Section 1.2—Observations & Measurements

Taking Observations Qualitative descriptions  Color  Texture  Formation of solids, liquids, gases  Heat changes  Anything else you observe

Clear versus Colorless Clear See-through Cloudy Parts are see- through with solid “cloud” in it Opaque Cannot be seen through at all Words to describe transparency Colorless does not describe transparency  You can be clear & colored  You need to describe the color of the solution & the cloud if it’s cloudy (examples: blue solution & white cloud or colorless solution and blue solid)

Clear versus Colorless Cherry Kool-ade Example: Describe the following in terms of transparency words & colors Whole Milk Water

Clear versus Colorless Cherry Kool-adeClear & red Example: Describe the following in terms of transparency words & colors Whole Milk Water Opaque & white Clear & Colorless

Gathering Data Quantitative measurements International System of Units (SI Units) are used Quantity Mass (how much stuff is there) Unit Kilogram (kg) Instrument used Balance Volume (how much space it takes up) Liters (L) Graduated cylinder Temperature (how fast the particles are moving) Kelvin (K) or Celsius (°C) Thermometer Length Meters (m) Meter stick Time Seconds (sec) stopwatch Energy Joules (J) (Measured indirectly)

Uncertainty in Measurement Every measurement has a degree of uncertainty The last decimal you write down is an estimate  Write down a “5” if it’s in-between lines  Write down a “0” if it’s on the line 5 mL mL 5 mL mL Remember: Always read liquid levels from the bottom of the meniscus (the bubble at the top) Example: Read the measurements

Uncertainty in Measurement Every measurement has a degree of uncertainty The last decimal you write down is an estimate  Write down a “5” if it’s in-between lines  Write down a “0” if it’s on the line 5 mL mL 5 mL mL Example: Read the measurements It’s in- between the 10 & 11 line 10.5 mL It’s on the 12 line 12.0 mL

Uncertainty in Measurement Example: Read the measurements

Uncertainty in Measurement Example: Read the measurements It’s right on the 4.3 line 4.30 It’s between the 3.8 & 3.9 line 3.85

Uncertainty in Measurement Choose the right instrument  If you need to measure out 5 mL, don’t choose the graduated cylinder that can hold 100 mL. Use the 10 or 25 mL cylinder The smaller the measurement, the more an error matters—use extra caution with small quantities  If you’re measuring 5 mL & you’re off by 1 mL, that’s a 20% error  If you’re measuring 100 mL & you’re off by 1 mL, that’s only a 1% error