Acids, Alkalis and Salts
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What does concentration mean?
How much solid is dissolved in a certain volume of solution
What does dilute mean?
Relatively few particles in a given volume
What does concentrated mean?
Relatively many particles in a given volume i.e. particles much closer together
How do you convert cm^3 to dm^3?
1 dm^3 = 1000 cm^3 To convert cm^3 into dm^3, divide by 1000
What is the formula for mass concentration?
Mass concentration (g/dm^3) = Mass (g) / Volume (dm^3)
What is the formula for mole concentration?
Mole concentration (mol/dm^3) = Number of moles / Volume (dm^3)
What is the formula for the number of moles?
Number of moles = Mole concentration x Volume (dm^3)
What is the formula for mass concentration with moles?
Mass concentration = Mole concentration x Mass of one mole
What are formula for some common acids?
Nitric acid - HNO3 Hydrochloric acid - HCl Sulphuric acid - H2SO4 Phosphoric acid - H3PO4 Ethanoic acid - CH3CO2H
What is an acid?
A substance that releases H+ (aq) ions when added to water
What is a base?
A substance that reacts with acids
What are the three types of base?
Metal oxide e.g. CaO Metal hydroxide e.g. Ca(OH)2 Metal carbonates e.g. CaCO3
What are alkalis?
Substances that release OH- (aq) ions when added to water
What is the difference between a strong and a weak acid?
In strong acids all molecules ionise and release H+ ions in water in an irreversible reaction e.g. Hydrochloric In weak acids only a small fraction of the molecules ionise and release H+ ions in water in a reversible reaction e.g. Ethanoic
How does concentration of H+ ions affect pH?
Each time the concentration of H+ ions increases by 10 the pH decreases by 1
What is the pH at H+ concentration of 0.1 mol/dm^3?
1
What is the reaction of an acid and a metal?
Acid + metal –> Salt + hydrogen (not a neutralisation reaction)
What is the reaction of an acid and a metal oxide (base)?
Acid + metal oxide –> Salt + water
What is the reaction of an acid and a metal hydroxide (base)?
Acid + metal hydroxide –> Salt + water
What is the reaction of an acid and a metal carbonate (base)?
Acid + metal carbonate –> Salt + water + carbon dioxide
What is a titration?
An experiment that is used to find out the concentration of an unknown solution E.g. You have a solution of unknown concentration of an alkali and an acid of known concentration. You add the acid until an indicator shows it is exactly neutralised. By using the volume of acid, concentration of acid, and volume of alkali you can calculate the concentration of alkali
How would you carry out a titration?
Wash the burette with acid and the pipette with alkali Place a white tile under a conical flask Fill the burette with acid. Use the pipette to fill a conical flask with a certain volume of alkali Add a few drops of indicator to the conical flask Using the burette add acid to the conical flask drop by drop. Swirl the conical flask The indicator changes colour when all the acid has been neutralised Repeat the process to get similar results
What colour does phenolphthalein turn in acids and alkalis?
Acids - Colourless Alkalis - Pink
What colour does methyl orange turn in acids and alkalis?
Acids - Red Alkalis - Yellow