Quantitative Chemistry Flashcards
What is the equation linking moles, mass , and Mr?
mass = moles X Mr
moles=mass/Mr
What is Ar?
Relative atomic mass aka. the average mass of all the isotopes of an element.
What is Mr?
Relative formula mass aka. all the Ar’s of a comppound or molecule added together.
What is a limiting reactant?
The reactant which limits how much product can be produced. (It all reacts).
What do we call the process of oxygen burning in air?
Combustion
What does it mean for a reactant to be ‘in excess’ ?
It does not all react, and has no profound effect on the amount of product formed.
What is the calculation for volume of a gas?
Volume = moles x 24
moles = volume/24
What are the problems with low atom economy?
- There will be more waste products to dispose of.
- It will be less sustainable as it will use more resources.
What are the solutions for a low atom economy?
- Use a more efficient reaction.
- Find a use for the waste products.
What is the atom economy equation?
Mr of desired products/Mr of all reactants
x 100
what are important factors in deciding how profitable a reaction is?
%yield
cost of raw materials
the position of equilibrium
the rate of reaction
the cost of maintaining the right conditions (temperature, pressure).
What is atom economy?
A measure of the proportion of starting materials that end up as useful products.
What is percentage yield?
What percentage of the theoretical yield we actually got.
What is the equation for percentage yield?
actual yield/theoretical yield x100
What does the law of conservation of mass state?
No atoms are lost or made during a chemical reaction.
What is a chemical change?
A rearrangement of the atoms in the reactants, to form the products.
Suggest why the mass of a reaction vessel might decrease during a reaction.
One of the products is a gas and all the reactants are not. Before reaction, all reactants are contained in the reaction vessel. If this isn’t enclosed, the gas can escape from the reaction vessel as the product is formed. Therefore you cannot account for its mass.
Suggest why the mass of a reaction vessel might increase during a reaction.
One of the reactants is a gas, and the products are not. Before the reaction, the gas is floating in the air, not contained in the reaction vessel, so you can’t account for its mass. When the gas reacts to form part of the product, it becomes contained inside the reaction vessel so the total mass of substances inside the reaction vessel increases.
How can you tell the number of moles that would react together from the balanced symbol equation?
Molar ratios
Concentration
A measure of how many particles of solute are dissolved in a given volume.
What is r.t.p
room temperature and pressure
(20degrees celsius and 1atm)
Why may the balance reading for products be less than that of the reactants? (2 reasons)
-Some of the reactants may have been spilled.
-One of the products was a gas and floated off
Why might the balance reading for the products be more than the reading for the reactants? s i m p l e
Gas from the air reacted with the reactants.
Give 3 reasons why percentage yield may be less than 100%
-Incomplete reactions
-Side reactions
-Practical losses (e.g spilling of some liquid reactant)
If the percentage of oxygen in MgCO3 is 57%, and you have 25g of MgCo3, what mass of that is Oxygen?
0.57 x 25 = 14.25g
percentage mass formula
mass of element in compound/ total mass of compound
x 100
Explain how a fluorine atom can change into a fluoride ion, F-.
The atom must gain one electron to gain a full outer shell and become stable. This means that:
protons +9
electrons-10
charge -1
Why should steel be recycled?
To conserve resources of iron/iron ore
To avoid the need for mining
To reduce the amount of landfill
How do we calculate Mass of an unknown substance in Reactions?
1Write out the balanced equation
2Find the moles of the known substance (moles = mass ÷ Mr)
3Find the moles of the unknown substance (using the molar ratio from the balanced equation)
4Find the mass of the unknown substance (mass = moles x Mr)
How do we calculate concentration?
Mass/volume or mol/volume
Explain why a student’s results may not support the law of conservation of mass (3)
Carbon dioxide is a gas
The gas escapes during the reaction
So the mass at the end would be less than expected
