Chemical Reactions & pH

Why This Matters for Nursing: Understanding reactions and pH is essential for interpreting blood gases, understanding medication interactions, and recognizing acid-base imbalances that can be life-threatening.

What You Need to Know

Chemical Reactions

A chemical reaction occurs when substances interact to form new substances with different properties.

General form: Reactants → Products

🧠 Memory Trick

pH Scale: "pH = Power of Hydrogen"

• Low pH = ACIDIC (more H⁺)
• High pH = BASIC (less H⁺)
• pH 7 = NEUTRAL

Blood pH: 7.35-7.45 (slightly basic) "Basic blood keeps you alive"

Types of Chemical Reactions

Enzymes and Reactions

Enzymes are biological catalysts that:

• Speed up reactions without being consumed
• Lower activation energy needed (increasing the rate at which equilibrium is reached)
• Are specific to certain reactions
• Are usually proteins (a few are RNA molecules called ribozymes)

Factors Affecting Enzyme Activity:

Acids and Bases

Common Acids and Bases in the Body:

The pH Scale

pH Math:

• Each pH unit = 10× difference in H⁺
• pH 5 is 10× more acidic than pH 6
• pH 4 is 100× more acidic than pH 6

Buffers

Buffers resist changes in pH by absorbing or releasing H⁺.

Blood buffer system:

• Carbonic acid (H₂CO₃) ↔ Bicarbonate (HCO₃⁻) + H⁺
• If blood too acidic: Bicarbonate absorbs H⁺
• If blood too basic: Carbonic acid releases H⁺

Acid-Base Imbalances

Normal blood pH: 7.35 - 7.45

✏️ Worked Examples

Example 1: Identify Reaction Type

Reaction: 2Na + Cl₂ → 2NaCl

Step 1 — Count the reactants and products. On the LEFT side of the arrow (reactants): 2 things — sodium (Na) and chlorine gas (Cl₂). On the RIGHT side (products): 1 thing — sodium chloride (NaCl, table salt).

Step 2 — Apply the pattern matching. Ask: are things coming together or breaking apart?

• Two separate things (Na and Cl₂) are combining → forming one new product (NaCl)
• Pattern: A + B → AB
• This is synthesis (also called a combination reaction). Like building a car — you take parts and put them together.

Step 3 — Confirm by eliminating other types.

• Decomposition would be AB → A + B (breaking apart). Here things are coming together, not apart. ✗
• Single replacement would be A + BC → AC + B (one element kicks out another). Not the case here. ✗

Answer: Synthesis — Two reactants (Na and Cl₂) combine into one product (NaCl).

Example 2: pH Interpretation

Question: A patient's blood pH is 7.30. What condition is this?

Step 1 — Know normal blood pH. Normal blood pH is 7.35 – 7.45. The body fights very hard to maintain this narrow range. Even small deviations can be life-threatening.

Step 2 — Compare. The patient's pH = 7.30. Normal minimum = 7.35. The patient's pH is BELOW the normal minimum.

Step 3 — Name the condition.

• pH below 7.35 = acidosis (blood is too acidic)
• pH above 7.45 = alkalosis (blood is too basic/alkaline)

It doesn't matter that 7.30 is still above pH 7 (which is technically neutral). We're comparing to the body's normal, not to the chemistry-neutral point. Anything below 7.35 in the blood = acidosis.

Answer: Acidosis — pH 7.30 is below the normal range of 7.35-7.45.

🏥 Nursing connection: In the clinical setting, you'll interpret arterial blood gases (ABGs) regularly. Acidosis can come from respiratory causes (too much CO₂ building up — respiratory acidosis) or metabolic causes (diabetic ketoacidosis, kidney failure — metabolic acidosis). The treatment differs based on the cause. A pH of 7.30 would trigger immediate clinical concern and intervention.

Example 3: Acid vs. Base

Question: Stomach acid has a pH of 2. Is this acidic or basic?

Step 1 — Know the pH scale. The pH scale runs from 0 to 14:

• 0-6.9 = acidic (more H⁺ ions)
• 7 = neutral
• 7.1-14 = basic/alkaline (fewer H⁺ ions, more OH⁻)

Step 2 — Locate pH 2 on the scale. pH 2 is very far on the acidic end — below 7, much below 7. This is strongly acidic.

Step 3 — Contextualize. Stomach acid (hydrochloric acid, HCl) at pH 1-3 is one of the most acidic substances in the body. It needs to be this acidic to:

• Activate pepsin (the protein-digesting enzyme, which only works in acidic conditions)
• Kill pathogens in food
• Help denature (unfold) proteins for easier digestion

Answer: Acidic — pH 2 is far below 7, making it strongly acidic.

🏥 Nursing connection: Proton pump inhibitors (PPIs) like omeprazole work by reducing the amount of acid the stomach produces — raising the stomach pH. Antacids (like Tums) work by neutralizing existing acid. Both are treatments for conditions like GERD (gastroesophageal reflux disease), where stomach acid splashes into the esophagus. Understanding pH helps you understand why these drugs work.

💡 Pro Tips

• Blood pH is slightly BASIC (7.35-7.45) — remember "basic blood"
• Lower pH = more acidic = more H⁺
• Enzymes have optimal pH — stomach enzymes work at low pH; intestinal enzymes at higher pH
• pH scale is logarithmic — each number is 10× different
• On the TEAS: Know normal blood pH and basic acid/base concepts

⚠️ Common Mistakes to Avoid

• Thinking pH 7 is basic: pH 7 is NEUTRAL; above 7 is basic
• Confusing acidosis/alkalosis: Acidosis = pH too LOW; Alkalosis = pH too HIGH
• Forgetting blood is slightly basic: Not neutral! (7.35-7.45)
• pH scale direction: LOWER pH = MORE acidic (counterintuitive)

Quick Reference

pH Quick Guide

Reaction Types

Chemical reactions and pH mastered! 💪 Next up: Scientific Measurement & Lab Safety