The pH scale and salts

what happens to an aqueous solution

when a substance dissolves in water, they dissociate into their individual ions

what do H+ ions make

hydrogen ions (H+) make solutions acidic

what do OH- ions make

hydroxide ions (OH-) make solutions alkaline

how do you measure pH

the pH of a solution is measured using a pH probe or a universal indicator

what is an indicator

a indicator is a dye that changes colours to tell you wether a substance is acidic or alkaline

litmus paper?

litmus paper changes from red → blue and vice versa

universal indicator

a universal indicator is a mixture of dyes that show a range of colours to indicate how acidic or alkialine a substance is

what is a alkiline

are soluble bases

what is a base

bases are insoluable

connection between alikline and bases

• all alkaline’s are bases

• but bases aren’t all alkaline

what happens when H+ and OH- react

form water- neutralisation reaction

why is it called a neutralisation reaction

• acid in neutralised by an alkali

• the solution that remains has a pH of 7 showing its neutral

acid + metal oxide / hyroxide →

salt + water

acid + metal carbonate →

salt + water + carbon dioxide

what salt does hydrochloric acid produces

chloride salts

what salt does nitric acid produces

nitarte salts

what salt does sulfuric acid produces

sulfate salts

what makes an acid acidic

H+ ions

what is pH

the concentration of H+ ion

the more H+ ions,

the lower the ph (more acidic)

what is a strong acid

one that completely dissociates (splits up) into ions when its dissolved in water

what is a weak acid

one where only partially splits up into ions in dilute solution and many unchanged molecules remain

what is the strength

how much an acid dissociates

what is the concentration

how much acid there is in a certain volume

what are the two things you can have when it comes to strength and conc

• you can have a strong acid with a high or low concentration

• you can have a weak acid with a high or low concentration

what is a strong acid like HCl like

• you could achieve a low pH at most conc. because each particle fully dissociates

• so overall you’d have lots of H+ ions released

what is a weak acid like carbonic acid like

• to get a low pH it would have to be very concentrated because few of the acid particles would ionise releasing their hydrogen ions

at any given concentration a strong acid will…

• have a low pH than a weak acid

• because a higher a proportion of the strong acid molecules will dissociate to release their hydrogen ions

• and its only the concentration of hydrogen ions that determine the pH

a pH decrease of one unit

indicates a that the concentration of hydrogen ions has increased by a factor of 10

examples of acids

• sulfuric acid

• HCL

• citric acid

• ethanoic acid

examples of bases

• K2CO3 (potassium carbonate)

• CuO (copper oxide)

• Fe2O3 (iron oxide)

• Al2O3 (aluminium oxide)

examples of alkaline

• LiOH (Lithium hyrdoixe)

• NH3 (ammonia)

• potassium hyroxide

examples of salts

• NaBr (sodium bromide)

• AgCl (silver chloride)

• copper sulfate

• KNO3 (potassium nitarte)

how do you know if smth is an acid

will always have hydrogen in it

how do you know if smth is a base

if it had carbonate or oxide it will be an insoluable base

how do you know if smth is an alkaline

when you have hydroxide, or ammonia dissolved into a solvent/liquid

how do you know if smth is an salt

when there is a metal bonded to nitarte/sulfate or halogen

practical

obstaining a pure, dry sample of a soluable salt

method

1) measure the certain volume of solution

2) warm the sulphuric acid gently

3) add some copper to the acid and stir

4) continue adding copper in excess until no more dissolves

5) filter the solution

6) the filtrate is put in an evapourating basin and you gently heat it using a bunsen burner

7) leave that to dry (the longer it take to cool down/you leave it to cool down, the larger the crystal will be)

8) crystals will form

what are some hazards/risks

• corrosive acid can cause damage to eyes, so use goggles

• hot equipment can cause burns, so care must be taken when the salt solution is warmed

how can soluble salts be made

be reacting acids with insoluble bases such as metal oxides, metal hydroxides and metal carbonates