Earlier we learned that a homogeneous mixture of two or more substances is called a solution. If one of the substances is present in much greater quantities than all the other substances then it is called the solvent. The other substances in solution are known as solutes. For example, when a small amount of NH4Cl is dissolved in a large quantity of water we refer to water as the solvent and NH4Cl as the solute. Another example is Napthalene (used in mothballs) can be dissolved in benzene. In this example benzene is the solvent and napthalene is the solute. Show Solutes dissolved in water (solvent) are called aqueous solutions. Not all substances are soluble in water. Why do some substances dissolve in water and others don't? It has to do with the structure of the water molecule.  Oxygen has a greater attraction for electrons, so the shared electrons (bonding electrons) spend more time close to oxygen then to either of the hydrogens. This gives oxygen a slightly excess negative charge and hydrogen a slightly more positive charge. This unequal charge distribution makes water a polar molecule, and gives water its ability to dissolve compounds. When an ionic solid dissolves in water, the positive ends of the water molecule are attracted to the negatively charged anions and the negative ends of the water molecule are attracted to the positively charged cations. For example, when NaCl is dissolved in water we find So when an ionic substance (salt) dissolves in water, it is broken up into individual cations and anions which are surrounded by water molecules. For example, when NH4 NO3 is dissolved in water it breaks up into separate ions. NH4+ and NO3- ions are floating around in H2O essentially independent of each other. Water also dissolves non-ionic substances. For example, C2H5OH (ethanol) is very soluble in H2O. This is because C2H5OH has a polar OH bond that the water molecules like to hang around. Many substances do not dissolve in water and that is because they are non-polar and do not interact well with water molecules. A common example is oil and water. Oil contains molecules that are non-polar, thus they do not dissolve in water. How do we know that ionic solids dissolve in water and form cations and anions that float around separately? One clue comes from conductivity experiments. Anions and Cations should act as charge carriers in solution. Therefore a solution with dissolved ions should conduct electricity. Let's look at a few examples. Pure (distilled) water contains no dissolved ions. Therefore pure water will not conduct electricity. In a simple conductivity experiment as shown below we would not expect the light to be on. An aqueous NaCl solution, however, will have dissolved ions present and therefore will conduct electricity. Therefore the light in our conductivity experiment will be on if dipped in an aqueous NaCl solution. NaCl ionizes completely when dissolved in water. It's helpful to think of this process as two steps: Substances that exist in solution almost completely as ions are called strong electrolytes. Substances that do not form ions when they dissolve in water are called non-electrolytes. And example of a non-electrolyte is sugar. Sugar will readily dissolve in water but doesn't form cations and anions in solution. That is, there are no charge carriers formed. Substances that only partially ionize into ions when dissolved in water are called weak electrolytes. For example, Acetic Acid (HC2H3O2) dissolves in water, but only partially dissociates into ions. Be careful not to confuse how soluble a substance is in water with whether it is a weak, strong, or non-electrolyte. For example, sugar dissolves completely in water but it is a non-electrolyte. Another example are salts that can be very insoluble in water but the small amount of salt that does dissolve in water is a strong electrolyte.
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Today’s experiment is very simple, but hopefully fascinating for even very young children. We’re going to investigate which solids dissolve in water. When a substance dissolves in water, you can’t see it anymore, it’s still there, but has mixed with the water to make a transparent liquid called a solution. We call substances that dissolve in water soluble. Sugar and salt are examples of soluble substances. Substances that do not dissolve in water are called insoluble. Sand and flour are examples of insoluble substances.
You’ll need
InstructionsAdd a teaspoon of whichever solid you are testing to a glass of cold water and a glass of warm water, stir and observe the difference. Watch to see if the solid dissolves in the warm water and cold water and if one is better than the other. Remember to use the same amount of each solid and the same amount of cold and warm water to make the investigation a fair test. Can you design a chart to record your observations? Which solids dissolve in waterThings like salt, sugar and coffee dissolve in water. They are soluble. They usually dissolve faster and better in warm or hot water. Pepper and sand are insoluble, they will not dissolve even in hot water. For older children Everything is made of particles which are always moving. When a soluble solid ( solute ) is mixed with the right liquid (solvent), it forms a solution. This process is called dissolving. Two things that affect the speed at which a solid dissolves are temperature and the size of the grains of the solid. Caster sugar which is made of fine particles will dissolve quickly, but bigger sugar particles will take longer. Solids dissolve faster in hot water as in hot water the water molecules are moving faster, so bump into the solid more often which increases the rate of reaction. More Dissolving ExperimentsMake a naked egg and watch as vinegar dissolves the calcium carbonate of the eggshell. Lava lamps work because the effervescent tablet dissolves in water releasing carbon dioxide. More Science for KidsDon’t forget we have lots more easy science experiments for kids at home you can try. You might also like our science books! This IS Rocket Science contains 70 fun space experiments for kids, including bottle rockets, film canister rockets, space marble runs and shadow puppets. Snackable Science contains 60 tasty and edible science snacks!! Contains affiliate links Last Updated on February 4, 2022 by Emma Vanstone |
Something that cannot be dissolved into a solution is called
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