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Chemistry 4 - Inorganic Chem And The Periodic Table > Flame Tests and the Test for Ammonium Ions > Flashcards

Flame Tests and the Test for Ammonium Ions Flashcards

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1
Q

what do flame tests basically do

A
  • they indicate the presence of group 1 or 2 metals

- in the form of ions

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2
Q

after you have worn safety gear and have lit the bunsen burner in a fume cupboard, what are the steps for how to do a flame test for a small quantity of a solid

A
  • using a dropper add a few drops of concentrated HCl to the solid
  • mix them so the metal begins to dissolve
  • dip a clean nichrome wire into the mixture to obtain a sample
  • hold the end of the wire in the flame and observe the colour
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3
Q

why is HCl used to dissolve the metal compound

A
  • it converts and metal compound to a chloride
  • chlorides are more volatile than other salts
  • so they are more likely to give better results
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4
Q

what other alternatives are there other than nichrome wire

A
  • platinum wire

- silica rod

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5
Q

what is one problem with flame tests regarding the metals purity

A
  • many metal compounds contain small traces of sodium compounds as impurities
  • so the intense colour of it can mask other colours
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6
Q

what is another problem with flame tests regarding their manner of obervation

A
  • describing the colours is subjective
  • people have different levels of colour vision
  • so a word description may mean different colours according to the person
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7
Q

what is a simple example of how colour description can become subjective easily

A
  • if someone describes a colour as brick red
  • it not only relies on the subjective recollection of what a brick looks like
  • but it also assumes everyone has seen the same shade of red on a brick
  • some people have seen multiple shades or brick red
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8
Q

regarding the flame tests, what is the colour of lithium ions

A

red

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9
Q

what is the colour of sodium ions

A

yellow-orange

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10
Q

what is the colour of potassium ions

A

lilac

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11
Q

what is the colour of rubidium ions

A

red-purple

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12
Q

what is the colour of caesium ions

A

blue-violet

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13
Q

what is the colour of beryllium ions

A

no colour

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14
Q

what is the colour of magnesium ions

A

no colour

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15
Q

what is the colour of calcium ions

A

brick red

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16
Q

what is the colour of strontium ions

A

crimson red

17
Q

what is the colour of barium ions

A

apple green

18
Q

what is the simple reason for these colours appearing during flame tests

A

electron transitions

19
Q

how do electrons result in these colours appearing when the metal compound is being heated

A
  • the electrons absorb energy from the flame and quantum leap to higher energy levels
  • from this excited state, the electron quickly loses its energy and leaps back to its original quantum shell
  • this results in the emission of electromagnetic radiation
  • if it has the right wavelength it will fall within the range of visible light which we can see
20
Q

therefore why does magnesium have no colour in the flame test

A
  • because the electromagnetic radiation emitted doesnt have a wavelength that falls within the range of the visible spectrum
  • therefore we cant see it
  • but it would still be infrared or ultraviolet
21
Q

what is the process for the test for ammonium ions

A
  • add sodium hydroxide solution
  • warm the mixture
  • the warming releases ammonia gas
22
Q

what is the reaction occurring between the ammonium ions and sodium hydroxide solution

A

NH4+ + OH- = NH3 + H2O

23
Q

how do you know if ammonium ions were present from this test

A
  • it can be recognised from its smell
  • but its better to use damp litmus paper
  • if it turns blue ammonia gas is present
  • therefore the ions were present
24
Q

what is a further reaction you could carry out to prove the ammonia ions presence

A
  • react the ammonia gas with HCl
  • it forms white fumes of ammonium chloride
  • NH3 + HCl = NH4Cl

Chemistry 4 - Inorganic Chem And The Periodic Table (9 decks)

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