Materials that Do and Do Not Dissolve in Water

SC.5.P.8.2: Investigate and identify materials that will dissolve in water and those that will not and identify the conditions that will speed up or slow down the dissolving process.

What Materials Dissolve in Water?

There are some materials that will dissolve, or break apart completely, in water. Salt, sugar, and baking soda are three common materials that will dissolve in water. Baking powder is different from baking soda: baking powder will not dissolve in water.

If a tablespoon of salt is added to a cup of water and allowed to sit undisturbed overnight, the salt will dissolve into the water. Table salt, the most common form of salt that we use, has particles or pieces that are already very small. Those particles will break apart completely in water. The salt has become mixed into the water so well the individual particles can no longer be seen. This kind of mixture is called a solution. We know that the salt is still in the water because the water will now taste salty. Ocean water is water with salt dissolved in it. Ocean water can be evaporated, leaving behind another commonly used form of salt, sea salt. Sea salt often coarser, or has a larger particle size, than table salt.

Sugar will also dissolve, or break apart completely, in water. Baking soda also dissolves in water. Salt, sugar, and baking soda, because they do dissolve in water, are often used in cooking and preparing foods. When cooking,heatis often used to speed up the process of dissolving.Stirringis also used to speed up the process of dissolving. Salt and sugar can also be crushed toreduce particle sizeto speed up the process of dissolving.

What Materials Do Not Dissolve in Water?

Some materials like salt and sugar dissolve, or break apart completely, in water. There are many materials that do not dissolve in water. Sand is one of the most common materials on Earth that does not dissolve in water. How do we know this? When you go to a beach or lake, or even see a puddle in the grass, we can see sand settled at the bottom of the water. The sand at the bottom of the ocean has not dissolved in water.

Other common materials that do not dissolve in water are baking powder and flour. If you have ever made cookies, bread, or a cake, you have mixed flour with water. Flour does not dissolve in water: it forms a mixture called dough.

It is easy to identify materials that do not dissolve in water: just ask yourself if they’ve ever disappeared after it rained! Most things are still there after it rains. If you want to test this out at home or at school, set out one bowl of salt and one bowl of sand before a rainstorm. Then, after the rain has fallen, see which material has dissolved. Which of the two do you think will still be there after the rain?

What Conditions Affect the Process of Dissolving?

Some materials will break apart completely, or dissolve, in water, and some will not. If you have ever been to the beach, you have seen sand on the beach. Does the sand break apart completely in the water? It does not. Sand falls to the bottom and settles under the water.

There are three factors that can speed up or slow down the dissolving process: particle size, temperature, and stirring. Temperature and stirring are very common ways to speed up the process of dissolving. Particle size is less common, but easy to understand.

 To explain the three factors that affect the process of dissolving, we will use salt as the material dissolved in water. Most of the salt we use is called table salt. Table salt comes from mines: salt forms as a layer of rock under an ocean which long ago disappeared. These layers of salt, sometimes miles thick, provide almost all the salt we use. Because salt is dissolved in ocean water, ocean water can also be used to provide salt. If the water is evaporated or boiled away, sea salt is left behind. Sea salt is commonly found in foods. Sea salt is coarser than table salt: it has larger particles that table salt. Rock salt, with particles the size of small rocks, is often used in home water softeners.

We will use table salt, coarse sea salt, and rock salt to investigate the factors that speed up or slow down the dissolving process.

How Does Particle Size Affect the Process of Dissolving?

We will investigate how particle size can speed up or slow down the process of dissolving. A particle is a piece of something larger. When salt is mined, larger rocks of salt can be broken down into smaller size. Two common sizes of salt that come from salt mines are table salt, used on food, and coarse sea salt, which comes from evaporating or boiling ocean water. A third size of salt, rock salt, is often used in home water softeners. coarse sea salt, comes from evaporating or boiling ocean water.

Particle size affect the affects the dissolving process. The reason for this is that 10 grams of table salt, the smallest particle of salt, has a greater surface area than 10 grams of coarse sea salt. Water simply has more space to work when particles are broken apart. After all, that is what dissolving is doing in the first place: breaking the material apart. 

The effect of particle size on the dissolving process explains why we mash some things up during cooking. Reducing the size of the particles gives moresurface areafor water to dissolve the particle. If you were mixing a cup of hot chocolate, you might use your spoon to crush up the larger clumps of chocolate. This would speed up the dissolving process, and your cocoa would be ready sooner!

How Does Temperature Affect the Process of Dissolving?

Some materials will dissolve, or break apart completely, in water. Materials that dissolve in water include salt, sugar, and baking soda. Each of these materials will break apart completely in water. They will no longer be visible, but they are still present in the water. They have been mixed in completely. One factor that speeds up or slows down the process of dissolving is particle size. Larger particles dissolve slower than smaller particles of the same materials.

Another factor that will speed up or slow down the dissolving process is temperature. Hot water will dissolve materials faster than cold water. The reason for this is that there is more energy in hot water than cold water. That energy acts on the materials being dissolved, and speeds up the process.

When cooking, temperature can be used to dissolve some ingredients. For example, simple syrups can be made by dissolving sugar into water. If cold water is used, sugar will not dissolve. As the temperature of the water is increased, the process of dissolving will speed up. Eventually so much sugar will be dissolved into the water that a syrup, which is thicker than water, will be made.

How Does Stirring Affect the Process of Dissolving?

When materials dissolve in water, they break apart and are completely mixed into the water. Salt, sugar, and baking soda are examples of materials that dissolve in water. When salt is dissolved in water, you can no longer see the particles of salt. You can taste the salt in the water: this provides evidence that the salt is still there. Smaller particles dissolve faster than larger particles, and hot water dissolves materials faster than cold water.

Stirring will also speed up the process of dissolving. If you have ever mixed a powdered drink, you have observed this. When you pour the drink mix into water, the particles of mix sometimes clump up. You could wait for the particles of mix to dissolve into the water. most people will use a spoon to stir the mixture. You have probably observed that the faster you stir, the faster the mix will dissolve.

These three factors: particle size, temperature, and stirring, can speed up or slow down the process of dissolving. Many times, all three factors are used together: smaller particles are used, the temperature of the water is increased, and the water itself is stirred. This combination will dissolve a material such as a drink mix the fastest.