C4 Quantative Chemistry
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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