Applied Chemistry: How Chemists Test and Use Materials

What is applied chemistry?

Applied chemistry means using chemistry to do a real job. The job can be to find out what something contains, to make something useful, or to fix a problem.

It has some branches. Analytical chemistry asks "what is in it and how much?". Organic chemistry builds carbon compounds such as medicines, plastics and dyes. Chemical technology turns a lab reaction into a factory process (see the lesson on industrial chemistry).

A good test has four parts: a fair sample, a method, an exact measurement and a decision. If the sample is not fair, the best method still gives a wrong answer.

Analysis: sampling, titration and chromatography

Sampling. A tanker holds thousands of litres, but we test a few millilitres. So we mix first and take the sample from different parts. Then the small sample stands for the whole.

Titration finds how strong a solution is. A burette adds a solution of known strength slowly into a measured amount of the unknown. An indicator changes colour at the end point, when the reaction has just finished. For an acid and a base that react 1 : 1:

M_acid × V_acid = M_base × V_base

Chromatography separates a mixture. A spot is placed on paper, and a liquid (the solvent) climbs up the paper. Parts that stick less climb higher. We note the distance ratio R_f = distance moved by the spot ÷ distance moved by the solvent. R_f is always between 0 and 1 and helps us name a substance by comparing with known ones.

Materials: choosing and making

Every product starts with a choice of material. Chemists ask: how strong, how light, does it rust, can it be recycled, what does it cost? Metals, ceramics, plastics (polymers) and composites all have different answers.

Chemistry can change a material. Adding a little carbon to iron gives steel. Joining small molecules into long chains gives plastics. Coating iron with zinc stops rust. Quality control then tests each batch with the same methods as above, so the thousandth product is as good as the first.

Biotechnology: health and the environment

Biotechnology uses living cells or their parts to do useful work. Chemists check and control these processes.

For health: yeast and bacteria are grown in tanks to make medicines such as insulin and vaccines. Tests such as chromatography check that the medicine is pure and the right strength.

For the environment: some bacteria clean oil spills or waste water by eating pollutants. Analysis shows how much pollutant is left. Compost and biogas plants turn waste into soil food and fuel.

In every case the chemist measures first, then acts, then measures again to prove the job worked.

Try it

In the 3D: in step 3, move the slider and stop the moment the liquid turns pink. Note the volume. In step 5, try Acid B and predict the end point before you slide.

At home (safe): cut a coffee filter into a strip. Put a dot of a black water-based marker near the bottom. Stand the strip in a little water, so only the paper end touches the water, and the dot is above water. Wait 10 minutes and see the black split into colours. Measure the distances and find R_f for each colour.

Key formulas and definitions

• M₁V₁ = M₂V₂ (acid and base reacting 1 : 1, at the end point)
• Rf = distance moved by spot ÷ distance moved by solvent (0 to 1)
• Strength of unknown (mol/L) = M(burette) × V(burette) ÷ V(sample)
• Fair sample: mix well, take from several places, same volume each time

Worked examples

Common mistakes

• Reading the burette at the wrong level. Read the bottom of the curve at eye level, and read the volume used as final minus start.
• Going past the end point. Add drops slowly near the end; one extra drop can turn the colour too far.
• Letting the spot sit under the solvent in chromatography. The start line must stay above the liquid, or the colours wash away.
• Testing a sample that is not fair (for example only the top of a tank). The answer will not stand for the whole.