Ion-exchange resin

Make a filter that can purify water of heavy metals!

Difficulty:
Danger:
Duration:
20 minutes
Ion-exchange resin

Reagents

Safety

  • Put on protective gloves and eyewear.
  • Conduct the experiment on the plastic tray.
General safety rules
  • Do not allow chemicals to come into contact with the eyes or mouth.
  • Keep young children, animals and those not wearing eye protection away from the experimental area.
  • Store this experimental set out of reach of children under 12 years of age.
  • Clean all equipment after use.
  • Make sure that all containers are fully closed and properly stored after use.
  • Ensure that all empty containers are disposed of properly.
  • Do not use any equipment which has not been supplied with the set or recommended in the instructions for use.
  • Do not replace foodstuffs in original container. Dispose of immediately.
General first aid information
  • In case of eye contact: Wash out eye with plenty of water, holding eye open if necessary. Seek immediate medical advice.
  • If swallowed: Wash out mouth with water, drink some fresh water. Do not induce vomiting. Seek immediate medical advice.
  • In case of inhalation: Remove person to fresh air.
  • In case of skin contact and burns: Wash affected area with plenty of water for at least 10 minutes.
  • In case of doubt, seek medical advice without delay. Take the chemical and its container with you.
  • In case of injury always seek medical advice.
Advice for supervising adults
  • The incorrect use of chemicals can cause injury and damage to health. Only carry out those experiments which are listed in the instructions.
  • This experimental set is for use only by children over 12 years.
  • Because children’s abilities vary so much, even within age groups, supervising adults should exercise discretion as to which experiments are suitable and safe for them. The instructions should enable supervisors to assess any experiment to establish its suitability for a particular child.
  • The supervising adult should discuss the warnings and safety information with the child or children before commencing the experiments. Particular attention should be paid to the safe handling of acids, alkalis and flammable liquids.
  • The area surrounding the experiment should be kept clear of any obstructions and away from the storage of food. It should be well lit and ventilated and close to a water supply. A solid table with a heat resistant top should be provided
  • Substances in non-reclosable packaging should be used up (completely) during the course of one experiment, i.e. after opening the package.

FAQ and troubleshooting

I poured resin into the pipette over the “3” mL mark. What should I do?

This isn’t a big deal. To remove the resin, pinch the filter at “3” mL mark and pour the excess resin back into the vial. Continue the experiment.

The second cotton cylinder is sticking out slightly. What should I do?

The cylinder shouldn’t stick out the top. Gently push it further in. You need to compress the resin well.

What do I need the first vial for?

You will use it to compare the properties of the unfiltered and filtered solutions. This way, you can check how effectively your filter works!

Can I use the filter after adding (NH4)2CO3?

Yes! We removed the copper using ammonium carbonate, so the resin can be reused. Pour a new solution of copper sulfate through the filter and collect the filtrate in a new vial.

Step-by-step instructions

Prepare a filter made of ion-exchange resin. To increase its effectiveness, compress the resin slightly using cotton cylinders and a wooden stick.

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Set up the test stand.

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Contaminate some water using copper sulfate CuSO₄. Here, copper acts as our heavy metal.

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Pour some of the tainted water straight into the first vial. You will need it later, to help assess the effectiveness of your filter.

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Pour some of the tainted water through the filter into the second vial.

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Now, perform a qualitative test for copper ions Cu²+ by adding ammonium carbonate (NH₄)₂CO₃ to the test vials. If a solution contains copper ions, the liquid will turn blue. If your filter succeeded in cleaning the water in the second vial, this water will remain clear.

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What happens if you apply some ammonium carbonate to the filter?

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Wash both vials to repeat the experiment.

Expected result

Your self-made filter with ion-exchange resin purifies water from ions of a heavy metal - copper.

The reaction between ammonium carbonate (NH4)2CO3 and copper ions Cu2+ changes the color of the initial solution from light-blue to deep indigo. The water sample purified through the filter remains colorless, proving the effectiveness of the filter.

Any copper ions left on the ion-exchange resin can be detected by adding a few drops of ammonium carbonate into the filter.

Disposal

Dispose of solid waste together with household garbage. Pour solutions down the sink and wash with an excess of water.

Scientific description

Power plants, factories, and cars all produce exhaust mixtures containing heavy metals. These exhausts don’t just pollute the air we breathe—they dirty our water as well. These heavy metal ions are harmful to our health, so they must be eliminated from drinking water.

We use copper ions  to test our filter because it is easy to identify them in a solution using a simple qualitative test. Resin-based filters work equally well on other heavy metal ions  too.

These resins are long polymers with ions of alkali metals, such as sodium ions , “attached” to them. The heavy metal ions  replace the sodium ions , clinging more tightly to the resin. Meanwhile, the water molecules  pass freely through. As a result, sodium ions , safe to consume in small amounts, replace the more dangerous heavy metal ions in the water.

Though this filter is effective against heavy metals, it is powerless against many organic pollutants . Activated carbon can take care of such materials, as you’ll see in another experiment from this set.

What is ion-exchange resin?

Ion-exchange resin often resembles small, solid, yellowish microbeads. Each microbead is a porous substrate consisting of an organic polymer. This polymer contains special fragments with some ions bound to them. In this experiment, these ions are potassium K+ or sodium Na+. When copper sulfate solution passes through the resin, the resin captures the copper ions Cu2+, releasing sodium Na+ or potassium K+ ions in their stead. This earns it its ‘ion-exchange’ name.

Learn more

In fact, the resin we use in the experiment is cation-exchange, because the ions replacing each other are positively-charged ions – cations. However, anion-exchange resins also exist, and their working principle is almost the same: when a solution containing some negatively-charged ions – anions – passes through the resin, it replaces the anions in it with other anions in its structure. Anion-exchange resins are widely used in laboratories to purify various chemical substances.

How does the ion-exchange resin purify water?

Due to its ability to replace ions, the resin is highly effective against heavy metal ions like copper Cu2+, cadmium Cd2+, mercury Hg2+, and iron Fe2+ and Fe3+. It can even bind to calcium Ca2+ and magnesium Mg2+ ions to decrease water hardness.

This is possible because the sodium Na+ and potassium K+ ions are bound to the resin rather weakly. Moreover, these ions can form only one weak bond with each of the resin fragments. Meanwhile, the target pollutants (heavy metals, calcium, magnesium) can form bonds with two fragments at once, and easily displace the sodium and potassium ions from the resin. In contrast to the copper ions Cu2+ in our experiment, the ions of sodium and potassium do not react with ammonium carbonate (NH4)2CO3, so the filtered solution does not change colors.

We can thus use ammonium carbonate in a simple qualitative test to make sure that our ion-exchange resin filter removed the copper ions Cu2+ from the water sample.

Why does the initial solution turn blue when ammonium carbonate is added?

This solution was not filtered through the resin, and consequently contains copper ions. When these copper ions meet with the ammonium carbonate solution, they form a tetraamminecopper complex [Cu(NH3)4]2+, which has a deep blue color. This is a qualitative reaction testing for the presence of copper ions in a solution. So if there are no copper ions in the solution, like the solution that passed through the resin, its color will not change.

Learn more

In the solution, ammonium carbonate can undergo the following transformations:

(NH4)2CO3 → 2NH4+ + CO32-

NH4+ → NH3 + H+

The ammonia NH3 that forms in this process reacts with copper ions:

Cu2+ + 4NH3 → [Cu(NH3)4]2+

As a result, a tetraamminecopper complex forms, which gives the solution its deep blue color.

What happens when we add ammonium carbonate to the pipette with the resin?

Ammonium carbonate can liberate copper ions from their bonds with the ion-exchange resin, as copper ions prefer to exist in the form of a tetraammine complex rather than be bound to the resin. The blue color of this complex, combined with the yellowish color of the resin, results in the resin turning rather green. At the same time, the resulting solution has a light blue color because of the presence of the tetraamminecopper complex.

That's interesting!

Heavy metals in water

Heavy metals are a family of chemical elements mostly toxic to humans, especially if they are present in fairly large amounts. In water, they normally exist in the form of positively-charged particles (cations) — take, for example, copper Cu2+, lead Pb2+ or iron Fe3+.

Interestingly, our bodies need certain heavy metals in small quantities, such as iron Fe, zinc Zn, copper Cu, and molybdenum Mo. However, these can be harmful if accumulated in greater quantities. Meanwhile, such heavy metals as lead, cadmium, and mercury are harmful to our bodies even in small amounts.

Many heavy metals are found in water in the form of cations. These must be filtered out for water to be drinkable. We can use an ion-exchange resin filter to accomplish this.