SECTION B
14 This question is about barium and barium compounds.
(a) The graph shows the first eight ionization energies of barium.
(i) Write an equation, including state symbols, for the third ionization energy of barium.
(1)
ANSWER
Ba2+ (g) → Ba3+ (g) + e-
(ii) State how the graph confirms that barium is in Group 2 in the Periodic Table.
(1)
ANSWER
There is a large jump/increase in ionisation energy between 2nd and 3rd i.e. during the 2nd and 3rd electron removal and such large jump is not visible in other electron removals.
(b) An acidified aqueous solution of barium chloride, BaCl2, is used to test for sulfate ions.
(i) Draw a dot‑and‑cross diagram for barium chloride.
Show the outer electrons only.
(2)
ANSWER
(ii) Calculate the mass of barium chloride needed to form 150cm3 of BaCl2 (aq) with a concentration of 0.200moldm–3.
Give your answer to an appropriate number of significant figures.
(2)
ANSWER
Step 1: calculating Moles by using ratio method
0.200 mol = 1000cm3
X mol = 150 cm3
Therefore,
X mol = 0.03 mol
Step 2: calculating Mr of BaCl2
Mr of BaCl2 = 138 + 2(35.5) = 209
Step 3: Finding mass of BaCl2
1 mole of BaCl2 = 209 g
0.03 mol of BaCl2 = X gram
Therefore,
X in grams = 6.27 grams of BaCl2 required
(iii) The barium chloride solution is acidified to prevent carbonate ions giving a false positive result.
Write the ionic equation for the reaction of hydrochloric acid with carbonate ions. State symbols are not required.
(1)
ANSWER
2H+ + CO32− → H2O + CO2
(c) Give a reason why solid barium chloride does not conduct electricity.
(1)
ANSWER
Barium chloride is an ionic compound and they conduct electricity only when in aqueous and molten state. It is so because in solid state, the ions are not free to move and carry charge i.e. they are held at fixed position.
