PH Scale: Acids, Bases, and Common Materials

What is the pH Scale?

The pH scale measures how acidic or basic (alkaline) a substance is. It ranges from 0 to 14. A pH of 7 is neutral. Values below 7 are acidic, and values above 7 are basic. Pure water has a neutral pH of 7.

When substances dissolve in water, they can shift the pH. For example, vinegar and lemon juice are acidic, while substances like ammonia and laundry detergent are basic. Just like hot and cold describe temperature, acidic and basic describe chemical properties.

How is pH Measured?

PH is measured using a pH meter or pH paper. The meter uses a glass electrode to detect the concentration of hydrogen ions in a solution. PH paper contains indicators that change color based on the acidity or alkalinity of the substance it contacts.

pH Scale of Common Acids and Bases

All pH values are measured in aqueous solutions at a concentration of 10 mM.

Strong Acids

Complete dissociation in water (pKa < –1)

Weak Bases

Partial dissociation or low solubility (Kb small or insoluble)

PH Scale of Common Materials

pH 0 – Extremely acidic

• Battery acid (sulfuric acid) – highly corrosive, industrial use

pH 1 – Very strong acid

• Stomach acid (hydrochloric acid) – essential for digestion

• Industrial acid solutions

pH 2

• Lemon juice – natural fruit acid

• Vinegar (acetic acid) – used in cooking and cleaning

• Cola and sports drinks – acidic due to phosphoric acid

pH 3

• Orange juice – citrus-based acid

• Soda and carbonated beverages

• Pickled foods

pH 4

• Tomatoes and tomato juice

• Acid rain – environmental concern, often around pH 4.0–4.5

• Apples and grapes

pH 5

• Black coffee – slightly acidic due to organic acids

• Bananas

• Bread

pH 6

• Urine – varies depending on hydration and diet

• Milk – close to neutral but slightly acidic

• Saliva (resting state)

pH 7 – Neutral

• Distilled water – baseline for neutrality

• Human blood (technically ~7.4 but considered close to neutral for reference)

pH 8

• Sea water – slightly basic due to dissolved minerals

• Eggs (especially egg whites)

• Baking powder (mildly basic when dissolved)

pH 9

• Baking soda (sodium bicarbonate) – common antacid

• Toothpaste (some types)

• Hand soap (mild base)

pH 10

• Milk of magnesia (magnesium hydroxide) – used to relieve indigestion

• Great Salt Lake water – mineral-rich, alkaline environment

• Some detergents

pH 11

• Ammonia solution (household cleaner)

• Window cleaners

• Mild bleach products

pH 12

• Soapy water – alkaline due to sodium salts

• Heavy-duty detergents

• Hair relaxers

pH 13

• Oven cleaner – contains strong bases like sodium hydroxide

• Household bleach (concentrated)

pH 14 – Extremely basic (alkaline)

• Liquid drain cleaner – highly caustic, often pure sodium or potassium hydroxide

• Industrial degreasers

Other Questions Related to PH Scales

1. What are acids and bases? Examples?

Acids are substances that release hydrogen ions (H⁺) when dissolved in water, increasing the concentration of these ions. Bases, on the other hand, are substances that release hydroxide ions (OH⁻) or accept hydrogen ions, reducing their concentration.

Common acids include hydrochloric acid (found in the stomach), citric acid (found in citrus fruits), and vinegar (acetic acid). Bases include substances like sodium hydroxide (lye), baking soda (sodium bicarbonate), and ammonia.

2. Why is pH important? How does pH impact everyday life?

PH is crucial in various fields like chemistry, biology, and environmental science. In the human body, different pH levels are vital for enzyme function and maintaining homeostasis. In agriculture, pH affects soil quality and plant growth. Additionally, in industries such as water treatment, pH regulation is essential for safety and efficiency.

PH influences the taste of foods and beverages. For instance, acidic foods like lemons taste sour, while basic substances can taste bitter or soapy. PH also affects the effectiveness of cleaning products and the health of aquatic ecosystems.

3. Can pH levels change?

Yes, pH levels can change due to various factors. Adding acids or bases, chemical reactions, biological processes, and environmental factors can alter pH levels in substances like water, soil, and even within the human body.

Reference:

[1] NOAA Pacific Marine Environmental Laboratory CO2 Program (2021). The pH scale with some common examples [Photograph]. https://www.pmel.noaa.gov/co2/file/The+pH+scale+with+some+common+examples