Chemistry: Calculations Flashcards
What is relative atomic mass of magnesium?
What is relative atomic mass of oxygen?
What is relative molecular mass of Mgo? (Magnesium oxide
Mg - 24
O - 16
Mgo : 40 (16+24)
What symbol is relative atomic mass represented by?
(A(littleR))
What symbol is relative formula mass represented by?
(M(littleR))
What is relative atomic mass?
The mean mass of an atom of an element compared to carbon - 12 (basically just the mass number)
What is relative formula mass?
The sum of the relative atomic masses of all the atoms or ions in its formula
What is molecular formula?
Molecular formula represents the actual number of atoms of each element in one molecule
What is empirical formula?
The simplest ratio of different atoms in a compound
What do you need to know to work out empirical formula?
You need to know the mass (g) of each element and Relative atomic mass
What is number of moles equal to?
Mass
Ethene has a molecular formula of C(little2)H(little4)
What is the empirical formula?
Find highest common factor of two little numbers and divide both by this value
HCF of 2 and 4 is 2
Empirical formula = CH(little2)
Calculate the M(littleR) of Carbon dioxide
CO(little2)
=A(littleR) (C) + (2xA(littleR) (O))
=12+(2x16)
M(littleR) of CO(little2) = 44
Calculate the M(littleR) for Ca(NO(little3)(little2)
=A(littleR) (Ca) +2 (A(littleR)(N)+(3xA(littleR)(O)))
=40+2(14+(3x16))
What is concentration?
The amount of solute dissolved in a stated volume of solution
What are the units for concentration?
(gdm^-3)
What is the equation for concentration
Concentration = mass of solute / volume of solution
What are the SI units for mass of solute?
Grams (g
What are SI units for volume of solution?
Decimetre (dm^3)
What is the rule or what happens to mass during a chemical reaction.
Mass is not created or destroyed during the course of a chemical reaction
What is the law of conservation of a mass?
The mass of reactants must equal the mass of the products in a chemical reaction.
What do we do during a chemical reaction?
We rearrange atoms to produce new materials
During a chemical reaction, the mass of the reaction doesn’t change. What is this called?
A closed system
During a chemical reaction, the mass of the products appears to decrease. What is this called? Why does this happen?
Non-enclosed system, gas escaping
What happens in a closed system?
Mass doesn’t change because no gas is being produced/escaping
What happens in a open system?
Mass decreases as a gas is being given off
2Mg + O(little2) > 2Mgo
I react 10g of magnesium with 5g of oxygen. What mass of magnesium would I form?
10g +5g =15g
I react 15g of magnesium and form 25g of magnesium oxide. What mass of oxygen reacted?
15g +0(little2) =25g
O(little2) =10g
In a formula, what do the little numbers do?
E.g.: O(little2) = ?
Affect the element behind it
E.g.: O(little2) = o x 2
In a formula, what do the big numbers do?
E.g.: 2H(little2)O =?
E.g.: 2H(little2)O = 4xH, 2xO
Affect the whole compound
In a formula, what do the small numbers outside brackets do?
E.g.: (CO(little3))(little3) =?
E.g.: (CO(little3))(little3) =3xc, 9xO
Multiply everything inside the bracket by that number
What three things are balance in a chemical equation?
Atoms, mass, charge
What is the rule for little numbers in a formula?
You cannot add or change little numbers, only big
What is the easy way of saying what the relative formula mass of a compound is?
The relative atomic masses of all elements in compound added together
What mass of magnesium oxide is produced when 60g of magnesium is burned in air?
1: get your equation 2Mg + O(little2) > 2MgO 2: get relative atomic masses of: Mg - 24 O(little2) - 16 MgO - 40 2MgO - 80 2Mg=2x24=48 2MgO=2x(24+16)=80 3:Learn and apply the following points: 48g of Mg makes 80g of MgO 1g of Mg makes 80/48 = 1.66g of MgO 60g of Mg makes 1.66 x 60= 100g of MgO
What is a mole?
A way of counting
Give Avogadro’s number
6.02 x 10^23
What does 6.02 x 10^23 represent?
1 mole of substance
What is the mass of 1 mole of a substance?
The relative atomic mass or relative formulaic mass in grams
If the relative atomic mass of magnesium is 24, what is the mass of 1 mol of magnesium, and how many atoms does this contain?
1 mol of magnesium has a mass of 24g containing 6.02x10^28 atoms
What is the equation to calculate the number of moles in any substance?
Number of moles of substance= mass of substance (g) / Ar or Mr (use periodic table to find this)
What is the mass of 1 mol of carbon atoms?
1 x 12 = 1
What is 0.1mol of silver dioxide molecules?
S= 32
O(little 2) =16 x 2 = 32
32+32 = 64
0.1 mol: 6.4
What do moles tend to measure?
Particles (atoms or molecules of ions)
How many molecules are O(little2)?
1 molecule
How many molecules is 2MgO?
2 molecules
What type of equation is 2Mg+O(little2) > 2MgO? What does it tell us in relation to moles?
A balanced chemical equation. It shows us that 2 moles of magnesium reacts with 1 mole of oxygen
In chemical reactions, what is added in excess? What happens to it?
One of the reactants is added in excess and isn’t completely used up in the reaction
What is the amount of product in a chemical reaction controlled by? What is this called?
The reactant that is not in excess: the limiting reactant
What is the ratio of the moles of each substance called?
The stoichiometry of the reaction.
Calculate the number of molecules in 90g of water
Water = H(little2)O
1:calculate relative formula mass of water
Mr(H(little2)O): 1+1+16=18
2:calculate the number of moles in 90g of water
Mole = 90/18 = 5 moles of water
3:multiply the number of moles by Avogadro’s number
5x6.02x10^23=3.01x10^24
^ leave answer in standard form
How many atoms/particles/molecules does 1 mole have?
6.02x10^23
What are the 6 elements that travel in pairs?
I(little2), Cl(little2), Br(little2), O(little2), N(little2), H(little2)
Iodine, chlorine, bromine, Oxygen, Nitrogen, Hydrogen
