Acids And Bases Flashcards
What is the PH scale?
A measure of how acidic of alkaline a substance is which ranges from 0-14 (acid -alkali)
It is a measure of ion concentration
What PHs are acidic?
Ant PHs lower than 7(neutral) are acidic
-acid forms H+ ions when dissolved in water and so the higher concentration of hydrogen ions in a solution, the more acidic it is
What PHs are alkali?
Any PH above 7(neutral) is alkali
- an alkali is a base that is Soluble in water
- alkalis (hydroxide ions) form OH- ion when dissolved in water so the higher the concentration of OH- ions the higher the PH
What is a base?
A base is any substance that neutralises an acid to procure salt and water only
What is an indicator?
A dye that changes colour depending on weather it’s above a below a certain PH (e.g. universal indicator)
-you add a few drops to the solution you want to test
What are the affects if litmus paper as an indicator?
Litmus paper turns red in acidic solutions, purple in neutral solutions and blue in alkali solutions
What affect does methyl orange have as an indicator?
is red in acidic solutions and yellow in neutral and alkaline solutions
What affect does phenolphthalein have as an indicator?
It is colourless in acidic or neutral solutions and pink in alkaline solutions
What are stages 1,2 and 3 of investigating the neutralisation reaction between calcium oxide and dilute hydrochloric acid?
- measure out a set volume of dilute hydrochloric acid info a clinical flask
- measure a fixed mass of calcium oxide using a mass balance
- add the calcium oxide to the hydrochloric acid
What are stages 4, 5 and 6 of investigating the neutralisation reaction between calcium oxide and dilute hydrochloric acid?
- wait for the base to completely reach and record the PH of the solution
- repeat stages 2-4 until all the acid has reacted (you’ll know you’ve reached this point when the unrequited calcium oxide is sitting at the bottom of the flask
- then plot a graph to see how the PH changes with the mass of base added
What can all acids do?
Full dissociation in a solution - this means splitting up to produce a hydrogen ion H+ and and another ion depending on the solution
What are strong acids?
Strong acids have low PHs (0-2) and ionise almost completely in water - a large proportion of acid molecules dissociate to release H+ ions
What are weak acids?
Weak acids tend to have PHs around 2-6 and do not fully dissociate in a solution, only a small proportion of the acid molecules dissociate
-the ionisation of a weak acid is a reversible reaction, which sets up an equilibrium (yet as only a few of the acid particles release H+ ions p, the equilibrium lies well to the left)
What does acid strength tell you?
What proportion of the acid molecules dissociate in water
What us the concentration of an acid?
Concentration measures how many particles are dissolved in a certain volume of water (how watered down your acid is by the total number of dissolved acid molecules)
-you can either have a concentrated or diluted acid
If the concentration of H+ ions increase by factor 10 and 100 and decreases by 10?
- The PH decrease by 1
- The PH decrease by 2
- The PH increase by 1
What happens when acid reacts with a base?
Base + Acid —> salt + water
- BASHO
- a salt (ionic compound) is formed during a neutralisation compound
What happens when metal reacts with acid?
Metal + acid —> salt + hydrogen
- MASH
- you can test for hydrogen by lighting a splint and holding it in a test tube, if there is hydrogen you will hear a squeaky pop
What happens when acid reacts with metal carbonate?
Metal carbonate + Acid —> salt + water + carbon dioxide
- CASHOCO
- you can test for carbon dioxide by bubbling it through limewater, if the gas is carbon dioxide, the limewater should turn cloudy
What is acid/alkali neutralisation?
When the H+ ions from the acid react with the hydroxide ions OH- to form water
What does titration allow us to do?
Make an uncontaminated salt as it is a slow and gradual process and see precisely the volume of acid needed to neutralise a set amount of alkali
What are the first four stages of titration?
- Into the conical flask measure a set amount of alkali and add 3 drops of phenol (do on a white so colour change is easier to see)
- slowly add acid to the acid using a Burnett swirling the flask regularly and slow down when you think the alkali is almost neutralised (do a rough titration before so you have some idea)
- add the initial readings to your table
What are the last 4 stages of titration?
The indicator changes copping when all the alkali has been neutralised
- record the volume of acid used to neutralise the titre
- retreat this process a few times to make sure the results are similar and calculate the mean
- the solution at the end is only salt and water
What is the method to make an insoluble salt?
React two Soluble salts together in a precipitation reaction
Then wash and drop the precipitate
What is another way other than titration to make a Soluble salt?
React excess InSoluble bases with an acid
- heat in water bath so speed up reaction
- must be in excess so that you don’t have any leftover acid in your product
- filters of the excess solid to creates a solution containing only salt and Walter
- heat the solution gently using a Bunsen Bruner so evaporate of some of the water and then leave it to cool and the salt to crystallise
What are concentrated and dilute acids?
- concentrated acids ave a lot of acids particles dissolved in water
- dilute acid have a small amount of acid particles dissolved in water
What is an acid-alkali neutralisation reaction?
When hydrogen ions from the acid react with OH- ions from the alkali to form water
What are the general solubility rules?
- all common sodium, potassium and ammonium salts are
- all nitrates are
- common chlorides are soluble except those of silver and lead
- common sulphates are soluble except those of lead, barium and calcium
What are the general insoluble rules?
- exceptions
- most carbonates and hydroxides are insoluble except those of sodium potassium and ammonium
What do insoluble and soluble salts form?
- insoluble salts won’t dissolve in the water so are left as solids on the solution (precipitates)
- soluble salts will dissolve in the water making aqueous solutions
Why does titration have to be used?
You can’t tell when the reaction is finished as the salt is soluble and would be contained with excess alkali
-you must work out the exact right amount of alkali needed to neutralise the acid
How can you calculate concentration using titration results?
Concentration - number of moles/ volume of solution
How do you convert from g dm-3 to mol dm-3?
Divide by the Mr (relative formulas mass)
