Mixtures vs. Pure Substances
Solutions and heterogeneous mixtures are different in key ways. A solution is uniform throughout with consistent properties everywhere—like salt dissolved completely in water. In contrast, a heterogeneous mixture lacks uniformity—like sand in water where you can clearly see different components.
Pure substances and mixtures represent fundamental chemical classifications. A pure substance contains only one element or one compound (like pure helium or water). Mixtures combine two or more substances that aren't chemically joined together, like air or your breakfast cereal with milk.
When counting significant figures, remember these rules: all non-zero digits count as significant, zeros between significant digits count too, and trailing zeros only count when there's a decimal point present.
Quick Tip: When adding or subtracting measurements, your answer should have the same number of decimal places as the measurement with the fewest decimal places. For example: 12.467 + 5.2 = 17.7 (rounded to match 5.2's single decimal place).