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All Short Questions Flashcards

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1
Q

What are cathode rays?

A

streams of negatively charged particles called electrons

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2
Q

Bananas contain small quantities of potassium‐40, a radioactive isotope. What is the daughter nucleus when K‐40 emits an electron in beta decay?

A

40
Ca
20

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3
Q

State Avogadro’s law.

A

equal volumes of gases contain equal numbers of molecules under the same conditions of temperature and pressure

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4
Q

What is the oxidation number of sulfur in

(i) sulfur dioxide (SO2),
(ii) the sulfate ion (SO42–)?

A

i) + 4

ii) +6

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5
Q

Give two differences between a sigma and a pi covalent bond.

A

1) sigma covalent bond involves the head on overlap of orbitals while pi covalent bonds involves the sideways overlap over orbitals
2) sigma bonds are stronger that pi bonds as there is more of an overlap in sigma bonds than in pi bonds

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6
Q

In the electrolysis of aqueous KI with inert electrodes one half‐equation is:
2I– (aq) —> I2 (aq) + 2e–
Write a balanced half‐equation for the reaction that takes place at the negative electrode
during this electrolysis.

A

2H20 + 2e- —-> 2H2 + 20H-

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7
Q

Define bond energy.

A

it is the average energy needed to convert one mole of covalent bonds and to separate the neutral gaseous atoms completely from each other

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8
Q

The structure of ibuprofen is shown. Ibuprofen is the active ingredient in many fever and pain‐relief suspensions given to children. A single 5 cm3 dose, suitable for children aged 1 to 3 years, contains 4.86 × 10–4 moles of ibuprofen.
How many milligrams of ibuprofen are in this single dose?

A 
13(12)+2(16)+18(1)
206
mass=moles x molar mass
mass= 4.8x10-4 x 206
mass=.100116g
           x1000
mass= 100.116mg
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9
Q

Write a balanced equation for the reaction – between limestone and carbonic acid in rainwater – that gives rise to temporary hardness in the water.

A

H2CO3+ CACO3= CA(HCO3)2

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10
Q

Answer part A or part B.
A Why is nitrogen gas unreactive?
or
B Draw two repeating units of the polymer poly(propene).

A

A) it is inert due to the large amount of energy need to break the triple bond

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11
Q

What was the purpose of Millikan’s ‘oil drop’

experiments of 1908 to 1913?

A

used charged oil droplets to determine the size of the charge on the electron

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12
Q

State and give the reason for the trend in atomic radii across the second period
of the periodic table.

A

they are decreasing due to the increasing nuclear charge and no increase in the screening effect of inner shells

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13
Q

Write the electron configuration (s, p, etc) for an iron atom.

A

1s2 2s2 2p6 3s2 3p6

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14
Q

Give two reasons why real gases deviate from ideal behaviour at high pressures
and low temperatures.

A

1) molecules have attractive and repulsive forces
2) real gas molecules have intermolecular forces
3) real gas molecules have a volume

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15
Q

Identify in the following reaction the Brønsted‐Lowry acid and its conjugate base.
PO43– + HNO3 -> NO3– + HPO42–

A

HNO3 –> NO3-

ACID. > CONJUGATE BASE

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16
Q

During the Olympics in Rio de Janeiro in 2016 the water in some swimming and diving pools turned green. Sodium hypochlorite in the pools had reacted with hydrogen peroxide, added in error, and this allowed the rapid growth
of green algae. The reaction that occurred was:
NaOCl+H2O2 NaCl+H2O+O2
Use oxidation numbers to show whether chlorine was oxidised or reduced.

A 
NAOCL
\+1-2+1
NACL
\+1-1
Reduced
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17
Q

Write a balanced equation, or give the half equations, for the displacement reaction that occurs between chlorine gas and an aqueous solution of sodium bromide.

A

Cl2 +2e– → 2Cl–

2Br– →Br2 +2e–

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18
Q

State and explain the effect of adding a little tetraethyllead to an equimolar mixture of methane and chlorine
exposed to weak sunlight.

A

the rate of reaction increases as tetrahedral lead acts as a catalyst

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19
Q

Epoxyethane is used to manufacture car antifreeze. It is composed of 54.5% carbon, 9.1% hydrogen and 36.4% oxygen by mass.
Find the empirical formula of epoxyethane.

A
  1. 4 9.1 36.4
  2. =4.54 1. =9.1 16. = 2.275
  3. 54 9.1 2.275
  4. 275 =2 2.275=4 2.275= 1

C12H4O

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20
Q

Explain the term biochemical oxygen demand.

A

It is the amount of dissolved oxygen in ppm consumed by biological action when a sample of water is kept at 20oc in the dark for 5 days

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21
Q

Answer part A or part B.
A Which of the following gases makes the greatest contribution to the greenhouse effect?
carbon dioxide
water vapour methane
Give the reason for your choice.
or
B Give an example of (i) a molecular crystal, (ii) a covalent macromolecular crystal.

A

A) water vapour

it is the most abundant in the air

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22
Q

Why did Mendeleev place tellurium before iodine in his periodic table of the elements?

A

Mendeleev ordered the element in order of increasing atomic weight but tellurium which was heavier was placed before iodine the lighter one in order to make them fall into groups of elements with similar properties.

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23
Q 
Identify the main energy levels involved in the electron transition that gives rise to
the first (red) line of the Balmer series in the emission spectrum of the hydrogen atom.
A

energy level 2-3

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24
Q

identify the atomic symbol X and the atomic number Z of the daughter nucleus in the following nuclear equation. 137 137 0
Cs→ X+ e
55. Z –1

A

137
Ba
56

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25
Q

Write the oxidation number for

(i) oxygen in OF2,
(ii) xenon in XeF4.

A

i) +2

ii) +4

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26
Q

Calculate the mass of sodium chloride required to prepare 500 cm3 of a 0.9% (w/v) saline solution for use as an intravenous fluid.

A

500cm3 of 9%
.9g in 100=.9
.9x volume needed/volume given
.9x500/100=4.5g in 500cm3

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27
Q

Identify, in ammonia, the type of

(i) intramolecular bonding,
(ii) intermolecular forces, present.

A

i)3.04-2.2=.84
polar covalent bond
intermolecular
ii)hydrogen bond- dipole dipole

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28
Q

The structure of eugenol is shown.
(i) Write the molecular formula of eugenol.
(ii) Name a spectroscopic technique that could help confirm the identity of a sample of eugenol.
2017

A

i)C10H1202

II)mass spectromentry

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29
Q

Write a balanced equation for the displacement reaction between copper metal and AgNO3 solution to produce copper(II) nitrate

A

Cu+AgNO3 > Cu2NO3+Ag

Cu+2AgNO3. > Cu(NO3)2+2Ag

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30
Q

How does boiling remove any temporary hardness, caused by the presence of calcium hydrogencarbonate, in a water sample?

A

By boiling the water calcium hydrogen carbonate decomposes into water ,carbon dioxide and an insoluble precipitate of calcium carbonate > limescale
Ca(HCO3)2 >H2O+CO2+CACO3(DOWNARROW)

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31
Q 
Answer part A or part B.
A Explain using balanced equations how sulfuric acid in rainwater is formed from
sulfur dioxide in the atmosphere.
or
B How is aluminium anodised?
A

A) S+O2 >S02
SO2+1/2O2 >SO3
SO3+H2O > H2SO4

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32
Q 
A dipostaive ion M2+ has 25 electrons and 32 neutrons 
What is (i) the atomic number, (ii) the mass number, of M
A

i) 25+2 =27

ii) 27 +32 = 59

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33
Q

Describe the plum-pudding model of the atom proposed by Thomson around 1897.

A

The atom is like a sphere of positive charge with electrons embedded in it at random

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34
Q

Explain why the first ionisation energy of oxygen is lower than that of nitrogen despite the general increase in values across the second period of the periodic table.

A

nitrogen has a half full 2p sub level and therefor stable : 1s2 , 2s2 , 2p3 while oxygens is not half full and therefore more unstable

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35
Q

Distinguish between sigma and pi covalent bonding.

A

sigma is the head on overlap of orbitals while the pi bond in the sideways overlap of orbitals

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36
Q

Write (i) the conjugate acid, (ii) the conjugate base, of H2PO4–.

A

i) H3PO4

ii) HPO4 2-

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37
Q

What was Gay-Lussac’s observation about reactions involving gaseous reactants and products?

A

In a reaction between gases the volumes of the reacting gases and the volumes of any gaseous products are in the ratio of small whole numbers provided that the volumes are measured at the same temperature and pressure

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38
Q

The structure of the cinnamaldehyde molecule is shown. How many moles of cinnamaldehyde are there in 1.65 g
of the pure compound?
2016

A

9(12)+8(1)+1(16)=132
1.65
132 =.0125 moles

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39
Q

How would you confirm the presence of the sulfite ion in aqueous solution?

A

1) add a few drops of barium chloride using a dropper

2) a white precipitate of barium sulphite will appear indicating the presence of sulphite ions

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40
Q

What is meant by the activation energy of a reaction?

A

it is the minimum energy colliding particles must have for a reaction to take place.

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41
Q

Answer part A or part B.
A Describe a chemical method for removing acidic gases from industrial
chimney waste.
or
B Name the analytical technique that was the basis of the work for which Dorothy Hodgkin was awarded the 1964 Nobel Prize for Chemistry.

A

limestone scrubbers are put in the chimney stacks of coal fired power stations to remove the sulphur dioxide from the gases before the leave the power-station
CaCO3+SO2=CO2+CaSO3

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42
Q

How many (i) electrons, (ii) neutrons, has the aluminium ion, 27
AL3+
13

A

i) 13-3=10

ii) 27-13=14

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43
Q

Explain why relative atomic masses are rarely whole numbers.

A

as it is the average mass of a carbon 12 atom

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44
Q

What change takes place in the nucleus of an atom when beta decay occurs?

A

a neutron in an unstable nucleus changes into a proton and an electron is then emitted

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45
Q

Account for the difference in the shapes of the boron trifluoride (BF3) molecule and the ammonia (NH3) molecule.

A

boron trifluoride has 3 bond pair of electrons and no lone pairs so it is trigonal planar while ammonia has 3 bond pair of electrons and 1 lone pair so it is pyramidal

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46
Q

When 19.05 g of copper reacted with nitrogen, 20.45 g of copper nitride were produced.
Deduce the empirical formula of copper nitride.

A

19.05
63.5 =.3moles
1.4
14 =.1moles
3:1
Cu3N

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47
Q

Copy the structure of the aspirin molecule shown into your answer book.
(i) Draw a circle around the carboxylic acid group.
(ii) Draw a rectangle around the carbonyl part
of the ester group.
2015

A

i) o=c=oh

ii) c=o

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48
Q

In the periodic table, identify an element

(i) in the same period as magnesium but with larger atoms,
(ii) in the same group as magnesium but with smaller atoms.

A

i) sodium Na

ii) beryllium Be

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49
Q

What is the purpose of tertiary sewage treatment?

A

it removes nitrates and phosphates from the effluent because they cause eutrophication

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50
Q

Calculate the number of moles of nitrogen gas at a pressure of 1.85 × 105 Pa and a temperature of 293 K in the 6.50 × 10–5 m3 volume inside a new tennis ball. Give your answer correct to one significant figure.

A

p1v1. p2v2
t1. = t2
1.85x105(6.50 × 10–5 ) = 1.01x105 xv2
293. 273
V2=1.11×10-4 m3
1.11x10-4
22.4x10-3

= 0.005 (5 × 10–3)moles

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51
Q

Answer part A or part B.

A State two ways by which nitrogen is fixed in nature.

A

1) in electrical storms

2) nitrogen fixing bacteria

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52
Q

What colour is observed in a flame test on a salt of (i) barium, (ii) lithium?

A

(i) green (yellow-green) // (ii) crimson (red)

53
Q

Write a balanced nuclear equation for the beta-particle decay of the 223 Fr 87 nucleus.

A

223 223 0
Fr ——> Ra e
87 88 -1

54
Q

The scientist pictured on the right is Werner Heisenberg.

State the famous principle, published in 1927, which bears his name.

A

Heisenberg’s uncertainty principle states that it is not possible to measure at the
same time both the position and velocity of an electron.

55
Q

How many (i) sigma bonds, (ii) pi bonds, result from sharing of the valence electrons between the atoms in a molecule of nitrogen?

A

i) 1 sigma

(ii) 2 pi

56
Q

What is meant by one mole of a substance?

A

This is the amount of that substance which contains 6 x 10 23 particles of that
substance.

57
Q

Find the empirical formula of a compound containing 40% sulfur and 60% oxygen, by mass.

A

40/32 =1.25 =1
60/16=3.75 = 3
1:3
SO3

58
Q

Potassium iodide (KI) is sometimes added to table salt to supplement diets low in iodide ion (I–). Calculate the daily mass of potassium iodide needed to supply 0.15 mg of iodide ion, the Recommended Daily Amount (RDA) for normal human thyroid function.

A

moles of I - = mass ÷ molar mass = 0.15 ÷ 127 = 0.0012 (3)
Ratio I - : KI = 1 : 1 so we have 0.0012 moles of KI
Mass of KI = moles x molar mass = 0.0012 x (39 + 127) = 0.1992mg

59
Q

Give two structural features of hydrocarbons with high octane numbers.

A

short chains // branches // rings (cyclic)

60
Q

State two processes that are carried out during the primary treatment of sewage.

A

screening // passing over grit channels (traps) // settlement (sedimentation) (settling)

61
Q

Give two uses for the oxygen gas produced by the fractionation of liquid air

A

In hospitals for people who have breathing difficulties.

In the steel industry to remove impurities from iron.

62
Q

Write the electron configuration (s, p, etc.) of a zinc atom in its ground state.

A

1s 2 , 2s 2 , 2p 6 , 3s 2 , 3p 6 , 4s 2 , 3d 10

63
Q

Define relative atomic mass.

A

the average mass of the atoms of an element, taking their abundances into account,
relative to one-twelfth the mass of a carbon-12 atom.

64
Q

How many neutrons are there in 0.14 g of carbon–14?

A

moles = mass ÷ molar mass = 0.14 ÷ 14 = 0.01 moles
Number of particles = moles x 6 x 10 23 = 0.01 x 6 x 10 23 = 6 x 10 21
Mass number = protons + neutrons … So, Mass number – protons = neutrons
14 – 6 = 8
6 × 10 21 atoms × 8 = 4.8 × 10 22 neutrons

65
Q

Give the shape and the corresponding bond angle for a molecule of formula QX4 where Q is an element from Group 4 of the periodic table.

A

CH4 shape:tetrahedral

angle:109.5o

66
Q

When hydrogen gas was passed over 1.59 g of copper oxide, 1.27 g of metallic copper were produced. Find by calculation the empirical formula of the copper oxide.

A

1.27 .32
63.5= .02. 16. = .02
1:1
CuO

67
Q

Complete and balance the equation for the chemical reaction that occurs when a piece of sodium is added to ethanol: C2H5OH + Na →

A

2C2H6ONa +H2

68
Q

What reagents are needed to test a solution for the nitrate ion?

A

iron (II) sulfate solution // concentrated sulfuric acid

69
Q

StateCharles’law.

A

At constant pressure, the volume of a fixed mass of gas is directly proportional to its
temperature measured on the Kelvin scale.

70
Q

What happens during secondary sewage treatment?

A

This is a biological process in which aerobic micro-organisms use oxygen to break
down nutrients in the effluent. This happens within a large aeration tank that is kept
oxygenated by a mechanical rotor.

71
Q

What is meant by heterogeneous catalysis?

A

The reactants and catalyst are in different phases.

72
Q

Write a balanced equation for the formation of ozone in the stratosphere

A

0*+02=03

73
Q

State the number of (i) sub-levels (subshells), (ii) orbitals, occupied by electrons in an argon atom
in its ground state.

A

i) 5

ii) 9

74
Q

Write a balanced nuclear reaction for the beta particle decay of iodine-131.

A

131 0 0
I > Xe e
54 53. -1

75
Q

Using oxidation numbers, or otherwise, balance the following equation.
Cu + NO3– + H+ Cu2+ + NO2 + H2O

A

Cu + NO 3 - + H + → Cu 2+ + NO 2 + H 2 O
(0) (+5)(-2) (+1) (+2) (+4)(-2) (+1)(-2) Cu loses 2 electrons // N gains 1 electron
Cu + 2NO 3 - + H + → Cu 2+ + NO 2 + H 2 O Multiply Cu by 1 // NO 3 - by 2
Cu + 2NO 3 - + H + → Cu 2+ + 2NO 2 + 2H 2 O Multiply NO 2 by 2 and H 2 O by 2
Cu + 2NO 3 - + 4H + → Cu 2+ + 2NO 2 + 2H 2 O Multiply H + by 4
Check: 0 – 2 + 4 = +2 + 0 +0 …… correct

76
Q

Why does raising the temperature generally increase the rates of chemical reactions?

A

Temperature increases the kinetic energy of the reactants, resulting in more collisions
reaching the activation energy and therefore more effective collisions.

77
Q

Name (i) the gas, (ii) the ion, formed at the negative electrode when aqueous sodium sulfate solution is electrolysed.

A

(i) hydrogen // (ii) hydroxyl (hydroxide, OH¯) ions

78
Q

What happens in the scrubbing of waste acidic gases in industry?

A

Limestone scrubbers are fitted in chimney-stacks of coal-fired power stations to remove
sulfur dioxide from the gases before they leave the power station.

79
Q

Give two properties of cathode rays.

A

They are streams of negatively charged particles called electrons / They travel in
straight lines from the cathode to the anode / They have enough energy to move a
paddle wheel / They are deflected by an electric (magnetic field)

80
Q

Give two possible shapes for a covalent molecule of general formula AB2

A

linear//v-shaped

81
Q

Define the mole, the SI unit of chemical amount.

A

This is the amount of that substance which contains 6 x 10 23 particles of that substance.

82
Q

When 4.10 g of hydrated magnesium sulfate, MgSO4•xH2O, were heated strongly, 2.00 g of anhydrous magnesium sulfate were obtained.
Calculate the value of x, the degree of hydration of the crystals.

A

moles = mass ÷ molar mass.
MgSO 4 = 2.00 ÷ (24+32+4(16)) = 2.00 ÷120 = 0.0167
H 2 O = (4.10 – 2.00) ÷ (2(1) + 16) = 2.10 ÷ 18 = 0.1167 Simplest whole number ratio
0.0167 ÷ 0.0167 = 1
0.1167 ÷ 0.0167 = 6.988 = 7
Answer: x = 7

83
Q

Complete and balance the equation for the chemical reaction that occurs when a piece of aluminium is placed in a solution of copper(II) ions: Cu2+ + Al →

A

Cu 2+ + Al→ Cu + Al 3+– balance ions> 3Cu 2+ + Al→ Cu + 2Al 3+

Balance Atoms> 3Cu 2+ + 2Al→ 3Cu + 2Al 3+

84
Q

What is a homologous series of organic compounds?

A

It is a family of organic compounds that have similar chemical properties, // the same
general formula // and each member differs from the previous member by a CH 2 unit.

85
Q

What is the principle involved in the separation of a mixture by chromatography?

A

It is the separation of a mixture of components occurs as a result of selective
adsorbance of the components on the stationary phase while carried by a mobile
phase.

86
Q

What is meant by the greenhouse factor of a gas in the atmosphere?

A

It compares the greenhouse effect of different gases // relative to carbon dioxide.

87
Q

Write the electron configuration (s, p, etc.) of the oxygen (oxide) ion (O2–).

A

O 8 —– BUT O 2- has gained 2 electrons, so 8 + 2 = 10 electrons
1s 2 , 2s 2 , 2p 6

88
Q

State two differences between Mendeleev’s periodic table and the modern periodic table of the elements.

A

Elements are arranged in order of increasing atomic weight // The order of some
elements is reversed // Gaps were left for undiscovered elements // Only 60 elements
compared to more than 100 // The transition elements were not put in a separate block

89
Q

What are the two possible shapes of molecules of general formula QX2?

A

linear//v-shaped

90
Q

How many atoms of iron are there in a 30 g bowl of cornflakes that contains 0.0024 g iron
per 30 g serving?

A

moles = mass ÷ molar mass = 0.0024 ÷ 56 = moles
Number of particles (atoms)= moles x 6 x 10 23 = x 6 x 10 23
= 2.57 x 10 19 or 2.6 x 10 19

91
Q

What is an ideal gas?

A

It is a gas that obeys all the assumptions of the kinetic theory of gases // under all
conditions of temperature and pressure.

92
Q

Write a balanced equation for the reaction that occurs when sulfur dioxide from industrial gaseous emissions dissolves in water.

A

S2+H20= S2HO3

93
Q

The scientist pictured on the right used charged oil drops to determine the size of the charge on a sub-atomic particle. Name the scientist, and the sub-atomic particle involved in his experiments.

A

NAME: Millikan (3) PARTICLE: electron

94
Q

State the Heisenberg uncertainty principle.

A

it is not possible to measure at the same time both the position and velocity of an electron.

95
Q

Define a conjugate pair according to the Brønsted-Lowry theory.

A

DEFINE: acid and base that differ only by a proton

96
Q

When water that contains temporary hardness is boiled in a kettle, scale is formed on the heating element. Identify the chemical that is the main component of this scale.

A

calcium carbonate / CaCO 3 [Accept ‘magnesium carbonate’ or ‘MgCO 3 ’]

97
Q

Draw the structures of two acidic functional groups that occur in organic compounds.

A

An alcohol: O – H or OH (3)

A carboxylic acid:

98
Q

complete and balance the equation C2H6+CL2 —UV LIGHT>

A

C 2 H 6 +Cl 2 → C 2 H 5 Cl + HCl

99
Q

Identify the chemical hazard associated with each of the following warning symbols.

i) O
ii) skull

A

(i) oxidizing (ii) toxic / poisonous

100
Q

Write a balanced chemical equation for one of the following reactions from syllabus case studies based on the chemical industry:

(i) the synthesis of urea from ammonia;
(ii) the combustion of ammonia in air;
(iii) the formation of magnesium hydroxide from slaked lime and seawater.

A

MgCl 2 + Ca(OH) 2 → Mg(OH) 2 ↓ + CaCl2

101
Q

Write the electron configuration (s, p, etc.) of the aluminium ion (Al3+).

A

Al 13 —– BUT Al 3+ has lost 3 electrons, so 13 – 3 = 10 electrons
1s 2 , 2s 2 , 2p 6

102
Q

What contribution did Henry Moseley, the scientist shown in the photograph, make to the systematic arrangement of the elements in the periodic table?

A

Henry Moseley used x-rays to determine the number of protons in the nucleus of an
atom / This number is called the atomic number.

103
Q

Give two properties of alpha particles.

A

Positively charged / Low speed / Stopped by a few cm of air / Deflected by an electric
field / Cause cancer

104
Q

Name the type of spectroscopy, based on absorptions within
a particular range of electromagnetic frequencies, and used as a ‘fingerprinting’ technique to identify organic and inorganic compounds.

A

infra-red spectrometry

105
Q

Write the formula of (i) a substance which causes temporary hardness in water, (ii) a substance which causes permanent hardness in water.

A

(i) Ca(HCO 3 ) 2 / Mg(HCO 3 ) 2

(ii) CaSO 4 / Mg SO

106
Q

Name two metals which act as catalysts in the catalytic converters of modern cars.

A

platinum // palladium // rhodium

107
Q

Account for the difference in bond angle between water (104.5 o) and methane (109.5 o).

A

Water: v-shaped – 2 bond pairs of electrons and 2 lone pairs. // The 2 lone pairs have
greater repelling power and push the 2 bond pairs closer together. (Methane:
tetrahedral – 4 bond pairs of electrons and no lone pairs)

108
Q

Copy the diagram of an exothermic reaction profile into your answer book and mark clearly (i) the activation energy, (ii) ΔH for the reaction.

A

E A = activation energy under curve

ii) from line to dotted line

109
Q

Complete and balance the equation:

C2H5OH + Na. —>

A

C 2 H 5 OH + Na → C 2 H 5 ONa + ½ H 2 / 2C 2 H 5 OH + 2Na → 2C 2 H 5 ONa + H 2

110
Q

Define atomic (covalent) radius.

A

It is half the distance between the nuclei of two atoms / of the same element that are
joined together by a single covalent bond.

111
Q

What is the principal use made of oxygenates such as methyl tert-butyl ether, MTBE, in the petrochemicals industry?

A

increase octane number of a fuel / prevent auto-ignition

112
Q

How many iron atoms should be consumed daily to meet the recommended daily intake of iron in the diet of 0.014 g?

A

Moles = mass ÷ molar mass = 0.014 ÷ 56 = 2.5 x 10 -4

Number of particles = moles x 6 x 10 23 = 2.5 x 10 -4 x 6 x 10 23 = 1.5 x 10 20

113
Q

Name the two reagents used in the brown ring test for the nitrate ion.

A

iron(II) sulfate (FeSO 4 ) // concentrated sulphuric acid / H 2 SO 4

114
Q

Name and draw the structure of a carboxylic acid that is widely used as a food preservative.

A

benzoic acid

115
Q

A 500 cm3 can of beer contains 21.5 cm3 of ethanol. Calculate its % alcohol, i.e. the concentration of alcohol in the beer as a % (v/v).

A

(volume ÷ total volume) x 100 = (21.5 ÷ 500) x 100 = 4.3

116
Q

Explain in terms of bonding why it is more correct to represent the benzene molecule as instead of (3 diagram ) 2007

A

all the carbon-to-carbon bonds in benzene are identical (same length) / delocalised
structure / bonds intermediate between single and double / six valence (bonding)
electrons belong to whole molecule

117
Q

Ultraviolet absorption spectroscopy can be used in the quantitative analysis of some organic compounds (e.g. drug metabolites and plant pigments). What is the underlying principle of this analytical technique?

A

absorbance is // directly proportional to concentration of substance

118
Q

The use of CFCs as refrigerant gases has been discontinued. Name a group of substances used
5. (a)
to replace CFCs as refrigerant gases

A

A: hydrochlorofluorocarbons (HCFCs) / hydrofluorocarbons (HFCs) /

119
Q

Write the electron configuration (s, p, etc.) of a chromium atom in its ground state.

A

1s 2 , 2s 2 , 2p 6 , 3s 2 , 3p 6 , 4s 1 , 3d 5

120
Q

Name the scientist, shown in the photograph, who identified cathode rays as subatomic particles.

A

J J Thomson

121
Q

Give two differences between a nuclear reaction and a chemical reaction.

A

Electrons are not involved. Changes take place in the nucleus so a new element is
formed. // No chemical bonds are broken and formed.

122
Q

Calculatethepercentagecarbon,bymass,inmethylbenzene.

A 
(Mass of carbon ÷ mass of compound) x 100
c 7 h 8
7(12) + 8(1) 
84 + 8
92
(84 ÷ 92) x 100 = 91.30%
123
Q

What is (i) the conjugate acid and (ii) the conjugate base of H2O?

A

(i) H 3 O+ (ii) OH¯

124
Q

What contribution did Newlands make to the systematic arrangement of the elements known to him?

A

groups of elements arranged in order of increasing atomic weight, in which the first and
the eighth element of each group have similar properties

125
Q

What observation is made when a sample of ethanal is heated with Fehling’s reagent?

A

brick-red // precipitate produced

126
Q

The concentration of an aqueous solution of sodium hydroxide(NaOH)is 0.2g per litre. Calculate its pH.

A

TO DO

127
Q

Under what circumstances can ionic compounds conduct electricity?

A

when molten or // dissolved in water

128
Q

Which class of organic compound is responsible for the odour associated with fruits such as apples, oranges, pears, bananas and strawberries?

A

esters

129
Q

State two uses of nitrogen gas based on its chemical stability.

A

To flush tanks of flammable liquids // In food packaging to keep food fresh i.e. crisps //
Liquid nitrogen is used for fast freezing fruit.

CHEMISTRY (6 decks)

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