Chemical Analysis

Question 1

`What is a pure substance ?

Answer 1

a substance made up of only one type of element/compound

Question 2

What could you say about the relationship between Pure Substances and their Melting and Boiling Point ?

Answer 2

For pure substances, their MPs and BPs are fixed points

Question 3

What could you say about the relationship between Impure Substances and their Melting and Boiling Point ?

Answer 3

For an impure substance, there is a range of temperatures over which it can melt or boil

Question 4

What is the impact of a larger high proportion of impurities ?

Answer 4

The higher the proportion of impurities the larger the range of temperatures (of the MP/BP)

Question 5

What is formulation ?

Answer 5

Formulation: mixtures designed to be useful products

Question 6

What are some examples of products of formulation ?
List at least 3

Answer 6

Examples:
1. Paint - a pigment, a binder (helps paint stick) and a solvent
2. Drugs
3. Washing up liquids - surfactants (helps remove the grease), water, rinse agent (helps water drain off crockery), colour + fragrance
4. fuel
5. alloys
6. fertilisers

Question 7

How does the process of spectroscopy work ?

Answer 7

Flame emission spectroscopy:
1. A sample is heated in a flame
2. Energy provided makes electrons in the cations jump into higher energy levels (shells)
3. When these electrons fall back into their original energy levels (shells) they emit the energy as light energy
4. The wavelength of the emitted light is passsed through the spectroscope

Question 8

A scientist uses a flame test to analyze a sample of an unknown metal ion. She observes the unique line spectrum of radiation emitted by the metal and compares it with the data stored in a computer database.

a) Explain how the line spectrum of a metal can be used to identify the metal ion present in the sample. (2 marks)

b) Why does each type of metal ion produce a unique line spectrum? (2 marks)

Answer 8

a) Each type of metal ion absorbs and emits its own characteristic pattern of radiation –> its line spectrum
b)this is used to identify the metal by comparing the analysis with the database on the computer

Question 9

What else can a spectrometer measure ?

Answer 9

Spectrometer can also measure:
1. concentration of the metal ion in the sample
2. intensity of the light of a particular metal ion
This method can be used to measure the metal ions in water bottles + water in the body
- To avoid impurities you can purify the sample first with HCl

Question 10

How do animals become fossil fuels

Answer 10

Some of the remains of the ancient living things were crushed by the large scale movements of the Earth’s crust - this placed the organic matter under lots of heat and pressure which made them into fossil fuels

Question 11

What is coal ?

Answer 11

Coal = sedimentary rock

Question 12

How is natural gas and crude oil formed ?

Answer 12

Crude oil and natural gas were formed from the remains of plankton deposited in the seabed - these are normally found under seas/oceans under layers of rock

Question 13

Why hasn’t there been that many big change with the atmosphere ?

Answer 13

Over the past 200 million years, levels of CO2 has not changed much due to the carbon cycle
The noble gases are found in the air

Question 14

What are the main greenhouse gases ?

Answer 14

The main greenhouse gases are: CO2, methane and water vapour

Question 15

What do greenhouse gases do ?

Answer 15

Greenhouse gases absorb the energy radiated from the Earth’s surface

Question 16

Explain what happens to the remaining 70% of the Sun’s energy that reaches Earth. (2 marks)

Answer 16

The remaining 70% of the Sun’s energy is absorbed by Earth’s atmosphere, land, and oceans.
This absorbed energy warms the planet and is eventually radiated back as heat.
(2 marks)

Question 17

Describe one factor that affects the amount of solar energy reflected back into space. (2 marks)

Answer 17

Cloud cover, surface types (like ice or vegetation), or atmospheric particles can affect how much solar energy is reflected back into space.
For example, clouds and ice reflect more sunlight than water or land surfaces.
(2 marks)

Question 18

How to obtain hydrogen gas ?

Answer 18

Add a few crystals of copper sulfate as a catalyst
zinc+sulfuric acid —-> Zinc Sulphate + Hydrogen
Zn(g)+H2SO4(aq) —-> ZnSO4(aq)+H2(g)

Question 19

How do you test for Hydrogen gas ?

Answer 19

Get a lighted splint in the test gas — if there is a squeaky pop then hydrogen is present .

Question 20

How to test for Oxygen gas?

Answer 20

Put a glowing splint into gas
if it relight and a flame is present then oxygen gas is present

Question 21

How do you obtain Oxygen gas ?

Answer 21

To obtain O2 gas: decomposition of hydrogen peroxide - H2O2. The catalyst for this reaction is manganese (IV oxide)
2H2O2(aq) —–>2H2O(l) + H2(g)

Question 22

What is the test for carbon dioxide ?

Answer 22

Run the unknown gas into a solution of limewater — if the solution turns cloudy then carbon dioxide is present

Question 23

How to obtain carbon dioxide ?

Answer 23

marble chips react with dilute HCl
metal carbonate + acid –> salt + CO2 + H2O

CaCo3(s)+2HCl(aq) —>CO2(g)+H2O(l)+CaCl2(aq)

Question 24

How to test for Chlorine ?

Answer 24

Put damp litmus paper in the gas – > If it whitens or is bleached then chlorine is present

Question 25

What colour flame does these metal ions produce ?
1)L1+
2)Na1+
3)K+
4)Ca2+
5)Cu2+

Answer 25

1)Crimson
2)Yellow
3)Lilac
4)Orange-red
5)Green-Blue