Week 24 – pH, Acids, and Why Your Mouth Is a Chemistry Lab

In chemistry this week, we did a lab measuring the pH of common household substances. We tested vinegar, baking soda, lemon juice, milk, and soap — watching the indicator change color at each step. It was simple, but it changed how I think about something I write about every week: cavities.

Your Mouth Has a pH

Healthy saliva sits around pH 7, neutral. But every time you eat something sugary or starchy, bacteria in plaque feed on those carbohydrates and produce acid as a byproduct. That acid drops the pH in your mouth to around 5.5 or lower — and that’s where the trouble starts.

Tooth enamel begins to demineralize when pH drops below about 5.5. This number is called the critical pH, and I wrote about the damage it causes in my posts on enamel and cavities. But seeing it in a lab with actual pH paper made it click differently. It’s not abstract — it’s a measurable chemical shift happening in your mouth after every snack.

Acid Attacks Are Constant

What surprised me most was thinking about the frequency of acid attacks. It’s not about how much sugar you eat in one sitting — it’s about how often you expose your teeth to acidic conditions. Each time you sip a soda or eat a piece of candy, your mouth’s pH drops and stays low for 20–30 minutes before saliva neutralizes it.

In chemistry terms, it’s a repeated equilibrium shift. The enamel crystal (Ca₁₀(PO₄)₆(OH)₂) is in equilibrium with calcium and phosphate ions dissolved in saliva. Acid pushes that equilibrium toward dissolution — pulling minerals out of the tooth.

Buffers and Protection

We also learned about buffers — substances that resist pH change. Saliva acts as a natural buffer in the mouth, which is why staying hydrated matters so much for oral health. Fluoride, calcium in dairy products, and even chewing sugar-free gum (which stimulates saliva) all help restore pH balance faster.

Connecting the Dots

This week tied together three things I’ve been studying separately: the pH lab in chemistry, the cavity progression I wrote about in Week 15, and the daily habits from Week 22. They’re all the same story told from different angles.

The mouth isn’t separate from chemistry — it is chemistry. Every cavity is a chemical reaction. Every brushing session is an intervention in that reaction.

Final Thoughts

I used to think of cavities as a hygiene problem. Now I see them as a chemistry problem that hygiene prevents. That shift in perspective is exactly why I’m glad I’m taking chemistry alongside this dental journal — the two subjects are teaching each other.