Quantitative Chemistry Flashcards
Paper 1 - C3
What is the law of conservation of mass?
No atoms are lost or made during a chemical reaction so the mass of products equals the mass of the reactants.
How can the overall charge of zero form in an ionic compound?
The charges on the ions have to cancel out to leave an overall charge of zero.
What is the relative atomic mass (Ar)?
Its the average mass of the isotopes of that element weighted to take into account the abundance of each isotope.
What is the relative formula mass (Mr)?
Its the sum of the Relative Atomic Masses of the atoms in the numbers shown in the formula and has no units and never involves big numbers.
What is the Formula for Percentage by mass of an element?
Total RAM of the atoms of that element
——————————————————- x 100
Relative formula mass (Mr) of compound
How do we calculate the number of moles in an element?
Mass (g) / RAM (Ar)
How do we calculate the number of moles in a compound?
Mass (g)
———— = Number of moles in a compound
RFM (Mr)
What is the number for Avogadro’s constant?
6.02 x 10²³
What is it meant by a limiting reactant?
A reactant that is fully used up
What is it meant by the excess reactant?
The reactant that is not used up
What is it meant by concentration?
Tells us the mass of a solute in a given volume of solution or the number of moles of a solute in a given volume of solution.
What is it meant by a solute?
A chemical that is dissolved in a solvent.
What is concentration measured in?
g / dm³ and mol / dm³
How do we calculate concentration?
Mass (g)
——————— = Concentration (g / dm³)
Volume (dm³)
How can we increase the concentration in a solution?
If we increase the mass of the solute and keep the volume the same, then we increase the concentration.
How can we decrease the concentration in a solution?
If we increase the volume of the solution and keep the mass of the solute the same, then we decrease the concentration.
(Triple only) Why is it not always possible to achieve 100% yield in a chemical reaction?
-Some of the product may be lost when it is separated from the reaction mixture.
-Some of the reactants may react in different ways to the expected reaction so we do not get the product we expect.
-Reversible reactions may not go to completion.
(Triple only) What is the equation for percentage yield?
Mass of product actually made
——————————————————– x 100 = % Yield
Maximum theoretical mass of product
(Triple only) Why can we not achieve greater than 100% yield?
This would mean that we had created atoms which due to the law of conservation of mass we cannot create atoms.
(Triple only) What is Atom economy?
Its a measure of the amount of starting materials that end up as useful products.
(Triple only) What are the advantages of Atom Economy?
-By minimising the production of unwanted products, we save money.
-We also increase sustainability by not wasting resources.
(Triple only) What is the equation for atom economy?
RFM of desired products
—————————————— x 100 = Atom Economy
Sum of RFM of all reactants
(Triple only) How do chemists use unwanted side-products to save money in atom economy?
They try to find a use for the side-products for example in other reactions.
(Triple only) How much does a gas occupie a volume?
24 dm³
