Ion-exchange resin

Make a filter to get rid of heavy metals in water!

Difficulty:
Danger:
Duration:
20 minutes
Experiment's video preview

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. Just take some resin out using a wooden stick and continue the experiment.

What do we need the first vial for?

You will use it to check how effectively your filter works by comparing the properties of the initial solution with those of the filtered one.

Step-by-step instructions

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

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Set up the test stand.

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

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Pour some of the tainted water straight into the first vial. We will need it later, to help us assess the effectiveness of our 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 reaction testing for copper ions Cu2+ by adding ammonium carbonate (NH4)2CO3 to our test vials. If copper ions are present in a solution, the liquid will turn blue. If our filter succeeded in cleaning the water in the second vial, this water will remain clear.

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

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To repeat this experiment, wash both vials.

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. Wash with an excess of water.

Scientific description

What is ion-exchange resin?

This substance often looks like 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 our 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 which replace each other are cations. However, anion-exchange resins also exist, and their working principle is almost the same: when a solution containing some anions passes through the resin, it replaces the anions in it with other anions in its structure. The anion-exchange resins are widely used in the laboratory to purify various chemical substances.

How does the ion-exchange resin purify water?

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

This is possible because sodium and potassium cations are bound to the resin rather weakly. Moreover, these ions can form only one weak bond with each of the resin fragments. Heavy metals, calcium and 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 in our experiment, the ions of sodium and potassium do not react with ammonium carbonate, so the filtered solution does not change its color.

Thus, we can 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 is because this solution was not filtered through the resin, and consequently it still has copper ions in it. 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 which has 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 which 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 in it.

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.

Harmful lead

The risk of “poisoning” water with lead is particularly high in old homes, where plumbing systems haven’t been replaced in a long time. The older a pipe, the higher the probability that it contains some of this heavy metal.

Lead intoxicates a body relatively slowly - it acts differently than the poisonous apple in the “Snow White and the Seven Dwarves”. Lead poisoning more closely resembles radiation exposure, causing progressive organ failure, weakness, and accelerated aging. The longer someone is exposed to lead-contaminated water, the more powerful the effect.

The impact of a poison on the human body also depends on each individual’s physical health: the healthier the body, the stronger it resists the negative effects. Lead-contaminated water is most hazardous to children: even a small dose is critical, and a prolonged intake of such drinking water (over the course of several years) can lead to heart, kidney, and lung failure.

Lead and the imperial family

1633 saw the introduction of a piping system in the Moscow Kremlin. The new water reservoirs were cludded with sheets of lead and soldered with tin. The pipes themselves were also made of lead. Water was pumped from wells into reservoirs, from which it ran through the piping system to the Emperor’s kitchen and the gardens.

For one hundred years, water was fed through lead pipes into the palace. This water seemed no different from regular water -- no peculiar color, taste or smell. The traces of lead didn’t cause any immediate harm, and so it took years to notice the effects of lead poisoning. Some even believe that the lead-contaminated drinking water had a significant negative impact on the health of the second Russian emperor and his sons in the Romanov Dynasty.

It is likely not a coincidence that during the period when the lead piping was in use, Russian emperors and their children led shorter-than-average lives, even for that era. Out of Aleksey Mikhailovich’s six sons, three didn’t live to their 20s, and two more died before reaching 30. Only one son, the sixth, Peter Alexeyevich (who became Peter the Great) drank the lead-contaminated water less frequently than his brothers. Peter spent his childhood and adolescence in the suburbs of Moscow, far from Kremlin. He later founded Saint Petersburg and moved the imperial capital there from Moscow. It would be fair to mention, however, that Peter Alexeyevich was the only son of Aleksey Mikhailovich’s second wife, Natalya Naryshkina. Thus, besides water quality, genetics may have also played a role in protecting the young Emperor’s health.

Lead in the White House

The sudden illness of George Bush, Sr. has also been associated with lead poisoning. The former president of the USA suffered failure of immune, respiratory, and blood circulatory systems. Later on, his wife Barbara and even his dog were diagnosed with the same symptoms.

The lead piping in the White House, originally built over 200 years ago, wasn’t replaced until the end of the 20th century.