C3 - Quantitive Chemistrt Flashcards
(21 cards)
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What is the formula to calculate the relative formula mass (Mr)?
Mr = sum of the relative atomic masses of all atoms in the formula.
What is the unit for relative formula mass (Mr)?
It has no units.
What is the formula for number of moles?
Moles = Mass (g) / Mr
What is the unit of moles?
mol (mole)
What is the Avogadro constant?
6.02 x 10²³ particles per mole.
What does the term ‘conservation of mass’ mean in a chemical reaction?
No atoms are lost or gained; total mass of reactants equals total mass of products.
Why might mass appear to increase in a reaction?
A gas from the air (e.g., oxygen) reacts and becomes part of the product.
Why might mass appear to decrease in a reaction?
A gas is formed and escapes into the air.
What is the formula to calculate concentration?
Concentration = Mass of solute (g) / Volume of solution (dm³)
How do you convert cm³ to dm³?
Divide by 1000 (e.g., 250 cm³ = 0.25 dm³)
What is the equation for percentage mass of an element in a compound?
Percentage mass = (Ar x number of atoms / Mr of compound) x 100
What is a limiting reactant?
The reactant that is completely used up first, stopping the reaction.
What is meant by ‘excess reactant’?
The reactant that is not fully used up in a reaction.
How do you calculate the mass of a product from a given mass of reactant?
Find moles of reactant → use ratio to find moles of product → convert to mass.
Why are balanced equations important in quantitative chemistry?
They show the ratio of moles of reactants and products.
What is a mole in terms of particles?
One mole contains 6.02 x 10²³ atoms, molecules, or ions.
What is meant by the term ‘yield’?
The amount of product obtained from a reaction.
How do you calculate percentage yield?
Percentage yield = (Actual yield / Theoretical yield) x 100
Why is the percentage yield often less than 100%?
Due to loss during transfer, incomplete reactions, or side reactions.
What does the term ‘empirical formula’ mean?
The simplest whole-number ratio of atoms in a compound.
