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Chemistry (Tim) > Chemical Bonding part 2 > Flashcards

Chemical Bonding part 2 Flashcards

1
Q

Recrystallisation

A

a technique used to purify certain crystalline substances

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2
Q

what concept is recrystallisation based on

A

the fact that some substances are more soluble in hot solvents than in cold solvents

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3
Q

what are benzoic acid crystals soluble in?

A

hot water but only slightly in cold water

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4
Q

Benzoic acid crystals experiment; soluble impurity

A

NaCl

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5
Q

Benzoic acid insoluble impurity

A

Charcoal

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6
Q

why is the minimum amount of water used in the benzoic acid crystals experiment?

A

to get the maximum yield of benzoic acid crystals

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7
Q

what stays behind in the benzoic acid crystals experiment after the first filtration?

A

charcoal

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8
Q

first thing you do in the benzoic acid experiment

A

dissolve impure crystals in the hot water

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9
Q

what type of solution with impure benzoic acid crystals do you want?

A

saturated solution

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10
Q

what stays behind in the second filtration in the benzoic acid experiment?

A

benzoic acid crystals

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11
Q

what goes through the second filtration in the benzoic acid crystals experiment

A

NaCl and water

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12
Q

why would you rinse the benzoic acid crystals with water after the second filtration?

A

if they are damp with water still, that water could still contain the soluble impurity i.e NaCl

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13
Q

where do you finally dry the benzoic acid crystals?

A

in the air or a hot oven

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14
Q

why must the first filtration of benzoic acid crystals be done quickly?

A

So that recrystallisation doesn’t occur on the filter paper

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15
Q

what can help speed up the recrystallisation?

A

scraping the inside with a glass rod

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16
Q

what is the flask used in the cold filtration called

A

buchner funnel

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17
Q

why is a buchner funnel used?

A

it uses air suction to speed up filtration, causes a partial vacuum

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18
Q

what is connected to the buchner funnel?

A

a t junction connected to a pipe of flowing water from a tap

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19
Q

what does benzoic acid look like

A

white crystals

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20
Q

what is benzoic acid used for?

A

food preservative

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21
Q

4 pieces of apparatus used in melting point determination

A

a hot plate
a melting point block
a thermometer
capillary tubes

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22
Q

what has to be special about he thermometer in melting point determination

A

it has to read up to about 150 degrees celsius

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23
Q

what are capillary tubes

A

very light and narrow glass tubes

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24
Q

what has to be special about the capillary tubes used in melting point determination

A

sealed at one end

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25
Q

how do you know when the crystals have reached their melting point?

A

they break down and turn to a colourless liquid

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26
Q

probably impure if…

A
  1. they melt over a large range eg. 6 degrees

2. they melt under the normal melting poingt

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27
Q

anions

A

negative ions

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28
Q

where are anions found

A

in salts with positive ions

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29
Q

what substance is used to test for a chloride?

A

potassium chloride (KCl)

30
Q

1st step in testing KCl for chloride

A

make an aqueous solution of it by adding a few crystals to a beaker 1/4 full of deionised water. shake well and it gives a colourless solution

31
Q

after aqueous solution is made of KCl in a test for chloride

A

add a few drops of silver nitrate and white ppt forms

32
Q

silver nitrate equation

A

Ag plus NO3 minus

33
Q

how do you confirm that the white ppt formed is a chloride?

A

add a quarter test tube of ammonia solution and shake gently

34
Q

what shows you is a chloride?

A

ppt dissapears

35
Q

equation to show that some sort of carbonate is presnent

A

Ca(OH)2 + CO2 -> CaCO3 +H2O

36
Q

how do you no if its CO3 minus 2 or HCO minus?

A

add a 1/4 test tube of MgSO4 to 1? test tube of the solution
carbonate: precipitate
hydrogen carbonate : no precipitate

37
Q

making nitrate solution for testing nitrate ion

A

fill test tube 1/4 full with deionised water and add some crystals of nitrate salt and shake to dissolve

38
Q

salt tested for nitrate

39
Q

what do you add to nitrate aqueous solution

A

the same quantity of iron sulphate to the tube

40
Q

after you add iron sulphate to the nitrate

A

slant the tube and add carefully concentrated sulphuric acid with a dropper

41
Q

after you slant and add sulphuric acid to nitrate

A

brown ring appears

nitrate is present

42
Q

why does a brown ring appear if nitrate is present

A

becuase concentrated sulphuric acid is more dense than NaNO3 and FeSO2

43
Q

the brown ring in the test for nitrate contains which complex?

44
Q

Sulphate salt to test

45
Q

sulphite salt to test

46
Q

making an aqueous solution of sulphite/ate salt

A

fill the test tube 1/4 the way with deionised water and add a few crystals to it

47
Q

what do you do with the aqueous solutions of sulphate/ite salts

A

using a dropper add a few drops of BaCl2

cloudy white precipitate forms

48
Q

after BaCl2 in sulphate/ite

A

add 1/4 test tube of dilute HCl and shake gently

  1. ppt stays-> sulphate
  2. ppt goes-> sulphite
49
Q

sulphate ppt formula

A

BaSO4 (insoluble in HCl)

50
Q

sulphite ppt formula

A

BaSO3 (soluble in HCl)

51
Q

making an aqueous solution of a phosphate

A

fill test tube 1/10 of the way with deionised water and add a very small amount of phosphate crystals, shake well, gives clear solution

52
Q

phosphate crystals used

A

ammonium phosphate

53
Q

after you make aqueous solution of phosphate

A

pour in ammonium molybdate solution until its half full

54
Q

in phosphate test, after ammonium molybdate

A

add carefully 4 or 5 drops of concentrated nitric acid, forms bright yellow ppt, it is a phosphate

55
Q

if a bright yellow ppt doesnt appear

A

place tube in 60 degree water

56
Q

what is the yellow ppt?

A

ammonium phosphomolybdate

57
Q

Test for chloride ion word formula

A

Potassium chloride, silver nitrate, white precipitate, add ammonia solution, white ppt dissolves, confirmed

58
Q

Test for chloride ion formula

A

KCl, AgNO3, white ppt, add NH3 solution, white ppt disappears, confirmed

59
Q

Test for carbonate word formula

A

Sodium carbonate, hydrochloric acid, carbon dioxide fizz (limewater), add magnesium sulphate, white ppt., carbonate

60
Q

test for carbonate formula

A

Na2CO3, HCl, CO2fizz (limewater), add MgSO4, white ppt, confirmed

61
Q

Test for hydrogen carbonate word formula

A

Sodium bicarbonate, Hydrochloric acid, CO2 fizz (lime water), add MgSO4, no white ppt., confirmed

62
Q

Test for hydrogen carbonate formula

A

NaHCO3, HCl, CO2 fizz, add MgSO4, no white ppt., confirmed

63
Q

Test for nitrate word formula

A

sodium nitrate, iron sulphate, concentrated sulphuric acid (slanted tube) Brown ring, confirmed

64
Q

Test for nitrate formula

A

NaNO3, FeSO4, Conc, H2SO4 (slanted tube), brown ring, cofirmed

65
Q

Test for sulphate word formula

A

sodium sulphate, barium chloride, white ppt., add diluted hydrochloric acid, white ppt remains, confirmed

66
Q

test for sulphate formula

A

Na2SO4, BaCl2, white ppt., add dil. HCl, white ppt remains, confirmed

67
Q

test for sulphite word formula

A

Sodium sulphite , Barium chloride , white ppt, add diluted hydrochloric acid, white ppt dissolves, confirmed

68
Q

test for sulphite formula

A

Na2SO4, BaCl2, White ppt., add dil. HCl, white ppt dissolves, confirmed.

69
Q

test for phosphate word equation

A

ammonium phosphate, ammonium molybdate, clear solution., add concentrated nitric acid, heat to 60 degrees if necessary, yellow ppt, confirmed

70
Q

test for phosphate equation

A

(NH4)3PO4, amm. molybdate, clear soln., add conc. HNO3 (60 degrees), yellow ppt.,confirmed

Chemistry (Tim) (8 decks)

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