❌ Disappearing cross: virtual chemistry experiment
Thiosulfate + acid turns cloudy with sulfur. Warmer means faster.
▶ Launch this experiment freeRuns in your browser on any phone, tablet or laptop. No sign-up, no install, no chemicals needed.
What you'll do
- Light the burner under the right beaker and warm it to ~50 °C
- Add 10 mL HCl to both beakers
- Compare which turns opaque first
The chemistry behind it
S₂O₃²⁻ + 2H⁺ → S↓ + SO₂ + H₂O. Raising the temperature by 10 °C roughly doubles the rate.
Why do this experiment virtually?
Many school labs can't run this experiment safely or don't have the chemicals. In Faradium you set it up in seconds, repeat it as often as you like, change the amounts and see the real result: colours, gases, precipitates and temperature changes. The lab notebook records every observation with the balanced equation for your write-up.
Frequently asked questions
How do you do the disappearing cross experiment?
1. Light the burner under the right beaker and warm it to ~50 °C 2. Add 10 mL HCl to both beakers 3. Compare which turns opaque first You can run every step free in the Faradium virtual chemistry lab.
What is the chemistry behind disappearing cross?
S₂O₃²⁻ + 2H⁺ → S↓ + SO₂ + H₂O. Raising the temperature by 10 °C roughly doubles the rate.
Can I do the disappearing cross experiment online for free?
Yes. Faradium sets up the bench for you and ticks off each step as you complete it. It runs in any browser on a phone, tablet or laptop with no sign-up and no chemicals.
Chemistry in this experiment
Elements involved: Hydrogen (H), Oxygen (O), Sulfur (S).
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