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chemistry > C8 - Chemical Analysis > Flashcards

C8 - Chemical Analysis Flashcards

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1
Q

What is a pure substance?

A

Made up of just one substance either an element or a compound.

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2
Q

What is a mixture?

A

A combination of two or more substances.

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3
Q

What effect does an impurity have on melting and boiling points?

A

The presence of an impurity lowers the melting point and increases the boiling point.

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4
Q

What is a formulation?

A

A mixture designed as a useful product

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5
Q

What can be said about substances that move far up chromatography paper?

A

They are soluble - attracted to the mobile phase.

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6
Q

What can be said about substances that don’t move far up chromatography paper?

A

They are less soluble - attracted to the stationary phase.

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7
Q

What is the mobile phase?

A

The water.

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8
Q

What is the stationary phase?

A

The chromatography paper.

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9
Q

How do you calculate retention factor?

A

Height of dot / height of solvent

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10
Q

Describe the test for hydrogen.

A

React Mg and HCl. Place a burning splint in the test tube with the mixture. If test is +, squeaky pop sound.

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11
Q

Describe the test for oxygen.

A

React MgO2 and H2O2. Place a glowing splint in the test tube with the mixture. If test + the splint relights.

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12
Q

Describe the test for carbon dioxide.

A

React CaCO3 and HCl. The gas produced should make limewater turn cloudy if +.

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13
Q

Describe the test for chlorine.

A

Electrolysis of salt solution with damp blue litmus paper.
If +, should durn red then bleach white.

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14
Q

What is the speed of a solvent with a high Rf?

A

Fast

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15
Q

What is the speed of a solvent with a low Rf?

A

Slow

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16
Q

What is the only circumstance under which the Rf changes?

A

Solvent is changed.

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17
Q

Colour of sodium chloride in flame?

A

Orange/yellow

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18
Q

Colour of copper chloride in flame?

A

Turquoise blue/ green

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19
Q

Colour of lithium chloride in flame?

A

Red

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20
Q

Colour of potassium chloride in flame?

A

Purple/lilac

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21
Q

Colour of calcium chloride in flame?

A

Orange/red

22
Q

How do you test for halide anions?

A

Add dilute nitric acid, then add silver nitrate.

23
Q

What colour precipitate forms from the test for negative chloride ions?

A

White - silver chloride

24
Q

What colour precipitate forms from the test for negative bromide ions?

A

Cream - silver bromide

25
Q

What colour precipitate forms from the test for negative iodide ions?

A

Yellow - silver iodide

26
Q

Describe test for negative carbonate ions.

A

Add dilute nitric acid. Carbon dioxide gas is produced. Fizzing. Should turn limewater cloudy.

27
Q

3 benefits of instrumental methods.

A

They are accurate and sensitive.
They are quick.
They enable small samples to be analysed.

28
Q

3 disadvantages of instrumental methods.

A

Expensive.
Takes special training to use.
Results can only be interpreted by comparison with data from known substances.

29
Q

What do the flame tests test for?

A

Positive ions.

30
Q

Describe the precipitate formed from the sodium hydroxide test for copper (II).
State the ionic equation.

A

Blue precipitate formed.
Cu 2+ + 2OH- -> Cu(OH)2

31
Q

Describe the precipitate formed from the sodium hydroxide test for iron (II).
State the ionic equation.

A

Forms dirty green precipitate.
Fe2+ + 2OH- -> Fe(OH)2

32
Q

Describe the precipitate formed from the sodium hydroxide test for iron (III).
State the ionic equation.

A

Form brown precipitate.
Fe3+ + 3OH- -> Fe(OH)3

33
Q

What 3 positive ions form a white precipitate (in the sodium hydroxide tests) , however what ion becomes a colourless solution and why ?

A

Al3+, Ca2+, Mg2+.
Al3+ forms colourless solution as Al(OH)3 dissolves in excess NaOH, to form colourless solution.

34
Q

What is the ionic equation for the test of halide ions with silver nitrate?

A

Ag+ + X- -> AgX

35
Q

What is the ionic equation for the test of carbonate ions with dilute nitric acid?

A

CO3(2-) + 2H+ -> CO + H2O

36
Q

What is the ionic equation for the test of sulfate ions with barium chloride?

A

Ba2+ + SO4(2-) -> BaSO

37
Q

What is flame emission spectroscopy?

A

Instrumental method used for identifying metal ions in a solution.

38
Q

What is a spectrosope?

A

Measures the exact wavelength of the light emitted by a metal ion. Which allows for definite identification - sometimes colours are difficult to distinguish.

39
Q

How is the concentration of metal ions in a solution determined?

A

Measuring the intensity of the light emitted. The higher the intensity, the greater the concentration.

40
Q

What are cations?

A

Positive ions.

41
Q

What are anions?

A

Negative ions.

42
Q

How can you find the concentration of metal ions in a graph?

A

From a concentration-intensity graph, you can read a concentration from a given intensity.

43
Q

What type of method is a flame emission spectroscopy?

A

Instrumental method.

44
Q

How is flame emissions spectroscopy carried out?

A

Sample placed in a flame, light emitted is passed through a spectroscope to give a spectrum which can be compared to a reference.

45
Q

How can chromatography show the difference between pure and impure substances?

A

Pure ones will not separate into a number of spots.

46
Q

What does a substance’s Rf value depend on?

A

How soluble it is in the solvent.

47
Q

Why does carbon dioxide turn limewater cloudy?

A

Solid calcium carbonate forms

48
Q

Other than flame tests, how can metal ions be identified?

A

Use of sodium hydroxide

49
Q

How can compounds of calcium and magnesium be distinguished from each other?

A

Using flame tests calcium compounds produce an orange - red flame

50
Q

What is the test for sulfate ions?

A

Add barium chloride and hydrochloric acid, forms white precipitate.

51
Q

Why is it hard to identify the metal ions from the colour of the flame when there is a mixture of metal ions?

A

Flame colours will be masked.

52
Q

What name is given to a useful product?

A

Formulation

chemistry (10 decks)

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