Topic 3: Quantitative Chemistry ✅ Flashcards
What is the Law of Conservation of Mass equation?
The total mass of reactants equal the total mass of products
How do you calculate the relative formula mass of a compound?
By adding the relative atomic masses of the elements that make the compound and then multiply it by the number of atoms of that element in the compound, then add the numbers together.
What is the law of conservation of mass?
A law that states that no atoms can be created or destroyed in a chemical reaction.
What is relative atomic mass?
The average mass of the atom.
What is another name for the relative formula mass of a compound?
Relative molecular mass
How does burning of wood change the mass of products?
It decreases it as carbon dioxide and water (and other gases) is released.
Give 3 example of how the mass of the product can change?
Burning wood
Corrosion if metals
Zinc+Hydrochloric acid
Every chemical measurement involves some…
… uncertainty
How can you reduce uncertainty?
By repeating the measurement from experiments several times and calculating an average from them.
Why must chemical equations be balanced?
To make sure that there are the same number or atoms of an element before and after a reaction.
What does the molecular formula show?
The actual amount of atoms which make up a molecule.
Name an example of a molecular formula.
Glucose C6H12O6
What does Empirical formula show?
The simplest ratio of atoms which make up a molecule.
Name and example of empirical formula.
Glucose CH2O
What are moles?
A measurement if chemical amounts.
One mole is a substance is ____ atoms of that substance.
6.02 X 10 to the power of 23
What is the number 6.02 X 10 to the power of 23 known as in terms of moles?
Avogadros Constant
The relative formula mass of a substance is equal to the mass of…
1 mole of that substance
How do you calculate relative formula mass?
The sum of the relative atomic mass of the elements X number of atoms in elements
What is the equation for using moles to balance equations?
Moles=mass/relative formula mass
What is a limiting reactant?
The reactant that is completely used up and therefore stops the reaction.
What 2 things do you need to know to work out the moles of a substance?
-Mass
-Mr
How do we make sure there is no acid left after the reaction when neutralising and acid?
Use an excess amount of the other reactant.
What can we use to calculate the number of moles when a substance is dissolved in a solution?
We can use the solutions concentrations.
What 2 units is concentration measured in?
G/dm3
Mol/dm3
The percentage yield for any reaction is always less than…
…100%
What 4 factors make sure the percentage yield of reactions stays below 100%?
Incomplete Reactions
Waste
Extraction
Side Reactions
What 2 reasons may a reaction be incomplete?
-It is very slow and may not be given enough time to happen
-The reaction is reversible and some of the products have been converted back into reactants
How does waste make sure the percentage yield stays below 100%?
Some of the chemicals will remain stuck to the apparatus and will be wasted.
How does extraction make sure the percentage yield stay below 100%?
It might be difficult to fully separate the product from the reaction mixture.
How do side reactions make sure the percentage yield stays below 100%?
Unexpected reactions can happen, which mean that the intended product is not created.
What is real yield?
The mass of a desired product obtained from a reaction.
What is theoretical yield?
The maximum mass of a product that could possibly be created from a reaction.
What can theoretical yield be calculated from?
A balanced equation if we know the mass of the reactants.
How is percentage yield of a reaction calculated?
Real yield / theoretical yield X 100
What is percentage yield?
A comparison of the real and theoretical yields of a reaction.
Why are reaction pathways with high atom economies good (2 reasons)?
Cost effectiveness
Low waste
What 6 things should you consider when selecting a reaction pathway?
-Atom economy
-How much the reactants will cost
-What the percentage yield will be
-How quickly the reaction will happen
-How useful the by-products of the reaction are
-The position of the equilibrium
What 2 things can the concentration of a solution be measured in terms of?
Moles
Mass
What 2 things do we have to know to calculate the amount of a solute in a solution?
The concentration of the solution
The volume of the solution
What is a solute?
A dissolved substance
What 2 things do we need to know in order to calculate the concentration of a solution?
The volumes of 2 solutions that react completely
The concentration of 1 of these solutions
If the temperate and pressure conditions are the same, the same amounts of any gases (when measured in moles) will take up…
…Identical volume
