Video Transcript
Which of the following is correct when we add sugar to water? (A) They form a heterogeneous mixture and are called a colloid. (B) They form a homogeneous mixture and are called a colloid. (C) They form a heterogeneous mixture and are called a solution. (D) They form a heterogeneous mixture and are called suspensions. (E) They form a homogeneous mixture and are called a solution.
In this question, we are given the scenario of adding sugar to water. Mixing sugar and water is the physical combination of two substances. The result of this physical combination is a mixture. The answer choices provided are a set of statements about mixtures. Our job is to determine which of the statements is true about the mixture of sugar and water.
Recall that there are two main types of mixtures: heterogeneous mixtures and homogeneous mixtures. Heterogeneous mixtures do not have uniform compositions, and they are further classified as either colloids or suspensions. In a colloid, particles are dispersed through a medium. These particles are too small to be seen with the naked eye. However, colloids are not transparent. A good example of a colloid is milk. Even though we cannot see them, the particles inside the milk are large enough to scatter light. If we had a light source and shined it through the glass of milk, we would be able to see the path of the light beam.
Colloids are considered stable mixtures, which means that if left at rest, the dispersed particles will not settle out of the mixture. Finally, the dispersed particles in the colloid are too small to be removed by filtration. Even though a colloid like milk looks like it has a uniform composition, under magnification, it’s obvious that the composition is nonuniform. Different-sized fat droplets and particles are dispersed in the water-based medium.
Let’s take a look at answer choice (B). Answer choice (B) states that sugar and water form a homogeneous mixture called a colloid, but we know that colloids are heterogeneous mixtures. For this reason, we can eliminate answer choice (B) as an incorrect answer choice. In suspensions, larger particles are suspended in a medium. These particles may be big enough to see, will settle out of the suspension if it’s left undisturbed, and are large enough to be removed from the suspension by filtration. While a mixture of water and dirt is stirred, the dirt particles are suspended in the water medium. If left at rest, the solid dirt particles will settle out of the liquid water and accumulate in the bottom of the container.
There are only two types of heterogeneous mixtures: colloids and suspensions. Let’s pause and take a look at answer choice (C). Answer choice (C) states that the sugar and water would form a heterogeneous mixture called a solution. But solutions are a different type of mixture called a homogeneous mixture. Let’s go ahead and eliminate answer choice (C). As we just mentioned, homogeneous mixtures are known as solutions. Homogeneous mixtures have uniform compositions. We know from experience that sugar dissolves in water. The dissolved particles in a solution may be atoms, ions, or molecules, all of which are too small to see or filter out of the solution. Unlike suspensions, the particles of a solution will not settle out. The particles dissolved in a solution are also smaller than the dispersed particles of colloids and suspensions.
When adding sugar to water, sugar is the solute and gets dissolved by water, which is the solvent. Once the sugar crystals have completely dissolved in the water, they are no longer visible and the sugar–water solution has formed. The solution is transparent and has a uniform composition. In the sugar–water solution, the dissolved particles are individual sugar molecules. Each sugar molecule is completely surrounded by water molecules, and the sugar molecules are evenly distributed throughout the solution. Sugar has a molecular formula of C12H22O11.
Water molecules are attracted to some of the atoms in the sugar molecule. These attractions are called intermolecular forces. Because water can surround the individual sugar molecules in this way, the sugar molecules are evenly distributed throughout the solution. In fact, the dissolved solute particles of a solution are the most uniformly distributed of all three types of mixtures, which is why we classify solutions as homogeneous mixtures with uniform compositions. When sugar is mixed with water, it dissolves and forms a solution, which is a homogeneous mixture. The correct answer is answer choice (E).
