This question is about elements in Period 3 and their compounds - AQA - A-Level Chemistry - Question 3 - 2021 - Paper 1
Question 3
This question is about elements in Period 3 and their compounds.
0 3.1 When a piece of sodium is added to 200 cm³ of water in a large beaker a vigorous reaction occ... show full transcript
Worked Solution & Example Answer:This question is about elements in Period 3 and their compounds - AQA - A-Level Chemistry - Question 3 - 2021 - Paper 1
Step 1
When a piece of sodium is added to 200 cm³ of water in a large beaker a vigorous reaction occurs.
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Answer
The equation for the reaction of sodium with water is:
2Na(s)+2H2O(l)→2NaOH(aq)+H2(g)
It is dangerous to react a similar piece of sodium with 10 cm³ of water in a boiling tube because the rapid production of hydrogen gas can lead to an explosive situation if the gas ignites due to the heat generated. The increased surface area of sodium in a smaller volume of water can also lead to a more vigorous reaction.
Step 2
Give an equation for the reaction of phosphorus(V) oxide with water.
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Answer
The equation for the reaction of phosphorus(V) oxide with water is:
P2O5(s)+6H2O(l)→2H3PO4(aq)
The pH of the solution formed is typically acidic, around 1 or 2, due to the formation of phosphoric acid.
Step 3
Explain, in terms of crystal structure and bonding, why silicon(IV) oxide has a higher melting point than phosphorus(V) oxide.
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Silicon(IV) oxide (SiO₂) has a higher melting point than phosphorus(V) oxide (P₂O₅) due to its strong covalent network structure. In SiO₂, each silicon atom is covalently bonded to four oxygen atoms in a tetrahedral arrangement, resulting in a vast 3D network of bonds that require significant energy to break. Conversely, P₂O₅ exists as discrete molecular covalent structures, which have weaker van der Waals forces between them, leading to lower melting points.
Step 4
An element in Period 3 forms an oxide that is insoluble in water.
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Answer
The formula for this oxide is likely Al2O3 (aluminum oxide). This oxide reacts with sulfuric acid as follows:
Al2O3(s)+3H2SO4(aq)→Al2(SO4)3(aq)+3H2O(l)
Step 5
Give the formula of a hydroxide of an element in Period 3 used in medicine.
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A common hydroxide is Mg(OH)2 (magnesium hydroxide), which is often used as an antacid.
Step 6
Identify the element in Period 3, from sodium to chlorine, that has the largest atomic radius.
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Answer
The element in Period 3 with the largest atomic radius is sodium (Na).
