CHEM 105N 1st Edition Lecture 4 Outline of Last Lecture I. Significant Figures- Sandwiched Zeros- Trailing Zeros- Leading ZerosII. Exact NumbersIII. Multiplication and Division of Significant FiguresIV. Addition and Subtraction of Significant FiguresV. Metric Equalities Outline of Current Lecture I. Percent as a Conversion FactorII. Parts Per MillionIII. Parts Per BillionIV. Toxicology and Risk-Benefit testsCurrent LectureI. Percent as a Conversion Factor:- Uses a ratio of the parts to a whole in a fraction- Uses the same unit of measure for both- The whole is always equal to: 100- Can be written two waysEXAMPLES:1. % = part/whole x 100%2. Apples contain 18% (by mass) fat= 18 grams of fat/ 100 grams of appleOR= 100 grams of apple/ 18 grams of fat3. A BMI calculator indicates a person has 13% body fat. Write a Percent Factor for body fat in kg.= 13 kg fat/ 100 kg of massOR= 100 kg of mass/ 13 kg fatII. Parts Per Million (ppm):- Is equal to mg per kilogram of substance = mg/kg or (10^6)These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.III. Parts Per Billion (ppb):- Is equal to µg per kilogram of substance = µg/kg or (10^9)-Ex. The maximum amount of lead in paint is 3 ppm= 3 mg lead/ 1 kg paintOR=1 kg paint/ 3 mg leadIV. Toxicology and Risk-Benefit Tests:- One measure of toxicity is the LD50, or the lethal dose.- This is the measure of concentration that causes death in 50% of test animals.- A dose is typically measured in ppm (mg/kg) of body mass or ppb
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