Environmental impact of chemical hazards and effective presentation of scientific data
Chemical hazards can be broadly classified into several categories based on their properties and effects:
Substances that cause adverse health effects in living organisms.
Acute or chronic poisoning, organ damage, neurological disorders
Chemicals that remain in the environment for long periods and bioaccumulate through the food web.
Long half-life, lipophilic, resistant to degradation, global transport
Chemicals that interfere with hormonal systems, potentially causing reproductive, developmental, and immune problems.
Reproductive disorders, developmental abnormalities, immune suppression
Substances that cause cancer, genetic mutations, and birth defects respectively.
Cancer development, genetic damage, birth defects
Excess nutrients, particularly nitrogen and phosphorus from fertilizers and sewage.
Eutrophication – oxygen depletion in water bodies harming aquatic life
Remember the 4 P’s of Chemical Hazards:
Volatile Organic Compounds (VOCs) emitted from industrial processes, vehicular emissions, and chemical solvents contribute to ground-level ozone and smog formation.
VOCs, SO₂, NOₓ, CO, particulate matter, heavy metals, ozone-depleting substances
Pesticides, fertilizers, and industrial chemicals runoff into rivers, lakes, and oceans, contaminating water supplies and harming aquatic life.
Pesticides, fertilizers, heavy metals (Hg, Pb, Cd), industrial chemicals, pharmaceuticals, microplastics
Pesticides and herbicides degrade soil quality, harm beneficial microorganisms, and reduce agricultural productivity.
Pesticides, herbicides, heavy metals, petroleum hydrocarbons, industrial waste, salts
Remember the 3 Pathways:
Fact-based, measurable, and observable. If two people make the same measurement with the same tool, they get the same answer.
Example: Mass = 25.3 g, Volume = 50.0 mL
Numerical measurements that can be analyzed statistically.
Example: Temperature = 25.4°C, Concentration = 0.1 M
Descriptive observations about qualities.
Example: Color change, precipitate formation, gas evolution
The best way to organize data is to put it in a data table. Remember these rules:
| Time (s) | Concentration of Reactant A (M) | Concentration of Product B (M) | Reaction Rate (M/s) |
|---|---|---|---|
| 0 | 1.00 | 0.00 | 0.020 |
| 10 | 0.80 | 0.20 | 0.016 |
| 20 | 0.64 | 0.36 | 0.013 |
| 30 | 0.51 | 0.49 | 0.010 |
| 40 | 0.41 | 0.59 | 0.008 |
| 50 | 0.33 | 0.67 | 0.007 |
Graphs are used to display data because it’s easier to see trends. In graphs:
Line graphs are ideal for showing continuous changes over time
A student measures the changes in volume when different objects are added to a graduated cylinder.
Read the volume at the bottom of the meniscus. For water and most liquids, the meniscus is concave (U-shaped).
Carefully add the object to the graduated cylinder without splashing.
Read the new volume at the bottom of the meniscus.
ΔVolume = Final Volume – Initial Volume
When reading a graduated cylinder, you must mentally subdivide the distance between marks. For example, between 21 and 22 cm³ marks, estimate to the nearest 0.1 cm³.
Correct reading: 21.6 cm³ (2 and 1 are certain, 6 is estimated)
Rule: Measure to one tenth of the smallest scale division.
A calorimeter contains 100 grams of water. A student uses a digital thermometer to measure temperature changes.
Initial temperature: 22.38°C (digital thermometers include estimated values)
Place heated aluminum metal rod into the calorimeter.
Monitor temperature until equilibrium is reached. Final temperature: 43.96°C
ΔT = Final Temperature – Initial Temperature = 43.96°C – 22.38°C = 21.58°C
Digital thermometers typically display temperatures to 0.01°C precision. When subtracting, the result should have the same number of decimal places as the least precise measurement (both have 2 decimal places, so result has 2 decimal places).
Remember:
The correct reading is determined by reading the bottom of the meniscus at eye level.
Current Reading: 19.50 cm³
Correct reading: 19.50 cm³ (read at bottom of meniscus)
Incorrect due to parallax: 19.62 cm³ (reading from above) or 19.42 cm³ (reading from below)
Start with a clean burette to avoid contamination. Rinse with the solution to be used.
Fill the burette above the zero mark, ensuring no air bubbles are present in the tip.
Record starting volume at eye level with the meniscus. Read to the nearest 0.05 cm³.
Perform a preliminary titration to estimate the endpoint volume needed.
Record final volume at eye level after titration is complete.
Titre = Final Volume – Initial Volume (difference between readings)
Remember: “Eyes Level with the Meniscus”
Test your knowledge with these multiple choice questions. Select your answer and click submit to check your score.