Making Measurements Two Types of Measurements Qualitative Quantitative

Making Measurements

Two Types of Measurements Ø Qualitative Ø Quantitative Ø Describes something without using numbers Ø Types: color, smell, texture, etc… Ø Types: mass, volume, etc…

What are the parts of quantitative measurements? Ø Number Ø Unit Ø Tells you how much of something you have Ø Tells you in what capacity you have of that something In chemistry, numbers are meaningless without units! Example: 50 cents, 50 dimes, 50 dollars, 50 million

What types of units do we use in chemistry? • Metric Units: – Mass: Grams (g) or (mg) or (kg) – Volume: Liters (L) or (m. L) – Distance: Meters (m) or (cm) or (km) – Time: Seconds (s)

Metric System Conversion Units

Reporting Measurements Ø Purpose: To know how close we are to the “true” value. Ø When reporting a measurement, two things need to be considered… Ø Accuracy and Precision

What is accuracy? • Tells you how close a single measurement is to the “true” value.

What is precision? • Tells you how close a series of measurements are to each other.

Left Side pg 14 • With the person next to you, decide whether the following examples are accurate, precise, both, or neither.

Problem 1: Problem 2: Answer: Neither Answer: Precise Problem 3: You measure the volume of a liquid to be 35. 8 m. L. Your lab partner measures the same liquid having a volume of 37. 2 m. L. The “true” volume is 36. 0 m. L. Who is more accurate? Answer: You Answer: Yes Problem 4: You measure the mass of a substance to be 110 g, 109 g, 111 g, and 110 g. Are these measurements precise?