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Magnesium carbonate has the formula MgCO₃ - Edexcel - GCSE Chemistry Combined Science - Question 2 - 2022 - Paper 1
Question 2
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 Combined Science - Question 2 - 2022 - Paper 1
Step 1
What is the electronic configuration of the Mg²⁺ ion?
Answer
The atomic number of magnesium is 12, which means it has 12 electrons in its neutral state. The electronic configuration for magnesium is written as 1s² 2s² 2p⁶ 3s². When magnesium loses two electrons to form the Mg²⁺ ion, the two outermost electrons (3s²) are lost. Therefore, the electronic configuration of the Mg²⁺ ion becomes 1s² 2s² 2p⁶, which can be simplified to a notation of '2.8' (indicating the distribution of electrons in the first and second shells). Thus, the correct answer is B: 2.8.
Step 2
Explain why solid magnesium carbonate cannot conduct electricity but solid magnesium can.
Answer
Solid magnesium can conduct electricity because it contains free-moving electrons. In its solid state, magnesium is made up of metal atoms that share their valence electrons, forming a sea of electrons that allows for the flow of electric current.
On the other hand, solid magnesium carbonate does not conduct electricity due to the nature of its ionic structure. While it contains Mg²⁺ and CO₃²⁻ ions, these ions are held in a rigid crystal lattice structure. In this solid state, the ions cannot move freely, thus preventing the conduction of electricity. Only when dissolved in water or melted can the ions move and carry an electric current.
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.
The molar mass is calculated as follows:
- Magnesium (Mg): 24.0 g/mol
- Carbon (C): 12.0 g/mol
- Oxygen (O): 16.0 g/mol × 3 = 48.0 g/mol
Thus, the total molar mass of MgCO₃ is:
Now, to find the percentage by mass of magnesium: ext{Percentage of Mg} = rac{ ext{mass of Mg}}{ ext{molar mass of MgCO₃}} imes 100 = rac{24.0}{84.0} imes 100 \\ = 28.57 ext{%}
Therefore, the percentage by mass of magnesium in magnesium carbonate is approximately 28.57%.