Question

Classify the following as mixtures or pure substances. a. the vegetable soup you had for lunch b. the fertilizer your dad spreads on the front lawn in the spring c. the salt you sprinkle on your French fries d. the hydrogen peroxide you cleaned a cut finger with

Short answer

a. Vegetable soup - mixture b. Fertilizer - mixture c. Salt - pure substance d. Hydrogen peroxide - pure substance

Step-by-step solution

a. Vegetable soup

The vegetable soup you had for lunch is likely composed of various ingredients, such as vegetables, water, and seasoning. These components are not chemically combined and can be separated by physical means. Therefore, the vegetable soup is a mixture.

b. Fertilizer

The fertilizer your dad spreads on the front lawn in the spring contains various nutrients and other ingredients to help promote plant growth. These include nitrogen, phosphorus, potassium, and other minerals, which are not chemically combined. Hence, the fertilizer is a mixture.

c. Salt

The salt you sprinkle on your French fries is primarily composed of sodium chloride (NaCl), which is a chemical compound with a fixed composition and properties. As it consists of only one type of particle, salt is a pure substance.

d. Hydrogen peroxide

The hydrogen peroxide you cleaned a cut finger with has the chemical formula H2O2, which is a compound consisting of oxygen and hydrogen atoms. It has fixed properties and a constant composition. Therefore, hydrogen peroxide is a pure substance.

Key concepts

Chemical Compounds

Chemical compounds are substances formed when two or more elements combine chemically. This combination results in a substance with unique properties different from the individual elements. For example, salt is a chemical compound known as sodium chloride, with the formula NaCl.

• Compounds have fixed chemical structures and properties.
• They are represented by chemical formulas, such as H₂O for water.

Understanding chemical compounds is crucial because they form the foundation of various substances, including those used in everyday life.

Physical Separation

Physical separation involves separating the components of a mixture without altering their chemical identities. This process exploits the distinct physical properties of the components, such as size, magnetism, or boiling point. For example, in a vegetable soup, you can separate the vegetables from the broth using a strainer.

• Methods include filtration, distillation, and magnetism.
• Ideal for mixtures where components are not chemically bonded.

Physical separation is commonly used in everyday tasks like cooking or recycling, where different materials need to be grouped accordingly.

Chemical Formulas

Chemical formulas are representations of chemical compounds using element symbols and numerical subscripts. They convey important information about the composition and proportions of elements in a compound. Hydrogen peroxide, for instance, is represented by the formula H₂O₂, indicating it consists of two hydrogen atoms for every two oxygen atoms.

• Formulas display the type and number of each atom in a molecule.
• They serve as a shorthand way to communicate chemical information.

Chemical formulas are a fundamental aspect of chemistry, helping to predict reactions and properties of compounds.

Fixed Composition

Fixed composition refers to the consistent and definite proportion of elements within a chemical compound. This means that a compound has the same ratio of elements no matter the sample size. For example, water is always composed of two hydrogen atoms and one oxygen atom (H₂O).

• A compound's fixed composition ensures uniform properties throughout.
• This characteristic differentiates pure substances from mixtures.

Understanding fixed composition is essential in chemistry as it defines the exact nature and properties that distinguish a compound from a mixture.