C8: Acids, Bases and Salts

Aqueous solutions can be acidic, alkaline or neutral Indicators - used to tell if a solution is acidic, alkaline, basic or neutral

Litmus paper is commonly used as an indicator. Colour of litmus + type of solution:red - acidic purple - neutralblue - alkaline 

Universal Indicators (UI) - show strengths of solutions of acids and alkaliEach colour is linked to a number on the pH scale  

WHAT ARE ACIDS?Acids - substances that contain replaceable hydrogen atoms- acidic properties shown when water is present -- hydrogen ions H+ (protons) are formed from acids in water E.g.: HCl(aq) ----> H+(aq) + Cl-(aq)Basicity - describes how many hydrogen ions can be replaced in an acid molecule 

WHAT ARE BASES?Bases - substances that accept an H+ ion from an acid - Acids are proton (H+) donors in water- Bases are proton (H+) acceptors in water

limestone ---1200˚C --> quicklime + carbon dioxide

quicklime + slaked lime ---> calcium hydroxide (alkali) 

Neutral solutions: - pH of 7 - don't change colour of litmus paper but turn UI green- e.g. water

METAL HYDROXIDESacid + metal hydroxide --> salt + water

METAL OXIDESacid +metal oxide ---> a salt + water

METAL CARBONATES:acid + metal carbonate ---> a salt + water + carbon dioxide

during reaction:- temp rises - pH changes 

during reaction:- temp rises- pH changes 

during reaction: - bubbles of gas- carbon dioxide produced: test with limewater (turns cloudy) 

- dissolve in water, forms clear, colourless solutions- e.g. sodium hydroxide 

- dissolve in water; forms clear colourless solutions - not soluble in water e.g. copper(II) - e.g. sodium oxide 

- most not soluble e.g. calcium carbonate (chalk, limestone and marble)

Naming 

Naming salts: metal involvedacidsaltsodium hydroxide reacts withhydrochloric acidto make sodium chloridepotassium hydroxide reacts withsulphuric acid to makepotassium sulphatecopper oxide reacts withhydrochloric acid to makecopper chloridezinc oxide reacts withsulphuric acid to makezinc sulphatecalcium carbonate reacts withhydrochloric acid to makecalcium chloridesodium carbonate reacts withsulphuric acid to makesodium sulphate

WHAT ARE ALKALIS? Alkalis - bases that dissolve in water e.g. sodium hydroxide - pH more than 7 - turns litmus paper blue  

The first part of the salt's name if from the base used or the name of the metal in the base.Second part of the name comes from the acid used:- Chloride (hydrochloric acid used)- Nitrate (nitric acid used)- Sulfate (sulfuric acid used) 

Acid+Base→Salt + WaterHydrochloric acid+Copper oxide→Copper chloride + waterSulfuric acid+Sodium hydroxide→Sodium sulfate + waterNitric acid+Calcium hydroxide→Calcium nitrate + water

Oxi

Oxides - made by heating the element in air or oxygen 

2Mg(s) + O2 (g) ----> 2MgO(s) magnesium + oxygen--> magnesium oxide

for

- forms white ash- pH is greater than 7- forms an alkaline solution

S(s) + O2(g) ---> SO2(g)sulphur + oxygen ---> sulphur dioxide 

- forms gas - pH less than 7 - forms an acidic solution

Basic oxides - oxides of metals containing O2- e.g. 2Mg(s) + O2(g) ---> 2MgO(s)- have big ionic structures- react with acids (neturalisation) HCl(aq) + MgO(s) ---> MgCl2(aq) + H2O(l) acid + base ---> a salt + water 

The characteristic properties of acids and bases

controlling acidity

Making salts

Naming salts

Types of oxides