BIO-131 Lab 4

Base

A base, reduces the free hydrogen ion concentration as it mixes with water because basic (or alkaline) substances remove hydrogen ions by combining with them. As a result, bases shift the balance so that there are fewer H+ and more OH- ions in the solution. Bases are characterized by pH values greater than "7". The greater the amount of released OH- , the higher the pH value.

pH meter

A device used to determine the pH of a solution by measuring the voltage between the two electrodes that are placed in the solution. Measures the hydrogen ion concentration of a solution. When its electrode is placed in a solution, the needle moves to a position on the pH scale reading between 0 and 14.

Acid

An acid is a substance that increases the free hydrogen ion concentration as it mixes with water because the acid molecule releases H+ as it breaks apart. For example, hydrochloric acid (HCI) separates into the ions H+ and Cl-. Acids, therefore, are characterized by pH values less than "7". The greater the amount of released H+, the lower the pH value.

Quantitative test

Determines the actual amount (quantity) of the substance present.

Qualitative test

Determines the presence (quality) of a substance.

pH Value

Measurements of pH refer to the hydrogen ion concentration of a solution. The number given in a pH measurement (the pH value) can be applied to the following pH scale to determine whether a solution is acidic, basic, or pH neutral: between 0-7 Acidic, (7) Neutral pH, between 7-14 Basic.

Pure water

Pure water releases equal amounts of hydrogen ions (H+) and hydroxide ions (OH-) when its molecules partially ionize. (In other words: H2O <-> (H+) + (OH-). Pure water would correspond to the value "7" on the pH scale, meaning pH neutral.

Relationship between hydrogen ion concentration and pH value

The relationship between hydrogen ion concentration and pH value is inverse. That means that solutions with a highhydrogen ion concentration have a low pH value, and solutions with a low hydrogen ion concentration have a high pH value.