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Chemistry > Acids, bases and salt > Flashcards

Acids, bases and salt Flashcards

1
Q

what happens to acids when they dissolve in water

A

they produce H+ ions

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2
Q

what happens to alkalis when they dissolve in water

A

they produce OH+ ions

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3
Q

what are the properties of acids

A

all acids dissolve in water
pH of less than 7
turn blue litmus red
give a red colour with universal indicator

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4
Q

what are the properties of alkalis

A

all alkalis dissolve in water
pH greater than 7
turn red litumus blue
give a blue colour with universal indicator

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5
Q

what acid is present in citrus fruits

A

citric acid

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6
Q

what acid is present in fizzy drinks

A

carbonic acid

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7
Q

what acid is present in vinegar

A

ethanoic acid

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8
Q

what is an acid

A

a proton donor

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9
Q

what is a base

A

a proton acceptor

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10
Q

why are fizzy drinks acidic

A

carbon dioxide reacts with water in the drink to give carbonic acid

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11
Q

what are bases

A

any substance that reacts with an acid ,forming a salt and water e.g. metal oxides and metal hydroxides

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12
Q

acid + base =

A

salt + water

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13
Q

what is the neutralisation reaction

A

H+ + OH- = H2O

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14
Q

the lower the pH

A

the more acidic the solution

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15
Q

the higher the pH

A

the more alkaline the solution

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16
Q

what colour is methyl orange in acidic solutions

A

red

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17
Q

what colour is methyl orange in alkaline solutions

A

yellow

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18
Q

what colour is phenolphthalein in acidic solutions

A

colourless

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19
Q

what colour is phenolphthalein in alkaline solutions

A

pink

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20
Q

what colour is universal indicator in acids

A

red or orange

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21
Q

what colour is universal indicator in alkali

A

blue or purple

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22
Q

how to measure pH of a solution

A

pH meter or universal indicator

23
Q

what is a strong acid

A

an acid which completely dissociates into its H+ ions when it dissolves in water

24
Q

what is a weak acid

A

an acid which only partially dissociates into its ions when it dissolves in water and most of the acid remains as unchanged molecules so conc of H+ ions is low

25
Q

what is a concentrated acid

A

a concentrated acid contains a large mass of acid dissolved in a given volume of water

26
Q

what is a dilute acid

A

a dilute acid contains a small mass of acid dissolved in a given volume of water

27
Q

how do you dilute a concentrated acid

A

add the acid to the water slowly and NEVER the other way around

28
Q

why should acid always be added to water and not the other way around

A

if water is added to acid, the heat produced causes the mixture to boil and the liquid spills out whereas if the acid is added to water the water will absorb the heat generated and the mixture will not boil

29
Q

concentration in g dm^3 =

A

mass of solute / volume of solution

30
Q

what happens if the conc of hydrogen ions is increased by a factor of 10

A

the pH decreases by 1

31
Q

what happens if the conc of hydrogen ions is decreased by a factor of 10

A

the pH increases by 1

32
Q

metal + acid =

A

salt + hydrogen

33
Q

what do you see when a metal reacts with dilute acid

A

the metal dissolves because it reacts with the acid
fizzing is seen
the reaction mixture gets warmer

34
Q

what is the test for hydrogen

A

test the gas with a lighted splint

a squeaky pop is heard

35
Q

acid + alkali =

A

salt + water

36
Q

what do we observe in acid-alkali neutralisation reactions

A

the reaction mixture gets warmer

37
Q

acid + base =

A

salt + water

38
Q

metal carbonates + acid =

A

salt + water + carbon dioxide

39
Q

observations when a metal carbonate reacts with a dilute acid

A

the solid dissolves because it reacts with the acid
fizzing/effervescence

40
Q

what is the test for carbon dioxide

A

bubble the gas into limewater
the limewater turns cloudy

41
Q

what are the solubility rules

A

all sodium, potassium and ammonium salts are SOLUBLE

all nitrates are SOLUBLE

common chlorides, bromides and iodides EXCEPT silver and lead are SOLUBLE

common sulfates except lead, calcium and barium are SOLUBLE

common carbonates and hydroxides excpet sodium, potassium and ammonium are INSOLUBLE

42
Q

What is a precipitate

A

a solid which forms when two solutions are mixed

43
Q

how to make insoluble salts by precipitation

A

mix together solutions of silver nitrate and sodium chloride in a beaker, then filter the mixture to get the precipitate

the insoluble salt, silver chloride remains in the filter paper

pour a little distilled water over the residue in the funnel to remove impurities

carefully remove the filter paper with silver chloride and dry in a warm oven

44
Q

what do you do in a neutralisation reaction to make soluble salts

A

metals/metal oxide/metal carbonate + acid

45
Q

how do you make soluble salt by neutralisation

A

take 25cm^3 of hot sulfuric acid in a beaker

add small amounts of zinc oxide (with a spatula) to the acid and stir

continue to add small amounts of zinc oxide until all the acid is used up

filter the mixture to remove the excess zinc oxide

heat the filtrate gently until most of the water evaporates and crystals appear around the edges

leave it to cool at room temp and allow crystals to form

dry the crystals between filter papers

46
Q

how do you get large crystals

A

heat the evaporating basin using a water bath

47
Q

what do you do in a titration to make soluble salts

A

acid + alkali

48
Q

how do you get a soluble salt using titration

A

fill the burette with HCL to eye level

record the initial volume of acid in the burette

pipette out sodium hydroxide into a conical flask and add a few drops of the indicator, phenolphthalein. The solution in the flask turns pink

add the acid slowly from the burette while swirling the flask until the end point is reached

the end point is when the solution changes from pink to colourless

record the final volume of acid in the burette

calculate the titre (end reading - start reading)

use the burette to add this volume of acid to the alkali without the indicator

heat the solution gently till most water evaporates

leave it to cool at room temp and crystals will form

dry the crystals between filter papers

49
Q

why is a pipette used instead of a measuring cylinder in titrations

A

a pipette provides more accurate and repeatable measurements

50
Q

why must the titration be repeated

A

to improve the reliability of the investigation
to identify anomalous results
to be able to calculate an average value using concordant results

51
Q

how do you make sure that the titration is carried out correctly

A

read the volume of acid from the bottom of the meniscus
repeat the titration until concordant results are obtained
add the HCL dropwise towards the end point
place a white tile under the conical flask to see the end point clearly

52
Q

what are the reasons why a student’s mean titre is different from the accurate value

A

the student did not read the volume from the bottom of the meniscus
the jet of the burette was not filled
there was an error in the judgment of colour change at the end point
there was an airlock below the tap in the burette

53
Q

what are concordant titres

A

within + or - 0.10 cm^3

Chemistry (21 decks)

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