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Questions and Answers
If 1.5 × 10²² molecules of a substance are present, how many moles does this represent?
If 1.5 × 10²² molecules of a substance are present, how many moles does this represent?
0.025 moles
What is the relative molecular mass (Mᵣ) of carbon dioxide (CO₂)?
What is the relative molecular mass (Mᵣ) of carbon dioxide (CO₂)?
44
How many moles are there in 120 grams of calcium (Ca)?
How many moles are there in 120 grams of calcium (Ca)?
3 moles
What is the volume, in liters, occupied by 2 moles of nitrogen gas (N₂) at room temperature?
What is the volume, in liters, occupied by 2 moles of nitrogen gas (N₂) at room temperature?
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Calculate the mass of 0.5 moles of sodium chloride (NaCl).
Calculate the mass of 0.5 moles of sodium chloride (NaCl).
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What is the volume, in cm³, of 0.25 moles of oxygen gas (O₂) at standard temperature and pressure (s.t.p.)?
What is the volume, in cm³, of 0.25 moles of oxygen gas (O₂) at standard temperature and pressure (s.t.p.)?
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Explain Avogadro's Law in your own words.
Explain Avogadro's Law in your own words.
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How many moles are present in 11,200 cm³ of methane (CH₄) at standard temperature and pressure?
How many moles are present in 11,200 cm³ of methane (CH₄) at standard temperature and pressure?
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What is the volume in cm³ of 1 mole of a gas at standard temperature and pressure?
What is the volume in cm³ of 1 mole of a gas at standard temperature and pressure?
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How many moles are there in 336 cm³ of a gas at standard temperature and pressure?
How many moles are there in 336 cm³ of a gas at standard temperature and pressure?
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How many atoms are there in 0.5 moles of aluminum?
How many atoms are there in 0.5 moles of aluminum?
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What is the mass in grams of 2 moles of oxygen?
What is the mass in grams of 2 moles of oxygen?
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How many molecules are there in 0.25 moles of carbon dioxide?
How many molecules are there in 0.25 moles of carbon dioxide?
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What is the molar mass of ethane (C₂H₄)?
What is the molar mass of ethane (C₂H₄)?
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How many moles are there in 3 × 10²² atoms of silver?
How many moles are there in 3 × 10²² atoms of silver?
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What is the mass in grams of 3 × 10²² molecules of methane (CH₄)?
What is the mass in grams of 3 × 10²² molecules of methane (CH₄)?
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What is a mole and how is it used in chemistry?
What is a mole and how is it used in chemistry?
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How many atoms are present in 1 mole of CH₄ molecules?
How many atoms are present in 1 mole of CH₄ molecules?
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Using Avogadro's number, how many molecules are there in 0.15 moles of CH₄?
Using Avogadro's number, how many molecules are there in 0.15 moles of CH₄?
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Calculate the number of atoms in 0.15 moles of CH₄.
Calculate the number of atoms in 0.15 moles of CH₄.
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What is the molar mass of Carbon and Copper, and why is it relevant?
What is the molar mass of Carbon and Copper, and why is it relevant?
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How many moles are represented by 1.5 × 10²² molecules of oxygen?
How many moles are represented by 1.5 × 10²² molecules of oxygen?
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Explain the difference between the terms 'moles' and 'molecular weight'.
Explain the difference between the terms 'moles' and 'molecular weight'.
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In the reaction H₂ + Br₂ → 2HBr, how many moles of HBr are produced from 1 mole of H₂?
In the reaction H₂ + Br₂ → 2HBr, how many moles of HBr are produced from 1 mole of H₂?
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Study Notes
The Mole
- A mole is the unit for the amount of a substance.
- 1 mole of Copper = 63.5 g, which has the same number of atoms as 12 g of Carbon.
- A mole of a substance contains as many particles (atoms, molecules, or ions) as there are atoms of ¹²C in 12g of ¹²C.
- Avogadro's Number (L) is 6 × 10²³ atoms, which is the number of atoms in 12g of ¹²C.
- 1 mole = 6 × 10²³ atoms or molecules or ions.
Moles in Chemical Formulas
- Moles are represented in chemical formulas, e.g., H₂ + Br₂ → 2HBr, where 1 mole of hydrogen reacts with 1 mole of bromine to form 2 moles of hydrogen bromide.
Calculations Involving Moles
- To find the number of molecules in a given number of moles, multiply the number of moles by 6 × 10²³ molecules.
- To convert the number of molecules to atoms, multiply by the number of atoms in each molecule.
- To find the number of moles in a given number of molecules, divide by 6 × 10²³ molecules.
Relative Atomic Mass (Aᵣ) and Relative Molecular Mass (Mᵣ)
- Aᵣ is the symbol for relative atomic mass and is used in association with atoms.
- It can be read from the periodic table, e.g., Mg has an Aᵣ of 24.31, which is rounded down to 24 for calculations.
- Mᵣ is the relative molecular mass and is associated with molecules, calculated by adding up the Aᵣ ’s of the individual atoms.
Converting Moles to Grams
- The formula to convert moles to grams is: moles × Mᵣ = Mass (in grams).
- This formula also works for Aᵣ.
Molar Volume of Gases
- Avogadro's Law states: Equal volumes of gases, under the same conditions of temperature and pressure, contain equal numbers of molecules.
- At standard temperature and pressure (s.t.p.), 1 mole = 22.4L = 22,400cm³.
- At room temperature and pressure, 1 mole = 24L = 24,000cm³.
Calculations Involving Moles, Volume, and Mass
- To find the number of moles in a given volume of gas, use the formula: moles = volume ÷ 22.4L (or 24L for room temperature and pressure).
- To find the mass in grams, use the formula: moles × Mᵣ = Mass (in grams).
- To find the number of atoms or molecules, use the formulas: moles × 6 × 10²³ atoms (or molecules) or mass ÷ Mᵣ.
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Description
Learn about the concept of moles, a unit of measurement for the amount of a substance, and how it applies to atoms and molecules of different elements like copper and carbon.
