Salt and sugar dissolve in water because they interact with water molecules, breaking down into individual ions (in the case of salt) or molecules (in the case of sugar). When you stir these substances in water, the water molecules' polar nature allows them to surround and interact with the ions or molecules in salt and sugar, causing them to disperse evenly throughout the solution. This process is called dissolution. Stirring is important while heating a solution to ensure even temperature distribution, preventing supersaturation, and speeding up the dissolution process. While cooling, stirring helps maintain the uniform distribution of solute molecules and prevents the formation of large crystals, which is particularly essential for achieving desired textures in foods like candy. In summary, stirring ensures efficient dissolution and uniformity in temperature and solute distribution during both heating and cooling processes.

Dr Zakir Hussain thank you for your contribution to the discussion

Water molecules pull the sodium and chloride ions apart, breaking the ionic bond that held them together. After the salt compounds are pulled apart, the sodium and chloride atoms are surrounded by water molecules, as this diagram shows. Once this happens, the salt is dissolved, resulting in a homogeneous solution. The reason that the sugar seems to disappear is that the sugar molecules are now more attracted to water molecules. When the water is stirred the sugar molecules mix with the water molecules. The water molecules insert themselves with the sugar molecules and begin to surround each individual molecule. Salt also contains ions. Water helps in separating these ions by decreasing the interionic forces allowing the salt to disperse throughout the water. So, the particles of salt occupy the spaces in between the particles of water and hence get dissolved. This happens because water molecules are not tightly packed and have space between them hence when we dissolve the salt in it the salt particles occupy the space between the molecules of the water and thus the water level doesn't rise up. Dissolving a solid in liquid, such as table salt in water, is a physical change because only the state of the matter has changed. Physical changes can often be reversed. Allowing the water to evaporate will return the salt to a solid state. Therefore, dissolving salt in water is a chemical change. The reactant (sodium chloride or NaCl) is different from the products (sodium cation and chlorine anion). Thus, any ionic compound that is soluble in water would experience a chemical change. Salt (sodium chloride) is made from positive sodium ions bonded to negative chloride ions. Water can dissolve salt because the positive part of water molecules attracts the negative chloride ions, and the negative part of water molecules attracts the positive sodium ions. When water is heated and cooled it goes through a series of reversible changes. Water in its solid state is called ice. When ice is heated, it melts and becomes liquid water. Further heating causes the liquid to change to a gas, water vapor. The NaCl compound (the main compound of table salt) is an ionically bound, crystalline compound. Water molecules dissolve the Na and Cl atoms, which are bound in crystal form before being dissolved. As a result, water is a solvent.

Salt and sugar disappear when stirred in water because they dissolve in water. Salt is an ionic compound, which means that it is made up of positively charged ions (sodium ions) and negatively charged ions (chloride ions). When salt is added to water, the water molecules are attracted to the ions and surround them. This breaks up the salt crystals and the ions are evenly distributed throughout the water.

Sugar is a molecular compound, but it has polar covalent bonds. This means that the electrons in the bonds are not shared equally between the atoms. The oxygen atom in sugar has a slightly negative charge, while the hydrogen atoms have a slightly positive charge. The water molecules are also polar, with the oxygen atom having a slightly negative charge and the hydrogen atoms having a slightly positive charge. This makes the water molecules attracted to the sugar molecules, and the sugar dissolves in the water.

It is important to keep stirring the solution while it is heating and cooling because this helps to distribute the solute (the salt or sugar) evenly throughout the solvent (the water). When the solution is heated, the water molecules are moving faster and this helps to dissolve the solute more quickly. When the solution is cooled, the water molecules slow down and this can cause the solute to precipitate out of the solution. Stirring helps to prevent this by keeping the solute evenly distributed.

Here are some additional details about the dissolving process:

• The amount of salt or sugar that can dissolve in water depends on the temperature of the water. More salt or sugar can dissolve in hot water than in cold water.
• The size of the solute particles also affects the dissolving process. Smaller particles dissolve more quickly than larger particles.
• The presence of other solutes in the water can also affect the dissolving process. Some solutes can interfere with the dissolution of other solutes.

Dr Murtadha Shukur thank you for your contribution to the discussion

Initially the salt and sugar are attracted towards the water molecules and later they are completely surrounded by the water molecules which make them seem disappeared. When you stir these substances in water, the water molecules' polar nature allows them to surround and interact with the ions or molecules in salt and sugar, causing them to disperse evenly throughout the solution. The reason that the sugar seems to disappear is that the sugar molecules are now more attracted to water molecules. When the water is stirred the sugar molecules mix with the water molecules. The water molecules insert themselves with the sugar molecules and begin to surround each individual molecule. Dissolving sugar in water will occur more quickly if the water is stirred. The stirring allows fresh solvent molecules to continually be in contact with the solute. Substances that dissolve completely in water are called soluble substances. Salt and sugar are examples of soluble substances. When mixed with water, salt and sugar will completely dissolve in it without settling down. The faster the water molecules are moving, the more energy they give to the sugar molecules when they collide with them. Think about it this way: a sugar crystal is just a lot of sugar molecules stuck together. As the sucrose dissolves, the molecules become completely surrounded by water molecules and move throughout the water. It is the polar nature of water as well as the polar nature of sucrose that explains why sugar dissolves in water.Stirring and agitating chemical reactions is desirable and stirring reflux systems or any system under heating is necessary to a) distribute the heat evenly throughout the system and b) to prevent splashing and boilovers.Stirring mixes the surface layer into the bulk maintaining the temperature gradient and speeding the heat transfer. Does blowing on a hot liquid actually cool it faster? Yes, for the same reason that you feel cooler when there's a fan. Stirring allows hot liquid to reach the surface much faster than unassisted convection. At the surface this hot water evaporates cooling the remaining water as a result. Moving water convicts heat better than static water. The stirring allows fresh solvent molecules to continually be in contact with the solute. If it is not stirred, then the water right at the surface of the solute becomes saturated with dissolved sugar molecules, meaning that it is more difficult for additional solute to dissolve. When sugar dissolves in water, it dissolves faster if the water is agitated. The stirring ensures that new solvent molecules are constantly in touch with the solute. Every matter is made up of tiny particles, these particles have spaces in between them. When sugar particles dissolved in water, the particles of sugar get into intermolecular spaces of water. Hence, it seems like sugar particles get disappears in the water. Salt also contains ions. Water helps in separating these ions by decreasing the interionic forces allowing the salt to disperse throughout the water. So, the particles of salt occupy the spaces in between the particles of water and hence get dissolved. When salt is dissolved in water then the ions so formed get hydrated by the water molecules and decrease the movement of water molecules and solubility also decreases, hence, on agitation and stirring the solubility increases.