C4 Quantative Chemistry Flashcards
What is a mole?
The relative atomic mass of a substance in grams.
What is the formula for working out mass?
mass, m = no. of moles x Mr
What is Avogadro’s constant?
The number of atoms/molecules in 1 mole of a substance.
6.02 x 10^23
What is a limiting reactant?
The reactant that gets used up first. It is NOT in excess.
What is yield?
The mass of the desired product that is made in a chemical reaction.
What is percentage yield?
How much product is made compared to the maximum theoretical yield.
What is the formula for percentage yield?
percentage yield = (actual mass/theoretical mass) x 100
What affects percentage yield?
- Reversible reactions
- Unwanted products from alternative reactions
- Lost in apparatus
- Not pure reactants
- Lost in separation
What is atom economy?
Measure of the amount of starting material ends up as useful products
What is the formula for percentage atom economy?
percentage atom economy =
formula mass of desired product/sum of masses of reactants x 100
including big numbers
Why is atom economy important?
- Conserves resources
- Minimises pollution
What is concentration?
The amount of a substance dissolved in 1 dm^3 of solution
or
the mass of a solute in a given volume
What is the concentration formula?
c (g/dm^3) = solute, m (g)/volume, v(dm^3)
or
c (mol/dm^3) = no. of moles / volume
How can the concentration of an aqueous solution be increased?
- Add more solute in v of solution
- Evaporate water to have same m of solute and less solution
What is a titration?
A method to measure the volumes of two solutions that react together
What is the end point?
When the acid and alkali have completely reacted with each other.
What does a certain volume of gas always contain?
The same number of gas molecules under the same conditions
What is the molar gas volume?
the v of 1 mole of any gas is 24dm^3 at r.t.p
what is the formula for molar gas volume?
n = v (dm^3)/24dm^3
How many cm^3 are in 1dm^3?
1000 cm^3 = 1 dm^3
what is the equipment needed for a titration?
pipette pipette filler beaker conical flask burette funnel indicator
why use a conical flask in titrations?
it reduces risk of splashing
why is the conical flask placed on a white tile in titrations?
to see a colour change more easily
how do you read the reading on the burette?
make sure the eye is level with the BOTTOM of the meniscus
how many times to you repeat the titration?
until you get concordant results within 0.1 cm^3
how do you convert a concentration in mol/dm^3 into g/dm^3?
multiply by the relative formula mass of the substance
which non-metal ions are positive?
H+ (hydrogen ion)
NH4+ (ammonium ion)
why is the overall charge of an ion zero?
the charges of the ions have to be cancelled out
why can the little numbers of a chemical formula not be altered?
it will produce a different molecule
what makes a balanced equation?
the same number of atoms on the left and right hand side
what is relative formula mass (Mr)?
the sum of the relative atomic masses of the atoms of the number shown in the formula
what are two key facts about relative formula mass?
it has no units
it never involves big numbers (the numbers in front of formulas e.g. 2CH4, you would not use the 2 when working out the Mr)
what is the percentage by mass?
the percentage of the relative formula mass that is due to one of the elements in a compound
what is the formula for percentage by mass of an element?
% by mass = (total Ar of the atoms in element / Mr) x 100
what is the method for balancing an equation using masses and moles?
using the masses given, work out the number of moles using n=m/Mr
put these numbers in front of the chemical formulas
divide all the big numbers by the smallest number in front of a chemical formula
boom - you done
what is the method to calculate the mass of a chemical in a reaction when you are given the mass of one of the other chemicals?
calculate the number of moles of the chemical with the known mass
see the ratio of the amount of moles of the two chemicals (look at the big numbers)
work out mass (use m = n x Mr(or Ar))
what is a solute?
a chemical dissolved in a solvent
what does 100% yield mean?
that every single atom of the reactants reacts to produce the maximum amount of product possible
why can you not have a greater yield/atom economy that 100%?
it would mean you created atoms
what do chemists try to do with unwanted side products of reactions?
find a use for them so it does not waste money
what does concentration mean? (in terms of moles)
the number of moles of a solute in a given volume of solution
what are the values of room temperature and pressure?
temp - 20 degrees c
pressure - 1 atmosphere
