Category
Chemistry Calculators
Chemistry calculators for the lab bench: find cell potential under non-standard conditions with the Nernst equation, and work out viable cell counts from agar plates with the CFU calculator.
Nernst Equation Calculator (Cell Potential Calculator)
Calculate cell potential (E) using the Nernst equation from E°, temperature, electrons transferred, and reaction quotient Q.
CFU Calculator
Calculate Colony Forming Units (CFU/mL or CFU/g) from plate count, dilution factor, and volume or sample weight. Supports multi-plate averaging and scientific notation output.
Electrochemistry: cell potential under real conditions
Standard reduction potentials (E°) describe a cell at 25 °C with every species at unit activity, which almost never matches a real beaker. The Nernst Equation Calculator corrects E° for the actual temperature, the number of electrons transferred (n), and the reaction quotient (Q), so you can see how far a cell has moved from standard conditions.
The sign of the correction tells you a lot. When Q is less than 1, products are scarce and the cell potential rises above E°; when Q is greater than 1, it falls. At equilibrium the cell potential reaches zero, which is why the same equation links E° to the equilibrium constant.
Microbiology: counting viable cells with CFU
Colony Forming Units estimate how many viable microorganisms were in the original sample. You plate a known volume of a diluted sample, count the colonies that grow, and work back through the dilution. The CFU Calculator handles serial dilutions, plated volume or sample weight, and averaging across replicate plates.
Because each colony is assumed to come from a single cell, CFU is an estimate rather than a direct count. Clumped cells form one colony and cells that are alive but do not grow on the medium are missed, so CFU results usually understate the true population.
Key formulas
- Nernst equation
- E = E° − (RT / nF) × ln Q
- Base-10 form
- E = E° − (2.303 RT / nF) × log₁₀ Q
- Plate count
- CFU/mL = colonies ÷ (dilution × volume plated in mL)
Getting accurate results
- Enter temperature in °C; the Nernst calculator converts it to kelvin (T = °C + 273.15) for you.
- n is the number of electrons in the balanced redox reaction, not the number of species involved.
- Count plates with roughly 30–300 colonies. Fewer is statistically unreliable; more and colonies merge.
- Average replicate plates at the same dilution rather than picking the one that looks best.
Frequently asked questions
- What is the Nernst equation used for?
- It calculates the potential of an electrochemical cell when concentrations or temperature differ from standard conditions, using the standard potential, temperature, electrons transferred, and the reaction quotient.
- Why does my cell potential go negative?
- A negative potential means the reaction as written is not spontaneous under those conditions. It usually happens when Q is very large, meaning products have built up relative to reactants.
- What dilution should I plate for a CFU count?
- Plate several serial dilutions and use the one that gives roughly 30–300 colonies. That range balances counting error against overcrowded plates.
- Can CFU be used for food or soil samples?
- Yes. Enter the sample weight instead of a volume and the calculator reports CFU per gram.
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