C3 Flashcards
(20 cards)
State the law of conservation of mass
The total mass of the reactants = the total mass of the products.
Calculate the relative formula mass of calcium carbonate (CaCO3)
40+12+(16x3) = 100
Why must a symbol equation balance
Because no atoms are lost or made, the products of a chemical reaction are made from exactly the same atoms as the reactants.
when a metal forms a metal oxide, why does the mass increase
Because oxygen atoms have chemically bonded to the metal atoms.
Calculate the relative formula mass of water
H2O = (2x1) + 16 = 18
what does the state symbol (aq) stand for?
Aqueous (dissolved in water)
What is avogadro’s number (number of atoms/molecules in a mole)?
6.02 x 10^23
What is the equation that links moles, mass and Mr?
Mass = Mr x moles
69g of sodium reacts with chlorine to produce sodium chloride:
2Na + Cl2 → 2NaCl
Calculate the number of moles of sodium present.
69g ÷ 23 = 3 moles of Na
Using the same equation as in Q9, calculate the number of moles of Chlorine (Cl2) that would be required to react exactly with the sodium.
from the ratio of Na:Cl = 2:1, but we have 3 moles of Na not 2, so 3:1.5, so 1.5 moles of Cl2 required
What is the equation we use to calculate the concentration of a liquid?
Concentration = mass or moles/volume in dm3.
What are the units of concentration?
g/dm3 or moles/dm3
1.50 moles of solute is dissolved in 1.00dm3 of solvent. What is the concentration of the solution formed?
1.5moles ÷ 1.00dm3 = 1.50mol/dm3
2.00g of solute is dissolved in 2.00dm3 of solvent. What is the concentration of the solution formed?
2.00g ÷ 2.00dm3 = 1.00g/dm3
0.20moles of solute is dissolved in 500cm3 of solvent. What is the concentration of the solution formed?
0.20moles ÷ 0.50dm3 = 0.40mol/dm3
Why might the actual yield of a reaction be less than the theoretical yield of the reaction?
Some product is lost when it is separated from the reaction mixture/ If the reaction is reversible it may not go to completion/ some of the reactants react in different ways to the expected reaction and by-products are formed.
A reaction has a theoretical yield of 13g but an actual yield of 8.5g. What is the percentage yield of this reaction?
(8.5 ÷ 13) x 100 = 65.4%
Why are reactions that have a high atom economy good for the environment?
They produce less waste material that could end up damaging the environment e.g. CO2 and global warming
The equation for the formation of ammonia, NH3, is: N2 + 3H2 → 2NH3
What is the percentage atom economy of this reaction?
100% (there is only one product)
What is a limiting reactant?
A reaction finishes when one of the reactants is all used up. The other reactant has nothing left to react with, so some of it is left over: the reactant that is all used up is called the limiting reactant
