Acids and Bases in Everyday Life

Why Acids and Bases Matter in Daily Life

Acids and bases are not just abstract concepts from chemistry class—your body, your food, your cleaning products, and even the environment depend on acid–base reactions. In this chapter, we focus on recognizing acids and bases around you and understanding, in simple terms, why their properties are useful (or sometimes dangerous).

We will use the ideas of Brønsted and Lewis acids/bases and acid–base equilibria without re-explaining them in depth.

Recognizing Acids and Bases in Everyday Substances

Typical Household Acids

Common weak acids:

• Vinegar: contains acetic acid, $ \text{CH}_3\text{COOH} $
• Citrus fruits (lemon, orange, grapefruit): contain citric acid
• Apples, grapes: contain malic and tartaric acid
• Yogurt, sauerkraut: contain lactic acid
• Carbonated drinks: contain carbonic acid, formed when $ \text{CO}_2 $ dissolves in water
• Vitamin C tablets and many fruits: contain ascorbic acid

Stronger household acids:

• Toilet descalers and limescale removers: often contain hydrochloric acid ($\text{HCl}$) or sulfamic acid
• Some rust removers and drain cleaners: can contain sulfuric acid ($\text{H}_2\text{SO}_4$) or other strong acids

Characteristic properties you can notice:

• Sour taste (never taste unknown substances for safety reasons!)
• Often react with limescale (calcium carbonate) with fizzing (release of $ \text{CO}_2 $)
• Can be corrosive to skin, eyes, metals, limestone, and certain fabrics if sufficiently strong and concentrated

Typical Household Bases

Common weak to moderate bases:

• Baking soda (bicarbonate of soda): sodium hydrogen carbonate, $ \text{NaHCO}_3 $
• Washing soda (soda ash): sodium carbonate, $ \text{Na}_2\text{CO}_3 $
• Some “antacid” tablets for heartburn: usually contain carbonates, hydrogen carbonates, or hydroxides of magnesium and aluminum
• Ammonia solution (household ammonia, glass cleaners): $ \text{NH}_3 $ dissolved in water

Strong bases (usually in cleaning products):

• Oven cleaners: often contain sodium hydroxide, $ \text{NaOH} $
• Drain cleaners: may contain sodium or potassium hydroxide (caustic soda, caustic potash)
• Some heavy-duty degreasers: strongly alkaline

Typical observable properties:

• Slippery or soapy feel on skin (this is actually the start of a chemical reaction with skin fats and proteins)
• Bitter taste (never taste bases for safety reasons)
• Can feel “burning” or cause damage, especially in concentrated form
• Efficient at dissolving fats and many organic residues

Acid–Base Indicators in Everyday Life

Many natural substances change color depending on $\text{pH}$ (how acidic or basic a solution is). These are natural indicators.

Examples:

• Red cabbage juice: purple around neutral, red in acid, green–yellow in base
• Black tea: darkens with strong acids; can become more brown with bases
• Flower pigments (anthocyanins) in hydrangeas, some berries, and petals: change hue with soil acidity

Hydrangeas are a widely known example:

• In acidic soil: flowers tend to be blue
• In neutral to weakly basic soil: flowers tend to be pink or red

This color change results from acid–base interactions affecting the structure of the anthocyanin dye molecules in the plant.

Commercial indicators (litmus paper, universal indicator, $\text{pH}$ strips) rely on the same principle but use defined mixtures of synthetic dyes.

Acids and Bases in Food and Cooking

Taste and Food Preservation

Acidity is one of the basic taste qualities (sour). A food’s $\text{pH}$ and its acid–base balance affect:

• Taste: sharpness, freshness, “brightness”
• Microbial stability: many bacteria grow poorly in strongly acidic environments
• Texture and color of foods

Common acid–base related phenomena:

• Pickling and preserving
  Vinegar (acetic acid) and lactic acid from fermentation lower the $\text{pH}$:
• Inhibits growth of many spoilage microorganisms
• Used in pickles, sauerkraut, kimchi, yogurt
• Carbonated drinks
  Dissolved $ \text{CO}_2 $ forms carbonic acid:
  $$ \text{CO}_2 + \text{H}_2\text{O} \rightleftharpoons \text{H}_2\text{CO}_3 $$
  This contributes to the tangy, slightly sour taste.
• Citrus and flavor balance
  Lemon juice or vinegar is often added to:
• “Brighten” flavors
• Balance sweetness or fattiness
• Slightly denature proteins (e.g., in ceviche) through acid–protein interactions

Baking and Leavening with Baking Powder

Baking powder is a mixture of:

• A weak base: usually sodium hydrogen carbonate, $ \text{NaHCO}_3 $ (baking soda)
• One or more weak acids (e.g., cream of tartar, sodium aluminum sulfate)
• A drying agent (e.g., starch)

When moistened (and often heated), the acid and base react to release $ \text{CO}_2 $, which leavens the dough:

$$
\text{NaHCO}_3 + \text{H}^+ \rightarrow \text{Na}^+ + \text{CO}_2 \uparrow + \text{H}_2\text{O}
$$

Key points:

• The base alone (baking soda) will only generate enough $ \text{CO}_2 $ if the dough contains a suitable acid (e.g., buttermilk, yogurt, lemon juice).
• If there is not enough acid present, unreacted $ \text{NaHCO}_3 $ can give a soapy, bitter taste and a yellowish color.
• Baking powders are formulated to provide a predictable acid–base ratio and time profile of gas release (single-acting vs double-acting).

Protein and Texture Changes with Acids

Acids can alter protein structure (denaturation), influencing food texture:

• Curdling milk with lemon juice or vinegar:
• Casein proteins reach their isoelectric point at a certain $\text{pH}$ and aggregate, forming curds (cheese) and whey.
• Ceviche:
• Fish protein is “cooked” (denatured) by citric acid without heat.
• Marinades:
• Acids (vinegar, wine, yogurt, lemon juice) partially denature surface proteins and can change meat texture and flavor uptake.

Color Changes in Vegetables

Plant pigments are often acid–base sensitive:

• Red cabbage, beetroot, red onions:
• Can change color when cooked with vinegar (more red) or baking soda (more blue/green).
• Green vegetables (chlorophyll):
• Overcooking and acidity may turn them olive/brown.
• Mild alkalinity can keep them greener but may damage texture and vitamins.

These changes show how acid–base balance affects not only taste but also appearance and nutritional quality.

Acids and Bases in the Human Body

Stomach Acid and Digestion

The stomach produces hydrochloric acid ($\text{HCl}$) to reach a strongly acidic $\text{pH}$ (around 1–2):

• Activates digestive enzymes (like pepsin) that require acidic conditions
• Helps kill ingested microorganisms
• Aids in dissolving and ionizing minerals (e.g., iron, calcium), improving their absorption

Excess acid or weakened protective mucus can lead to heartburn or ulcers. “Antacid” medications use bases (often carbonates, hydrogen carbonates, or hydroxides) to neutralize excess acid:

$$
\text{HCl} + \text{NaHCO}_3 \rightarrow \text{NaCl} + \text{CO}_2 \uparrow + \text{H}_2\text{O}
$$

Blood pH and Buffers

Blood $\text{pH}$ is tightly controlled within a narrow, slightly basic range (about 7.35–7.45). This is crucial because many enzymes only function properly in a limited $\text{pH}$ window.

This stability is achieved by buffer systems, particularly the carbonic acid/hydrogen carbonate system:

$$
\text{CO}_2 + \text{H}_2\text{O} \rightleftharpoons \text{H}_2\text{CO}_3 \rightleftharpoons \text{H}^+ + \text{HCO}_3^-
$$

Respiration (removal of $ \text{CO}_2 $) and kidney function (adjusting levels of $ \text{H}^+ $ and $ \text{HCO}_3^- $) together regulate this equilibrium.

Disturbances of acid–base balance (acidosis, alkalosis) have serious health consequences and are diagnosed and treated using the concepts of $\text{pH}$, buffers, and equilibrium from acid–base chemistry.

Cleaning and Household Chemicals

Acids and bases are deliberately used in cleaning products because of the types of dirt or deposits they dissolve.

Acidic Cleaners

Acidic cleaners target mineral deposits:

• Limescale removers (for kettles, coffee makers, bathroom fixtures):
• Contain acids that dissolve calcium carbonate (limescale)
• Typical reaction (for hydrochloric acid):
  $$
  \text{CaCO}_3 + 2\,\text{HCl} \rightarrow \text{CaCl}_2 + \text{CO}_2 \uparrow + \text{H}_2\text{O}
  $$
• Rust removers:
• Often contain acids that dissolve iron oxides and form soluble salts.

Important practical aspects:

• Acidic cleaners should not be used on acid-sensitive surfaces (marble, limestone, certain metals).
• Strong acids are corrosive to skin and eyes and require appropriate protective measures.

Basic (Alkaline) Cleaners

Basic cleaners are effective against organic and fatty residues:

• Oven cleaners, drain cleaners:
• Often contain sodium hydroxide or potassium hydroxide.
• These strong bases break down fats via saponification: fats (triglycerides) are converted into glycerol and soap-like substances.
• Dishwashing powders and some laundry detergents:
• Mildly alkaline formulations help emulsify fats and oils.

Safety considerations:

• Strong bases can cause severe chemical burns and permanent eye damage.
• React vigorously with aluminum and can produce hydrogen gas.
• Must never be mixed with certain other products (see below).

Dangerous Mixtures: Why Some Cleaners Must Not Be Mixed

Combining some household chemicals can produce harmful gases or vigorous reactions:

• Acidic cleaners + bleach (sodium hypochlorite solutions):
• Can release chlorine gas, $ \text{Cl}_2 $, which is toxic.
• Ammonia-based cleaners + bleach:
• Can form chloramines and related compounds, which are also harmful to breathe.
• Strong acids + strong bases:
• Release a lot of heat during neutralization, causing splattering and boiling.

Even if the overall reaction is a “simple” acid–base neutralization, the heat and gases released can be dangerous in everyday settings.

Acids, Bases, and the Environment

Acid Rain

Acid rain is rain with a $\text{pH}$ lower than normal “clean” rain (which is already slightly acidic due to dissolved $ \text{CO}_2 $). It results when:

• Sulfur dioxide ($\text{SO}_2$) and nitrogen oxides ($\text{NO}_x$) from combustion enter the atmosphere,
• Are oxidized and dissolve in water to form sulfuric and nitric acids.

Consequences:

• Acidification of lakes and soils, affecting plant and aquatic life
• Increased dissolution of metals (e.g., aluminum) into water
• Damage to buildings and monuments made from carbonate-containing stones (e.g., limestone, marble) through acid–carbonate reactions

Soil pH and Plant Growth

Soil acidity affects:

• Nutrient availability (some nutrients dissolve and become available only in certain $\text{pH}$ ranges)
• Toxicity of certain ions (e.g., aluminum can become more soluble in very acidic soils)
• Microbial activity and decomposition

Gardeners and farmers manage soil $\text{pH}$ using:

• Lime (calcium carbonate or calcium oxide) to reduce acidity (make soil more basic)
• Acidic fertilizers or organic materials to decrease $\text{pH}$ when soil is too basic

These adjustments are practical applications of acid–base neutralization and buffering.

Everyday Acid–Base Safety

Because acids and bases are so common, basic safety practices are important:

• Never taste or smell unknown chemicals to identify them.
• Use eye and skin protection when handling concentrated acids or bases (e.g., drain cleaners, strong descalers).
• Add acid to water, not water to acid, when diluting concentrated acids to avoid splashing.
• Do not mix different cleaning agents unless the instructions explicitly say it is safe.
• Store household chemicals out of reach of children and clearly labeled.

Understanding that many household products are acids or bases helps explain why these precautions are necessary.

Summary: Connecting Theory to Practice

• Many foods, drinks, and preservatives are weak acids or involve acid–base reactions (e.g., pickling, baking, marinades).
• Your body relies on controlled acid–base environments (e.g., stomach acid for digestion, buffered blood $\text{pH}$ for metabolism).
• Cleaning products use acids to dissolve mineral deposits and bases to remove fats and organic residues.
• Environmental phenomena such as acid rain and soil fertility are governed by acid–base chemistry.
• Natural and synthetic indicators reveal $\text{pH}$ changes by color changes in everyday contexts.

Knowing where acids and bases appear in daily life allows you to use them more effectively, interpret labels and warnings, and recognize when practical situations are governed by the same principles as in acid–base theory.