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Calculate the relative formula mass of calcium carbonate, CaCO₃ - Edexcel - GCSE Chemistry - Question 4 - 2016 - Paper 1
Question 4
Calculate the relative formula mass of calcium carbonate, CaCO₃. (relative atomic masses: C = 12, O = 16, Ca = 40) Magnesium reacts with sulfur to form magnesium su... show full transcript
Worked Solution & Example Answer:Calculate the relative formula mass of calcium carbonate, CaCO₃ - Edexcel - GCSE Chemistry - Question 4 - 2016 - Paper 1
Step 1
Calculate the relative formula mass of calcium carbonate, CaCO₃.
Answer
To calculate the relative formula mass of calcium carbonate (CaCO₃), we sum the relative atomic masses of each element in the compound:
- Calcium (Ca): 40 g/mol
- Carbon (C): 12 g/mol
- Oxygen (O): 16 g/mol, and there are 3 oxygen atoms. Therefore:
Thus, the relative formula mass of CaCO₃ is 100 g/mol.
Step 2
The ratio of magnesium atoms to sulfur atoms in magnesium sulfide is
Answer
In magnesium sulfide (MgS), the molar mass of magnesium (Mg) is 24 g/mol and sulfur (S) is 32 g/mol. From the combination:
- 24 g of magnesium contains 1 mole of Mg.
- 32 g of sulfur contains 1 mole of S.
Therefore, the ratio of magnesium atoms to sulfur atoms is:
Step 3
Step 4
What is the molecular formula of the hydrocarbon with the empirical formula CH₂?
Answer
The molecular formula can be determined by examining the given empirical formula (CH₂). Hydrocarbons with CH₂ as the empirical formula could have molecular formulas such as C₂H₄ (ethene) or C₃H₆ (propene). Therefore, the molecular formula options are:
- A (C₄H₈)
- B (C₂H₄)
- C (C₃H₆)
- D (C₄H₈)
The correct answer is C₂H₄, which can be marked with a cross (🗹).
Step 5
Calculate the percentage yield of zinc oxide.
Answer
The percentage yield is calculated using the formula:
ext{Percentage Yield} = rac{ ext{Actual Yield}}{ ext{Theoretical Yield}} imes 100
Given:
- Actual Yield = 7.2 g
- Theoretical Yield = 9.0 g
Thus: ext{Percentage Yield} = rac{7.2}{9.0} imes 100 = 80 ext{ %}
Step 6
Explain why the actual yield of a product in an experiment is usually lower than the theoretical yield.
Answer
The actual yield of a product is often lower than the theoretical yield due to several factors:
- Incomplete Reactions: Not all reactants may have reacted, leading to less product formation.
- Side Reactions: Other unwanted chemical reactions may occur, producing by-products instead of the desired product.
- Loss of Product: Some product may be lost during the transfer or purification processes, which lowers the measured yield.
Step 7
Calculate the percentage by mass of zinc in zinc oxide, ZnO.
Answer
To find the percentage by mass of zinc in zinc oxide (ZnO), we first need to determine the molar mass of ZnO:
- Zinc (Zn): 65 g/mol
- Oxygen (O): 16 g/mol
Total molar mass of ZnO:
The percentage by mass of zinc is given by: ext{Percentage by Mass of Zn} = rac{ ext{Molar Mass of Zn}}{ ext{Molar Mass of ZnO}} imes 100 = rac{65}{81} imes 100 \\approx 80.25 ext{ %}