Chemistry 1.7 by Taylor keates

Making a standard solution

3185561 — 2019-01-30 12:12:49 UTC

Accurately measure the mass of the solid
Dissolve this solid into the minimum possible amount of water - no more than 150ml.
Transfer the solution into a volumetric flask using a funnel
Use a dropping pipette to add water until you reach the 250ml mark.

Acid- Base Neutralisation equation

taylorkeates — 2019-01-30 12:12:49 UTC

H⁺(aq) + OH^-(aq) --> H₂O (l)
acid + base --> salt + water
HCl(aq) + NaOH(aq) --> NaCl(aq) + H₂O(l)

Forming Bases

taylorkeates — 2019-01-30 12:12:49 UTC

An alkali is a solution of a base.
When we neutralise an acid, the H+ (aq) ions are removed from the solution. Alkaline solutions contain OH- (aq) ions, i.e hydroxide ions.
They neutralise acidity.
Bases are H+ (aq) acceptors.

Forming Acids

3185561 — 2019-01-30 12:12:49 UTC

Hydrogen in acids enters solution H⁺ (aq) ions, i.e protons.
It is the H⁺(aq) ions that make a solution acidic.
The releasing of a hydrogen atom into water is called dissociation.
Acids are H⁺(aq) donors.

Acids and bases *LEARN

taylorkeates — 2019-01-30 12:12:49 UTC

HCl- Hydrochloric acid
H₂SO₄- Sulfuric Acid
HNO₃ - Nitric Acid
CH₃COOH - Ethanoic Acid
NaOH - Sodium hydroxide

Size of Kc

taylorkeates — 2019-01-30 12:12:49 UTC

When the products are favoured, Kc will have large values.
When the reactants are favoured, Kc will have small values.

Equilibrium constant

taylorkeates — 2019-01-30 12:12:49 UTC

Generally: aA + bB ⇌ cC + dD
[X]_eq : concentration of chemical X at equilibrium
Equilibrium constant, K_c-[C]^c x [D]^d ÷ [A]^a x [B]^bExample: H2(g) + I2(g) ⇌ 2HI(g)
K_c = [HI]² ÷ [H₂] x [I₂]

Change 3: Changing temperature

taylorkeates — 2019-01-30 12:12:49 UTC

If we increase the temperature, the PoE shifts to try to counteract the temperature change. But we need to know whether the forward/reverse reaction are exothermic(giving out heat) or endothermic(taking in heat).
In general:
increasing temp. favours endothermic reactions
decreasing temp. favours exothermic reactions
Example:
2NO₂(g) ⇌ N₂O₄(g)
-> exothermic
<- endothermic
ΔH = negative tells us forward reactions is exo
ΔH = positive tells us forward reaction is endo
ΔH = kJ mol^-1

Adding a catalyst

taylorkeates — 2019-01-30 12:12:49 UTC

A catalyst will speed up the reaction by lowering the activation energy go the reaction. The catalyst will not affection the PoE, but equilibrium is reached faster.

Change 2: Changing pressure

taylorkeates — 2019-01-30 12:12:49 UTC

If we increase pressure, the equilibrium shifts to try to reduce it. Moving the PoE to the side with least gas molecules will lower the pressure.
If we decrease pressure, the equilibrium shifts to try to increase it again. Moving PoE to the side with most molecules will increase the pressure.
Example:
CO₂(g) ⇌ CO₂(aq) (coke bottle opening)
On opening the bottle, pressure decreases & PoE shifts left, the fizz means more gas

Change 1: Changing concentration

3185561 — 2019-01-30 12:12:49 UTC

If we increase the concentration of a chemical, the equilibrium will try to minimise the change by using up the chemical. This shift the position of the equilibrium ‘away’ from the chemical in the equation.
Example:
The Haber Process is an example, if the N₂ concentration is increased, the forward reaction taking place happens strongly. The position of equilibrium moves to the right & the amount of ammonia is increased.
If we decrease the concentration of a chemical, the equilibrium will try to minimise the change by making more of the chemical. This shifts the PoE 'towards' the chemical in the equation.

Reversible Reactions

3185561 — 2019-01-30 12:12:49 UTC

The CuSO₄.5H₂O is hydrated copper sulfate & the CuSo₄ in the products is anhydrous.

Example

CuSO₄_^.5H₂O ⇌ CuSO₄ + 5H₂O

pH equation

taylorkeates — 2019-01-30 12:12:49 UTC

pH = -1log₁₀ [H⁺(aq)]

[H⁺(aq) ] = conc. of H⁺[H⁺ ] = 10^-pH

Strong and Weak Acids

3185561 — 2019-01-30 12:12:49 UTC

The stronger an acid is, the easier it can fall apart.

Le Chatelier’s Principle

3185561 — 2019-01-30 12:12:49 UTC

The position of equilibrium shifts to try to cancel out any changes that you introduce.

Primary Standards

3185561 — 2019-01-30 12:12:49 UTC

Primary standards have the following properties:

High purity
Stability, i.e low reactivity
Weight changes due to humidity are minimised
High molar mass

Acid Standardisation

3185561 — 2019-01-30 12:12:49 UTC

Acid standardisation allows us to find the concentration of an acid using a standard solution, which is prepared from a chemical that is a primary standard.

Simple Equilibria

taylorkeates — 2019-01-30 12:12:49 UTC

At dynamic equilibrium the forward & reverse reactions happen at the same rate.
The position of equilibrium(PoE) can lie in favour of the reactants or products.