4a) Acids and Alkalis

Indicators:

1. Universal indicator is a very useful combination of dyes which give one of the colours on the pH scale
2. Litmus paper tests whether a solution is acidic or alkaline because it changes colour at pH 7.  
1. Red in acidic solutions 
2. Blue in alkaline solutions 
3. Purple in neutral solutions 
3. Phenolphthalein will change from colourless in acidic solutions to bright pink in alkaline solutions 
4. Methyl Orange changes from red in acidic solutions to yellow in alkaline solutions. 

pH Scale:

+----+---------------------------+---------+--------------------------------+
|    |           Acids           | Neutral |            Alkaline            |
+----+---------------------------+---------+--------------------------------+
| pH | 0 | 1 | 2 | 3 | 4 | 5 | 6 |    7    | 8 | 9 | 10 | 11 | 12 | 13 | 14 |
+----+---+---+---+---+---+---+---+---------+---+---+----+----+----+----+----+

Acids;

• below pH scale 
• produce hydrogen ions, H+ when dissolved in water 
• acids + metal ----> salt and hydrogen 
• acids + metal oxides ----> salt and water 
• acids + metal carbonates ----> salt and water and carbon dioxide 

Common acids and salts produced

-hydrochloric acid to chloride

-nitric acid to nitrates 

-ethanoic acid to ethanoates 

Alkalis:

• above pH 7 
• produce OH- (hydroxide) ion when dissolved into water
• alkalis + acids ----> salt and water 

Common alkalis 

-sodium hydroxide 

-ammonia solution 

General rules for predicting the solubility of salt in water:

• All common sodium, potassium and ammonium salts are soluble 
• All nitrates are soluble 
• Common chlorides are soluble, except silver chloride 
• Common sulfates are soluble, except those of barium and calcium
• Common carbonates are insoluble, except those of sodium, potassium and ammonium 

Preparing soluble salts from acids and insoluble bases:

• Add excess solid to ensure that all the acid has reacted 
• Filter it 
• Evaporate half water 
• Leave to crystallise 

Insoluble salts using precipitation reactions:

• Mix the two solutions which contain the ions you need 
• filter precipitate
• wash 
• dry

Acid-Alkais titration:

• Using a pipette and pipette filler, add some alkali to a conical flask, along with two or three drops of indicator 
• Fill a burette with acid 
• Using the burette, add the acid to the alkali a bit at a time- giving the conical flask a regular swirl. Go especially slowly when you reach the end point of the colour change of the indiactor
• The indicator changes colour when all the alkali has been neutralise 
• Record the volume of acid used to neutralise the alkali, it's best to repeat the process several times to make sure you have reliable results. 

Section 4

Physical Chemistry

3d) Ethanol

This whole section is for Paper Two:

Manufacture of Ethanol by Ethene and Steam (H₂O):  

-C₂H₄ + H₂O  C₂H₅OH
-hydration- exothermic
-300C and 60-70 atm
-phosphoric acid catalyst
-un-reacted ethene recycled

fast reaction 
pure ethanol
continuous 

non-renewable resources 
energy needed to make steam 

Manufacture of Ethanol from Fertilisation: 

-C₆H₁₂O₆ -----> 2C₂H₅OH + 2CO₂
-anaerobic respiration
-exothermic reaction
-20-60 hrs

-30-40C
-purified by fractional distillation

renewable resources 
organic waste material 

impure ethanol due to water 
slow process
only 15% ethanol in each batch 

Dehydration of Ethanol to Ethene:

Ethanol    ------> Water and Ethene 

C₂H₅OH ------>  H₂O  and C₂H4 

3c) Alkenes

• general formula - CnH2n
• double bond - unsaturated 

Ethene		C2H4
Propene		C3H6
Butene		C4H8

Butene Isomers:

Isomers have the same molecular formula,but a different structural formula 

Commonly represented as:

Methylpropene:

Addition reaction of alkenes and bromine

Test for C = C, Add Bromine water
It turns from orange to colourless

3b) Alkanes

• Single covalent bonds of hydrocarbon 
• General formula of CnH2n+2

Name	Displayed formula	Molecular formula
Methane		CH4
Ethane		C2H6
Propane		C3H8
Butane		C4H10
Pentane		C5H12

Isomers- different structures 

• Butane 
• Methylpropane 

Complete and Incomplete combustion:

Complete: Alkane and Oxygen -----> Carbon dioxide and water
                    CH4   and   2O2     ---->          CO2          and 2H2O

Incomplete: Carbon monoxide- C3H8 + 3.5O2 -----> 3CO + 4H2O
                     Carbon (soot)- C3H8 + 2O2 -----> 3C + 4H2O

Methane Substituion Reaction /w Halogen
CH4 + Br2 ---UV Light---> CH3Br + HBr  

3a) Introduction

Homologous series ----------> - have same general formula
                                                - successive members differ by CH4
                                                - similar chemical reactions
                                                - tread in physical properties --> boiling and melting points

Hydrocarbon -----------> compound made up of only carbon and hydrogen

Saturated: no double bonds
Unsaturated: double bonds

Isomerism: Referring to isomers which are molecules that have the same molecules but have different displayed formulas.

Section 3

Organic Chemistry

2g) Tests for ions and gases

Flame tests for metal ions:

• dip in HCl
• Heat in flame 
• Clean
• dip in crystals 
• place on burnsen burner flame 
• identify colour 

+-------------+-----------+---------------------+
| Metal ions  |           | Flame test colour   |
+-------------+-----------+---------------------+
| Li+         | Lithium   | Brick red/ Crimson  |
+-------------+-----------+---------------------+
| Na+         | Sodium    | Yellow              |
+-------------+-----------+---------------------+
| K+          | Potassium | Purple/Lilac        |
+-------------+-----------+---------------------+
| Ca3+        | Calcium   | Brick red           |
+-------------+-----------+---------------------+

Tests for gases

+--------------------+------------------------+----------------------------+
| Hydrogen H2        | Light                  | Burns with a 'squeaky pop' |
+--------------------+------------------------+----------------------------+
| Oxygen O2          | glowing splint         | Relights                   |
+--------------------+------------------------+----------------------------+
| Carbon Dioxide CO2 | Limewater              | Makes it go cloudy/milky   |
+--------------------+------------------------+----------------------------+
| Ammonia NH3        | Damp red litmus paper  | turns blue                 |
+--------------------+------------------------+----------------------------+
| Chlorine Cl2       | Damp blue litmus paper | turns red                  |
+--------------------+------------------------+----------------------------+

Tests for cations:

+------+---------------+----------------------------------------+
| NH4+ | Add NaOH (aq) | NH3 released;test --> damp red litmus  |
|      |               | paper goes blue                        |
+------+---------------+----------------------------------------+

+-------+-----------+------------------------+
| Cu2+  | Add NaOH  | Pale blue precipitate  |
+-------+-----------+------------------------+
|       | Cu2+(aq) + 2OH-(aq) --> Cu(OH)2(s) |
+-------+------------------------------------+

+-------+-----------+-------------------------+
| Fe2+  | Add NaOH  | Dirty green precipitate |
+-------+-----------+-------------------------+
|       | Fe2+(aq) + 2OH-(aq) --> Fe(OH)2(s)  |
+-------+-------------------------------------+

+-------+------------+-----------------------+
| Fe3+  | Add NaOH   | Red-brown precipitate |
+-------+------------+-----------------------+
|       | Fe3+(aq) + 3OH-(aq) --> Fe(OH)3(s) |
+-------+------------------------------------+

Tests for anions:

+-------+-------------------------------+-------------+
| Ion   |                               | Precipitate |
+-------+-------------------------------+-------------+
| Cl-   | dilute nitric acid. Add AgNO3 | white       |
+-------+-------------------------------+-------------+
|       |        Ag+(aq) + Cl-(aq) --> AgCl(s)        |
+-------+---------------------------------------------+
| Br-   | dilute nitric acid. Add AgNO3 | cream       |
+-------+-------------------------------+-------------+
|       |        Ag+(aq) + Br-(aq) --> BrAg(s)        |
+-------+---------------------------------------------+
| I-    | dilute nitric acid. Add AgNO3 | yellow      |
+-------+-------------------------------+-------------+
|       |         Ag+(aq) + I-(aq) --> AgI(s)         |
+-------+---------------------------------------------+
| SO42- | Acidify with HCL. Add BaCl2   | white       |
+-------+-------------------------------+-------------+
|       |      Ba2+(aq) + SO42-(aq) --> BaSO4(s)      |
+-------+---------------------------------------------+
| CO32- | Add acid, CO2 is released.    | milky       |
|       | Bubble through limewater      |             |
+-------+-------------------------------+-------------+