Chemistry P1 - Quantitative Chemistry

Question 1

What is the conservation of mass?

Answer 1

The idea that the total mass of the products is equal to the total mass of the reactants - there must be the same number of atoms of each element on both sides of the equation

Question 2

What does a HALF REACTION show?

Answer 2

What happens to one reactant in a chemical reaction, with electrons written as e-
For example:
Fe(s) + CuSO4(aq) —-> Cu(s) + FeSO4(aq)
==
Fe(s) —> Fe^2+(aq) + 2e-
and
Cu^2+(aq) + 2e^- —> Cu(s)

Question 3

What is the relative formula mass?

Answer 3

The sum of the relative atomic masses of all the atoms in the numbers shown in the formula

Eg What is the relative formula mass of CO2
Carbon(12 X 1) + Oxygen(16 X 2) = 44

Question 4

Why might an equation appear to change mass?

Answer 4

Because it was carried out in a non-closed system, so gasses can enter and leave

E.g. When magnesium is burned in air to produce magnesium oxide, the mass of the solid increases.

Question 4

When calcium carbonate is heated in a non-closed system, the mass of the products is lower than the reactants, why?

Answer 4

Because it decomposes to form calcium oxide and carbon dioxide. The CO2 escapes into the air

Question 4

Why must a symbol equation balance?

Answer 4

Because the law of conservation of mass states that there must be the same number of atoms on both sides of the equation

Question 5

Calculate the relative formula mass of H2O
Ar: Hydrogen = 1 Oxygen = 16

Answer 5

18

Question 5

Calculate the relative formula mass of CaCO3
Ar: Calcium = 40 Carbon = 12 Oxygen = 16

Answer 5

(401)+(121)+(16*3) = 100

Question 6

What is a mole (mol)?

Answer 6

• A mole is a measure of the number of particles (atoms, ions or molecules) contained in a substance.
• Any mole contains 6.02 X 10^23 particles

Question 7

What is the mass of one mole of a substance?

Answer 7

It is it’s relative atomic mass or relative formula mass in grams

Question 8

How do you calculate moles?

Answer 8

amount (mol ) = mass of substance(g) / atomic(or formula) mass (g/mol)

Question 9

Calculate the number of moles of carbon dioxide in 33g of the compound

Answer 9

amount = mass / formula mass
= 33 / 44
= 0.75 mol

Question 10

69g of sodium(23) reacts with chlorine to produce sodium chloride:
a) Calculate the moles of sodium present
b) Calculate the moles of chlorine required
c) Calculate the mass of chlorine required

Answer 10

a) 3
b) 1.5
c) 106.5