Use the six linked lessons for reading, guided practice, homework, or review. The prompts below are short enough for an entrance ticket or discussion and include the reasoning to listen for.
A metal sample has a mass of 54.0 g and a volume of 20.0 mL. Calculate its density. What additional evidence would make an identification more convincing?
Use ρ = m/V: 54.0 g ÷ 20.0 mL = 2.70 g/mL. A comparison with a reliable reference value helps, but students should mention uncertainty and possible effects from composition, temperature, or trapped material.
An ion has 17 protons and a 1− charge. How many electrons does it have, and why?
It has 18 electrons. A neutral atom with 17 protons has 17 electrons; a 1− charge means one extra electron. Proton count remains the element identity.
Explain why 2H₂ + O₂ → 2H₂O is balanced even though the molecules have been rearranged.
The left side contains four hydrogen atoms and two oxygen atoms. Two water molecules contain those same totals. Coefficients count particles; they do not change the formula or create atoms.
Two solutions have the same pH. Can they contain different amounts of dissolved solute? State an assumption.
Yes. In the introductory dilute aqueous model, pH describes hydronium concentration; it does not identify every solute or its total amount. Equal pH does not establish equal composition or total concentration.
| Student claim | Ask next | Then assign |
|---|---|---|
| “The heavier sample is denser.” | What two quantities define density? | Compare equal-volume samples and calculate ρ = m/V. |
| “An isotope is a different element.” | Which particle sets element identity? | Label protons and neutrons in two isotopes. |
| “A coefficient changes the substance.” | What stays fixed in a formula? | Draw 2H₂O and H₂O₂ for comparison. |
| “Strong means concentrated.” | Are ionization tendency and amount per volume the same? | Compare particle sketches of strength and concentration. |