Question

The properties of a mixture are typically averages of the properties of its components. The properties of a compound may differ dramatically from the properties of the elements that combine to produce the compound. For each process described below, state whether the material being discussed is most likely a mixture or a compound, and state whether the process is a chemical change or a physical change. a. An orange liquid is distilled, resulting in the collection of a yellow liquid and a red solid. b. A colorless, crystalline solid is decomposed, yielding a pale yellow-green gas and a soft, shiny metal. c. A cup of tea becomes sweeter as sugar is added to it.

Short answer

a. Mixture and Physical Change b. Compound and Chemical Change c. Mixture and Physical Change

Step-by-step solution

Scenario (a)

An orange liquid is distilled, resulting in the collection of a yellow liquid and a red solid. Here we identify the material as most likely a mixture because distillation is a process of separating components of a mixture based on their different boiling points. Since two different materials were obtained from the original liquid, they were not bound together as a compound would be. The process is a physical change because distillation involves a change of state (liquid to vapor and back to liquid), and no new substances are formed. Answer: Mixture and Physical Change

Scenario (b)

A colorless, crystalline solid is decomposed, yielding a pale yellow-green gas and a soft, shiny metal. In this case, the material being discussed appears to be a compound since it is decomposed into different elements (gas and metal). Decomposition is a process where a compound breaks down into its constituent elements. This process is a chemical change because new substances (gas and metal) are formed from the original substance (crystalline solid), and the process involves breaking or forming chemical bonds. Answer: Compound and Chemical Change

Scenario (c)

A cup of tea becomes sweeter as sugar is added to it. The material being discussed in this scenario is most likely a mixture. Adding sugar to a cup of tea does not form a new compound, but instead, the sugar dissolves into the tea and the properties of the mixture change (becoming sweeter). This is a physical change as no new substances are formed, and it involves only mixing the sugar with the tea without altering their chemical structures. Answer: Mixture and Physical Change

Key concepts

Mixtures

Mixtures are combinations of two or more substances where each retains its own chemical properties. These components mix physically without forming any new chemical bonds. An example is a cup of tea with sugar; the sugar dissolves, but its molecular structure remains unchanged.
Mixtures are classified into homogeneous and heterogeneous:

• Homogeneous: The composition is uniform throughout, such as a cup of coffee.
• Heterogeneous: Different components are visibly distinct, like sand in water.

Physical processes like filtration and distillation are often used to separate mixtures based on physical properties such as boiling point or particle size.

Compounds

Compounds are chemical substances formed when two or more elements chemically bond together in fixed proportions. When forming compounds, elements lose their individual properties, creating a new substance with distinct characteristics.
A classic example is water (H₂O), where hydrogen and oxygen combine to form a liquid that behaves differently from either gas.
Unlike mixtures, breaking down compounds requires chemical reactions such as decomposition, where the compound is split back into its original elements or simpler compounds.

Distillation Process

Distillation is a separation technique used primarily for mixtures based on differences in boiling points. This process involves heating a liquid until it vaporizes. The vapor is then cooled to collect it as a liquid again, separate from other components.
Distillation is commonly used in laboratories to purify liquids or separate volatile components from less volatile ones. For example, distilling seawater allows us to separate fresh water from salt.
This process is considered a physical change since it alters the state of a substance without changing its chemical composition.

Decomposition

Decomposition is a chemical change where a compound breaks down into simpler compounds or elements. This process often involves breaking chemical bonds and can occur naturally or through induced chemical reactions.
An everyday example is the decomposition of hydrogen peroxide into water and oxygen gas. Decomposition is a key factor in processes like digestion and decay.
This chemical change contrasts with physical changes like mixing or dissolving, where no chemical bonds break.

Solution Formation

Solution formation is a physical process where one substance (the solute) dissolves into another (the solvent), forming a homogeneous mixture. Solutions are characterized by their uniform composition and appearance.
When sugar dissolves in tea, it results in a sweetened beverage, where the sugar is the solute and the tea acts as the solvent. During this process, no new chemicals form, and the original substances retain their chemical identities.
Factors affecting the rate of solution formation include temperature, agitation, and particle size of the solute.