07 November 2025

Rates of Reaction – The Effect of Concentration Using the PASCO Colourimeter

The rate of a chemical reaction depends on how frequently particles collide with enough energy to react. One of the easiest ways to explore this relationship is with the reaction between sodium thiosulfate and hydrochloric acid, which produces a cloudy sulfur precipitate. Using a PASCO colourimeter, students can measure this change precisely, transforming a classic “disappearing cross” experiment into a fully quantitative study of reaction kinetics.

The Experiment

Reaction:

\text{Na}_2\text{S}_2\text{O}_3(aq) + 2\text{HCl}(aq) \rightarrow 2\text{NaCl}(aq) + \text{SO}_2(g) + \text{S}(s) + \text{H}_2\text{O}(l)

Traditional method:
Students mix sodium thiosulfate and hydrochloric acid, and time how long it takes for a printed cross beneath the flask to disappear as sulfur forms.

With the PASCO colourimeter:

The colourimeter measures light transmission through the solution at regular intervals.
As sulfur forms, the solution becomes cloudy, reducing the amount of transmitted light.
The data are recorded automatically in PASCO Capstone, producing a transmission vs time graph.

By repeating the experiment with different thiosulfate concentrations, students can plot reaction rate against concentration and determine the order of reaction with respect to thiosulfate.

The Science

As concentration increases, more particles occupy the same volume, leading to more frequent collisions and a faster rate of reaction.

The colourimeter allows students to calculate initial reaction rates objectively, avoiding human error and giving a clear quantitative link between concentration and rate.

\text{Rate} = k [\text{Na}_2\text{S}_2\text{O}_3]^n

The graph of rate versus concentration reveals whether the reaction is first, second, or zero order with respect to thiosulfate.

Skills Highlight

Using PASCO colourimeters for real-time quantitative data
Measuring reaction rate from absorbance or transmission curves
Controlling variables: temperature, volume, and acid concentration
Analysing graphs to interpret reaction order and rate laws

Why It Works in Teaching

The experiment connects a familiar reaction with advanced data analysis. Students see the transition from a qualitative observation to precise measurement and mathematical modelling — exactly the kind of scientific thinking needed at GCSE and A-Level.

06 November 2025

Demonstrating and Visualising Electric Fields

Electric fields are often described in theory, but they can also be made visible in the lab. With a simple setup using castor oil, semolina, and electrodes, students can see how invisible forces act between charges — a striking and memorable demonstration of field lines in physics.

The Experiment

Equipment:

90 mm petri dish
Castor oil (enough to cover the base)
A pinch of semolina grains
Two metal electrodes (pins, rods, or plates)
High-voltage DC power supply (around 1–5 kV, current-limited for safety). We find that a Wimshurst machine works best as we can turn the handle a few times to see the effect

Method:

Pour a thin layer of castor oil into the petri dish — this acts as an insulating medium that allows particles to move freely without conducting electricity directly.
Sprinkle a light dusting of semolina grains evenly over the surface.
Insert the two electrodes in the oil — start with parallel plates for a uniform field.
Apply voltage gently and observe the movement of semolina grains.
- The grains align themselves along the electric field lines, forming a visual map of the field.

Repeat the demonstration with different configurations:

Parallel plates: uniform straight lines.
Point and plate: radial pattern showing divergence from a point charge.
Two points: curved lines showing attraction or repulsion.
Parallel wires: more complex patterns with symmetrical curves.

The Science

The semolina grains become polarised in the electric field. One side becomes slightly positively charged, the other negatively charged, so each grain aligns with the direction of the field. The castor oil slows the motion, allowing the pattern to form clearly and remain stable.

This visualisation shows how electric field lines represent direction and strength:

Lines are closer together where the field is stronger.
Lines curve smoothly, never crossing.
The pattern changes shape with each electrode configuration, matching textbook diagrams almost perfectly.

Skills Highlight

Constructing experimental setups safely for electrostatics
Observing and recording field patterns qualitatively
Linking visual evidence to theoretical field diagrams
Understanding polarity, potential difference, and charge interaction

Why It Works in Teaching

Seeing the invisible is always powerful in physics. The semolina-in-oil demonstration makes electric fields concrete, a vivid link between diagrams on the board and the real behaviour of charges in space. Students grasp the geometry and symmetry of electric fields far more effectively when they can see them form before their eyes.

05 November 2025

Calculus in Context – Finding Maximum Profit

Calculus is often seen as an abstract mathematical tool, but in reality, it’s one of the most powerful methods for solving real business and economic problems. One of the clearest examples is finding maximum profit — where differentiation turns raw data into decision-making power.

The Concept

Profit depends on revenue and cost:

Profit = Revenue - Cost

If revenue and cost each depend on the number of units sold ( $x$ ), then profit is a function of $x$ . The goal is to find the value of $x$ that gives the greatest profit.

By differentiating the profit function with respect to $x$ , we can find where the slope = 0, meaning profit stops increasing — the maximum point.

Example

Suppose a company’s profit function is:
$P (x) = - 2 x^{2} + 40 x - 100$
Differentiate to find the turning point:
$\frac{d P}{d x} = - 4 x + 40$
Set this to zero to find the maximum:
$- 4 x + 40 = 0 \Rightarrow x = 10$
Substitute back into the original equation:
$P(10) = -2(10)^2 + 40(10) - 100 = 100$
So the maximum profit is £100, when 10 units are sold.

The second derivative, $\frac{d^2P}{dx^2} = -4$ , is negative — confirming a maximum point.

The Real-World Connection

This simple process mirrors how businesses use data:

If sales grow too slowly, revenue won’t cover costs.
If production expands too far, costs rise faster than income.
The sweet spot — found through calculus — gives the best balance of output and efficiency.

Skills Highlight

Differentiating quadratic and polynomial functions
Using the first and second derivatives to locate maxima and minima
Interpreting results in economic and practical contexts
Applying mathematical reasoning to real decision-making

Why It Works in Teaching

Linking calculus to business and economics transforms it from pure theory into something purposeful. Students see that differentiation isn’t just about curves — it’s about optimisation, helping to make real-world decisions about efficiency, profit, and performance.

04 November 2025

Conservation of Momentum in Two Dimensions

The law of conservation of momentum states that in a closed system, the total momentum before and after a collision remains the same, provided no external forces act. Most students first encounter this concept in one dimension, but momentum becomes much more interesting when collisions occur at angles. Using an air hockey table or an air puck system, students can observe momentum conservation in two dimensions and see the theory unfold frame by frame.

The Experiment

An air hockey table or an air track with gliders provides a near-frictionless surface. Two pucks are set on a collision path, either head-on or at an angle. A top-down video camera records the collision.

Using software such as PASCO Capstone, Tracker, or Logger Pro, students can:

Track each puck’s motion before and after impact.
Draw velocity vectors showing direction and magnitude.
Split momentum into x- and y-components and calculate totals before and after the collision.

Total momentum before = Total momentum after

m_1u_{1x} + m_2u_{2x} = m_1v_{1x} + m_2v_{2x}

m_1u_{1y} + m_2u_{2y} = m_1v_{1y} + m_2v_{2y}

The results show that even when the pucks scatter in different directions, the total momentum in both axes remains constant.

The Science

Collisions can be elastic (kinetic energy conserved) or inelastic (some energy lost as heat or deformation). However, momentum is always conserved.
The vector approach shows that momentum is not just about speed but direction — making it essential for understanding real-world physics such as vehicle collisions, snooker impacts, or atomic interactions.

Skills Highlight

Recording and analysing motion using video tracking
Decomposing vectors into x- and y-components
Verifying conservation laws experimentally
Linking abstract vector mathematics to physical evidence

Why It Works in Teaching

The combination of air hockey, sensors, and video analysis makes an abstract law tangible. Students can see how momentum balances in both directions, not through equations alone but through real motion, geometry, and evidence.

03 November 2025

Investigating Photosynthetic Pigments with a Pasco Spectrometer

Photosynthesis depends on a range of pigments that capture light energy from different parts of the spectrum. While chlorophyll dominates, other pigments, such as carotenoids and xanthophylls, also contribute, extending the range of light that plants can use. Using a PASCO spectrometer and coloured filters, students can investigate how different wavelengths affect light absorption — and discover why plants aren’t simply “green.”

The Experiment

Students set up a PASCO light sensor with a white light source and a series of coloured filters (red, blue, and green).
They:

Measure the light intensity passing through a pigment extract or leaf sample at each wavelength.
Record how much light is absorbed (low transmission) or reflected (high transmission).
Plot a spectral absorption graph, showing how pigment extracts respond to different colours of light.

Alternatively, a PASCO spectrometer can be used to collect continuous absorption data across the visible spectrum.

The Science

Each pigment absorbs specific wavelengths of light due to the arrangement of its electrons.

Chlorophyll a absorbs mainly red and blue light, reflecting green.
Chlorophyll b, carotenoids, and xanthophylls absorb in slightly different regions, broadening the plant’s overall light-harvesting ability.

By comparing absorption and photosynthesis rates, students can link pigment properties to plant adaptation and efficiency in different environments.

Plants contain a variety of photosynthetic pigments, primarily

chlorophylls and carotenoids (which include carotenes and xanthophylls), that allow them to absorb a broader range of light wavelengths for photosynthesis. These different pigments can be separated and identified using chromatography.

Plants with Different Photosynthetic Pigments

While most green plants contain the same primary pigments, the relative abundance and specific types can vary, particularly across different plant and algal groups:

Different plants to test could include:

Green leaves (e.g., spinach, grass) for typical chlorophylls and carotenoids.
Red or purple leaves (e.g., red cabbage, some Ficus benjamina cultivars) to observe anthocyanins (though these are not photosynthetic pigments, they co-exist).
Brown algae (seaweed) contain chlorophyll c and fucoxanthin.
Carrots or corn for high amounts of carotenes and xanthophylls, respectively.

Testing Photosynthetic Pigments

The standard method for separating and identifying these pigments is chromatography (paper or thin-layer chromatography, TLC), often followed by spectrophotometry.

Materials

Leaf samples (e.g., spinach, a red leaf variety)
Pestle and mortar
Acetone (organic solvent)
Chromatography paper or TLC plate
Chromatography solvent (e.g., a mixture of petroleum ether, acetone, and trichloromethane)
Capillary tube
Pencil and ruler
Beaker or test tube with a cover

Procedure (Thin-Layer Chromatography)

Extract the pigments: Grind a piece of leaf tissue in a mortar and pestle with a small amount of acetone to break open the cells and dissolve the pigments.

Spot the plate: Draw a pencil line near the bottom of a TLC plate. Use a capillary tube to repeatedly spot the pigment extract onto the line, allowing each spot to dry before applying the next, to create a concentrated spot.
Develop the chromatogram: Place the plate in a beaker containing a shallow layer of chromatography solvent, ensuring the solvent level is below the pencil line. Seal the container to saturate the atmosphere with solvent vapour.
Separate the pigments: Allow the solvent (mobile phase) to move up the plate by capillary action. Different pigments travel at different speeds because they vary in size and solubility in the mobile phase compared to their affinity for the stationary phase (the plate material).
Analyse the results: Once the solvent has nearly reached the top, remove the plate and immediately mark the solvent front with a pencil. You will see colored spots (bands) at different heights.
Identify pigments:
- Colour: Carotenes (orange) travel furthest, followed by xanthophylls (yellow), chlorophyll a (blue-green), and chlorophyll b (yellow-green).
- Rf value: Calculate the retention factor (Rf) for each pigment using the formula:
  $cap R sub f equals the fraction with numerator distance travelled by pigment and denominator distance travelled by solvent end-fraction$
- Compare the calculated Rf values to known standards for identification.
Further testing: The individual pigment bands can be scraped off the TLC plate, dissolved in a suitable solvent (e.g., alcohol), and analysed using a spectrophotometer to determine their specific light absorption spectrum. This confirms which wavelengths each pigment absorbs most effectively.

Skills Highlight

Using spectrometers to measure light absorption.
Plotting and interpreting graphs of intensity vs wavelength.
Relating pigment chemistry to photosynthetic efficiency.
Understanding experimental design and controlled variables.

Why It Works in Teaching

This investigation turns colour into data. Students can see the relationship between wavelength, absorption, and plant adaptation — a clear, visual link between physics and biology that strengthens understanding of photosynthesis.

02 November 2025

The Role of the Family in Modern Society

The family has long been seen as the cornerstone of social life, shaping identity, behaviour, and values. Yet, in modern society, the meaning and structure of “family” have undergone dramatic changes. A-Level Sociology students study these shifts to understand how social institutions adapt to cultural, economic, and technological change.

The Functionalist View

Functionalist sociologists such as Parsons and Murdock see the family as performing vital functions for both individuals and society. These include:

Socialisation: Teaching children norms, values, and culture.
Stabilisation: Providing emotional and economic support for members.
Reproduction: Ensuring the continuation of society.

Even as society evolves, Functionalists argue that the family remains central to maintaining social stability.

The Marxist and Feminist Perspectives

Marxists see the family as part of the capitalist system — a means of reproducing inequality. The family provides labour power, transmits property, and socialises children into accepting hierarchy and obedience.

Feminists, meanwhile, view the family as a site where gender inequality is reinforced. Traditional domestic roles and unpaid labour continue to disadvantage women, even as family forms diversify.

Both perspectives challenge the idea of the family as purely beneficial, arguing that it also reflects wider power structures.

The Postmodern and Contemporary View

In modern society, families take many forms: single-parent, reconstituted, same-sex, and cohabiting households. Sociologists such as Giddens and Beck describe this as part of a “risk society,” where individuals have more choice but also more uncertainty.

Modern families are less about fixed roles and more about negotiated relationships, built on shared values rather than traditional expectations. The rise of technology, dual incomes, and shifting gender norms has changed how families function — but not their emotional significance.

Skills Highlight

Comparing sociological perspectives on the family
Evaluating evidence for changing family roles
Understanding how social and economic change influences family life
Applying theory to contemporary examples

Why It Works in Teaching

Studying the family helps students connect sociological theory with their own experiences. It encourages critical thinking about the structures and values that shape society and helps individuals understand how personal relationships reflect broader social forces.

01 November 2025

Using Python Lists to Analyse Data Sets

Python is one of the most powerful tools for data analysis — and it all starts with the humble list. Lists allow students to store, sort, and process data efficiently, turning raw numbers into meaningful results. This simple programming concept introduces key computational thinking skills that underpin data science, statistics, and AI.

The Concept

A list in Python is a collection of data items stored under one variable name. Lists can hold numbers, text, or even other lists.

Example:


data = [12, 15, 18, 20, 22, 25]

From here, students can calculate averages, find maximum and minimum values, or even visualise data using libraries such as matplotlib.

The Experiment in Code


data = [12, 15, 18, 20, 22, 25]

mean = sum(data) / len(data)
max_value = max(data)
min_value = min(data)
sorted_data = sorted(data)

print("Mean:", mean)
print("Highest:", max_value)
print("Lowest:", min_value)
print("Sorted:", sorted_data)

The code above teaches iteration, built-in functions, and how to use Python as both a calculator and a simple data tool.

Students can then extend the activity to analyse real data — for example, daily temperatures, test results, or experiment readings — turning abstract numbers into trends and insights.

Skills Highlight

Creating and manipulating Python lists
Using built-in functions like sum(), max(), min(), and sorted()
Calculating statistical measures programmatically
Applying coding to practical data handling in science and maths

Why It Works in Teaching

Python bridges mathematics, computing, and science. Analysing data through code encourages logical thinking and problem solving. Students see instant feedback, gain confidence in coding, and learn a vital skill used in universities and industries worldwide.