How to prepare a solution at the right concentration
Start by deciding which concentration unit the protocol wants. The Molarity Calculator gives moles per litre of solution, which is the default in most labs, while the Molality Calculator uses moles per kilogram of solvent and is what you need when temperature will change, since mass does not expand.
To get there from a solid, the Moles Calculator converts grams to moles using molar mass. To get there from a stock solution, the Dilution Calculator applies C1V1 = C2V2. For trace amounts, the Parts Per Million Calculator is the practical unit.
When you need pH rather than concentration
pH is a logarithmic restatement of hydrogen ion concentration, which is why it compresses an enormous range into a 0-14 scale. The pH Calculator converts [H⁺] into pH, and the pH and pOH Calculator moves between pH, pOH, [H⁺] and [OH⁻] in one step.
The practical consequence of the log scale is that each whole pH unit is a tenfold change — pH 4 is ten times more acidic than pH 5 and a hundred times more than pH 6. That is worth remembering before describing a change of one unit as small. Concentration itself still comes from the Molarity Calculator.
How to work through gas law and yield problems
For gases, identify which variables are held constant. The Boyle's Law Calculator covers constant temperature, the Charles's Law Calculator constant pressure, and the Combined Gas Law Calculator handles both changing at once. All of them require absolute temperature in kelvin — using celsius is the most common error in this topic.
For reaction outcomes, the Percent Yield Calculator compares what you actually isolated with the theoretical maximum, and the Percent Error Calculator measures how far a measurement sits from an accepted value. A yield below expectation usually points at losses during workup rather than at the reaction itself, so it is worth recording where each step lost material before blaming the chemistry.
Frequently asked questions
- How do I calculate molarity?
- Divide the moles of solute by the volume of solution in litres. To get moles from a mass, divide the grams by the compound's molar mass.
- What is the difference between molarity and molality?
- Molarity is moles per litre of solution and molality is moles per kilogram of solvent. Molarity changes with temperature because liquid volume expands, while molality does not.
- How do you use the dilution formula C1V1 = C2V2?
- Multiply the stock concentration by the volume you will take, and set it equal to the final concentration times the final volume. Solve for the unknown, usually V1.
- Why must gas law calculations use kelvin?
- Because the gas laws are proportional relationships and celsius has an arbitrary zero, so ratios computed in celsius are meaningless — and division by zero occurs at 0°C. Kelvin starts at absolute zero, making the proportions physically correct.
- What is a good percent yield?
- In practice 70-90% is typical for a well-run synthesis, and multi-step routes drop lower because losses compound at each stage. Yields above 100% usually indicate residual solvent or impurities in the product rather than success.