R2.1 - how much? the amount of chemical change Flashcards
What is a chemical reaction?
Shows the ratio of products and reactants that can be written as a chemical or symbol equation.
What are stoichometric co-efficients?
Numbers in front of products and reactants that are used to balance the equations.
What can a mole ratio determine?
1) The mass or volumes of reactants and products.
2) Concentration of products and reactants in a solution.
What is Avogadro’s Law?
Equal volumes of all gases under STP contain equal number of moles.
What is molar volume?
Volume occupied by 1 mole of a gas
How is titration carried out?
1) Use a pipette to measure a known volume of one solution into a conical flask, and add universal indicator.
2) Put the other solution in a burette, which is a calibrated glass tube.
3) Open the burette to allow the solution into the conical flask and mix it.
4) Add indicator and keep mixing until there is a permanent colour change.
How is back titration carried out?
1) Known excess of one of the reactants is added to the reaction mixture.
2) Unreacted excess is determined by titration of a standard solution.
3) Subtract the unreacted amount from the original to work out the reacting amount.
- Used when the end point is hard to identify for impure substances.
What assumptions are made during a back titration?
1) All of the substance reacts with the acid.
2) Only NaHCO3 reacted with the acid.
3) Took place under standard conditions.
What is the equation involving mass, moles and Mr?
moles = mass / Mr
What is the equation involving mass, molar volume and volume?
molar volume = moles / volume
What is the limiting reactant?
Reactant that gets used up in a reaction and determines the theoretical yield of a product.
What is the difference between theoretical and experimental yield?
Theoretical yield - maximum amount of product obtained if 100% of the limiting reactant is converted into products.
Experimental yield - yield that is actually produced from a reaction.
How do you work out % yield?
% yield = (experimental yield / theoretical yield) x 100
What can cause EY < TY?
- Side reactions
- Decomposition of reactants or products
- Product lost during purifying
- Reversible chemical reaction
- Incomplete reaction
Wh cause TY < EY?
- Impurities in a product
- Product not fully dried
- Incomplete reaction