Measuring Reaction Rates with an Ohaus Balance and PASCO Capstone

One of the most reliable ways to determine the rate of a chemical reaction is to measure mass change over time. By combining an Ohaus balance with @PASCOScientific Capstone, students can collect high-quality, continuous data that turns an abstract idea into something they can see happening live.

The Reaction

Calcium carbonate + hydrochloric acid

$$\text{CaCO}_{3}(s) + 2\text{HCl}(aq) \rightarrow \text{CaCl}_{2}(aq) + \text{H}_{2}\text{O}(l) + \text{CO}_{2}(g)$$

As carbon dioxide gas escapes, the total mass of the system decreases. Tracking this mass loss allows us to calculate the rate of reaction directly.

Why Use an Ohaus Balance with Capstone?

• High sensitivity – ideal for small but measurable mass changes

• Live data logging – no stopwatches, no missed readings

• Instant graphs – mass vs time appears as the reaction happens

• Excellent for exam skills – gradients, tangents, and rate calculations

In Capstone, the balance streams data continuously, allowing students to:

• See a plot mass vs time

• Calculate rate from the gradient

• Compare rates when changing acid concentration, surface area, or temperature

Perfect for GCSE and A-Level Chemistry

This setup works brilliantly for:

• GCSE required practicals on rates of reaction

• A-Level quantitative rate analysis

• Teaching variables, control, and reliability

• Demonstrating how real scientists collect kinetic data

It also avoids common problems like reaction mixtures frothing over or students struggling to synchronise timing and readings.

Teaching Tip

Once students have the graph from Capstone, then they can:

• Draw a tangent at the start to find the initial rate

• Explain why the curve flattens as reactants are used up

• Compare experimental curves when one variable is changed