartburn. The reaction forms salt and water, which do not irritate the stomach lining.

Another common example is the reaction between vinegar (acetic acid) and baking soda (sodium bicarbonate, a base). This produces carbon dioxide bubbles, which cause the fizzing and bubbling in many science fair volcanoes. Utilizing acid-base reactions is fundamental in various industries, such as pharmaceuticals, agriculture, and food processing. For instance, in the food industry, controlling the pH is vital for fermentation processes, which are used in making products like cheese, yogurt, and sourdough bread.