Final answer:
The half-life, denoted by t1/2, relates to the time when a substance's concentration falls to half its original value. The LD-50 is the dose that is lethal to 50% of a test population, and it is used to measure a chemical's toxicity. Percentages, such as a half-percent, are expressed in terms of weight/volume or weight/weight (0.5% = 0.5g/100g solution or 0.5g/100ml).
Step-by-step explanation:
When expressing dosage and half-percent, it's important to use the correct symbols and understand the relevant concepts. For example, the half-life of a substance, indicated by the symbol t1/2, is the time required for the concentration of a substance to decrease to half its initial value. The concept of Lethal Dose-50% (LD-50) is used to indicate the dose required to kill 50% of a test population; this measure is crucial in assessing the toxicity of a substance. Similarly, percent completion indicates how much of a reaction has occurred, such as a 97% completion after 5 half-lives.
Percentages in solutions, like a half-percent, can be expressed as 0.5%, which means 0.5 grams of solute per 100 grams of solution, or as a mass per volume concentration (e.g., 0.5 g/100 mL). It's also important to consider unit conversions when dealing with dosages: for instance, when converting liters to milliliters, 0.500 liters would be expressed as 500 mL, to ensure proper unit cancellation. Additionally, parts per million (ppm) and parts per billion (ppb) are used to express very dilute concentrations.