C3 - Quantitative Chemistry Flashcards
Moles
What should you always show when answering questions about moles?
Your working!!
Moles
What is relative formula mass?
The relative mass of a chemical compound (sum of the atomic masses within the compound)
Moles
True or false: Mr means RFM
True
Moles
What does Ar mean?
The atomic mass of a particle
Moles
How do you work out the percentage of an element in a compound?
Mass of element (Ar) / Mr (RFM) of compound x 100
Moles
How do you work out the RFM of a substance?
Sum of the Ar of each element in compound
Moles
What are moles a measure of?
How many particles there are in a substance
Moles
How many particles does 1 mole of a substance contain?
6.02 x 10 to the power 23
Moles
What is avogadro’s constant?
6.02 x 10 to the power 23 (how many particles there are in 1 mole of a substance)
Moles
The mass of 6.02 x 10 to the power 23 particles of a substance is equal to the _____ of that substance in grams
RFM
Moles
Derive the equation for moles in any way you want
Mass = moles x RFM because moles is how many lots of RFM there are
Moles
What is the symbol for moles and the symbol for mass?
m - mass
n - moles
Moles
True or false: moles are measured in grams
False - they are measured in moles
Moles
Have you done practice questions using moles?
Yes
Moles
What is the law of the conservation of mass?
No atoms are created or destroyed in a chemical reaction, they only join together in different ways
Moles
True or false: the law of the conservation of mass is useful to remember when doing worksheets about moles
True
Moles
What is a molar reacting ratio?
The number of moles of each particle there are in a balanced equation
Moles
What is relative atomic mass?
The average mass of an element (total mass of all isotopes of an element/number of atoms of that element)
Total mass of all isotopes = abundance of isotope x mass of isotope (obviously)
Limiting reagents
What is a limiting reagent?
The reactant that is completely used up first and therefore limits the amount of product formed
Limiting reagents
How do you work out which particle is the limiting reagent in a chemical reaction?
Compare the actual molar ratio to the theoretical molar ratio
Moles
How do you answer a question asking you to find the missing mass of a substance in a chemical reaction
- Check if equation is balanced - Balance equation if not balanced
- Work out how many moles of each substance has been used in the experiment
- Use the molar ratio to find out how many moles of the missing substance should be used
- Convert moles back to mass
(This should all be common sense and effortless in an exam)
Empirical formula + yield + atom economy
What is empirical formula?
The simplest molar ratio of atoms in a compound
Empirical formula + yield + atom economy
What is the empirical formula of C2H8?
CH4 (methane)
Empirical formula + yield + atom economy
How do you work out the empirical formula from given masses of elements in a compound?
Work out the molar quantity of both elements and then simplify the ratio of moles between them
