Chemistry Calculator

Molarity (M) is moles of solute per liter of solution, so it depends on the total solution volume. Molality (m) is moles of solute per kilogram of solvent, so it depends on solvent mass rather than volume. Because volume can expand or contract with temperature, molality is often preferred in thermodynamics and colligative property calculations. For solution preparation at room conditions, molarity is commonly used because volumetric glassware measures liters directly.

Use C1V1 = C2V2 when you are diluting a solution by adding solvent and the amount of solute stays the same. It works well for making standards, preparing working solutions from a concentrated stock, and performing serial dilutions. Make sure your concentration units are consistent (both in M, for example) and that volumes are in compatible units (mL or L). The calculator will convert mL to L internally when needed, but the equation itself assumes the same unit system.

The conversion is straightforward: 1000 mL equals 1 L. To convert from mL to L, divide by 1000. For example, 250 mL becomes 0.250 L. This matters most in molarity because M is defined as mol/L. If you accidentally use 250 as liters instead of 0.250 liters, your molarity will be off by a factor of 1000. In this calculator, selecting “mL” triggers an automatic conversion step that is shown in the breakdown so you can verify the unit handling.

Many introductory problems use 25°C because the ionic product of water (Kw) at that temperature makes the common approximation pH + pOH = 14. In reality, Kw changes with temperature, so the “neutral” pH is not always exactly 7.00 at temperatures far from 25°C. This calculator keeps the standard 25°C relationship as a practical baseline, and it lets you enter a temperature to record context, but it does not compute a temperature-dependent Kw model. For rigorous work, use data tables or a dedicated equilibrium approach.

The gas constant R must match the pressure and volume units you use. A popular classroom pairing is R = 0.082057 (atm·L)/(mol·K) with pressure in atm and volume in liters. Another common pairing is R = 8.314 (kPa·L)/(mol·K) with pressure in kPa and volume in liters. Temperature must be in Kelvin in both cases. In this calculator, you choose an R system in Advanced options, and then the tool converts pressure/volume/temperature as needed and shows the converted internal values in the steps.

This pH mode is designed for situations where you already know the hydrogen-ion concentration [H+] or hydroxide-ion concentration [OH−], such as measurements, strong acid/base approximations, or problems that provide ion concentrations directly. Weak acids and bases usually require an equilibrium calculation using Ka or Kb, often with an ICE table and approximations that depend on concentration. If you only know the initial weak acid concentration and Ka, you should solve the equilibrium first to find [H+], then you can use this tool to convert [H+] into pH and interpret where it falls on the 0–14 scale.

Percent composition by mass tells you what fraction of the total mass comes from each component. If a component is 35%, it contributes 35 g of every 100 g of total mass. In mixtures, this helps with formulation and reporting mass fractions. In compounds or sample analysis, it can help compare measured composition to a theoretical expectation. The calculator shows a bar for each component and the bars should add up to about 100%. If they don’t, check that you entered all components and that masses are in the same unit (grams).

The displayed results use a default of 4 significant figures for readability and typical chemistry reporting. Internally, calculations are performed with normal floating-point precision, and the steps show intermediate values so you can trace what happened. If you need higher precision, keep extra digits from your measurements or intermediate calculations and round only once at the end. You can also copy the full summary and manually adjust the number of significant figures based on your instrument uncertainty or lab instructions. When in doubt, follow your course or lab’s reporting standard.