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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 (Máµ£) of carbon dioxide (COâ‚‚)?
What is the relative molecular mass (Máµ£) of carbon dioxide (COâ‚‚)?
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 (Nâ‚‚) at room temperature?
What is the volume, in liters, occupied by 2 moles of nitrogen gas (Nâ‚‚) at room temperature?
Calculate the mass of 0.5 moles of sodium chloride (NaCl).
Calculate the mass of 0.5 moles of sodium chloride (NaCl).
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.)?
Explain Avogadro's Law in your own words.
Explain Avogadro's Law in your own words.
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?
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?
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?
How many atoms are there in 0.5 moles of aluminum?
How many atoms are there in 0.5 moles of aluminum?
What is the mass in grams of 2 moles of oxygen?
What is the mass in grams of 2 moles of oxygen?
How many molecules are there in 0.25 moles of carbon dioxide?
How many molecules are there in 0.25 moles of carbon dioxide?
What is the molar mass of ethane (Câ‚‚Hâ‚„)?
What is the molar mass of ethane (Câ‚‚Hâ‚„)?
How many moles are there in 3 × 10²² atoms of silver?
How many moles are there in 3 × 10²² atoms of silver?
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)?
What is a mole and how is it used in chemistry?
What is a mole and how is it used in chemistry?
How many atoms are present in 1 mole of CHâ‚„ molecules?
How many atoms are present in 1 mole of CHâ‚„ molecules?
Using Avogadro's number, how many molecules are there in 0.15 moles of CHâ‚„?
Using Avogadro's number, how many molecules are there in 0.15 moles of CHâ‚„?
Calculate the number of atoms in 0.15 moles of CHâ‚„.
Calculate the number of atoms in 0.15 moles of CHâ‚„.
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?
How many moles are represented by 1.5 × 10²² molecules of oxygen?
How many moles are represented by 1.5 × 10²² molecules of oxygen?
Explain the difference between the terms 'moles' and 'molecular weight'.
Explain the difference between the terms 'moles' and 'molecular weight'.
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 (Aáµ£) and Relative Molecular Mass (Máµ£)
- Aáµ£ 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 Aáµ£ 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 Aáµ£.
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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