5 - acids Flashcards
Define acid
An acid is a proton donor
How do we know if a substance is an acid if we have the chemical formula?
It contains H+ ions
What happens when you put an acid in water?
It releases H+ ions and the other negative ion
What are the chemical formulae of the 4 main acids?
Hydrochloric = HCl
Sulphuric = H~2 SO~4
Nitric = HNO~3
Ethanoic = CH~3 COOH
What does dissociate mean?
When an acid is put into water and the ions are released into the water
What makes an acid strong or weak?
A strong acid completely dissociates
A weak acid partially dissociates
What is a H+ ion physically?
Just a proton
Define base
A proton accepter
What are the main examples of bases?
Hydroxides, oxides, ammonia etc.
Define alkali
A type of base which dissolves in water to release OH- ions
basically, a hydroxide
What is the only common alkaline gas?
Ammonia
What happens when ammonia is put in water?
Ammonium ions and hydroxide ions are released
Define salt
A substance which is formed when a H+ ion from an acid is replaced by another positive ion (could be metal ion)
What happens when a salt and base react?
Salt and water are formed
What are the salts formed by the 4 main acids?
Hydrochloric –> chloride
Sulphuric –> sulphate
Nitric –> nitrate
Ethanoic –> ethanoate
What is the state of matter of acids, bases and salts?
acids are aqueous
salts are usually aqueous unless specified otherwise
Bases are either aqueous or solids
How do the 4 main acids dissociate?
H~2 SO~4 –> 2H+ + SO~4 2-
HCl –> H+ + Cl-
HNO~3 –> H+ + NO~3-
CH~3 COOH –> H+ + CH~3 COO-
What is the ionic equation for all reactions between acids and alkalis?
H+ + OH- –> H~2 O
What is the ionic equation between acids and bases?
Find the salt and deduce which 2 ions it’s made from
You write that those 2 ions go to the salt
That is the ionic equation
What happens when a acid reacts with a metal?
Acid + metal –> salt + hydrogen gas
When happens when an acid reacts with a carbonate?
Acid + carbonate –> salt + carbon dioxide + water
What happens when an acid reacts with ammonia?
Ammonia + acid –> ammonium salt (and nothing else)
What happens when an acid reacts with any other base?
Acid + base –> salt + water
Describe how to prepare a standard solution
Weigh the solid accurately
Dissolve the solid in a beaker but don’t fill it
Transfer the solution to a volumetric flask and rinse traces of solution from the beaker to the flask
Carefully fill the volumetric flask to the graduation line (read the meniscus at eye level)
Invert the flask several times to ensure the solution is well mixed
Describe the method of titration
Using a pipette, we measure a volume of the standard solution into a conical flask
The other solution is placed in a burette and the volume is recorded
A few drops of indicator is added to the solution in the conical flask
The solution in the burette is added to the conical flask until the reaction has just completed (this is the equivalence point) and we see a different colour
The volume of solution added from the burette is calculated (this is called the titre)
The experiment is repeated until 2 titres are concordant to 0.1 cm^3
The mean titre is calculated to 1 decimal place and only concordant titres are used in the mean
Explain the effect on the titre of filling the flask above the graduation line
This would cause the standard solution to be less concentrated
This means the titre volume would be larger in order to neutralise the standard solution
Explain the effect on the titre of not inverting the flask
The concentration would now be inaccurate because it wouldn’t be the same throughout the standard solution
This causes the titre to be simply inaccurate
Explain the effect of the burette readings being taken from the top of the meniscus
Looking at the readings from above will give less accuracy in the readings because it is harder to differentiate between the different reading marks
This would cause the calculated titre to be less accurate than if the readings were taken at eye level
