Quantitive Chemistry

What is relative formula mass (Mᵣ) ?

Relative sum of the relative atomic masses of the atoms in a molecule

What is the formula for relative formula mass (Mᵣ)?

Mᵣ = Σ Aᵣ

What is relative atomic weight (Aᵣ)

The mean weight of all the isotopes

What is the formula for relative atomic weight (Aᵣ)?

Σ (Probability) * (Atomic weight)

What is the law of conservation of mass?

★ The law of conservation of mass states that no atoms are lost or made during a chemical reaction ➜ The mass of the products equals the mass of the reactants.

What is percentage element?

Percentage element is the percentage of the element in a compound

What s the formula for percentage element?

Percentage element = (Mᵣ of element) / (Mᵣ of molecule)

How much is one mole?

One mole is 6.02 x 10²³

What is the formula for moles?

moles = mass / Aᵣ

Why might it appear as if mass has been created/destroyed during a chemical reaction?

If it appears as if mass has been created/destroyed in a chemical reaction: ★ One of the products/reactants is likely a gas

What are chemical amounts measured in?

Chemical amounts are measured in moles

What is the symbol for a mole/

The symbol for a mole is mol

How much does 1 mole of a substance weigh?

One mole of a substance weighs its a relative formula mass

If you have the same amount of moles of two substances, what does that mean?

If you have the same amount of moles of two substances, it means that there is the same number of particles

How many particles are in a mole?

There are Avragado's number of particles in a mole of a substance

What is Avragado's number?

Avragado's number = 6.02 x 10²³

Is the number of atoms in 1 mole of C the same number of molecules in CO₂?

Yes, the number of atoms in 1 mole of C the same number of molecules in CO₂ are equal

What is a limiting reactant?

The limiting reactant is the reactant that runs out first

Why do chemists use limiting reactants?

Chemists use limiting reactants as it is not practical to measure perfectly the amount of substances

Does it matter which reactant is the limiting reactant?

★ Yes, it does matter which reactant is the limiting reactant ★ For example, you wouldn't want acid evaporating into the air

How many dm is a meter?

10dm is one meter

What two things is 1000cm³ equal to?

1000cm³ = 1dm³ = 1L

What is the unit for concentration?

g/dm³ or mol/dm³

How do we convert between g/dm³ and mol/dm³?

★ g/dm³ = mol/dm³ x Mᵣ ★ This comes from mass = mol x Mᵣ

What is a solute?

The solute is the substance that is dissolved

What is a solvent?

The solvent is the substance in which the solute (the substance that is dissolved) dissolves

What is a common example of a solvent?

A common example of a solvent is water

What is concentration? [definition, not the formula]

Concentration tells use the mass of a solute in a given volume of solution

What is the formula for concentration?

concentration = mass/volume ★ concentration - (g/dm³ or mol/dm³) ★ mass - (g or mol*) ★ volume - (dm³)

• mol is not a unit of mass

What happens to the concentration if the mass of the solute increase (and the volume stays the same)?

★ If we increase the mass of solute ★ (and the volume stays the same) ➜ The concentration increases

What happens to the concentration if the volume increases (and the mass of solute stays the same)?

★ If the volume of solution increases ★ (and the mass of the solute stays the same) ➜ The concentration decreases

True or False: if no atoms are gained or lost, the amount of substance we get is as expected

False, even though no atoms are gained or lost in a chemical reaction, it is not always possible to obtain the calculated amount of a product

What is yield?

The amount of a product obtained is known as the yield

What is % yield?

% yield is yield when compared with the maximum theoretical amount as a percentage

Why is % yield not always 100%?

★ The reaction may not go to completion because it is reversible ★ Some of the product may be lost when it is separated from the reaction mixture ★ Some of the reactants may react in ways different to the expected reaction

What is the formula for % yield?

% yield = actual yield/theoretical yield x 100

What is atom economy? [Definition, not the formula]

Atom economy is a measure of the amount of starting materials that end up as useful products

What does a high atom economy mean?

A high atom economy means that very little atoms were wasted and vice versa

What are 2 advantages of a high atom economy?

Two advantages of a high atom economy: ★ Save money by minimising unwanted products ★ Increase sustainability (due to less waste)

What is the formula for atom economy?

The formula for atom economy is: % atom economy = (mass of desired product / total mass of reactants/products) x 100

How do chemists deal with unwanted products in reactions?

If there are unwanted products, chemists: ★ Try to find uses for these side-products e.g. to be used in other chemical reactions ✔︎ This means money isn't being wasted

When do gases occupy the same volume?

Equal amounts in moles of gases occupy the same volume under the same conditions of temperature and pressure.

What is room temeperature?

Room temperature is 20°C

What is normal pressure?

Normal pressure is one atmosphere pressure

How can we calculate the volume gas takes up?

The volume of one mole of any gas at room temperature and pressure (20°C and 1 atmosphere pressure) is 2