magnesium sulfate experiments

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Making magnesium carbonate: the formation of an insoluble salt in water

In association with Nuffield Foundation

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When solutions of two soluble salts are mixed, a solid may form. The solid is called a precipitate, and the reaction is called a precipitation reaction. Precipitation reactions are used to make insoluble salts

In this experiment the soluble salts are magnesium sulfate and sodium carbonate, and the insoluble salt formed is magnesium carbonate, which can be filtered, dried and collected.

This is a short standard class experiment. It should take no more than 20 minutes to the point at which the wet product can be set aside to dry.

If the solutions can be provided in pre-measured 25 cm 3  quantities in labelled containers, distribution of chemicals and control of quantities can be easily managed, and the practical work can begin without delay.

Sodium carbonate in dilute solution is weakly alkaline. So the few other safety issues are essentially restricted to safe handling of glassware. Even these can be minimised by the use of polythene filter funnels. This experiment is therefore suitable as a class experiment for most classes.

• Eye protection
• Conical flasks (100 cm 3 ) x2
• Filter funnel (65 mm diameter or similar, note 1)
• Filter papers (size suited to funnels used)

Apparatus notes

• Polythene filter funnels are safer and cheaper than glass funnels. The size of filter paper, when folded, should match the funnel size. The cheapest grade of filter paper is okay for this experiment.
• Sodium carbonate solution, 0.5 M, 25 cm 3
• Magnesium sulfate solution, 0.5 M, 25 cm 3

Health, safety and technical notes

• Read our standard health and safety guidance
• Wear eye protection. 
• If the reagent solutions can be distributed in pre-measured quantities, waste is reduced and lesson organisation is easier. All containers used for these solutions should be labelled.
• Sodium carbonate solution, Na 2 CO 3 (aq) – see CLEAPSS Hazcard HC095a and CLEAPSS Recipe Book RB080.
• Magnesium sulfate solution, MgSO 4 (aq) – see CLEAPSS Hazcard HC059b .  
• Magnesium carbonate, 3MgCO 3 .Mg(OH) 2 .3H 2 O(s) – see CLEAPSS Hazcard HC059b . 
• Mix 25 cm 3  of magnesium sulfate solution and 25 cm 3  of sodium carbonate solution in a conical flask.
• Place the filter funnel in the neck of another conical flask.
• Fold the filter paper to fit the filter funnel, and put it in place.
• Swirl the reaction mixture gently, and pour a little at a time into the filter paper in the funnel. Only pour in enough solution at a time to leave the solution level 1 cm below the rim of the filter paper. Allow to filter through.
• A clear solution should collect in the flask. If the solution is not clear, and white cloudiness remains in it, you will need to repeat the filtration.
• Remove the wet filter paper carefully from the funnel and place on a clean dry paper towel. Label with your name(s) and leave in a warm place, safe from interference, until it has dried completely (a few hours).

Source: Royal Society of Chemistry

The apparatus set-up for the experiment making magnesium carbonate

Teaching notes

There are no significant hazards in this experiment, except for the risk of broken glass if a flask is knocked over.

The formation of precipitates on mixing two solutions is met frequently in chemistry. This experiment is intended as a first introduction to this phenomenon for 11–14 year olds, as well as to practical filtration techniques. The experiment can be made more exciting visually by making a coloured salt such as copper(II) carbonate; in this case the chemical hazard level is slightly higher, since copper(II) carbonate is HARMFUL.

Because this is intended as a first introduction, the interpretation should be restricted to developing the word equation as a summary of what has happened:

magnesium sulfate + sodium carbonate → magnesium carbonate + sodium sulfate

Suggesting the name of the salt left in solution is not easy for students at this stage. It needs to be approached carefully, probably by group or whole class discussion. Using cut-out card labels: ‘sodium’, ‘magnesium’, ‘carbonate’ and ‘sulfate’ for students to move around will help many of them grasp the idea of ‘swapping partners’.

You could add some interest to which salts are used, and which salts are formed. Mention their uses, if this helps the class to see that these substances are not just important in the laboratory. See below.

Background information

Magnesium sulfate is known as Epsom salts. This is because the water found at the spa at Epsom in Surrey contains this salt in quite high concentration. Epsom salts are rarely used nowadays, but were used in medicine as a purgative.

Sodium carbonate is found naturally in high concentrations in the soda lakes of Kenya and Tanzania in East Africa. It is also manufactured in vast quantities and used in many different industries, including the chemical industry itself and in glass making. It is found in the home as washing soda, and in some detergent powders. For more about sodium carbonate in general, you may be interest in the Royal Society of Chemistry Book,  Sodium carbonate: a versatile material .

Magnesium carbonate is found in the mineral dolomite, mixed with calcium carbonate. Most limestones contains a proportion of magnesium carbonate – some a very high proportion. Magnesium carbonate is used in industry as a major source of magnesium compounds, it is used in many medical preparations to treat indigestion and it is also used as gym chalk.

Sodium sulfate, known as Glauber’s salt, is found (like Epsom salts) in some natural brines. It is used in large quantities in industries such as wood pulp production, glass-making, and detergents, and is also as a mild laxative.

If this experiment is used with older students, you can ask them to work out the symbol equation:

MgSO 4 (aq) + Na 2 CO 3 (aq) → MgCO 3 (s) + Na 2 SO 4 (aq)

The ionic equation, together with the concept of ‘spectator ions’, is likely to be appropriate for fewer students. However, this is not likely to be the experiment where the concept of spectator ions is introduced, as there are better examples, with visual colour clues to what is happening. The ionic equation is:

Mg 2+ (aq) + CO 3 2- (aq) → MgCO 3 (s)

and the spectator ions are: Na + (aq) and SO 4 2- (aq)

Student questions

Here are some possible questions for students.

• What did you see happen in the flask when the solutions mixed?
• What has collected in the filter paper? Describe what you can see.
• What is the name of the solid salt you have made?
• Suggest the name of the salt left in solution in the flask at the end. Explain how you decided on this name.
• Complete the word equation for this reaction: magnesium sulfate + sodium carbonate → … + …

Additional information

This is a resource from the  Practical Chemistry project , developed by the Nuffield Foundation and the Royal Society of Chemistry.

Practical Chemistry activities accompany  Practical Physics  and  Practical Biology . 

© Nuffield Foundation and the Royal Society of Chemistry

• 11-14 years
• 14-16 years
• Practical experiments
• Reactions and synthesis

Specification

• AT.4 Safe use of a range of equipment to purify and/or separate chemical mixtures including evaporation, filtration, crystallisation, chromatography and distillation.
• AT4 Safe use of a range of equipment to purify and/or separate chemical mixtures including evaporation, filtration, crystallisation, chromatography and distillation.
• 3.21 Describe the method used to prepare a pure, dry sample of an insoluble salt
• 7 Production of pure dry sample of an insoluble and soluble salt
• C4 Production of pure dry sample of an insoluble and soluble salt
• preparation of insoluble salts by precipitation
• Precipitation is the reaction of two solutions to form an insoluble salt called a precipitate.
• Information on the solubility of compounds can be used to predict when a precipitate will form.
• The formation of a precipitate can be used to identify the presence of a particular ion.
• (o) the preparation of insoluble salts by precipitation reactions
• (i) atoms/molecules in mixtures not being chemically joined and mixtures being easily separated by physical processes such as filtration, evaporation, chromatography and distillation
• 2. Develop and use models to describe the nature of matter; demonstrate how they provide a simple way to to account for the conservation of mass, changes of state, physical change, chemical change, mixtures, and their separation.
• 4. Classify substances as elements, compounds, mixtures, metals, non-metals, solids, liquids, gases and solutions.

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Science Projects > Chemistry Projects > How To Make Fast-Growing Crystals  

How To Make Fast-Growing Crystals

Introduction.

Salt is an naturally-occurring mineral and a chemical compound with amazing properties. These properties enable salt to be used in everything from preserving food to making it taste better. Epsom salt is primarily used for health reasons. People use it to make soft water for relaxing , treat constipation, and sore muscles. You can use it to make Epsom salt crystals!

Usually it takes several days to grow crystals . However, this super-easy recipe gives you a cup full of needle-like Epsom salt crystals in just a few hours!

How to Make Fast Growing Crystals Epsom Salt Crystals  Home Science Tools

What you need:.

• Food coloring
• Beaker , cup, or small bowl

What You Do:

1. In the beaker, stir 1/2 cup of Epsom salts with 1/2 cup of very hot tap water for at least one minute. This creates a saturated solution , meaning no more salt can dissolve in the water. (Some undissolved crystals will be at the bottom of the glass.)

2. Add a couple drops of food coloring if you want your crystals to be colored.

3. Put the beaker in the refrigerator.

4. Check on it in a few hours to see a beaker full of epsom salt crystals! Pour off the remaining solution to examine them.

What Happened:

Epsom salt is another name for the chemical magnesium sulfate. The temperature of the water determines how much magnesium sulfate it can hold; it will dissolve more when it is hotter.

Cooling the solution rapidly encourages fast crystal growth since there is less room for the dissolved salt in the cooler, denser solution. As the solution cools, the magnesium sulfate atoms run into each other and join together in a crystal structure.

Crystals grown this way will be small, thin, and numerous. Left undisturbed, the crystals should last months or more!

To grow large single crystals, you’ll need to follow the evaporation procedure in this project .

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How to Make a Drying Agent (Anhydrous Magnesium Sulfate)

Introduction: How to Make a Drying Agent (Anhydrous Magnesium Sulfate)

Welcome to Dangerous Lab, the safest place on the internet.

This is a comprehensive guide to making a drying agent (Anhydrous Magnesium Sulfate). Feel free to check out the above video to see it in action.

Outline (For the above video)

Purpose of experiment, safety precautions and disclaimer.

• Material to be used
• Pre-weigh multiple batches for different test configurations
• Small-scale testing on different temperature
• Start of experiment

Literature data on Magnesium sulfate dehydration

• Calculation and analysis of the results
• Recommended steps and configuration
• Notable mentions
• Tips and tricks for dehydration
• Things to avoid
• Demonstration of hygroscopic properties
• Demonstration of dissolution properties
• Crush the powder and bottle it up

For those who just need the instructions for making it but not the scientific details, please follow the steps below, some of the information (Background/Science) is skipped.

• Epsom salt (1 pack)
• Oven (Must be able to reach 250°C/482°F)
• Over tray (Preferrably a disposable aluminium baking tray)
• Air-tight storage container

(As an Amazon Associate, I earn from qualifying purchases)

Step 1: Experiment Prerequisite

All experiments should be carried out with extreme caution, please read till the end to fully understand this experiment before proceeding.

• Don't touch the oven when it is hot.

(This experiment is actually pretty safe.)

A desiccant is very useful in many experiments, we are going to make anhydrous magnesium sulfate by dehydration of Epsom salt, which is the heptahydrate form of magnesium sulfate.

The steps for this experiment are pretty straightforward and simple, I will however include many tips and tricks, things to avoid and a detailed explanation along with the experiment, feel free to skip to the part you need.

Step 2: Experiment Steps

Preparing the Epsom salt

The bag of Epsom salt is poured onto the disposable oven tray and spread evenly across the surface.

Place the Epsom salt inside the oven

Place the tray inside the oven and turning on the heat to 250°C/482°F and bake it for 2 hours.

Collect the Anhydrous Magnesium Sulfate

After baking for 2 hours, the salt should turn into a solid chunk of anhydrous magnesium sulfate, you can then wobble or flex the tray slightly to break the chunks apart.

Step 3: Tips and Tricks

• Disposable aluminium oven tray is highly recommended over normal oven tray (The reusable one that usually comes with your oven), since Epsom salt tends to harden and stick to the tray surface as it hardens, it will be very difficult to clean up.
• A brand new/clean/lab-only oven is highly preferred, as oil and grease inside a used oven will easily deposit on the Epsom salt as it heats up, turning the magnesium sulfate brown which is contaminated with oil.

Step 4: Experiment Mechanism

According to this book*, magnesium sulfate starts losing its first 4 water molecules at 70-80°C, the 5th water at 100°C, 6th water at 120°C, the last one is pretty tough to lose though, it turns anhydrous at around 250°C.

*:O'Neil, M.J. (ed.). The Merck Index - An Encyclopedia of Chemicals, Drugs, and Biologicals. 13th Edition, Whitehouse Station, NJ: Merck and Co., Inc., 2001., p. 1018

Step 5: Collect the Product and Storage

There are few ways you can store the product, but keeping it as a larger chunk form will prolong its shelf life by reducing the ability of it absorbing moisture from the air, and only crush the chunk before every use.

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