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Magnesium carbonate has the formula MgCO₃ - Edexcel - GCSE Chemistry - Question 9 - 2022 - Paper 1
Question 9
Magnesium carbonate has the formula MgCO₃. (a) Magnesium carbonate contains Mg²⁺ and CO₃²⁻ ions. (i) The atomic number of magnesium is 12. What is the electronic ... show full transcript
Worked Solution & Example Answer:Magnesium carbonate has the formula MgCO₃ - Edexcel - GCSE Chemistry - Question 9 - 2022 - Paper 1
Step 1
What is the electronic configuration of the Mg²⁺ ion?
Answer
The electronic configuration of the Mg²⁺ ion can be determined by first noting that the atomic number of magnesium is 12. This means that in its neutral state, magnesium has 12 electrons arranged as follows: 2 in the first shell and 8 in the second shell (2.8). When magnesium loses two electrons to form the Mg²⁺ ion, it will have 10 electrons remaining. Therefore, the configuration for the Mg²⁺ ion is: 2 in the first shell and 8 in the second shell, which corresponds to the answer option B 2.8.
Step 2
Explain why solid magnesium carbonate cannot conduct electricity but solid magnesium can.
Answer
Solid magnesium carbonate (MgCO₃) cannot conduct electricity because its ions (Mg²⁺ and CO₃²⁻) are held in fixed positions within a rigid ionic lattice structure. This means that the ions are not free to move and thus cannot carry an electric current. In contrast, solid magnesium metal consists of positively charged metal ions surrounded by a 'sea' of delocalized electrons. These delocalized electrons are free to move throughout the metal lattice, allowing solid magnesium to conduct electricity effectively.
Step 3
Calculate the percentage by mass of magnesium in magnesium carbonate, MgCO₃.
Answer
To calculate the percentage by mass of magnesium in magnesium carbonate (MgCO₃), we first need to determine the molar mass of MgCO₃:
Molar mass of Mg = 24.0 g/mol Molar mass of C = 12.0 g/mol Molar mass of O = 16.0 g/mol (there are 3 oxygen atoms)
Total molar mass of MgCO₃ = 24.0 + 12.0 + (3 × 16.0) = 24.0 + 12.0 + 48.0 = 84.0 g/mol
Now, to find the percentage by mass of magnesium in MgCO₃, we use the formula:
ext{Percentage by mass of magnesium} = rac{ ext{Mass of magnesium}}{ ext{Mass of MgCO₃}} imes 100
Substituting in the values gives us:
ext{Percentage by mass of magnesium} = rac{24.0}{84.0} imes 100 ≈ 28.57\\%