Inorganic Chemistry
8 marks · NormalAnswer all parts about compounds and predicted properties in Group 1 and Group 7.
State the typical colour and solubility in water of sodium oxide.
Potassium manganate(VII) is a purple compound. State which ion gives rise to the colour, and what colour you would observe if pure potassium chloride is dissolved in water.
Predict the colour and physical state at room temperature of astatine, the halogen below iodine.
Predict whether sodium astatide would be soluble in water, and what colour its solution would be. Explain your reasoning.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) Sodium oxide is a white solid; it is soluble in water. · must show white (not colourless), soluble in water
(b) The manganate(VII) ion is responsible for the purple colour. Potassium chloride when dissolved in water gives a colourless solution. · must show manganate(VII) ion gives colour, potassium chloride gives colourless solution
(c) Astatine would be a very dark grey or black solid at room temperature. · must show very dark grey or black, solid at room temperature
(d) Sodium astatide would be soluble in water and the solution would be colourless. This is because Group 1 metal salts are generally soluble and their solutions are colourless when the anion is colourless. · must show soluble in water, solution colourless, reason: Group 1 salts generally soluble, solution colourless if no coloured ions
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States sodium oxide is white.
B2 (a) · 1 mark · States sodium oxide is soluble in water.
B3 (b) · 1 mark · Identifies manganate(VII) ion as responsible for purple colour.
B4 (b) · 1 mark · Correctly states that potassium chloride solution is colourless.
B5 (c) · 1 mark · Predicts very dark grey or black for astatine.
B6 (c) · 1 mark · Predicts solid state at room temperature for astatine.
B7 (d) · 1 mark · Correctly predicts sodium astatide is soluble and would give a colourless solution.
B8 (d) · 1 mark · Explains solubility and lack of colour with correct reference to Group 1 compound properties.
Worked solution
a) Sodium oxide is a white solid and is soluble in water.
b) The colour comes from the manganate(VII) ion; potassium chloride gives a colourless solution when dissolved in water.
c) Astatine would be a very dark grey or black solid at room temperature.
d) Sodium astatide would be soluble in water and the solution would be colourless, because Group 1 metal salts are typically soluble and colourless unless the anion is coloured, which astatide is not.