Cations, and the idea of a titration
Answers are for parents and teachers.
1
Complete and balance: Cu(NO₃)₂ + H₂S → ? Name the colour of the solid (paper only).
Cu(NO₃)₂ + H₂S → CuS + 2HNO₃; the solid CuS is black.
2
Complete and balance: Fe(NO₃)₃ + NaOH → ? Give the colour of the precipitate.
Fe(NO₃)₃ + 3NaOH → Fe(OH)₃ + 3NaNO₃; reddish-brown.
3
Both Al³⁺ and Fe²⁺ give a white precipitate with ammonium hydroxide. Which extra test separates them?
Add excess NaOH: Al(OH)₃ dissolves, while the iron(II) precipitate stays and turns green-white in air.
4
What volume of 0.100 M HCl just neutralises 25.0 mL of 0.0400 M NaOH, using HCl + NaOH → NaCl + H₂O?
n(NaOH) = 25.0 × 0.0400 ÷ 1000 = 0.00100 mol; n(HCl) = 0.00100 mol; V = 0.00100 ÷ 0.100 = 0.0100 L = 10.0 mL.
5
In the kitchen model, cup A needed 9 drops of vinegar. Cup B has three times as much baking soda. About how many drops should cup B need? Say that the numbers are invented.
About 3 × 9 = 27 drops (invented numbers; real counts will differ a little).