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Questions and Answers
What is the empirical formula of copper oxide determined from the ratio of copper to oxygen?
What is the empirical formula of copper oxide determined from the ratio of copper to oxygen?
If a student burns 9 g of magnesium, what mass of magnesium oxide will be formed?
If a student burns 9 g of magnesium, what mass of magnesium oxide will be formed?
What volume of carbon dioxide is produced from burning 30 g of carbon in excess oxygen?
What volume of carbon dioxide is produced from burning 30 g of carbon in excess oxygen?
In the reaction between magnesium and oxygen, what is the total mass of magnesium oxide produced from 48 g of magnesium?
In the reaction between magnesium and oxygen, what is the total mass of magnesium oxide produced from 48 g of magnesium?
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What is the ratio of moles of magnesium to moles of oxygen in the formation of magnesium oxide?
What is the ratio of moles of magnesium to moles of oxygen in the formation of magnesium oxide?
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What is the relative molecular mass of calcium oxide, CaO?
What is the relative molecular mass of calcium oxide, CaO?
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What is the empirical formula of glucose?
What is the empirical formula of glucose?
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How do you find the molecular formula from the empirical formula?
How do you find the molecular formula from the empirical formula?
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Given 5.4 g of copper oxide yields 4.8 g of copper, what is the mass of oxygen in copper oxide?
Given 5.4 g of copper oxide yields 4.8 g of copper, what is the mass of oxygen in copper oxide?
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What percentage of calcium is present in calcium oxide, CaO?
What percentage of calcium is present in calcium oxide, CaO?
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What is the percentage composition of oxygen in calcium oxide, CaO?
What is the percentage composition of oxygen in calcium oxide, CaO?
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What would the molecular formula of glucose be if it has a relative molecular mass of 180?
What would the molecular formula of glucose be if it has a relative molecular mass of 180?
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If n represents the number used to get the molecular formula from the empirical formula, what is true about the value of n?
If n represents the number used to get the molecular formula from the empirical formula, what is true about the value of n?
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Study Notes
Stoichiometry
- Stoichiometry is the branch of chemistry that relates the amounts of reactants and products in a chemical reaction.
- It is essential for determining the quantities of reactants needed to produce a specific amount of product.
Calculating Percentage Composition
- To determine the percentage composition of an element in a compound:
- Calculate the relative molecular mass of the compound.
- Divide the atomic mass of the element by the relative molecular mass of the compound.
- Multiply the result by 100 to get the percentage.
Example (CaO)
- Relative molecular mass of CaO = 56
- Percentage of Ca = (40/56) * 100 = 71.43%
- Percentage of O = (16/56) * 100 = 28.57%
Empirical Formula Calculation
- Molecular formula: Shows the number and types of atoms in a molecule.
- Empirical formula: Shows the simplest whole number ratio of atoms in a compound.
- Molecular formula = empirical formula * n (where 'n' is a whole number)
Example (Glucose)
- Empirical formula of glucose = CH₂O
- Relative molecular mass of glucose = 180
- 180 = (12 + 2 + 16) * n
- n = 6
- Molecular formula of glucose = C₆H₁₂O₆
Calculating Empirical Formula from Masses
- In an experiment involving a reaction between an oxide of copper and hydrogen, the mass of copper oxide can be used to determine the empirical formula.
Example (Copper Oxide):
- If 5.4 g of copper oxide produces 4.8 g of copper, the mass of oxygen is 0.6 g.
- Calculate the moles of each element (copper and oxygen).
- Determine the ratio of copper to oxygen atoms to find the empirical formula (Cu₂O in this example).
Calculating Masses of Reactants/Products using Balanced Chemical Equation
- Using balanced chemical equations(example Mg + O₂ → MgO).
- To calculate the mass of magnesium oxide formed when 9 g of magnesium is burned in excess oxygen, use the molar ratio approach.
- Example: Given the mass of a reactant, use stoichiometry to find the mass of the product.
Gas Volume Calculations
- To determine the volume of CO₂ formed when 30 g of carbon are burned in excess oxygen, using the balanced chemical equation and molar volume information
- Determine Moles of carbon
- Calculate CO₂ volumes at standard temperature and pressure
- Example: 30 g of carbon produced 56 L of CO₂.
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