C8 - Chemical Analysis

Question 1

What is a pure substance?

Answer 1

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

Question 2

What is a mixture?

Answer 2

A combination of two or more substances.

Question 3

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

Answer 3

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

Question 4

What is a formulation?

Answer 4

A mixture designed as a useful product

Question 5

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

Answer 5

They are soluble - attracted to the mobile phase.

Question 6

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

Answer 6

They are less soluble - attracted to the stationary phase.

Question 7

What is the mobile phase?

Answer 7

The water.

Question 8

What is the stationary phase?

Answer 8

The chromatography paper.

Question 9

How do you calculate retention factor?

Answer 9

Height of dot / height of solvent

Question 10

Describe the test for hydrogen.

Answer 10

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

Question 11

Describe the test for oxygen.

Answer 11

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

Question 12

Describe the test for carbon dioxide.

Answer 12

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

Question 13

Describe the test for chlorine.

Answer 13

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

Question 14

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

Answer 14

Fast

Question 15

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

Answer 15

Slow

Question 16

What is the only circumstance under which the Rf changes?

Answer 16

Solvent is changed.

Question 17

Colour of sodium chloride in flame?

Answer 17

Orange/yellow

Question 18

Colour of copper chloride in flame?

Answer 18

Turquoise blue/ green

Question 19

Colour of lithium chloride in flame?

Answer 19

Red

Question 20

Colour of potassium chloride in flame?

Answer 20

Purple/lilac

Question 21

Colour of calcium chloride in flame?

Answer 21

Orange/red

Question 22

How do you test for halide anions?

Answer 22

Add dilute nitric acid, then add silver nitrate.

Question 23

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

Answer 23

White - silver chloride

Question 24

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

Answer 24

Cream - silver bromide

Question 25

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

Answer 25

Yellow - silver iodide

Question 26

Describe test for negative carbonate ions.

Answer 26

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

Question 27

3 benefits of instrumental methods.

Answer 27

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

Question 28

3 disadvantages of instrumental methods.

Answer 28

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

Question 29

What do the flame tests test for?

Answer 29

Positive ions.

Question 30

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

Answer 30

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

Question 31

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

Answer 31

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

Question 32

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

Answer 32

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

Question 33

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

Answer 33

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

Question 34

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

Answer 34

Ag+ + X- -> AgX

Question 35

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

Answer 35

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

Question 36

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

Answer 36

Ba2+ + SO4(2-) -> BaSO

Question 37

What is flame emission spectroscopy?

Answer 37

Instrumental method used for identifying metal ions in a solution.

Question 38

What is a spectrosope?

Answer 38

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

Question 39

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

Answer 39

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

Question 40

What are cations?

Answer 40

Positive ions.

Question 41

What are anions?

Answer 41

Negative ions.

Question 42

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

Answer 42

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

Question 43

What type of method is a flame emission spectroscopy?

Answer 43

Instrumental method.

Question 44

How is flame emissions spectroscopy carried out?

Answer 44

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

Question 45

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

Answer 45

Pure ones will not separate into a number of spots.

Question 46

What does a substance's Rf value depend on?

Answer 46

How soluble it is in the solvent.

Question 47

Why does carbon dioxide turn limewater cloudy?

Answer 47

Solid calcium carbonate forms

Question 48

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

Answer 48

Use of sodium hydroxide

Question 49

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

Answer 49

Using flame tests calcium compounds produce an orange - red flame

Question 50

What is the test for sulfate ions?

Answer 50

Add barium chloride and hydrochloric acid, forms white precipitate.

Question 51

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

Answer 51

Flame colours will be masked.

Question 52

What name is given to a useful product?

Answer 52

Formulation