| What does Mr stand for? | Relative formula mass. |
| What is relative formula mass? | The sum of all relative atomic masses of atoms involved. |
| How do you calculate the Mr? | You add together the total atomic masses of all atoms involved. |
| What is the Mr of NaCl? | Na atomic mass = 23
} 58.5g/mol
Cl atomic mass = 35.5 |
| What is a mol? | A way of representing a large quantity of atoms.
It represents 6.022 × 10²³. The number is called the Avogadro constant. |
| What is the Mr of CaCO₃? | Ca atomic mass = 40
C atomic mass = 12 }. 100g/mol
O atomic mass = 16 × 3 = 48
We multiplied the atomic mass of oxygen by 3 because there were 3 atoms in the compound. This means that the atomic mass was tripled. |
| What is the formula for moles? | Moles = Mass / Mr
Moles = Mol
Mass = grams
Mr = g/mol |
| What is the number of moles in 30 grams of CO₂? | Moles = Mass / Mr
C = 12
} 44
O = 16 × 2
> 30/44
= 0.681 mol |
| What is the mass of 5 moles of Cl₂? | Mass = Moles × Mr
Cl = 25.5 × 2 = 71
→ 5 × 71 = 355g |
| What is ionic formulae? | The formula for ionic compounds. |
| How would you make an ionic formulae? | Because ionic compounds have no overall charge, you need to make sure that you have enough of one ion to cancel out the other ion. |
| What is the ionic formulae for magnesium chloride? | Mg = 2+
Cl = 1-
To have a compound with no overall charge, you need to have two chloride ions to cancel out the magnesium.
= MgCl₂ |
| What is the ionic formulae for sodium oxide? | Na₂O |
| What is the formulae for iron oxide? | Fe = 3+
O = 2+
We need to cancel these out if we want to get a neutral charge. To do this, they both need to be the same number, and they both go into six.
Two iron ions = Fe⁶⁺. Three oxygen ions = O⁶⁻.
= Fe₂O₃ |
| What are polyatomics? | Ions with more than one atom. |
| What are the 3 common polyatomics/ common ions? | OH⁻ = Hydroxide ion.
CO₃²⁻ = Carbonate ion.
SO₄²⁻ = Sulfate ion. |
| Balance the equation;
C₆H₁₂O₆ → C₇H₁₆ + C₃H₆ + C₂H₄ | Here we need to balance the equation with moles because we don't know how many atoms are present.
First, we need to work out the moles of each compound by dividing the mass by the Mr.
By doing this, we'll see that an element double the number of moles more than others, making the ratio 1:1:1:2.
We can now balance the equation, knowing that there's 1 C₆H₁₂O₆, 1 C₇H₁₆, 1 C₃H₆, but 2 C₂H₄.
= C₆H₁₂O₆ → C₇H₁₆ + C₃H₆ + 2C₂H₄ |
| In a reaction, 9.2g of sodium reacted with 3.2g of oxygen gas to give 12.4g of sodium oxide. Balance the equation. (5 marks) | Here we need to balance the equation with moles because we don't know how many atoms are present.
First, we need to work out the moles of each compound by dividing the mass by the Mr.
By doing this, we'll see that an element double the number of moles more than others, making the ratio 4:1:2.
We can now balance the equation, knowing that there are 4 Na, 1 C₇H₁₆, and 1O₂, but 2 Na₂O.
= 4Na + O₂ → 2Na₂O |
