Why does substances dissolve in water

Students will be able to explain, on the molecular level, why water can dissolve salt. Students will be able to identify the variables in their experiment. Students will also be able to explain why a less polar liquid, such as alcohol, is not good at dissolving salt. Download the student activity sheet , and distribute one per student when specified in the activity. Be sure you and the students wear properly fitting goggles.

Isopropyl alcohol is flammable. Keep it away from flames or spark sources. Read and follow all warnings on the label. Alcohol should be disposed of according to local regulations. You may choose to laminate the water molecules, sodium ions, and chloride ions located on the last page of the activity sheet so that you can reuse them with your students next year.

Project the image Sodium Chloride Crystal. Remind students that the green balls represent negative chloride ions and the gray balls represent positive sodium ions. Students will record their observations and answer questions about the activity on the activity sheet. Look at the teacher version of the activity sheet to find the questions and answers. Project the image Sodium Chloride Dissolving in Water. Point out that several water molecules can arrange themselves near an ion and help remove it from the crystal.

Show students that the positive area of a water molecule will be attracted to the negative chloride ion and that the negative area of a water molecule will be attracted to the positive sodium ion.

Look at the pictures showing how water molecules dissolve salt. Then arrange the water molecules around the sodium and chloride ions in the correct orientation. The positive part of the water molecules should be near the negative chloride ion. The negative part of the water molecules should be near the positive sodium ion. Project the animation Sodium Chloride Dissolving in Water. Point out that the water molecules are attracted to the sodium and chloride ions of the salt crystal.

Explain that the positive area of a water molecule is attracted to a negative chloride ion. The negative area water of a water molecule is attracted to a positive sodium ion. Dissolving happens when the attractions between the water molecules and the sodium and chloride ions overcome the attractions of the ions to each other.

This causes the ions to separate from one another and become thoroughly mixed into the water. Tell students that the amount of a substance that can dissolve in a liquid at a particular temperature is called solubility. Park Passes. Technical Announcements. Employees in the News. Emergency Management. Survey Manual. Examples Sugar, sodium chloride, and hydrophilic proteins are all substances that dissolve in water. Oils, fats, and certain organic solvents do not dissolve in water because they are hydrophobic.

Show Sources Boundless vets and curates high-quality, openly licensed content from around the Internet. October 16, Licenses and Attributions. CC licensed content, Shared previously. It means that wherever water goes, either through the air, the ground, or through our bodies, it takes along valuable chemicals, minerals, and nutrients. It is water's chemical composition and physical attributes that make it such an excellent solvent.

Water molecules have a polar arrangement of oxygen and hydrogen atoms—one side hydrogen has a positive electrical charge and the other side oxygen had a negative charge. This allows the water molecule to become attracted to many other different types of molecules. Water can become so heavily attracted to a different compound, like salt NaCl , that it can disrupt the attractive forces that hold the sodium and chloride in the salt compound together and, thus, dissolve it.

Our own kidneys and water's solvent properties make a great pair in keeping us alive and healthy. The kidneys are responsible for filtering out substances that enter our bodies from the foods and drinks we consume. But, the kidneys have got to get rid of these substances after they accumulate them.

That is where water helps out; being such a great solvent, water washing through the kidneys dissolves these substances and sends them on the way out of our bodies. This diagram shows the positive and negative parts of a water molecule. It also depicts how a charge, such as on an ion Na or Cl, for example can interact with a water molecule.

At the molecular level, salt dissolves in water due to electrical charges and due to the fact that both water and salt compounds are polar, with positive and negative charges on opposite sides in the molecule.