Effect of Temperature Acid and Marble Chips

Marble chips (calcium carbonate) react with hydrochloric acid to produce carbon dioxide. By running the reaction at several controlled temperatures and measuring mass loss over time as CO2 escapes, students compare initial rates and relate temperature to collision theory and activation energy.

1. Prepare one HCl solution (fixed concentration); divide into equal portions and equilibrate at target temperatures (e.g., 15 °C, 25 °C, 35 °C, 45 °C) in water baths; record actual temperatures.
2. Select and preweigh identical masses of similar-sized marble chips for each run.
3. Place a conical flask on a balance; add a fixed volume of temperature-equilibrated acid; insert a loose cotton-wool plug; tare to 0.00 g.
4. Start a timer; quickly add the preweighed chips; replace the plug; record mass every 5–10 s for ~1 min, then every 10–20 s until the curve levels.
5. Repeat for each temperature, keeping acid volume/concentration, marble mass/surface area, and timing identical.
6. Plot mass loss (CO2) vs time for each run; determine initial rate from the t = 0 tangent (slope).
7. Neutralize residual acid, dispose of solutions appropriately, and clean apparatus.

Experiment: The effect of temperature on the rate of reaction - Chemistry with Mrs V:

• Collect CO2 with a gas syringe or inverted buret and analyze initial volume per second instead of mass loss.
• Keep temperature constant and vary acid concentration to separate temperature and concentration effects.
• Prewarm the flask and marble chips (in a dry beaker sitting in the water bath) to reduce temperature drop at mixing; compare with un-prewarmed runs.
• Use a temperature probe and data logger to record acid temperature drift during the first minute and correct rates if needed.

• Wear chemical splash goggles, lab coat, and appropriate gloves.
• Hydrochloric acid is corrosive; avoid contact with skin and eyes. Rinse spills with plenty of water.
• Do not seal the reaction vessel; CO2 must vent freely. Use only a loose cotton wool plug to minimize spray.
• Use water baths to warm or cool acid; do not heat acid directly on a flame or hotplate.
• Handle warm glassware with care to avoid burns and thermal shock.
• Avoid inhaling marble dust if using finely divided CaCO3. Keep the workspace ventilated.
• Neutralize acidic waste with sodium bicarbonate before disposal, then follow local regulations for aqueous calcium chloride solutions.
• Wash hands after the experiment and remove gloves before touching shared equipment.

• Why does increasing temperature increase the initial rate? (A greater fraction of collisions have energy above the activation energy, and collisions occur more frequently.)
• Why should the total CO2 produced be similar at all temperatures if acid volume and concentration are constant? (The same limiting amount of H+ is present, so the same reaction extent is reached; only the speed changes.)
• Why use the initial rate rather than an average over the whole run? (At t = 0 the concentrations and temperature are best defined and most comparable across runs.)
• What experimental choices could make the “hot” run seem cooler than it is? (Acid cooling when poured into a room-temperature flask or when chips at room temperature are added; inadequate equilibration in the water bath.)
• If two curves at different temperatures overlap within error bars for the first 30 seconds, what should you check? (Temperature measurements, chip surface area consistency, and whether sampling intervals and mixing were the same.)