Acids and Bases
Define an acid according to Arrhenius theory.
An Arrhenius acid is a substance that produces hydrogen ions (H⁺) when dissolved in water.
Complete:
Acid + Base → ? + ?
Acid + Base → Salt + Water
What is the pH of a neutral solution at 25°C?
pH=7
State the formula for calculating moles.
n=cV
Define a Brønsted-Lowry acid.
A Brønsted-Lowry acid is a proton donor.
State TWO properties of acids.
Any two:
Complete:
Acid + Carbonate → ? + ? + ?
Acid + Carbonate→ Salt + Water + Carbon Dioxide
State the formula connecting pH and hydrogen ion concentration.
pH=−log[H+]
State the calorimetry equation.
q=mCΔT
Define a Brønsted-Lowry base.
A Brønsted-Lowry base is a proton acceptor.
Differentiate between a strong acid and a concentrated acid.
A strong acid completely ionises in water.
A concentrated acid contains a large amount of acid dissolved in solution.
Strength refers to ionisation.
Concentration refers to the amount dissolved.
Complete:
Acid + Metal →
Answer
Acid + Metal → Salt + Hydrogen Gas
Calculate the pH of:
[H+]=1.0×10^−3
pH=3
100 g of water is heated by 10°C.
Calculate q.
C=4.18Jg^−1°C^−1
q=(100)(4.18)(10)
q=4180J
Identify the conjugate base of:
HCl
Cl^-
Explain why hydrochloric acid is classified as a strong acid and ethanoic acid is classified as a weak acid.
Hydrochloric acid completely ionises in water:
HCl → H^+ +Cl^-
Ethanoic acid only partially ionises:
CH3COOH ⇌ H^+ +CH3COO^−
Therefore HCl produces more hydrogen ions than ethanoic acid at the same concentration.
Hydrochloric acid reacts with magnesium.
Write a balanced equation.
Mg + 2HCl → MgCl2 + H2
Calculate the hydroxide concentration if:
[H+]=1×10^−5
Use:
Kw=[H^+][OH^−]
1×10−14=(1×10^−5)([OH−])
[OH−]=1×10^−9
mol L⁻¹
0.100 mol of water is produced in a neutralisation reaction.
The reaction releases 5700 J.
Calculate ΔH.
ΔH= q/n
=−5.7kJ / 0.100
=−57kJmol^−1
Identify the conjugate acid-base pairs in:
HCl+H2O⇌H3O^+ +Cl^−
Pair 1:
HC l/ Cl^−
Pair 2:
H2O / H3O^+
Two solutions have a concentration of 0.10 mol L⁻¹:
Explain why they have different pH values.
Both solutions have the same concentration.
However, HCl completely ionises while CH₃COOH only partially ionises.
Therefore the concentration of hydrogen ions is much higher in HCl.
Since pH depends on hydrogen ion concentration, HCl has a lower pH.
A student adds hydrochloric acid to sodium carbonate.
Describe all observations and explain why they occur.
Observations:
This occurs because carbonates react with acids to produce carbon dioxide:
Acid + Carbonate → Salt + Water + CO2
The bubbles are carbon dioxide gas escaping.
A solution has:
[OH−]=1×10^−4
Calculate:
pOH=4
pH+pOH=14
pH=10
50.0 mL of 1.0 M HCl reacts completely with 50.0 mL of 1.0 M NaOH.
The temperature rises by 6.8°C.
Determine the enthalpy of neutralisation.
Assume density = 1 g/mL.
Mass:
100g
Energy:
q=mCΔT
q=(100)(4.18)(6.8)
q=2842.4J
Moles:
n=CV
n=(1.0)(0.050)
n=0.050
ΔH=−2.842 / 0.050
=−56.8kJmol^−1
Water is described as amphiprotic.
Explain what this means and provide TWO equations showing this behaviour.
Amphiprotic substances can act as both acids and bases.
Water acting as a base:
HCl+H2O→H3O^+ +Cl^−
Water accepts a proton.
Water acting as an acid:
NH3+H2O⇌NH4^+ +OH^−
Water donates a proton.