Acids & Bases Flashcards
Give the equation of the dissociation of water molecules.
H₂O ⇌ H⁺ + OH⁻
How do you name a salt?
The 1st part of the name comes from the 1st part of the base.
The 2nd part of the name comes from the type of acid. Eg: hydrochloric acid = chloride,
nitric acid = nitrate, phosphoric acid = phosphate, sulfuric acid = sulfate
Eg: copper oxide + nitric acid → copper nitrate + water
What does ⇌ mean?
⇌ means that a reaction is reversible.
Why is water a neutral substance?
Water is a neutral substance because it has an equal concentration of H⁺ and OH⁻ ions.
How you do carry out volumetric titration?
It involves reacting an acid with a base.
What three groups do chemicals fall under (in terms of pH)?
- neutral
- acidic
- basic
What is a standard solution?
A solution of accurately known concentration.
What makes substances acidic?
Acidic substances have a higher concentration of H⁺ ions to OH⁻ ions.
What is the definition of concentration?
Concentration is the measure of the amount of solute dissolved in a certain volume of solvent. It is measured in mol/l.
What is the formula for concentration?
n=cV
n = number of moles
c = concentration (mol/l)
V = volume (litres) (VOLUME MUST BE IN LITRES, TO CHANGE FROM CM3, DIVIDE BY 1000)
What makes substances basic?
Basic substances have a higher concentration of OH⁻ ions to H⁺ ions.
How can we tell acidic, basic and neutral substances apart?
We can use an indicator. An indicator is a chemical which changes colour depending on the acidity of what is being tested.
(examples include: red cabbage, universal indicator, pH paper)
Example calculation: Calculate the mass of NaOH which is needed to make 200cm3 of a 4 mol/l solution.
Step 1: Calulate number of moles
n=cV
n= 4x0.2
n= 0.8 moles
Step 2: calculate mass
m=nxGFM
m= 0.8x40
m= 32g
The mass of NaOH is 32g
What are the names of common acids?
- hydrochloric acid: HCl / H⁺Cl⁻
- sulfuric acid: H₂SO₄ / (H⁺)₂SO₄²⁻
- nitric acid: HNO₃ / H⁺NO₃⁻
- phosphoric acid: H₃PO₄ / (H⁺)₃PO₄³⁻
- citric acid
- ascorbic acid (vitamin C)
What are the steps of a titration calculation?
- Calculate the number of moles (n) using n=cV for the reactant whose concentration and volume is given.
- Use mole ratio to find the number of moles of the other reactant.
- Calculate the unknown (either c or V) using either c=n/V or V=n/c
How can an acid be made?
non-metal oxide + water → acid
examples include: sulfur dioxide + water → sulfuric acid
nitrogen oxide + water → nitric acid
SO₂ + H₂O → H₂SO₄
NO + H₂O → HNO₃
Example calculation: Calculate the concentration of NaOH if 100cm3 of NaOH is neutralised by 50cm3, 2 mol/l H₂SO₄
H₂SO₄ + 2NaOH → Na₂SO₄ + H₂O
- n=cV 2. 1 mole : 2 moles
n=2x0.05. 0.1 moles : 0.2 moles
n=0.1moles H₂SO₄ - c= n/V
c= 0.2/0.1
c= 2 mol/l
The concentration of NaOH is 2 mol/l.
What kind of salts does neutralisation produce?
Soluble salts
How are insoluble salts made?
Insoluble salts are made from precipitation.
Eg: Barium chloride (aq) + sodium sulfate (aq) → Barium sulfate (s) + Sodium chloride (aq)
(the precipitate)
Note: check pg 8 of the data book for Solubilities of Selected Compounds in Water
What are the names of common bases?
- sodium hydroxide: NaOH / Na⁺OH⁻
- potassium hydroxide: KOH / K⁺OH⁻
- sodium carbonate: Na₂CO₃ / (Na⁺)₂CO₃²⁻
How do you make an alkali?
metal oxide + water → metal hydroxide
What are the three types of base?
- metal oxides
- metal hydroxide
- metal carbonate
What is neutralisation?
It is the reaction of an acid with a base
How can acids and bases be neutralised?
- acid + metal oxide → salt + water
- acid + metal hydroxide → salt + water
- acid + metal carbonate → salt + water + carbon dioxide
Examples include:
hydrochloric acid + sodium hydroxide → sodium chloride + water
HCl + NaOH → NaCl + H₂O
sulfuric acid + sodium hydroxide → sodium sulfate + water
H₂SO₄ + NaOH → Na₂SO₄ + H₂O
phosphoric acid + sodium hydroxide → sodium phosphate + water
H₃PO₄ + NaOH → Na₃PO₄ + H₂O
Note: the acid and base should be of opposing strength
(example: if HCl = pH 1 then NaOH = pH 13)
What word is used to describe substances with pH:
a. Less than 7
b. exactly 7
c. More than 7
a. acidic
b. neutral
c. alkaline / basic
Explain how pure water can conduct.
Pure water can conduct (albeit poorly).
This is because some molecules of H₂O will dissociate into H⁺ and OH⁻ ions (which can conduct).
Describe the concentration of H⁺ ions and pH when an acid is diluted.
When an acid is diluted the concentration of H⁺ ions is decreased and the pH increases towards 7.
Describe the concentration of OH⁻ ions and pH when an alkali/base is diluted.
When an alkali is diluted the concentration of OH- ions is decreased and the pH decreases towards 7.
What word is used to describe ions that are present during the reaction but are unchanged by the reaction, and so are present in the same state on both sides of the equation?
Spectator ions
How would the following ionic equation be rewritten omitting the spectator ions?
H⁺(aq) + Cl⁻(aq) + Na⁺(aq) + OH⁻(aq) → Na⁺(aq) + Cl⁻(aq) + H2O(l)
H⁺(aq) + OH⁻(aq) → H2O(l)
How can the following equation be rewritten without the spectator ions?
2H⁺(aq) + 2NO₃⁻ (aq) + Ca²⁺(aq) + CO₃²⁻(aq) → Ca²⁺(aq) + 2NO₃²⁻(aq) + H₂O (l) + CO₂ (g)
2H⁺(aq) + CO₃²⁻(aq) → H₂O (l) + CO₂(g)
What is the purpose of a titration reaction?
This technique is commonly used in neutralisation reactions and to calculate an unknown concentration (of either the acid or alkali).
What is a precipitation reaction?
When soluble solutions produce an insoluble solid.
