Elements of life

Question 1

EL)w)v)

What is the flame colour for the flame test of the metal cation Li⁺

Answer 1

• Bright red

Question 2

EL)w)v)

What is the flame colour for the flame test of the metal cation Na⁺

Answer 2

• Orange

Question 3

EL)w)v)

What is the flame colour for the flame test of the metal cation K⁺

Answer 3

• Lilac

Question 4

EL)w)v)

What is the flame colour for the flame test of the metal cation Ca²⁺

Answer 4

• Brick red

Question 5

EL)w)v)

What is the flame colour for the flame test of the metal cation Ba²⁺

Answer 5

• Apple green

Question 6

EL)w)v)

What is the flame colour for the flame test of the metal cation Cu²⁺

Answer 6

• Blue green

Question 7

EL)v)

What is the electromagnetic spectrum in order of increasing frequency?

Answer 7

• Radiofrequency
• Microwave
• Infrared
• Visible light
• Ultraviolet
• X-ray
• Gamma ray

Question 8

EL)v)

What is the electromagnetic spectrum in order of increasing energy?

Answer 8

• Radiofrequency
• Microwave
• Infrared
• Visible light
• Ultraviolet
• X-ray
• Gamma ray

Question 9

EL)v)

What is the electromagnetic spectrum in order of decreasing frequency?

Answer 9

• Gamma ray
• X-ray
• Ultraviolet
• Visible light
• Infrared
• Microwave
• Radiofrequency

Question 10

EL)v)

What is the electromagnetic spectrum in order of decreasing energy?

Answer 10

• Gamma ray
• X-ray
• Ultraviolet
• Visible light
• Infrared
• Microwave
• Radiofrequency

Question 11

EL)v)

What is the electromagnetic spectrum in order of increasing wavelength?

Answer 11

• Gamma ray
• X-ray
• Ultraviolet
• Visible light
• Infrared
• Microwave
• Radiofrequency

Question 12

EL)v)

What is the electromagnetic spectrum in order of decreasing wavelength?

Answer 12

• Radiofrequency
• Microwave
• Infrared
• Visible light
• Ultraviolet
• X-ray
• Gamma ray

Question 13

EL)g)

Chemists have put forward various models to try to explain atomic structures. Scientific models often change in the light of new evidence.

The diagrams below show possible structures for atoms based on different models, A-D.

Match each statement with the appropriate corresponding model.

• Dalton suggests from experiments with gases that atoms are ‘indivisible’ and react in whole numbers
• Thompson discovers the negatively charged electron
• Rutherford, Geiger and Marsden find that some positively charged α particles bounce almost straight back when fired at a thin metal foil
• Excited atoms emit light which forms a line emission spectrum

Answer 13

• C
• B
• A
• D

Question 14

EL)g)

The current model of the atom describes a nucleus containing protons and neutrons surrounded by electrons in energy levels.

Complete the following table showing the properties of the sub-atomic particles

Answer 14

• relative mass of proton = 1
• relative charge of proton = +1
• relative mass of neutron = 1
• relative charge of neutron = 0
• relative mass of electron = 0.0005
• relative charge of electron = -1

Question 15

EL)a)

Explain why:

• mass numbers of atoms are always whole numbers
• the relative atomic mass of an element may not be a whole number

Answer 15

• mass number = protons + neutrons
  
  • protons and neutrons both have a relative mass of 1, and electrons have a negligible mass, therefore mass number is always whole
• relative atomic mass of an element (A_r) is only an average
• of naturally occuring isotopes
  
  • therefore may not be a whole number

Question 16

EL)h)

Geiger and Marsden used the radioactive isotope ²²⁶Ra in their experiments. ²²⁶Ra decays by α-emission.

Write a nuclear equation for this process.

Answer 16

Question 17

EL)w)ii)

Much of our knowledge of outer space is based on spectroscopic data.

Absorption spectra give information about the elements present in starts.

Describe the main features in the appearance of an atomic absorption spectrum.

Answer 17

• continuous coloured visible spectrum background
• black lines
• that get closer together at higher frequency

Question 18

EL)w)ii)

What are the similarities and differences between an atomic emission spectrum’s appearance and an absorption spectrum?

Answer 18

• Similarities
  
  • lines positioned in the same place for a given element
  • lines become closer at higher frequencies
  • series of lines representing transitions to or from a particular energy level
• Differences
  
  • coloured lines
  • black background

Question 19

EL)i)

Radiowaves can provide information about the molecules found in some regions of space. One molecule found in the coldest regions of outer space has the formula H₂CO. This molecule is represented in the diagram below

Draw the ‘dot-and-cross’ diagram for this molecule

Answer 19

• Diagram must have
  
  • two lone pairs on oxygen
  • two crosses and two dots between C and O
  • dot and cross between each C and H

Question 20

EL)k)

Use the diagram below of H₂CO to help you describe and explain its shape, giving the bond angle.

Answer 20

• bond angle = between 118-122
  *

Question 21

EL)g)

There has been a steep rise in demand in recent years for the isotope helium-3. This isotope is used widely in cold temperature research and medical imaging.

Complete the following table to show the atomic structures of helium-3 and helium-4.

Answer 21

• Number of protons
  
  • Helium-3 = 2
  • Helium-4 = 2
• Number of neutrons
  
  • Helium-3 = 1
  • Helium-4 = 2
• Number of electrons
  
  • Helium-3 = 2
  • Helium-4 = 2

Question 22

EL)h)

There has been a steep rise in demand in recent years for the isotope helium-3. This isotope is used widely in cold temperature research and medical imaging.

Helium-3 is also formed in the Sun by nuclear fusion processes involving isotopes of hydrogen.

Write the nuclear fusion equation for the production of helium-3 from two different isotopes of hydrogen.

Answer 22

Question 23

EL)h)

Nuclear fusion processes could be a useful energy source. It is very difficult, however, to create the high temperatures and pressures to bring about safe fusion on Earth.

Suggest why very high temperatures and pressures are needed for nuclear fusion.

Answer 23

• To overcome repulsion
• between two postively charged nuclei
• in order to join the nuclei to make a heavier nuclei

Question 24

EL)w)ii)

The presence of helium in the Sun was detected when its atomic absorption spectrum was recorded during a solar eclipse.

Describe the appearance of an atomic absorption spectrum.

Answer 24

• continuous coloured visible spectrum background
• black lines
• lines getting closer at higher frequency

Question 25

**EL)w)i)** Explain in terms of electronic energy levels, why the atomic absorption spectrum of a particular element is unique. In your answer you should include the relationship between energy and the radiation absorbed.

Answer 25

*

Question 26

**EL)d)** Gas lighters can be used to create a spark to light a Bunsen burner. These gas lighters contain one of three metals, iron, titanium or cerium, or possibly an alloy of two of these metals. When the metal is struck against a hard material, such as flint or ceramic wheel, a little piece of metal becomes detached and rapidly reacts with the oxygen in the air, glowing white hot and creating the spark. Write the equation for the reaction of cerium with oxygen to form the oxide Ce₂O₃

Answer 26

* State symbols * Ce (s) * O₂ (g) * Ce₂O₃ (s)

Question 27

**EL)b)i)** Gas lighters can be used to create a spark to light a Bunsen burner. These gas lighters contain one of three metals, iron, titanium or cerium, or possibly an alloy of two of these metals. When the metal is struck against a hard material, such as flint or ceramic wheel, a little piece of metal becomes detached and rapidly reacts with the oxygen in the air, glowing white hot and creating the spark. equation (reaction of cerium with oxygen to form one oxide) 4Ce + 3O₂ --\> 2Ce₂O₃ Cerium forms another oxide containing 81.4% by mass of cerium Calculate the empirical formula of this oxide. Show working A_r of Ce = 140.1

Answer 27

* ....

Question 28

**EL)j)** Flint is a form of silicon dioxide. Silicon dioxide has a melting point above 1600^oC, does not conduct electricity and does not dissolve in water. Suggest the structure and bonding of silicon dioxide.

Answer 28

* covalent network or giant covalent molecule

Question 29

**EL)i)** Silicon is in the same group as carbon. Draw a 'dot-and-cross' diagram for carbon dioxide. Show outer electrons only.

Answer 29

Question 30

**EL)i)** A 'dot-and-cross' diagram for silicon dioxide is different from the 'dot-and-cross' diagram for carbon dioxide. In what way is it different?

Answer 30

* no double bonds in SiO₂ *

Question 31

**EL)j)** Titanium has a giant metallic structure. Draw a labelled diagram to show a simple model of metallic bonding.

Answer 31

* cations/positive ions * sea of delocalised electrons * regular arrangement (at least 8 ions)

Question 32

**EL)m)** Mendeleev, in his early Periodic Table, arranged the known elements in order of their 'atomic weights.' However in several places, including between calcium and titanium, he left gaps. State the property used in a modern Periodic Table to arrange the elements.

Answer 32

* arranged in order of their atomic/proton number

Question 33

**EL)a** Molybdenum has several naturally occurring isotopes. Explain the term isotopes.

Answer 33

* Atoms of the same element because they have the same atomic number * But have a different mass number because have a different number of electrons

Question 34

**EL)a)** Beryllium is a Group 2 metal and has several modern day uses. It also played an important role in the development of ideas about the structure of the atom. In 1932, James Chadwick fired α-particles at beryllium metal and found that particles were emitted that were not deflected by the electric fields. Chadwick had discovered the neutron. Give the mass number and atomic number of this particle.

Answer 34

* mass number = 1 * atomic number = 0

Question 35

**EL)b)i)** Alloys of beryllium and copper are used for aircraft parts because of their high strength and resistance to corrosion. A typical copper-beryllium alloy contains 1.75% by mass of beryllium. Assume all the rest of the alloy is copper. Calculate the number of moles of beryllium and copper in 100g of the alloy.

Answer 35

* moles of Be = 1.75/9 * = 0.19 * moles pf Cu = 98.25/63.5 * = 1.55

Question 36

**EL)j)** The strength of metals and metal alloys is due to their strong metallic bonding. Draw a labelled diagram to show a simple model of metallic bonding.

Answer 36

* cations/positive ions * sea of delocalised electrons * regular array (at least 8 ions)

Question 37

**EL)i)** Many beryllium compounds are covalent in character. An example is beryllium chloride. The left-hand box below shows the bonding in a beryllium chloride molecule in the vapour state. Complete the 'dot-and-cross' diagram for this molecule in the right-hand box.

Answer 37

Question 38

**EL)j)** Name two physical properties of ionic chlorides which you would expect to be different from those of simple covalent chlorides. State how the properties would differ.

Answer 38

* **melting point is higher in ionic compounds** * ionic compounds conduct electricity when in solution or molten * ionic compounds are generally water soluble

Question 39

**EL)a)** A Russian agent died in London in November 2006, possibly as a result of drinking tea to which the radioisotope polonium-210 had been deliberately added. Polonium-210 has a half-life of 138 days.

Answer 39

*

Question 40

**EL)b)i)** In March 1962, the English chemist Neil Bartlett reacted a red vapour called platinum hexafluoride, PtF₆, with the noble gas xenon. An orange-yellow solid formed as shown in the equation below. Xe_(g) + PtF_6(g) --\> XePtF_6(s) Calculate the percentage by mass of platinum in PtF₆

Answer 40

* M_r = 309.1 * (195.1/309.1) x 100% * = 63%

Question 41

**EL)m)** Give the group and period of the Periodic Table in which xenon is found. Explain how this information is related to the electronic structure of xenon.

Answer 41

* Group 8 * Period 5 * period refers to the number of shells * group refers to the number of electrons in the outermost shell

Question 42

**EL)f)** Forest fires can be devastating, as large bush fires in Australia in recent years have shown. The ash that remains consists mainly of potassium carbonate that does not decompose in the fire. Potassium forms 1+ ions in its compounds. Write down the electron configuration for the K⁺ ion.

Answer 42

* 1s²2s²2p⁶3s²3p⁶

Question 43

**EL)d)** Limestone, impure calcium carbonate, CaCO₃, would have decomposed in the extreme heat of the fire. Write down the equation for the decomposition of calcium carbonate. Show state symbols.

Answer 43

* CaCO_3(s) --\> CaO_(s) + CO_2(g)

Question 44

**EL)w)ii)** Both potassium and calcium carbonate give a characteristic flame colour on strong heating. Analysis of the flame colours shows them to consist of a series of coloured lines at specific frequencies. What name is given to these line spectra?

Answer 44

* atomic emission spectra

Question 45

**EL)a)** The characteristic noise produced when Christmas crackers are pulled apart is caused by a small amount of gunpowder. Gunpowder typically contains 10 percent sulfur, 15 percent carbon and 75 percent potassium nitrate, KNO₃, by mass. Calculate the number of moles of KNO₃ in 100g of gunpowder.

Answer 45

* cc

Question 46

**EL)d)**