Question

Identify the following ingredients as either a pure substance or a mixture. (a) water (b) chicken stock (the liquid that remainsin the potaftercooking the chicken) (c) salt (d) mustard flour

Short answer

Water: Pure Substance, Chicken Stock: Mixture, Salt: Pure Substance, Mustard Flour: Mixture

Step-by-step solution

Define Pure Substance and Mixture

A pure substance consists of a single type of particle and has a uniform composition. Examples include elements and compounds. A mixture consists of two or more substances that are physically combined and can be separated by physical methods.

Identify Water (H₂O)

Water is a compound made of hydrogen and oxygen, and it has a uniform composition. Therefore, water is a pure substance.

Identify Chicken Stock

Chicken stock is made by boiling chicken, along with other ingredients such as vegetables and spices. The composition can vary and different substances are mixed together without forming a new compound. Therefore, chicken stock is a mixture.

Identify Salt (NaCl)

Salt, also known as sodium chloride, is a compound made of sodium and chlorine. It has a uniform and definite composition. Therefore, salt is a pure substance.

Identify Mustard Flour

Mustard flour is made by grinding mustard seeds and may contain varying amounts of different particles within it. It does not have a consistent composition throughout. Therefore, mustard flour is a mixture.

Key concepts

Chemical Compounds

Chemical compounds are substances formed when two or more elements combine in fixed proportions and undergo a chemical reaction. Each compound has unique properties different from its constituent elements. For instance, water (H₂O) is a compound made from hydrogen and oxygen. When elements form compounds, they engage in chemical bonds, such as ionic or covalent bonds.

• Compounds are always pure substances.
• They cannot be separated by physical methods—it requires chemical reactions to break them down into their elements.
• Examples include salt (NaCl), carbon dioxide (CO₂), and methane (CH₄).

Understanding these basics helps distinguish between compounds and simpler forms of matter like elements or mixtures.

Physical Mixtures

Physical mixtures are combinations of two or more substances that retain their individual properties and can be separated by physical methods. They do not involve chemical bonding. Thus, the chemicals maintain their separate identities within the mixture. When components of a mixture come together, they may mix uniformly or non-uniformly.

• Homogeneous mixtures, also known as solutions, have uniform composition, like salt dissolved in water.
• Heterogeneous mixtures have distinct parts and concentrations, like chicken stock, which can have chunks of vegetables and meat floating in a liquid base.

Mixtures can often be separated easily through various methods such as filtration, evaporation, or magnetic separation.

Elementary Chemistry

Elementary chemistry involves understanding basic concepts that form the foundation of chemical science. At its core, chemistry studies the composition, structure, properties, and changes of matter. Here are some fundamental concepts:

• Elements: These are pure substances consisting of only one type of atom. Examples include hydrogen (H), oxygen (O), and sodium (Na).
• Compounds: Formed from elements, compounds have specific, fixed ratios and chemical structures, like water (H₂O) or salt (NaCl).
• Mixtures: Physical combinations of two or more substances that retain their properties, like air or a salad.

Learning elementary chemistry involves recognizing and distinguishing these basic forms of matter, examining how they interact, and understanding the methods used to separate and analyze them.