acids, bases and salts

describe the use of litmus to distinguish between acid and alkaline solution

acid: purple → red
alkaline: purple → blue

describe the use of phenolphthalein to distinguish between acid and alkaline solution

acid: stays colourless
alkaline: colourless → pink

describe the use of methyl orange to distinguish between acid and alkaline solution

acid: orange → red
alkaline: orange → yellow

what are litmus, phenolphthalein and methyl orange used for ?

to tell if a solution is acidic or alkaline based on colour change

how is the pH scale used to classify solutions ?

• 0-3: strong acid

• 4-6: weak acid

• 7: neutral

• 8-10: weak alkaline

• 11-14- strong alkaline

low pH = ?

more acidic

high pH = ?

more alkaline

how is universal indicator used to measure approximate pH ?

universal indicator changes colour across the full pH range. the colour is matched to a pH chart to find the approximate pH value of the solution

what ions do acids produce in aqueous solution ?

hydrogen ions (H⁺)

what ions do alkalis produce in aqueous solution ?

hydroxide ions (OH^-)

what happens when an acid neutralises an alkali ?

acids react with alkalis to form salt and water
H⁺ ions react with OH^- ions to make H₂O

what are the general solubility rules for ionic compounds ?

• all sodium, potassium, ammonium compounds → soluble

• all nitrates → soluble

• chlorides except silver and lead → soluble

• sulfates except barium, calcium, lead → soluble

• carbonates except sodium, potassium, ammonium → insoluble

• hydroxides except sodium, potassium, calcium → insoluble

are sodium compounds soluble or insoluble ?

soluble

are potassium compounds soluble or insoluble ?

soluble

are ammonium compounds soluble or insoluble ?

soluble

are all nitrates soluble or insoluble ?

soluble

are all chlorides soluble or insoluble ?

soluble except for silver and lead

is silver soluble or insoluble ?

insoluble

is lead soluble or insoluble ?

insoluble

are all sulfates soluble or insoluble ?

insoluble except barium, calcium and lead

is barium soluble or insoluble ?

soluble

is calcium soluble or insoluble ?

soluble

are all carbonates soluble or insoluble ?

insoluble except sodium, potassium and ammonium

is sodium soluble or insoluble ?

soluble

is potassium soluble or insoluble ?

soluble

is ammonium soluble or insoluble ?

soluble

are hydroxides soluble or insoluble ?

insoluble except sodium, potassium and calcium

is calcium soluble or insoluble ?

slightly soluble

how are acids and bases explained using proton transfer ?

acid-base reactions involve the transfer of protons (H⁺ ions) from acids to bases

what is an acid ?

a proton donor

what is a base ?

a proton acceptor

how do hydrochloric, sulfuric and nitric acid react with metal, bases and carbonates ?

• acid + metal → salt + hydrogen (not nitric acid)

• acid + base → salt + water

• acid + metal carbonate → salt + water + carbon dioxide

• the salt name depends on the acid:

• hydrochloric → chloride

• sulfuric → sulfate

• nitric → nitrate
  

what substances act as bases ?

metal oxides, metal hydroxides and ammonia

what is an alkali ?

bases that dissolve in water

how do you prepare a pure, dry soluble salt from an insoluble reactant ?

1. warm the acid

2. add excess insoluble base until no more reactants

3. filter to remove the excess solid

4. heat the filtrate to concentrate

5. leave to crystallise

6. filter and dry the crystals

how do you prepare hydrated copper (II) sulfate crystals from copper (II) oxide ?

1. warm dilute sulfuric acid

2. add copper (II) oxide until in excess

3. filter off unreacted solid

4. gently heat the solution

5. leave to crystalise

6. filter and dry the blue crystals