Reactions of metals with water
5 marks · HardThe table shows a list of four metals. Each can be added to a beaker of cold water. For each metal, describe what you would observe, and name the gas produced.
Potassium is added to cold water.
Sodium is added to cold water.
Calcium granules are added to cold water.
Lithium is added to cold water.
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(a) Potassium moves rapidly on the surface, melts into a ball, effervesces/fizzes; may produce a lilac flame; gas produced is hydrogen. · must show rapid movement on surface, melting, fizzing/effervescence, lilac flame (credit), hydrogen produced
(b) Sodium melts, fizzes, moves on surface; hydrogen is produced. · must show melting, fizzing/movement, hydrogen produced
(c) Bubbles of gas around granules; white solid forms; hydrogen is produced. · must show bubbling, white solid forms, hydrogen produced
(d) Lithium floats, moves slowly, fizzes gently; hydrogen is produced. · must show floats, moves slowly, fizzes, hydrogen produced
Common mistakes: not mentioning gas produced; not stating colour/physical changes
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Marking points
B1 (a) · 1 mark · Describes at least two correct observations for potassium: e.g. rapid movement, melting, fizzing, lilac flame.
B2 (a) · 1 mark · Names hydrogen as the gas produced with potassium.
B3 (b) · 1 mark · Describes at least two correct observations with sodium and/or states hydrogen is produced.
B4 (c) · 1 mark · Describes bubbling/white solid or states hydrogen is produced with calcium.
B5 (d) · 1 mark · Describes two correct observations for lithium and/or states hydrogen is produced.
Worked solution
a) Potassium moves quickly across the surface, melts into a ball, fizzing/effervescence is seen, sometimes a lilac flame is visible. The gas formed is hydrogen.
b) Sodium melts, fizzes, moves on the surface. Hydrogen gas is produced.
c) Calcium sinks, but bubbles of hydrogen form around the granules, carrying them to the surface. White solid (calcium hydroxide) forms.
d) Lithium floats, moves slowly on the surface, fizzes gently. Hydrogen gas is produced.