MOLEs in Chemistry

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Questions and Answers

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)?

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?

48 liters Signup and view all the answers

Calculate the mass of 0.5 moles of sodium chloride (NaCl).

29.25 grams Signup and view all the answers

What is the volume, in cm³, of 0.25 moles of oxygen gas (O₂) at standard temperature and pressure (s.t.p.)?

5600 cm³ Signup and view all the answers

Explain Avogadro's Law in your own words.

Avogadro's Law states that equal volumes of different gases, under the same conditions of temperature and pressure, contain the same number of molecules. Signup and view all the answers

How many moles are present in 11,200 cm³ of methane (CH₄) at standard temperature and pressure?

At s.t.p., one mole of any gas occupies 22,400 cm³. Since we have 11,200 cm³, which is half of 22,400 cm³, this represents 0.5 moles of methane. Signup and view all the answers

What is the volume in cm³ of 1 mole of a gas at standard temperature and pressure?

22400 Signup and view all the answers

How many moles are there in 336 cm³ of a gas at standard temperature and pressure?

0.015 Signup and view all the answers

How many atoms are there in 0.5 moles of aluminum?

3 × 10²³ Signup and view all the answers

What is the mass in grams of 2 moles of oxygen?

64 Signup and view all the answers

How many molecules are there in 0.25 moles of carbon dioxide?

1.5 × 10²³ Signup and view all the answers

What is the molar mass of ethane (C₂H₄)?

30 Signup and view all the answers

How many moles are there in 3 × 10²² atoms of silver?

0.05 Signup and view all the answers

What is the mass in grams of 3 × 10²² molecules of methane (CH₄)?

0.45 Signup and view all the answers

What is a mole and how is it used in chemistry?

A mole is the unit for the amount of a substance, defined as containing $6 × 10^{23}$ particles (atoms, molecules, or ions). It allows chemists to compare quantities of different substances based on the number of particles they contain. Signup and view all the answers

How many atoms are present in 1 mole of CH₄ molecules?

In 1 mole of CH₄, there are 5 atoms per molecule, so there are $5 × 6 × 10^{23}$ atoms. Signup and view all the answers

Using Avogadro's number, how many molecules are there in 0.15 moles of CH₄?

There are $9 × 10^{22}$ molecules in 0.15 moles of CH₄. Signup and view all the answers

Calculate the number of atoms in 0.15 moles of CH₄.

There are $4.5 × 10^{23}$ atoms in 0.15 moles of CH₄. Signup and view all the answers

What is the molar mass of Carbon and Copper, and why is it relevant?

The molar mass of carbon is 12 g/mol and copper is 63.5 g/mol, indicating the mass of one mole of each element. It is relevant for converting between moles and grams in chemical calculations. Signup and view all the answers

How many moles are represented by 1.5 × 10²² molecules of oxygen?

1.5 × 10²² molecules of oxygen correspond to 0.025 moles. Signup and view all the answers

Explain the difference between the terms 'moles' and 'molecular weight'.

'Moles' refer to the quantity of substance, whereas 'molecular weight' refers to the mass of one mole of that substance in grams. Moles help quantify substances, while molecular weight aids in conversions from mass to moles. Signup and view all the answers

In the reaction H₂ + Br₂ → 2HBr, how many moles of HBr are produced from 1 mole of H₂?

1 mole of H₂ produces 2 moles of HBr. Signup and view all the answers

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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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