Preparing a 0.100 mol/L sodium carbonate standard solution and a tenfold dilution

The idea

A standard solution has a concentration known from a weighed primary standard made up to an exact volume, and dilution keeps the number of moles constant while the volume grows.

What you need

• Anhydrous sodium carbonate, dried at 110 degrees Celsius for one hour and cooled in a desiccator, about 2.65 g
• Electronic balance reading to 0.001 g, weighing boat
• 250.0 mL volumetric flask with stopper, 100.0 mL volumetric flask
• 10.00 mL bulb pipette and pipette filler
• 250 mL beaker, glass rod, small funnel, dropper, wash bottle of deionised water
• Conductivity meter (optional) to compare the two solutions

How to do it

1. Weigh about 2.65 g of dry sodium carbonate accurately (record the exact mass to 0.001 g).
2. Dissolve it in about 100 mL deionised water in the beaker, stirring; rinse the boat into the beaker.
3. Transfer the solution through the funnel into the 250.0 mL flask; rinse the beaker, rod and funnel three times with small volumes of water into the flask.
4. Add water to within 1 cm of the mark, then dropwise until the bottom of the meniscus sits on the mark at eye level; stopper and invert 20 times.
5. Calculate the concentration from the exact mass: c = (m/105.99)/0.2500.
6. Pipette 10.00 mL of the standard into the 100.0 mL flask, make up to the mark and mix; calculate the diluted concentration (c1V1 = c2V2).
7. Compare the conductivities of the two solutions if a meter is available and keep both solutions, labelled with concentration and date, for the titration practical.

What you should see

Weighing 2.650 g and making up to 250.0 mL gives 0.1000 mol/L to four significant figures (0.100009 mol/L, since 0.1000 mol/L needs 2.6498 g); a learner's actual mass of, say, 2.612 g gives 0.09858 mol/L, quoted to four significant figures. The tenfold dilution gives one tenth of that value (0.009858 mol/L). The diluted solution conducts less, but its reading is somewhat more than one tenth of the standard's, because ions move more freely in a more dilute solution. A solution that reads over the mark, or a cloudy solution, is discarded and remade.

What changes

This activity lists no variables to change, measure and keep the same.

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

• Adding 250 mL of water to the solid makes 250 mL of solution (the solid takes up volume; water is added to the mark).
• Diluting halves the number of moles (moles are unchanged; the concentration halves).
• Any pure solid makes a primary standard (it must be stable, dry, of known formula and weighable; sodium hydroxide absorbs water and carbon dioxide and is not one).

Safety card

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

• Chemistry Stage 6 Syllabus (2017), NESA; the current syllabus, taught in 2026 (codes read from the syllabus document)CH11-9CH11/12-4
• Chemistry Stage 6 Syllabus (2017), NESA; the current syllabus, taught in 2026 (codes read from the syllabus document); a Working Scientifically outcome not among those the syllabus targets in Module 2, which it allows in any moduleCH11/12-3
• Chemistry 11-12 Syllabus (2025), NESA; implemented from 2028, not yet taughtCH-11-02CH-11WS-03
• Australian Curriculum v9No Australian Curriculum v9 code is listed.

Sources

The pages the author read to write this activity.

1. www.nsw.gov.au/education-and-training/nesa/curriculum/science/chemistry-stage-6-2017
2. www.nsw.gov.au/sites/default/files/noindex/2025-03/chemistry-stage6-syllabus-word.docx
3. curriculum.nsw.edu.au/learning-areas/science/chemistry-11-12-2025/outcomes
4. edu.rsc.org/resources/standard-solution/2257.article
5. edu.rsc.org/resources/experimental-skills-16-18/4010280.article
6. education.nsw.gov.au/content/dam/main-education/teaching-and-learning/curriculum/key-learning-areas/science/s-6/chemistry/Chemistry-module-2-guide.docx