A Look at Water and its Contaminants Water Unit B A Look at Water and its Contaminants

Physical Properties of Water Liquid water has a density of 1.00 g/mL Ice has a density of 0.92 g/mL Water expands as it freezes. Boiling point of water is 100oC Freezing point of water is 0oC Has high surface tension that forms spherical drops and form a curved surface in a small container.

B.2 Mixtures and Solutions Two or more substances that combine but can still be physically separated are mixtures. A heterogeneous mixture is a mixture where the individual substances can be seen. An example is oil and water when left to sit for a while.

A solution is a mixture of two or more substances that are completely uniform throughout. Solutions are homogeneous because you cannot see the particles. For instance, salt dissolves in water forming a homogeneous solution.

All solutions have two parts: the solute and the solvent. The solute is the substance that is in the lesser amount. The solvent is the substance in the greater amount. Water is called the universal solvent because it dissolves many things. In the ocean’s salty water, which is the solute and solvent?

Suspensions are mixtures containing relatively large, easily seen particles that will settle out to form layers. Ex: dirt in water. Colloids have suspended particles that are distributed throughout the solution and stay suspended. Ex: milk and water

The Tyndall effect indicates you have a colloid if light is scattered throughout the solution from bouncing off of suspended particles.

B.5 Symbols, Formulas, and Equations Chemical symbols represent atoms, elements, and compounds on paper. Chemical formulas represent a different chemical substance. Subscripts show how many of each atom is present in a chemical formula: H2O has 2 hydrogen atoms and 1 oxygen atom.

Chemical equations show the details of a chemical reaction. Chemical reactions involve the breaking and forming of chemical bonds to produce new substances. Once a chemical reaction has taken place, the products are chemically and physically different than the reactants. Ex: 2H2 + O2  2H2O The hydrogen and oxygen are the reactants and water is the product.

B.6 The Electrical Nature of Matter All atoms have a nucleus that is comprised of protons (+ charge) and neutrons (no charge). These two particles make up the majority of the weight of an atom. Atoms also have electrons ( - charge) outside the nucleus. When there are equal numbers of electrons and protons, the atom has a neutral charge.

Like charges repel like charges; + and + repel one another as well as – and – charges. The attraction between + and – charges in atoms is the “glue” that results in chemical bonding. If charges are not evenly distributed around a molecule, that molecule is said to be polar. Example: water

Ions are atoms that have a positive or negative charge because they have either given away or taken an electron from another source. For example, potassium (K) has one outer electron. If it reacts with something else, it has a tendency to give that electron away, thus it has more protons than electrons and becomes positively charged. K+

Cations and Anions Cations are positively charged ions. Example: All metals give away electrons to form cations. Calcium gives away 2 electrons and becomes Ca2+ Anions are negatively charged ions. Example: Most nonmetals will take electrons with the exception of the carbon family which can give or take electrons.

Qualitative tests are used to find out what is in a substance. Lead nitrate + potassium iodide form solid lead iodide and potassium nitrate A precipitate is formed when two different solutions are mixed together and a solid is formed. Qualitative tests are used to find out what is in a substance. Quantitative tests are used to find out how much of something is in a substance.