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Chemistry Y10&Y11 > Chemical Analysis > Flashcards

Chemical Analysis Flashcards

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1
Q

What is and element?

A

A substance containing only 1 type of atom

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2
Q

What is a compound?

A

A substance containing atoms of different elements chemically joined together

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3
Q

What is a mixture?

A

A substance that contains more than one substance (not chemically joined) and easily separated using a physical property, EG WATER or AIR

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4
Q

Test and result for Hydrogen? (H2)

A

A lit splint placed in gas causes squeaky pop.

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5
Q

Test and result for Oxygen? (O2)

A

Glowing splint placed in gas re-ignites

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6
Q

Test and result for Carbon Dioxide? (CO2)

A

Bubble gas into limewater and it turns cloudy

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7
Q

Test and result for water. (H2O)

A

White anhydrous CuSO4 turns blue when water is added.

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8
Q

What is the definition for Pure Substances?

A

This substance is a single element or compound. In everyday language, a pure substance can mean a substance that has nothing added to it, so it is unadulterated and in its natural stage, eg pure milk.

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9
Q

What boiling and melting points do pure substances have?

Give an example.

A

They have fixed melting and boiling points.
Distilled water:
Melting point: 0 degrees C
Boiling point: 100 degrees C

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10
Q

What boiling and melting points do impure substances have?

Give an example.

A

They have a range of melting points and boiling points
Brine (salt water)
Melting point: -5 - -10 degrees C
Boiling point: 101 - 103 degrees C

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11
Q

What will impurities do to the melting and boiling points?

A
  • Reduce the melting point and increases the melting point range.
  • Increases the boiling point and give a range
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12
Q

What is a formulation?

A

A mixture of specific quantities/ratios designed as a useful product. Each component is present in a measured quantity and contributes to the properties of the formulation. e.g paint, cake mix, fuels, drugs, fertilisers.

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13
Q

What makes up Brass? (include percentages and uses)

A

70% Copper
30% Zinc
USES
musical instruments (doesn’t corrode)

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14
Q

What makes up Bronze? (include percentages and uses)

A

95% Copper
5% Tin
USES
statues, church bells (strong, doesn’t corrode, makes ringing noise)

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15
Q

What makes up Stainless Steel? (include and uses)

A 
Iron
Nickel
Chromium
USES
medical equipment, cutlery, chemical plants (doesn't rust)
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16
Q

What example of a formulation do farmers uses and what do they contain?

A

Fertilisers - farmers use NPK fertilisers: Nitrogen, phosphorous, and potassium of varying quantities based on what is needed to be returned to the soil.

17
Q

Why in a chromatography experiment is the base line drawn in pencil?

A

Pencil is graphite - this is insoluble and will not dissolve in the solvent and will not interfere with the experiment.

18
Q

Why in a chromatography experiment is the base line above the solvent?

A

Samples on the base line must be above the solvent to start with, or they would dissolve in the solvent.

19
Q

Why in a chromatography experiment samples must be placed on the base line?

A

To give a fixed point for measuring the distance they have moved.

20
Q

Why in a chromatography experiment should a lid be put on the equipment?

A

To stop solvents evaporating if they have a low boiling point.

21
Q

What should you remember when reading a chromatogram?

A
  • The number of spots above each letter, tells you how many pigments there are in the mixture.
  • If the pigments have travelled the same distance, they may be the same pigment.
22
Q

What is the formula for calculating the Rf value?

A

Rf value = distance moved by substance / distance moved by solvent front

23
Q

How can compounds be identified using Rf value?

A

Different compounds have different Rf values in different solvents, which can be used to help identify the compounds. The compounds in a mixture may separate into different spots depending on the solvent but a pure compound will produce a single spot in all solvents.

24
Q

What is the Stationary phase?

A

the piece of chromatography paper (molecules that cannot move)

25
Q

What is the Mobile phase?

A

the solvent (molecules can move either liquid or gas) eg water or ethanol

26
Q

Descibe how you carry out the chromatography experiment?

A

1) Use a ruler to draw a horizontal pencil line 2cm from the bottom of the chromatography paper
2) mark five pencil spots at equal intervals across the origin line
3) using a different capillary tube for each coloring, put a small spot of each colouring on four of the pencil spots
4) Use another capillary tube to put a small spot of the unknown mixture on the last pencil spot
5) pour water into the beaker to a depth no more than 1cm
6) clip the top of the paper to a wooden spill and rest on top of beaker. The bottom of the paper should dip in the solvent
7) wait for the water solvent to travel at least 3/4 of the way up the paper
8) remove the paper from the beaker and draw another pencil line as close to the wet edge as possible, this is the solvent front line
9) hang the paper up to dry thoroughly

27
Q

How does chromatography work?

A

1) mixture dissolves in the mobile phase as it moves through the stationary phase
2) the mixture is also interacting with the stationary phase (constantly switiching between phases)
3) the more soluble a component of the mixture, the further it will travel
4) different components have different Rf values

28
Q

Why do different substances travel different distances up the chromatography paper?

A
  • substances that have a stronger attraction to the solvent (more soluble), move quickly and travel a long way up the paper
  • substances that have a stronger attraction to the paper, move slower and travel a short distance up the paper
29
Q

What does a large Rf value indicate?

A
  • the substance is very soluble

- the substance spent a longer time in the mobile phase

30
Q

Why would a permanent marker have an Rf value of 0?

A

Because they are insoluble so don’t dissolve in the solvent and travel up the paper

31
Q

How can a more reliable result be given for chromatography experiments?

A
  • repeating the experiment using a different solvent
  • calculate the different Rf values and compare with the previous Rf value
  • the Rf values should match relative to the other substances
32
Q

How can paper chromatography be used to identify what impurity is present in the substance/mixture

A
  • run the mixture alongside pure samples of the possible impurity
  • if the spot from one of the possible impurities moves the same distance as the mixture, then it indicates that that is the impurity
  • this is the same if the calculated Rf values match
33
Q

What is the colour of the flame for lithium testing?

A

crimson

34
Q

What is the colour of the flame for sodium testing?

A

yellow

35
Q

What is the colour of the flame for potassium testing?

A

lilac

36
Q

What is the colour of the flame for calcium testing?

A

orange-red

37
Q

What is the colour of the flame for copper testing?

A

green

38
Q

What are the limitations to the flame tests?

A
  • it is diffucult to judge the colour
  • individuals see colour differently
  • results quoted (expected flame colours) are only for pure substances
  • if a mixture of ions is in the flame test, they can mask the colour of one ion
39
Q

What is the test and result for chlorine?

A

add damp litmus paper to the gas and if chlorine, it bleaches the paper white

Chemistry Y10&Y11 (21 decks)

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