quantitative chemistry

What is the law of conservation of mass?

Mass of reactants = mass of products

Why might some reactions appear to show a change in mass?

A reactant/product is a gas

Give 2 examples of a reaction where a change in mass may appear to take place

Metal reacting with oxygen or an acids. Thermal decomposition

Balance the following equations

H2 + O2 → H2O

Ca + HCl → CaCl2 + H2

Li + H2O→ LiOH + H2

NH3 + O2 → NO + H2O

K + O2 → K2O

2H2 + O2 → 2H2O

Ca + 2HCl → CaCl2 + H2

2Li + 2H2O→ 2LiOH + H2

4NH3 + 5O2 → 4NO + 6H2O

4K + O2 → 2K2O

How many atoms and elements are in the compound sodium alumina the, NaAl(OH)4?

Four elements and ten atoms

What die the following formulae tell you?

2HCl

Cl2

2HCl

Two molecules of hydrogen chloride. Each molecules contains one hydrogen atom and one chlorine atoms

Cl2

One molecule of chlorine made of two atoms

An aqueous solution of hydrogen peroxide (H2O2) decomposes to form water and oxygen

Write a balance symbol equation for this reaction. Include state symbols

Why does the water, produced during the reaction, have a lower mass than the original

2H2O2(aq) → 2H2O (L) + O2 (g)

What is the relative formula mass of a compound

Sum of the relative atomic masses of the atoms in the numbers show in the formula

What is the relative formula mass of:

MgCl2

6C12H6O

95

180

What can be said about the sum of the relative formula masses of the reactants and products of a reaction

In a balanced chemical equation

Why can you have relative atomic masses which are not whole numbers eg chlorine is 35.5

Isotopes

1. What is meant by the term 'mole'?

A measure of the chemical amount of a substance

1. What is the symbol for the unit mole?

Mol

1. What does 'Avogadro's constant' tell us?

Number of atoms, molecules or ions I’m a mole of a substance

1. What is the value for Avogadro's constant?

6 × 10 23 per mol

1. How many atoms in 1 mole of carbon?

6.02 × 10²³

1. How many atoms in 1 mole of chlorine gas, Cl2?

6.02 × 10²³

1. What can the following equation tell us about the number of moles of each substance?

Mg + 2HCI → MgCl2 + H2

1 mole of magnesium reacts with 2 moles of HCL to form 1 molecule of magnesium chloride and 1 mole of hydrogen

1. What is meant by the term limiting reactant'?

A reactants in a reaction which is completely

1. How many moles of helium are there in 0.04g of Helium?

0.04/4 =0.01 mol

1. What is the mass of 20 moles of calcium carbonate, CaCO? Answer in Kg.

40+12+(16×3) =

100 × 20 =2,000g =70.548 oz 2kg

1. Calcium carbonate decomposes to calcium oxide in a kiln in the following reaction

CaCO3: → CaO + CO2

Calculate the mass of calcium oxide that can be produced when 300 tonnes of calcium carbonate is heated.

Relative formula mass of calcium carbonate = 100 = 100g

Relative formula mass of calcium oxide = 56 = 56g

100 tonnes of calcium carbonate makes 56 tonnes of calcium 56 tonnes of calcium oxide so 300 tonnes make 168 tonnes

0.10g of hydrogen reacts with 3.55g of chlorine to produce 3.65g of hydrogen chloride. Use this information to work out the balancing numbers for hydrogen chloride.

H2 + Cl2 → _HCI

Mr : H2 =3,600 mins² 1 × 2 = 2

Mr - Cl2 =-1 cl² 35.5 × 2=71

HCl - 1 + 35.5 =

1. What units can be used for the concentration of a solution?

g/dm³

1. What does dm³ mean?

1000cm³

1. Give the equation for calculating concentration from the mass of substance and volume of solution.

Concerntration = mass / volume

1. HT Only: How can you increase the concentration of an aqueous solution?

Add more solute and dissolve in the same volume of water; evaporate off some of the water/decrease the volume of water

1. Calculate the concentration in g/dm³, for 50g of sodium chloride in 2.5m³ of water.

50/2.5 =20g/dm³

1. Calculate the concentration, in g/dm³ of 1.4g of potassium carbonate in 855cm³ of water.

(1.4/855) x 1000=1.64g/dm³

1. A teacher has a solution of lithium fluoride with a concentration of 72.6g/dm³

Calculate the mass of lithium fluoride dissolved in 25.0cm³ of solution.

25cm³ = 0.025dm³

72.6 × 0.025 =1.8g