Nature of science + CER; lab safety; observation vs inference

Explain how science works (testable claims, evidence, peer review), write claim-evidence-reasoning (CER), and follow lab safety rules. Observation: what you directly sense or measure. Inference: an explanation based on observations, which can be revised. CER: Claim (answer), Evidence (data), Reasoning (the science principle linking them). Lab safety: goggles for chemicals or heat, no food or tasting, know the eyewash and exits, report spills and injuries immediately. Observation: "The sidewalk is wet; the grass is dry." Inference: "A sprinkler aimed at the sidewalk" — rain would wet both. A scientific claim must be testable and could be shown wrong by evidence. Science builds reliable knowledge through repeated testing, open data, and peer review. A hypothesis is a testable explanation; a theory (cell theory, evolution) is a well-supported explanation of many observations — not a guess. Question: does salt water freeze faster than tap water? Claim: salt water freezes more slowly. Evidence: tap water froze in 95 min; salt water still liquid at 150 min (same volume, same freezer). Reasoning: dissolved salt lowers the freezing point, so it must get colder to freeze. Write a full CER answering "Does a lid help hot water stay hot?" using data you collect with two identical mugs and a thermometer over 20 minutes. Usual mistake: Treating an inference as an observation, or calling a theory "just a guess."