Year 11 Term 2 Flashcards
Conservation of mass
Mass is neither created nor destroyed during chemical processes, it’s conserved
Relative formula mass
The sum of the relative atomic masses of each atom in a compound
Reasons for uncertainty
Product or reactant is impure
The sample is wet
Gaseous products have escaped easily
What are measuring cylinders used for
To measure the volume of a liquid
How do you avoid a measurement error using a measurement cylinder
You have to measure to the bottom of the meniscus (the curve of the liquid being measured), also judge at eye level preventing parallax error
How to avoid a zero error when using a measuring cylinder
You have to set the syringe back at 0 before taking new reading otherwise you’ll get zero error where value appears larger than it would be
Top pan balance
Balance should always be tared (set at 0) before weighing to prevent zero error
Possible disruptions to measurement
People leaning on the table
Breeze blowing onto table
These will disrupt the balance
Possible contamination
Clear balance with soft paint brush before you measure anything so there’s no powder left on the balance
Uncertainty=
mean +/- the range of measurements
Why are moles useful
Allows chemists to calculate the required masses of reactants and it allows them to predict the mass of products for chemical reactions
What is a mole
The unit for the amount of substance. 1 mol of atoms, ions or molecules is around 6.03 x 10^23 which is the same number of carbon atoms in 12g of carbon
What is Agrovado’s number
6.03 x 10^23
What did Agrovado discover
If you have 6.03 x 10^23 atoms (1 mol) of an element, it will weigh its relative atomic mass (Ar) in grams
1 mol of any compound is equal to
Its relative formula mass
Mass =
Mr x mol
What can Avrogado’s constant be used to calculate
The number of atoms/ molecules/ ions present in a given amount of a substance
What are the coefficients in equations
The number in front of the formula, it’s proportional to the number of moles
Why would knowing the molar ration be useful for the chemist who’s trying to conduct this reaction
Because mass= Mr x mol
so we can calc the mass of product that’ll be produced of the mass of reactant needed
Using moles to balance equations
Divide mass by Mr to calculate moles on each
Divide each number of moles by the smallest to determine the ration
The molar ration is equivalent to the coefficients in the equation
What’s the limiting reactant
If the number of moles of a reactant is less than the stoichiometric ratio tells us then it’s the limiting reactant
This will limit how far the reaction goes
Why may reactions not always be perfect
Reaction may not go to completion as it’s reversible
Some of the product may be lost when separated from reaction mixture
Some of the reactants may react in ways different to the expected reaction
What is the percentage yield
The amount of product obtained is the yield. When compared with the maximum theoretical amount as a % it’s called the percentage yield
Percentage yield=
Actual yield/ theoretical yield x100
What’s the theoretical maximum
The amount you calculate using mass= Mr x moles equation. It’s the amount you’d get if the reaction went fully to completion and no product was lost
What’s atom economy
A measure of the amount of starting materials that end up as useful products
Why is it important to use reactions with high atom economy
For sustainable and economic reasons as most chemical reactions produce 2 or more products but only 1 is useful so there’s waste from the process
Atom economy=
Mr of desired product/ sum of Mr of all reactants x100
What factors are there to consider when choosing an appropriate method besides atom economy
% yield
Reaction rate
Reversibility
Energy cost
How do you convert from cm cubed to dm cubed
Divide by 1000
1 dm^3 is equal to
1 litre
Concentration =
Quantity of solute/volume
Factors affecting concentration
If you double volume, you half the concentration
If you halve the volume, you double the concentration
How do you convert from mol/dm^3 to g/dm^3
Multiply by Mr
How do you convert from g/dm^3 to mol/dm^3
Divide by Mr
Number of moles =
Concentration (mol/dm^3) x Volume (dm^3)
n=cv
