Preparing solutions – percentage concentration, molar concentration and dilution

Integrated ScienceMatter & MaterialsAges 13–14Virtual lab

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Use with my class

Weigh a solute (NaCl, CuSO₄, sugar) on an electronic balance, transfer it to a beaker or volumetric flask and add water step by step. The concentration C% = m_solute/m_solution·100% or c = n/V is calculated from the amounts actually used; dilution mode uses C₁V₁ = C₂V₂. The CuSO₄ solution gets darker or paler with concentration, and practice tasks ask you to prepare a given solution. The Concentration units screen converts one solution into mass percent, molarity, molality, mole fraction, ppm and ppb step by step; the Pollutant levels screen converts readings for water (mg/L), soil (mg/kg) and air (µg/m³ or ppm by volume) and compares them with WHO guideline values.

Lesson: Solutions and concentration – preparing a solution

What it shows

Concentration can be expressed as a mass percent, w = m_solute ÷ m_solution × 100 %, or as a molarity in mol/L, where n = m ÷ M; in dilution n stays the same, so C₁V₁ = C₂V₂, and a saturated solution leaves solid behind. The units screen takes one solution and shows how its molarity, molality (mol per kg of solvent), mole fraction, mass percent and ppm follow from the same masses and the density. The pollutant screen turns readings in mg/L, mg/kg, µg/m³ or ppm by volume into each other and compares them with WHO guideline values such as 0.01 mg/L of lead in drinking water.

How to use

On Preparing a solution, pick a Solute and a Method, calculate the amounts, then press the step buttons in order; finished runs fill the table. On Concentration units, set the Mass of solute and Mass of water and read each step of the conversions; turn off the measured density to try your own value, and press Record to compare solutions. On Pollutant levels, choose a Sample, a Pollutant and the unit it is Reported in, move the Measured level and see how far it is from the guideline. Each screen has a task with a Check button.

Parameters you can change

Solute Sodium chloride NaCl, Copper(II) sulfate CuSO₄, Sucrose (sugar)
Method Percentage concentration C%, Molar concentration c, Dilution C₁V₁ = C₂V₂
Mass of solute 0.1–40 g
Volume of water (C%) / volumetric flask 50–250 mL
Stock solution concentration (dilution) 0.1–2 mol/L
Screen Preparing a solution, Concentration units, Pollutant levels
Mass of solute (units screen) 0.0001–200 g
Mass of water (units screen) 10–1000 g
Use the measured density
Solution density (units screen) 0.95–1.4 g/mL
Sample (pollutant screen) Drinking water, Soil, Air
Pollutant Lead (Pb), Arsenic (As), Cadmium (Cd), Mercury (Hg), Nitrate (NO₃⁻), Fluoride (F⁻), Fine particles PM₂.₅, Nitrogen dioxide (NO₂), Sulfur dioxide (SO₂), Ozone (O₃), Carbon monoxide (CO)
Reported in mg/L, µg/L, mg/kg, µg/kg, µg/m³, ppm, ppb
Measured level 0.0001–100000

Questions to explore

What mass of anhydrous CuSO₄ must you weigh to prepare 100 mL of a 0.5 M solution?
How many grams of NaCl and how many mL of water are needed to make 50 g of a 10% solution?
During dilution, which quantity stays constant, and why does the blue CuSO₄ solution become paler?

Teaching ideas

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