Acids & Bases
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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)