Solutions and pH

What is a Mixture? A mixture is a material compound Mixtures are made of two or more elements or compounds that are physically mixed together but not chemically combined Example: Earth’s atmosphere is a mixture of gases

A homogeneous mixture is a mixture that is uniform (the same) in composition throughout. Example: Food coloring and water A heterogeneous mixture is a mixture that is not uniform (the same) throughout Example: Oil and Water

3 Types of Mixtures Solution – a homogeneous mixture Suspension – a mixture in which the particles are so large that they settle out unless the mixture in constantly stirred Example: Sand in Water Colloid – a mixture consisting of particles that are intermediate in size between those in solutions and those in suspensions Example: Milk

What makes up a solution? Solvent – the substance that does the dissolving in a solution Typically present in the greatest quantity Typically a liquid Water is the “universal solvent” Solute – the substance that is being dissolved in a solution Typically present in the least amount Typically a solid (can be a liquid)

Acids, Bases, and pH

pH Scale The pH scale indicates the concentration of H+ ions in a solution The pH scale ranges from 0 to 14 A pH of 7 is considered to be neutral Water has a pH of 7 pH values below 7 are considered to be acidic pH values above 7 are considered to be basic

What are acids? An acid is any compound that forms H+ ions when in solution. Acidic solutions have higher concentrations of H+ ions than pure water pH < 7 The strongest acids have a pH between 1 and 3, 1 being the strongest acid Example: Hydrochloric acid produced by the stomach

What are bases? A base is a compound that produces OH- ions when in a solution. Solutions that are basic have less H+ ions that pure water pH > 7 Strong bases have a pH between 11-14, with 14 being the strongest

How is pH maintained in the human body? The human body has a pH between 6.5-7.5 This pH must be maintained or chemical reactions that take place in the cells may not occur Buffers are weak acids or bases that can react with strong acids or bases to maintain a relatively steady pH Buffers help keep human blood at a pH of roughly 7