Section 4: Physical Chemistry
a) Acids, Alkalis and Salts
4.1 describe the use of indicators litmus, phenolpthalein and methyl orange to distinguish between acidic and alkaline solutions

• Litmus paper: red in acidic solutions, purple in neutral solutions, blue in alkaline solutions
• Phenolpthalein: colourless in acidic solutions, pink in alkaline solutions
• Methyl orange: red in acidic solutions, yellow in alkaline solutions

4.2 understand how the pH scale, from 0-14, can be used to classify solutions as strongly acidic, weakly acidic, weakly alkaline or strongly alkaline

Strongly acidic: pH of 0-2

Weakly acidic: pH of 3-6

Neutral: pH of 7

Weakly alkaline: pH pf 8-10

Strongly alkaline: pH of 11-14

4.3 describe the use of universal indicator to measure the approximate pH value of a solution

1.  Add a few drops of universal indicator to the sample
2. Mix and compare the colour produced to the pH scale

4.4 define acids as sourced of hydrogen (H+) ions, and alkalis as sources of hydroxide (OH-) ions

Acids: H+ ions

Alkalis: OH- ions

→ Alkalis are soluble bases (bases are substances that can neutralise acids)

Acid + Base → salt + water

4.5 predict the products of reactions between dilute hydrochloric , nitric and sulfuric acids; and metals, metal oxides and metal carbonates (excluding the reactions between nitric acid and metals)

Acid + metal oxide → salt + water

--Metal oxides are basic

eg.

Hydrochloric acid + copper oxide → copper chloride + water

2HCl + CuO → CuCl2  + H2O

Sulfuric acid + zinc oxide zinc sulfate + water

H2SO4 + ZnO → ZnSO4 + H2O

Nitric acid + copper oxide → copper nitrate + water

2HNO3 + CuO → Cu(NO3)2 + H2O

Acid + metal carbonate → salt + water + carbon dioxide

eg.

Hydrochloric acid + sodium carbonate  → sodium chloride + water + carbon dioxide

HCl + Na2CO3  → NaCl + H2O + CO2

Sulfuric acid + calcium carbonate → calcium sulfate + water + carbon dioxide

H2SO4 + CaCO3 → CaSO4 + H2O + CO2

Nitric acid + calcium carbonate →  calcium nitrate + water + carbon dioxide

2HNO3 + CaCO3 → Ca(NO3)2  +  H2O + CO2

Metal + acid → salt + hydrogen (MASH)

eg.

Hydrochloric acid + copper → copper chloride + hydrogen

HCl + Cu → CuCl2 + H2

Sulfuric acid + copper → copper sulfate + hydrogen

H2SO4 + Cu →  CuSO4 + H2

4.6 understand the general rules for predicting the solubility of salts in water

Soluble:

• all common sodium, potassium and ammonium salts
• all nitrates
• most common chlorides
• most common sulfates

Insoluble:

• silver chloride
• barium and calcium sulfate
• most common carbonates

4.6 describe experiments to prepare soluble salts from acids and insoluble bases

eg 2HNO3 + CuCO3 → Cu(NO3)2 + H2O + CO2 

(The base - copper carbonate - is insoluble, but the salt produced - copper nitrate - is soluble)

1. Add the base to the acid - the solid will dissolve as it reacts - excess will sink when all the acid has been neutralised
2. Filter out the excess to leave the salt solution
3. Evaporate off the water to leave soluble salt crystals

4.8 describe experiments to prepare insoluble salts using precipitation reactions

1. Pick 2 solutions that contain the ions you need. Eg. to make barium sulfate you need barium and sulfate ions. You can mix barium chloride (most chlorides are soluble but barium sulfate is insoluble) and sulfuric acid

H2SO4 + BaCl2 → BaSO4 + 2HCl

4.9 describe experiments to carry out acid-alkali titrations

Titrations are used to find out the concentrations needed to neutralise

1. Using a pipette and a pipette filler add some alkali eg 25 cm3 into a conical flask along with 2 to 3 drops of an indicator
2. Fill a burette with acid - BELOW EYE LEVEL - so if some spills none gets in your eyes
3. Using the burette add small amounts of acid to the alkali (swirling the conical flask)
4. The indicator will change colour once all of the alkali has been neutralised
5. Record the volume of acid used
6. Repeat to make sure you get around the same answer and calculate an average - to have a reliable result
7. Use the formula concentration = moles/volume, to find the concentration of acid needed (in mol/dm3)