Reaction Rate Virtual Lab

Sodium Thiosulfate ($Na_2S_2O_3$) & Hydrochloric Acid ($HCl$)

Collision Theory: Rate $\propto$ Concentration

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Lab Manual: Theory & Procedure

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Aim

To investigate the effect of varying the concentration of $Na_2S_2O_3$ on the rate of its reaction with $HCl$.

Principle

The reaction produces insoluble sulfur precipitate:

$Na_2S_2O_{3(aq)} + 2HCl_{(aq)} \rightarrow 2NaCl_{(aq)} + S_{(s)} \downarrow + SO_{2(g)} + H_2O_{(l)}$

Higher concentration means more particles per unit volume, leading to more frequent successful collisions.

Procedure

1. Select the volume of Thiosulfate and Water to vary the concentration.
2. Place the flask over the black 'X' marker.
3. Add $10\text{ mL}$ of $HCl$ and start the stopclock.
4. Monitor the cross; stop the clock when it is no longer visible.

🔮 Predict before you experiment

You will run the reaction at several thiosulfate concentrations (varying the Thio : Water ratio in a fixed 50 mL). Predict the trend first, then lock it to unlock the stopclock.

As the thiosulfate concentration increases, the cross disappears…

So the reaction rate (1/t) as concentration increases will be…

Your reasoning (≥15 characters)

⚠️ Safety

The reaction releases sulfur dioxide (SO₂) — a toxic, choking gas. Work in a well-ventilated room or fume cupboard; it can trigger asthma.
Dilute HCl is corrosive/irritant — avoid skin and eye contact, wear goggles.
Do not lean over and inhale the flask; view the cross from directly above only briefly.
The fine sulfur precipitate makes the mixture cloudy — dispose of it in the labelled waste, do not pour large amounts down the sink.
Keep the total volume fixed at 50 mL so only concentration changes (a fair test).

Station 1: Preparation

Thio: 50ml

Water: 0ml

$Na_2S_2O_3$

Water

Station 2: Reaction (Top View)

View through mouth

Digital Stopclock

00:00.0

Observation Log

Flask	Ratio (ml)	Time (s)	Rate (1/t)

Reaction Monitor

Adjust volumes at Station 1 to begin. Total volume must be $50\text{mL}$.