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Chemistry GCSE > Topic 8- Chemical Analysis. > Flashcards

Topic 8- Chemical Analysis. Flashcards

1
Q

Define a pure substance?

Define an impure substance?

A

A pure substance is one that is made up of a single element or compound, not mixed in with any other substances.

An impure substance is a mixture of two or more different elements or compounds.

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2
Q

How can a pure substance be identified and how does it differ from an impure substance?

A

A pure substance can be identified as they boil and melt at specific temperatures.

An impure substance often melts over a range of temperatures and impurities usually lower the melting point and/ or raise the boiling point. The greater the difference between the recorded and actual melting point, the lower the purity. An impure substance can also increase the boiling point and may result in the sample boiling at a range of temps.

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3
Q

Define formulations.

Why is important for the formation to stay consistent?

A

Formulations are useful mixtures with a precise purpose. Formulations are made by mixing the components in carefully measured quantities to ensure that the product has the required properties.

-It’s important for the formation to stay consistent as it has a precise purpose and the specific properties of the formulation help it to meet to its required function

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4
Q

Give examples of formulations?(4)

A

-Metal alloys, cleaning products, fuels, baby formulae.

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5
Q

Why is Chromatography used?

A

-it’s an analytical method to separate the substance in a mixture and can be used to identify substances and compounds.

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6
Q

What can chromatography be used for?(5)

A
  • it can be used to separate inks and dyes.
  • identify additives in food.
  • fingerprinting.
  • test water samples for pollution
  • detect bombs in airports.
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7
Q

What’s the mobile phase?

What’s the stationary phase?

A
  • The mobile phase is when the molecules can move and this is always a liquid or a gas and this is the solvent form.
  • Stationary phase- when the molecules can’t move and this is essentially the paper
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8
Q

How to calculate the retention factor?

A

Rf value=
distance travelled by the substance( this is the distance from the baseline to the centre of the spot) ____________________________________________
distance travelled by the solvent( base line to the solvent front)

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9
Q

Why can RF never be more than 1?

The more soluble the compound is?

A
  • that means the pigment would have moved further than the solvent and since the solute is carried by the solvent, it is not possible.
  • The more soluble the compound is, the further it travelled up the paper.
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10
Q

What are the 4 tests for common gases

A

1) Hydrogen- holding a lit split and when hydrogen present- squeaky pop test.
2) Chlorine- bleaches damp litmus paper turning it white.
3) Oxygen- the oxygen will relight a glowing splint.
4) Carbon dioxide- limewater where presence will allow it to turn cloudy.

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11
Q

How can anions(2) and cations(2) be identified?

A

Anions:

1) Test for sulphate with HCl and BaCl
2) Test for halide ions with nitric acid and silver nitrate.

Cations:

1) Flame tests identify mental ions.
2) Metals form a coloured precipitate with NaOh

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12
Q

What’s the method for carrying out a flame test?

A

1) Obtain a clean platinum wire loop by dipping it into dilute HCl or any acid, for it removes impurities and this must be done between each compound.
2) Hold the wire over a blue flame of a Bunsen burner until it burns without any colour.
3) Then dip the loop into the sample you want to test and put it back in the flame. Record the colour of the flame.
4) Use these colours to detect and identify different ions but it only works for samples that contain a single metal ion as if the sample tested contains a mixture of metal ions, the flame colours of some ions may be hidden by the colours of others.

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13
Q

List the colours of a flame test?

Lithium, Sodium (Na+), Potassium, Calcium (Ca2+), Copper (Cu2+)

A
  • Lithium ions, Li+, burn with a crimson flame.
  • Sodium ions, Na+, burn with a yellow flame.
  • Potassium ions, K+, burn with a lilac flame
  • Calcium ions, Ca2+, burn with an orange-red flame.
  • Copper ions, Cu2+, burn with a green flame.
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14
Q

Why do we see a flame?

A

When ions are heated over a flame, we promote the element to a higher energy level and there is a moment, where the flame is cooler, the electrons come back down to lower energy level and it releases energy. Energy is released at a particular frequency, and that frequency dictates the particular colour, hence why we see a flame.

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15
Q

What happens when metal reacts with NaOH?

A
  • Metals form a coloured precipitate with NaOH.
  • Most metal hydroxides are insoluble and precipitate out of solution when formed. Some of these hydroxides have a characteristic colour.
  • Add a few drops of sodium hydroxide solution to your chosen mystery compound and if you get a coloured insoluble hydroxide, you can often tell which metal was in the compound.
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16
Q

Colour of precipitate formed with metal ions when it reacts with hydroxide?

Calcium,
Copper II,
Iron II,
Iron(III),
Alumminium,
Magnesium.
A
  • Calcium, Ca2+-> colour of precipitate is white.
  • Copper(II), Cu2+-> colour of precipitate is blue.
  • Iron II- Fe2+-> green.
  • Iron(III)-Fe3+-> brown
  • Alumminium-> Al3+-> white at first until there is an excess of NaOH to form a colourless solution.
  • Magnesium-Mg2+ -> white.
17
Q

Give ionic equations for precipitate formation for each metal ions when it reacts with a hydroxide:

Calcium,
Copper II,
Iron II,
Iron(III),
Alumminium,
Magnesium.
A
  • Ca2+ (aq) + 2OH- (aq) -> Ca(OH)2 (s)
  • Cu2+ (aq) + 2OH- (aq) -> Cu(OH)2 (s)
  • -Fe2+ (aq) + 2OH- (aq) -> Fe(OH)2 (s)
  • -Fe3++ (aq) + 3OH- (aq) -> Fe(OH)3 (s)
  • Al3+ (aq) + 3OH- (aq) -> Al(OH)3(s)
  • Mg2+ (aq) + 2OH- (aq) -> Mg(OH)2 (s)
18
Q

What happens when an acid reacts with a carbonate?

What happens when sodium carbonate reacts with HCL? State the ionic eq

What’s the ionic equation when a hydrogen carbonate reacts with HCL?

State the ionic equation for NaHCO3 that reacts with HCL?

A

-it fizzes and produces carbon dioxide gas and the Co2 turns limewater cloudy as a precipitate is formed.

Na2CO3 + 2HCL -> 2NACL+CO2+H20
-> CO3 2- +2H+ -> CO2+ H20.

-HC03- + H+ -> H20 +CO2

NAHCO3 + HCL -> NACL + CO2 +H20
-> HCO3- + H+ -> CO2 +H20.

19
Q

What is a spectator ion?

A

Spectator ions are ions that are present during the reaction but are unchanged by the reaction, and so are present in the same state on both sides of the equation.

20
Q

How can you identify sulphate ions?

A

Sulphate ions, S04 2-, are detected using barium chloride solution and a white precipitate will be formed which is BaSO4 (s).

-First, add dilute HCl to check if it’s a metal carbonate as it will fizz and if there’s no fizzing, add BaCl2 to form a white dense precipitate which will indicate it’s a sulphate

21
Q

Test for halide ions? Why are these particular acids added?

A
  • Add dilute nitric acid before the silver nitrate and if a precipitate is formed, halide ions are present.
  • Nitric acid to dissolve the compound and to remove any carbonate ions as they will form a precipitate with the silver ions and interfere with the test.
22
Q

State the observations when reacted with AgNO3 and the ionic equations with the hallide ions:

  • Cl-,
  • Br-
  • I-
A

Cl-

  • white coloured percipitate.
  • Ag+ (aq) +Cl- (aq)- > AgCl(s)

Br-

  • cream coloured percipitate.
  • Ag+(aq) + Br- -> AgBr(s)

I-

  • yellow coloured percipitate.
  • Ag+ + I- -> AgI
23
Q

Why do we add NH3( ammonia) to halide ions?

State the observation for each halide ion.

A

-It helps us distinguish between precipitates and provide more clarity due to the colours being similar.

1) AgCl- = dilute NH3- AgCl dissolves.
2) AgBr = dilute doesnt work- concentrated dissolves so you know bromide ions.
3) AgI - dilute nor concentrated NH3 works so you know iodide ions are present.

24
Q

Why is the reaction instantaneous for hallide ions.

A

-Reaction was instantaneous and the percipitate was formed as there is a high conc of particles and hench high frequency of collisons- product is formed and there will be more successful collisions and there is a faster rate of reaction

25
Q

How can hydroxides be tested?

A

1) An alkali.
- test for hydroxide ions- UI will go purple or blue.
- litmus paper will got blue in the presence of hydroxide ions.

26
Q

Why are instrumental methods more preferable over older methods; List some adv and disadv (3)

A 
Adv:
-quicker.
-highly accurate and sensitive.
-allow v small samples to be analysed.
Disadv:
-v expensive.
-takes special training.
-
27
Q

Why is flame emission spectroscopy used?

What equipment helps?

A
  • test for pos metal ions
  • In the Spectrometer, the wl of light produced can be analysed by passing it through a spectroscope and each type of metal ion absorbs and gives out its own characteristic pattern of radiation and it’s line of spectrum can be used to identify the metal ion by comparing it with a database held on the computer. The conc of metal ions can also be detected.
28
Q

Adv and disadv of flame emission spectroscopy?(5) (2)

A

Adv:
-efficient for a small sample.
-automated process which eliminates human error.
-quick.
-brightness of spectra will determine the conc in the sample.
Disadv:
-sample is burned and completetly destroyed.
-only works for elements, doesn’t work for compounds.

29
Q

Why do substances travel different distances? (2)

A

They’re distributed differently between the mobile phase and the stationary phase.

30
Q

A student suggested that if the solvent was changed, the values would stay the same. Explain if the student was correct ( 3 marks)

A

No because substances have different rf values in different solvent as the attraction between the substance and the solvent changes.

31
Q

1) The student added a couple drops of HCL followed by a couple drops of BaCl. A white precipitate formed. Suggest what anion.
2) Write a balanced eq.
3) Student added a few drops of NaOH to the solution containing the compound. A blue precipitate was formed. Suggest what cation was present.
4) What’s the name of compound?

A

1) SO42-
2) Ba2+ + SO42- -> BaSo4.
3) Cu2+
4) Copper Sulphate.

32
Q

Describe how flame emission spectroscopy works( 2 marks)

What can you understand with flame emission spectroscopy (2 marks)

A

A sample is placed in a flame and as the ions in the sample heat up, they transfer energy as light (1 mark). The light spacces through a spectroscope and produces a line of spectrum specific to that ion (1 mark)

2)
- Conc of metal ion.
- The identity of the metal ion

33
Q

Define formulations (1 marks)

A
  • a MIXTURE DESIGNED AS A USEFUL PRODUCT
34
Q

Suggest 2 reasons why the maximum allowed percentage of carbon monoxide has been decreased for newer cars? (2 marks)

Give one reason for having a max allowed percentage of unburnt hydrocarbons in exhaust fumes?

Give 2 effects of atmospheric pollution which are reduced by using catalytic converters? (2)

A

1) carbon monoxide is dangerous
2) greater public concern/ greater awareness about pollution.
3) improved engine technology

1) reduce global dimming.
2) reduce health problems

1) reduced acid rain.
2) global dimming
3) respiratory problems.
4) carbon monoxide

35
Q

Plan a chromotography experiment to investigate the colours of an ink (6 mark)

A

1) PUT DOTS OF KNOWN COLOURS AND A DOT OF THE INK ON THE PENCIL LINE ON THE BOTTOM OF THE CHROMATOGRAPHY PAPER
2) Place the chro paper in the chosen solvent and the solvent will run through a spot of ink, separating into different spots of ink which will travel upwards
3) Remove filter paper and let it dry once the ink has reached near the top of the filter.
4) COMPARE POSITION OF DOTS FOR KNOWN COLOUR WITH THOSE OF INK

Chemistry GCSE (5 decks)

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