Acids And Bases

Question 1

What is the PH scale?

Answer 1

A measure of how acidic of alkaline a substance is which ranges from 0-14 (acid -alkali)
It is a measure of ion concentration

Question 2

What PHs are acidic?

Answer 2

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

Question 3

What PHs are alkali?

Answer 3

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

Question 4

What is a base?

Answer 4

A base is any substance that neutralises an acid to procure salt and water only

Question 5

What is an indicator?

Answer 5

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

Question 6

What are the affects if litmus paper as an indicator?

Answer 6

Litmus paper turns red in acidic solutions, purple in neutral solutions and blue in alkali solutions

Question 7

What affect does methyl orange have as an indicator?

Answer 7

is red in acidic solutions and yellow in neutral and alkaline solutions

Question 8

What affect does phenolphthalein have as an indicator?

Answer 8

It is colourless in acidic or neutral solutions and pink in alkaline solutions

Question 9

What are stages 1,2 and 3 of investigating the neutralisation reaction between calcium oxide and dilute hydrochloric acid?

Answer 9

• 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

Question 10

What are stages 4, 5 and 6 of investigating the neutralisation reaction between calcium oxide and dilute hydrochloric acid?

Answer 10

• 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

Question 11

What can all acids do?

Answer 11

Full dissociation in a solution - this means splitting up to produce a hydrogen ion H+ and and another ion depending on the solution

Question 12

What are strong acids?

Answer 12

Strong acids have low PHs (0-2) and ionise almost completely in water - a large proportion of acid molecules dissociate to release H+ ions

Question 13

What are weak acids?

Answer 13

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)

Question 14

What does acid strength tell you?

Answer 14

What proportion of the acid molecules dissociate in water

Question 15

What us the concentration of an acid?

Answer 15

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

Question 16

If the concentration of H+ ions increase by factor 10 and 100 and decreases by 10?

Answer 16

• The PH decrease by 1
• The PH decrease by 2
• The PH increase by 1

Question 17

What happens when acid reacts with a base?

Answer 17

Base + Acid —> salt + water

• BASHO
• a salt (ionic compound) is formed during a neutralisation compound

Question 18

What happens when metal reacts with acid?

Answer 18

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

Question 19

What happens when acid reacts with metal carbonate?

Answer 19

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

Question 20

What is acid/alkali neutralisation?

Answer 20

When the H+ ions from the acid react with the hydroxide ions OH- to form water

Question 21

What does titration allow us to do?

Answer 21

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

Question 22

What are the first four stages of titration?

Answer 22

• 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

Question 23

What are the last 4 stages of titration?

Answer 23

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

Question 24

What is the method to make an insoluble salt?

Answer 24

React two Soluble salts together in a precipitation reaction
Then wash and drop the precipitate

Question 25

What is another way other than titration to make a Soluble salt?

Answer 25

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

Question 26

What are concentrated and dilute acids?

Answer 26

• concentrated acids ave a lot of acids particles dissolved in water
• dilute acid have a small amount of acid particles dissolved in water

Question 27

What is an acid-alkali neutralisation reaction?

Answer 27

When hydrogen ions from the acid react with OH- ions from the alkali to form water

Question 28

What are the general solubility rules?

Answer 28

• 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

Question 29

What are the general insoluble rules?

Answer 29

• exceptions

- most carbonates and hydroxides are insoluble except those of sodium potassium and ammonium

Question 30

What do insoluble and soluble salts form?

Answer 30

• 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

Question 31

Why does titration have to be used?

Answer 31

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

Question 32

How can you calculate concentration using titration results?

Answer 32

Concentration - number of moles/ volume of solution

Question 33

How do you convert from g dm-3 to mol dm-3?

Answer 33

Divide by the Mr (relative formulas mass)