Effect of Concentration Acid and Marble Chips

Calcium carbonate marble chips react with hydrochloric acid to produce carbon dioxide, water, and calcium chloride. By running the reaction at different acid concentrations and tracking mass loss over time as CO2 escapes, students compare reaction rates and relate the results to collision theory.

1. Prepare four or more hydrochloric acid solutions that differ only in concentration, for example 0.10 M, 0.2 M, 0.3 M, and 0.4 M.
2. Dry marble chips with filter paper and select pieces to give the same total mass and similar size in every trial; record the surface area description you are using.
3. Set a clean conical flask on a top-loading balance, add a fixed volume of one HCl solution, and place a loose cotton wool plug in the neck to reduce spray while allowing CO2 to escape. Tare the balance.
4. Start a timer, quickly add the preweighed marble chips, replace the cotton plug, and record the mass every 5 to 10 seconds for several minutes until the mass change becomes small.
5. Repeat the run for each acid concentration, keeping temperature, marble mass, chip size, and solution volume the same in all trials.
6. Plot mass loss versus time for each concentration and compare initial slopes as a measure of initial reaction rate. Optionally fit a line to the first 30 to 60 seconds for a consistent initial rate.

Experiment: The effect of concentration on reaction rate - full experiment - Chemistry with Mrs V:

Effect of Concentration on the Rate of Reaction | Chemistry Practicals - Science with Hazel:

📄 Concentration of HCl and Reaction Rate with Marble Chips - EduBirdie: https://hub.edubirdie.com/examples/the-effect-of-concentration-on-hydrochloric-acid-on-the-rate-of-reaction-with-marble-chips/

• Keep concentration constant and compare large chips versus powdered CaCO3 to investigate surface area effects.
• Hold concentration constant and run at different temperatures using a water bath to test the temperature effect on rate.
• Measure reaction progress with a gas syringe or an inverted buret to collect CO2 volume instead of using mass loss.
• Compare different acids at the same molarity, such as hydrochloric versus acetic, to see how acid strength influences rate.
• Investigate the effect of stirring by using a magnetic stirrer at controlled speed.

• Hydrochloric acid is corrosive; avoid contact with skin and eyes. Work in a well ventilated space and clean spills immediately with plenty of water.
• Do not seal the flask; the reaction releases CO2 gas and pressure must not build up. Use a cotton wool plug to limit spray.
• Keep acid volumes small and use secondary containment when working on a balance to protect the instrument from spills.
• Avoid breathing any dust from marble powder if used; handle powders gently.

• Why does the mass of the flask decrease during the reaction? (CO2 gas leaves the flask, so the measured mass goes down.)
• How should initial rate be determined from your data fairly? (Use the slope of the mass loss curve at early times where it is approximately linear and conditions are most comparable.)
• Why does higher acid concentration usually give a faster rate? (More H+ and Cl− particles per volume means more frequent effective collisions with CaCO3.)
• Why do curves often level off with time? (Reactants are consumed and the surface may become less reactive; the frequency of collisions decreases.)
• What controlled variables are most important here? (Mass and surface area of CaCO3, total liquid volume, temperature, mixing, and apparatus.)
• What common source of error can make mass loss look too large? (Loss of liquid spray or splashing from effervescence; the cotton plug helps reduce this.)
• How would using powdered CaCO3 change the graph shape? (Much steeper initial slope because of larger surface area, reaching completion sooner.)
• If two concentration curves have overlapping error bars at most time points, what does that imply? (Any difference in rate may not be statistically significant with the current precision.)
• How could you reduce uncertainty in concentration preparation? (Use class A volumetric flasks and pipettes, prepare a concentrated stock, and make single-step dilutions when possible.)
• What evidence would indicate a temperature effect during a run? (Later trials in a warmer room show uniformly steeper initial rates even at the same concentration.)