Featured contributor PhD Applied Physics; former research associate at a national metrology lab.

Dr. Helena Ortiz

Senior Reviewer, Science & Engineering

0 calculators 0 articles Member since Jun 2026

About

Helena is the senior technical reviewer for physics, chemistry, and unit-conversion calculators. She is the last pair of eyes on every formula — checking constants, units, and edge cases against primary sources and standards bodies.

She holds a PhD in Applied Physics and previously held a research post at a national metrology lab.

Areas of expertise

Physics Chemistry Unit conversion Measurement standards

Education & credentials

BSc Physics — Universidad Complutense de Madrid
PhD Applied Physics — Stanford University

Chemistry

Mass Spectrometry m/z Calculator

Compute the mass-to-charge ratio (m/z) for an ion from its monoisotopic mass and charge state z. For multiply-charged io...

basic

13,097 4.3 1 min

Physics

Bohr Hydrogen Energy Level Calculator

Compute the electron energy at orbital level n in a hydrogen atom from the Bohr model: E_n = −13.6 / n² eV. Reports ener...

basic

7,884 4.6 1 min

Physics / Mechanics

Lunar Phase on Date Calculator

Compute the Moon's phase, age in days, and illuminated fraction for any date, plus the next new- and full-moon dates. Us...

basic

12,719 4.0 1 min

Chemistry

Percent Ionization of a Weak Acid Calculator

Compute the percent ionization of a weak monoprotic acid: % ionization = ([H⁺] / C₀) · 100, with [H⁺] ≈ √(Ka · C₀). Usef...

basic

9,998 4.5 1 min

Chemistry

Graham's Law of Effusion Rate Calculator

Compares effusion (or diffusion) rates of two gases at the same temperature using Graham's Law and their molar masses.

basic

18,689 4.3 1 min

Sports

Recovery Time Between Workouts from TSS Calculator

Estimates recovery hours ≈ TSS / 10 × recovery_factor. Low TSS (<100) = <24 h; moderate (100–200) = 24–48 h; high (>300)...

basic

24,714 4.8 1 min

Chemistry / Solutions

Raoult's Law Vapor Pressure Mixture Calculator

Calculates the total vapor pressure of an ideal binary liquid mixture using Raoult's Law from mole fractions and pure co...

basic

16,686 4.5 1 min

Statistics

Two-Sample Independent t-Test Calculator

Calculates Welch's t-statistic and approximate degrees of freedom for comparing means of two independent samples.

basic

15,840 4.9 1 min

Chemistry / Solutions

Freezing Point Depression Calculator

Calculates freezing point depression for a solution from van't Hoff factor, cryoscopic constant, and molality.

basic

9,805 4.7 1 min

Chemistry

Arrhenius Pre-Exponential Factor A from k, Ea, and T Calculator

Compute the Arrhenius pre-exponential (frequency) factor A given a measured rate constant k at temperature T and the act...

basic

9,672 4.8 1 min

Chemistry / Reactions

Solubility Product (Ksp) Calculator

Compute the solubility product Ksp = s² for a 1:1 (MX-type) sparingly soluble salt from its molar solubility s, plus a q...

basic

23,702 4.7 1 min

Physics / Electricity

RL Time Constant Calculator

Compute the time constant τ = L / R of a series RL circuit, the time to reach 63 % of final current, and the rough cutof...

basic

16,532 5.0 1 min

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Reviewed by Dr. Helena Ortiz

These calculators were technically reviewed by Dr. Helena Ortiz for accuracy.

Chemistry / Reactions

Equilibrium Constant Calculator

Compute the equilibrium constant K_c from the concentrations of two products (with stoichiometric coefficients 1) divide...

basic

5,060 4.0 1 min

Conversions / Length

Length Converter

Convert between meters, kilometers, miles, feet, inches, and yards.

Featured basic

4,964 4.2 1 min

Chemistry / Solutions

Combined Gas Law Calculator

Find the missing pressure, volume, or temperature using the combined gas law for a fixed amount of gas.

basic

5,360 4.2 1 min

Physics / Electricity

Capacitance Calculator

Compute the capacitance of a parallel-plate capacitor from plate area, plate separation, and the dielectric constant.

basic

12,524 4.1 1 min

Chemistry / Solutions

pOH Calculator

Compute pOH from hydroxide ion concentration and the matching pH at 25 °C.

basic

18,221 4.2 1 min

Ecology / Carbon Footprint

Carbon Footprint Calculator

Estimate your annual personal CO₂e footprint from home energy, driving, flying, and diet — with adjustable emission fact...

Featured basic

15,825 4.9 1 min

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Dr. Helena Ortiz

Mass Spectrometry m/z Calculator

Bohr Hydrogen Energy Level Calculator

Lunar Phase on Date Calculator

Percent Ionization of a Weak Acid Calculator

Graham's Law of Effusion Rate Calculator

Recovery Time Between Workouts from TSS Calculator

Raoult's Law Vapor Pressure Mixture Calculator

Two-Sample Independent t-Test Calculator

Freezing Point Depression Calculator

Arrhenius Pre-Exponential Factor A from k, Ea, and T Calculator

Solubility Product (Ksp) Calculator

RL Time Constant Calculator

Reviewed by Dr. Helena Ortiz

Equilibrium Constant Calculator

Length Converter

Combined Gas Law Calculator

Capacitance Calculator

pOH Calculator

Carbon Footprint Calculator