Lithium, sodium and potassium are reactive metals in group 1 of the periodic table - Edexcel - GCSE Chemistry Combined Science - Question 3 - 2018 - Paper 1
Question 3
Lithium, sodium and potassium are reactive metals in group 1 of the periodic table.
(a) Sodium metal tarnishes in air to form a layer of sodium oxide on its surface... show full transcript
Worked Solution & Example Answer:Lithium, sodium and potassium are reactive metals in group 1 of the periodic table - Edexcel - GCSE Chemistry Combined Science - Question 3 - 2018 - Paper 1
Step 1
Calculate the moles of sodium and oxygen
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Answer
To find the number of moles, use the formula:
n=molar massmass
For sodium (mass = 0.92 g, molar mass = 23 g/mol):
nNa=230.92=0.04 moles
For oxygen (mass = 0.32 g, molar mass = 16 g/mol):
nO=160.32=0.02 moles
Step 2
Determine the molar ratio
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Now, find the ratio of moles of sodium to moles of oxygen:
Ratio=nOnNa=0.020.04=2:1
This indicates that for every 2 moles of sodium, there is 1 mole of oxygen.
Step 3
Write the empirical formula
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Answer
From the ratio determined, the empirical formula of sodium oxide is given by:
Empirical Formula=Na2O.
Step 4
Explain the reaction of sodium with water
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Answer
When sodium reacts with water, it forms sodium hydroxide (NaOH) and hydrogen gas (H2). The reaction can be represented as:
2Na+2H2O→2NaOH+H2.
Step 5
Discuss the increase in reactivity from lithium to potassium
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The reactivity of alkali metals increases from lithium to sodium to potassium due to their electronic configurations.
Lithium (Li): 1s² 2s¹
Sodium (Na): 1s² 2s² 2p⁶ 3s¹
Potassium (K): 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹
As we move down the group, the outermost electron is further from the nucleus, making it easier to remove due to the increased shielding effect from inner electrons. This results in higher reactivity.
