C4 Chemical Calculations Flashcards
Why may some atomic masses may not be a whole number?
Because of isotopes
Why must chemical equations be balanced?
Chemical reactions need to be balanced to abide by the law of conservation of mass which states that matter cannot be created or destroyed.
What is the definition of the theoretical yield?
the maximum amount of product produced by a chemical reaction
What is the definition of the actual yield?
the amount of a product made in a chemical reaction once it has actually been completed.
What is the definition of the percentage yield?
the percent ratio of the weight of the product obtained to the theoretical yield.
What is the equation for percentage yield?
Percentage yield = (actual yield / theoretical yield) x 100
Why is the actual yield often lower than theoretical yield?
This happens generally because of the production of waste products like CO2 or H2O.
Why can percentage yield never be above 100%?
Because if the percentage yield is over 100% you would be creating atoms which is impossible.
How do you calculate the formula mass of a formula?
By adding all of the Atomic masses together.
How do you calculate the atom economy?
total number of atoms in the desired product/ the total number of atoms in all the reactants
How do you recognise a covalent compound?
If the compound is made of a non metal and another non metal.
Why is using reactions with high atom economy important?
Because it reduces the amount of waste produced, conserves resources, and minimises environmental impact.
why is the sum of the formula
masses of the reactants the same as
the sum of the formula masses of the
products?
This is because of the law of conservation of mass, as matter cannot be created or lost.
State a definition of atom economy.
The atom economy is a measure of the amount of starting materials that end up as useful products.
How can the concentration of a solution be changed?
Concentration can be increased by dissolving more solute in a given volume of solution.
Concentration can be decreased by diluting the solution.
What is the equation to calculate concentration?
Concentration = number of moles x volume
What does solute mean?
A solute is a substance that can be dissolved into a solution by a solvent
How do you calculate the titre?
By finding difference between the reading at the start and the final reading. E.g 1.00 cm3 and 26.50 cm3 the titre is 25.50cm3
How can an indicator be used to show the endpoint in titration?
When the indicator has a clear change colour this signifies that the endpoint has started.
In titration what do you use the volumetric pipette for?
To measure out 25cm3 of the known solution.
What is a burette used for in titration?
It is used to accurately dispense the unknown acid in the alkali in the conical flask.
How are precise results obtained in a titration?
Precise results in a titration are obtained by first doing a rough titration to find the endpoint, and then you do at least two accurate titrations by adding the acid drop wise as soon as you are nearing the endpoint. If you have 2 concordant results the experiment is done, if not repeat until you get 2 concordant results.
How can accuracy be improved in a titration?
By making sure to read your results by facing parallel to the burette and by adding the acid drop wise sooner to the conical flask.
Why do you use an indicator in an acid-base titration?
To indicate the endpoint.
How do you calculate the amount in moles of gas in a given volume at room temperature?
Moles = volume / 24dm3
