Acids, alkalis and salts

Question 1

What colour is:

Universal indicator

Answer 1

Neutral - green
Acid - Red
Alkali - Blue

Question 2

What colour is:

Litmus

Answer 2

Acid-Red
Alkali - Blue

Question 3

What colour is:

Methyl orange

Answer 3

Acid - red
Alkali - Yellow
Neutral - Orange

Question 4

What colour is:

Phenolphthalein

Answer 4

Acid - colourless
Alkali - pink

Question 5

What different groups are there in the pH scale:

Answer 5

0-3 strongly acidic - hydrochloric acid
4-6 weakly acidic - vinegar
7 - neutral - water
8-10 weakly alkaline - ammonia solution
11-14 - strongly alkaline - sodium hydroxide solution

Question 6

is carbon dioxide acidic?

Answer 6

Yes, because it reacts in water to form carbonic acid

Question 7

What are alkalis?

Answer 7

Soluble bases, as it needs to be dissolvable in water to be acidic/alkaline. These are also proton acceptors as they react with H+ to form H2O

Question 8

What are the different equations for metals and acids?

Answer 8

Metal + acid -> salt + hydrogen
Metal oxide + acid -> Salt + water
Metal hydroxide + acid -> Salt + water
Metal carbonate + acid -> Salt + water + carbon dioxide
Ammonia + acid -> Salt (contains ammonium)

Question 9

what is a neutralisation reaction?

Answer 9

When bases, e.g. metal oxides react with acids which neutralises to form water. OH+H=H2O

Question 10

What is a titration?

Answer 10

When a neutralisation reaction occurs between bases and alkalis where the reactant’s volumes are measured

Question 11

What are acids usually described as?

Answer 11

proton donors as they dissociate with a hydrogen ion which gives water a proton as H+ has just a proton

Question 12

What are bases described as?

Answer 12

Proton acceptors as they react with H+ (a proton). e.g., hydroxide accepts H+ to form water

Question 13

What are alkalis?

Answer 13

soluble bases that form OH- in water

Question 14

How can it be determined if dilute acids react with a metal?

Answer 14

Depending on the position in the reactivity series. The reaction is more vigorous up the series.

Question 15

Characteristics of strong and weak acids

Answer 15

Strong acid Weak acid
Nature Fully dissociated Partially dissociated
Examples Hydrochloric acid Ethanoic acid
Reaction with Mg Lots of bubbles, warm Some bubbles
Reaction with carbonates Bubbles Fewer bubbles
Colour of universal indicator with typical solution Red Orange -red

Question 16

What are the different methods of forming soluble and insoluble salts

Answer 16

soluble salt from acid and alkali (titration)
soluble salt from an acid and insoluble base/metal/carbonate (crystallisation)
insoluble salt from two soluble salt (precipitation reaction)

Question 17

Steps for making a soluble salt from an acid and an insoluble base

Answer 17

1. add excess solid to the acid (to neutralise all the acid) and stir
2. filter to remove excess solid when all acid has been neutralised
3. Heat pure salt solution to evaporate some of the solution which concentrates the solution until some crystals form
4. cool, leading to crystals forming (as at lower temperatures less solute can be dissolved in a solvent) and then filter to separate out the crystals
5. Dry salts in warm oven

Question 18

What are the steps for titration?

Answer 18

1. add 25cm^3 of alkali/acid to a conical flask using a volumetric pipette. Add 4 drops of indicator
2. use a burette to add acid/alkali till the first permanent colour change(swirl at the same time)
3. Repeat the titration 3 times doing it drop by drop when the end point is approaching
4. Do a titration without indicator adding the average volume of acid : alkali
5. Heat pure salt solution to evaporate some of the solution which concentrates the solution until some crystals form
6. cool, leading to crystals forming (as at lower temperatures less solute can be dissolved in a solvent) and then filter to separate out the crystals
7. Dry salts in warm oven

Question 19

Method for making an insoluble salt from 2 soluble parts

Answer 19

1. combine equal quantities of two solutions and stir
2. filter out the salt crystals (residue)
3. wash crystals with pure distilled water
4. dry salt crystals in warm oven

Question 20

What is solubility measured as?

Answer 20

grams that will dissolve in 100 grams
of water at a specific temperature

Question 21

what is the formula with moles, vol and conc

Answer 21

moles = vol * conc

Question 22

what would be on the x and y axis of a solubility curve

Answer 22

y axis - g/100 g of water
x axis - temperature

Question 23

How to find out:

volume of acid to neutralise an alkali

Answer 23

1. add indicator in conical flask, as well as 25cm^3 of alkali with volumetric pipette and add in acid using a burette
2. stop when colour change occurs (ideally name colour change)
3. start value - end value gets change in volume
4. do dropwise/swirling/repeating and using concordont results