C2.6 Acids, Bases and Salts Flashcards
What pH does a substance need to be, in order to be acidic?
Under than pH 7
What pH does a substance need to be, in order to be a base or an alkali?
Higher than pH 7
What pH does substance need to be, in order to be neutral?
7
What can be used to test the acidity of substances?
Indicators e.g. universal indicator which gives different colour at different pH values
What are examples of products which are acidic? (3)
Car battery acid, vinegar and lemon juice
What are examples of products which are alkaline? (3)
Bleach, soap powder and washing-up liquid
Besides pH, what else determines weather a substance is acidic or alkali?
The ions it releases when the substance is dissolved in water
What ions are released when acids are dissolved in water?
Hydrogen ion - H+(aq)
What ions are released when alkalis are dissolved in water?
Hydroxide ions - OH-(aq)
What does the state symbol (aq) mean?
Dissolved in water
What are the 4 state symbols?
aq, l, g and s
What is the word equation for a neutralisation reaction?
acid + base ==> salt + water
How can a neutralisation reaction be shown in terms of ions?
H+(aq) + OH-(aq) ==> H2*O(l)
What pH are the products from a neutralisation reaction (when an acid neutralises a base)?
They are neutral - they have a pH of 7
What is the word equation for reacting a metal with an acid?
acid + metal ==> salt + hydrogen
Why is it that not all metals can be used to make salts from reacting it with an acid? (2)
Because some metals are too reactive and will explode in the presence of an acid, and some metals are aren’t reactive enough and won’t produce any salt
How can the production of hydrogen be tested?
By using the burning splint test - a lit split at the mouth of a test tube whilst the acid and metal are reacting, will make a ‘squeaky pop’ sound if hydrogen is present, the louder the pop the more hydrogen present
What determines the name of a salt, from reacting a metal with an acid?
The first part of the salt is the name of the metal, and the second part of the salt is the from the type of ions present in the acid e.g. hydrochloric acid + magnesium ==> magnesium chloride + hydrogen
What are most metal oxide and hydroxides a form of?
Bases - though some are alkalis because they’re soluble in water
What is the word equation for the reaction of an acid and a base?
acid + metal oxide or metal hydroxide ==> salt + water
What determines the name of a salt, from reacting an acid with a base?
The first part is the metal from the metal oxide(/hydroxide) and the second part is the ions present in the acid e.g. hydrochloric acid + copper oxide ==> copper chloride + water
What is produced when ammonia is dissolved in water?
An alkaline solution
How can you make a salt from ammonia?
By reacting it with nitric acid
What is the word equation for reacting ammonia with nitric acid?
Ammonia + nitric acid ==> ammonium nitrate
What salts are soluble?
Most chlorides, sulphates and nitrates - besides, lead chloride, lead sulphate and silver chloride
How can you determine what reagents were used to make a particular salt?
By the name of the salt - remember that the salt is named after the acid and the metal, insoluble base or soluble base used to make it
What determines what method is used to make a salt?
On whether the reagents used are soluble or insoluble
How do you make a soluble salt from a metal or insoluble base? (Insoluble reactant = IR)
- Add the IR to the acid and stir - it will dissolve in the acid as it reacts
- Keeping adding the IR until it is in excess - this shows that the acid has been neutralised and the reaction has finished
- The IR is then filtered out using filter paper and a funnel - the solution left over is a salt solution
How do you make a soluble salt with an alkali (soluble base)?
Using the same method as you would with an insoluble base, however you need to use an indicator to see when the solution is neutralised and then repeat this with the same volume of acid and alkali so the salt isn’t contaminated with indicator
How can you convert a salt solution into a pure solid crystal?
By using crystallisation
How do you carry out crystallisation?
First off all, you heat the solution to evaporate most of the water and make it more concentrated, the left is then left at room temp. to allow the rest of the water to slowly evaporate, and for the salt to crystallise
How can you make insoluble salts?
By using a precipitation reaction
What is a precipitation reaction?
A reaction where one of the products is insoluble and so forms as a solid precipitate in solution
How do you carry out a precipitation reaction?
By mixing two aqueous solutions that contain the ions you need - once the precipitate has formed you can filter out the solution
What are other uses of precipitation reactions? (3)
To remove poisonous ions from drinking water, to remove calcium and magnesium ions from water to make it soft, and to remove unwanted ions during the treatment of effluent (sewage)
Why are precipitation reactions used?
Because it helps to remove specific ions from a solution
