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Walking Science Facts: Sample Problems

Try each one on paper first. Only then reveal the solution — reading a worked answer you never attempted teaches you almost nothing.

  1. 1. Without a calculator, estimate the mass in grams of 6 × 10²³ atoms if each atom is about 10⁻²³ g.

  2. 2. Why is water's ΔH(vap) about 40 kJ/mol while methanol's is about 35 kJ/mol?

  3. 3. A substance has ΔH(vap) of 5 kJ/mol. What kind of substance is it likely to be?

  4. 4. Estimate how much heavier air is per liter than water is per liter.

Al the Gator, the school mascot, wearing a lab coat with a blue D

Al says…

You are not memorizing exact values, you are memorizing the size of things. If your answer for an atom's mass comes out at 10⁻³ g, you already know it's wrong.