Writing and balancing molecular and ionic equations with state symbols, using equations to calculate reacting masses and gas volumes, and molar and mass concentration with standard solutions.
5 narrated scenes. Press play, listen and read along — the points appear as they are explained. Use ‹ Prev / Next › or the scene bar to jump to any scene.
A balanced equation is a recipe: it says how many particles of each substance react. Combine it with the mole and you can predict exactly how much product to expect.
Narration uses your device’s built-in voice. No sound? Switch to “Captions only” — the captions advance on their own.
Copy these into your notebook in your own words — that is how they stick.
Change coefficients only; never subscripts; add state symbols.
(s), (l), (g), (aq). Acids are (aq).
Write the ions that react; cancel spectator ions.
Use the coefficients in the balanced equation.
V = n × 24 dm³ at rtp.
c = n ÷ V (mol/dm³); n = c × V.
g/dm³ = c × M.
Accurately known concentration made in a volumetric flask.
3 quick games on this lesson. Earn XP and badges as you play — your best score for each game is saved. Games are for practice and do not change your exam readiness. More games in the Chemistry Arcade.
8 items modelled on real CSEC Paper 1 questions. Choose one answer for each, then check. Aim for 80% or better. Work each item on paper first.
Write full answers, then reveal the mark scheme and tick the points you earned (19 marks in total). Show all your working — method marks count. Your answers are saved on this device.
Question 1 [19 marks]
Relative atomic masses: H = 1, C = 12, O = 16, Mg = 24, Cl = 35.5, Ca = 40. Molar volume = 24 dm³ at rtp.
(a) (a) Write a balanced equation, with state symbols, for the reaction of magnesium with dilute hydrochloric acid. [3]
(b) (b) Write the ionic equation for this reaction. [2]
(c) (c) 1.2 g of magnesium reacts with excess acid. Calculate the volume of hydrogen at rtp. [4]
(d) (d) Calculate the mass of magnesium chloride produced in (c). [3]
(e) (e) Calculate the concentration in mol/dm³ of a solution containing 5.3 g of Na₂CO₃ (M = 106) in 250 cm³. [3]
(f) (f) Describe how to prepare 250 cm³ of a standard solution. [4]
Find these in your own past-paper booklets for extra timed practice. Items above are written in the style of these papers; any adapted from a specific question say so.