Quantitative Analysis
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What is a theoretical yield?
The maximum mass of product that can be formed the reactant
What is the actual yield?
The amount of product obtained when you carry out an experiment which is known as the actual yield
How do you find the theoretical yield for example for hydrogen from 36g of water?
Relative formula mass x the balancing numbers 2H20 = 2 x (1+1+16)= 36 (calculate this first), then, 2H2 = 2 x (1+1) = 4g
How do you work out the percentage change for yield?
actual yield / theoretical yield x 100
Give the three reasons why reactions don’t give 100% yields?
• reaction may be incomplete so not all of the reactants are used up (the reaction has not been left long enough) • some of the product was lost (e.g on the walls of the container) • there may be unwanted side reactions (e.g reactants make a different product
What has to increase in order for the reaction to be more useful?
The percentage yield
What does a high yield mean, amount of materials-wise?
Fewer raw materials are supposed to make the same high yield, so there is less waste and more profit can be made
What is atom economy?
Method of showing how efficiently a particular reaction makes use of the atoms in the reactants (some reactant will not get used for the specific purpose it is being made for)
How do you figure out atom economy?
the relative formula mass of the useful product / sum of all relative formula masses of all the reactants x 100
What is a by-product?
Something that is produced during the production or destruction of something else
How do you work out the atom economy from a balanced equation?
The reactant’s Mr will be the sum of all relative formula masses of all the reactants and the Mr of the useful product you are looking at, will be formula mass of the useful product for the top of the equation. Then do the calculation using the formula
Why is it better to make use of the waste by-products?
It means that you can increase the atom economy, meaning you have more ‘useful products’ as you are making use of all the products
What factors need to be taken into consideration when deciding on a reaction pathway?
• Energy consumption • Rate of reaction • Raw materials • Conditions are needed to produce a high yield if the reaction reaches equilibrium (such as temperature)
What is a volumetric flask?
They are calibrated to measure one volume of solution accurately
What two things should you do when accurately measuring the volume of solution at the graduation mark?
Measure from the bottom of the meniscus (the curve at the top of a solution) and make sure to measure at eye level to avoid random error
What is the concentration?
The amount of solute dissolved in a stated amount of solution
What is concentration measured in?
Gdm^-3
How do you work out concentration?
mass of solute (g) / volume of solution (dm^3)
How do you convert from cm^3 to dm^3
divide by 1000
How do you work out the concentration if you’re given the number of moles of solute?
number of moles of solute (mol dm^-3) / volume of solution (dm^3)
How do you work out the concentration in mol dm^-3
concentration (gdm^-3) / relative formula mass of solute
What is the mole ratio?
`The ratio in moles of the substances in a balanced equation
How do you work out the volume of a solution with a given volume of another
• Calculate the mole ratio from the balanced equation • Calculate the number of moles of the solution of the known volume and concentration • Use the balanced equation and mole ratio to find out the number of moles of acid that reacted • Calculate the volume of ‘acid’ needed PLEASE FIND WORKED EXAMPLE ON PAGE 115 TO HAVE A CLEARER UNDERSTANDING
What does Avogadro’s law state?
If the temperature and pressure are the same, equal volumes of different gases contain an equal number of molecules