MolarPrep

Stock solution and molarity preparation for laboratory workflows

→ Open the live app

---

What is MolarPrep?

MolarPrep is a browser-based solution preparation calculator that covers the two most common reagent setup scenarios in a laboratory: weighing a dry solid to a target molarity, and pipetting the right volume from a liquid stock defined by density and purity.

Both modules handle unit scaling automatically and validate inputs before computing, so the result is always expressed in a practical unit without manual prefix conversion.

No installation. No server. Runs entirely in the browser.

---

Why it matters

Preparing stock solutions involves multi-step unit conversions that are a frequent source of errors — especially under time pressure or when working across concentration scales (M, mM, µM, nM). Without a dedicated tool:

• Mass calculations require manually converting target molarity and volume into consistent units before applying m = M × V × MW
• Liquid reagent preparation involves a two-step calculation (density + purity → stock molarity, then C₁V₁ = C₂V₂) that is commonly collapsed or done incorrectly
• The appropriate output unit (g, mg, µg / L, mL, µL) must be chosen by the user, introducing another judgment call

MolarPrep handles all conversions internally and selects the output prefix automatically based on scale.

---

How it works

Module 1 — Solid reagent (mass to weigh)

Enter the target molarity, final volume, and molecular weight. MolarPrep returns the mass to weigh out.

Formula

$$m \ (\text{g}) = M \left(\frac{\text{mol}}{\text{L}}\right) \times V \ (\text{L}) \times MW \left(\frac{\text{g}}{\text{mol}}\right)$$

Supported molarity units: M, mM, µM, nM. Supported volume units: L, mL. Output is auto-scaled to g, mg, or µg depending on magnitude.

Module 2 — Liquid reagent (concentrated stock volume)

Use this when the reagent is a liquid sold by density and purity (e.g. acids, organic solvents). Enter density, purity, molecular weight, target molarity, and final volume.

Step A — Estimate stock molarity from density and purity

$$M_1 = \frac{P \times \rho \times 1000}{MW}$$

where P = purity fraction (e.g. 0.98), ρ = density in g/mL, MW = molecular weight in g/mol.

Step B — Apply dilution equation

$$V_1 = \frac{M_2 \times V_2}{M_1}$$

Output is auto-scaled to L, mL, or µL.

Output validation

Non-positive or missing values return ERR. All outputs are checked for physical consistency before display.

---

Features

Solid reagent module	Computes mass to weigh from molarity, volume, and MW
Liquid reagent module	Estimates stock molarity from density and purity, then solves C₁V₁ = C₂V₂
Auto unit scaling	Output switches between g/mg/µg and L/mL/µL based on magnitude
Input validation	Non-positive or missing values return ERR before computing
Offline-first PWA	Service Worker caches all assets; works without internet after first load
Bilingual UI	Full Spanish / English interface
No installation	Opens instantly in any modern browser; installable on Android, iOS, and desktop

---

Tech stack

Frontend

Deployment

Fully static — no backend, no framework, no build step.

---

Project structure

MolarPrep/
├── index.html              ← markup only
├── manifest.json           ← PWA manifest
├── sw.js                   ← Service Worker (cache-first, offline support)
├── icon-192.png
├── icon-512.png
├── icon-maskable-192.png
├── icon-maskable-512.png
├── og-image.png            ← Open Graph social preview
└── src/
    ├── css/
    │   └── app.css         ← all styles
    └── js/
        ├── i18n.js         ← translation strings (ES / EN)
        └── app.js          ← all application logic

---

Author

Emiliano Balderas Ramírez Bioengineer · PhD Candidate in Biochemical Sciences Instituto de Biotecnología (IBt), UNAM

---

Related

DiluteIt — universal dilution solver (C₁V₁ = C₂V₂) for any of the four variables.

CellSplit — Neubauer cell counting and passage planning for CHO cultures.

PulseGrowth — growth kinetics and metabolic rate estimation for mammalian cell culture.

CellBlock — shared biosafety cabinet scheduling for cell culture research groups.

---

MolarPrep — enter your target, get your mass or volume.