Standard Grade Chemistry –Topic 3
Credit Work – Questions and Answers
Topic 3
1
Atomic Theory
Copy and complete the above table about the atomic particles.
Name of particle
Electron
Proton
Neutron
Mass (amu)
Charge
2
Explain clearly why atoms are electrically neutral.
3
What is meant by;
a)
atomic number
b)
Location in atom
mass number
4
Explain as clearly as you can how electrons are arranged in the element
sodium. Use the expression “energy level” in your answer.
5
An atom has a mass number of 28 and an atomic number of 13.
a)
Write down how many protons, neutrons and electrons are in the atom.
b)
Identify the element and give its electron arrangement.
c)
Write the information about the element in nuclide notation (see
examples at foot of page).
6
An atom has 17 neutrons and 16 electrons.
a)
Write down how many protons, neutrons and electrons are in the atom.
b)
Identify the element and give its electron arrangement.
c)
Write the information about the element in nuclide notation.
7
An atom has a mass number of 17 and has 9 neutrons.
a)
Write down how many protons, neutrons and electrons are in the atom.
b)
Identify the element and give its electron arrangement.
c)
Write the information about the element in nuclide notation.
8
Write down how many electrons, protons and neutrons are in the following
ions then write the electron arrangement for each ion.
a)
b)
c)
d)
Ca2+
FO2K+
mass number =40
mass number=19
mass number = 17
mass number = 40
atomic number =20
atomic number=9
atomic number=8
atomic number =19
Examples of nuclide Notation:
23
37
Na
+
Cl
11
17
sodium ion
chlorine atom
Page 1
Standard Grade Chemistry –Topic 3
Credit Work – Questions and Answers
9
Explain what is meant by the term isotopes.
10
Explain what is meant by the term relative atomic mass.
11
The following mass spectrometer trace was obtained for the element sodium:
%
abundance
90
10
24
23
Mass (amu)
Which of these 4 values is most likely to be the relative atomic mass of sodium and
why?
a) 24 amu
b) 23.5 amu
c)
23.1 amu
d)
23 amu
12
Lithium has a relative atomic mass of 6.9 amu. However there are 2 lithium
isotopes, one having mass = 7 amu and another having mass = 6 amu. Explain
why this is the case.
13
Explain why relative atomic masses are often not whole number values.
Answers follow on next page
Page 2
Standard Grade Chemistry –Topic 3
Credit Work – Questions and Answers
1
Completed table
Name of particle
Electron
Proton
Neutron
Mass (amu)
1/2000
1
1
Charge
One negative
One positive
No charge
Location in atom
Orbits nucleus
In nucleus
In nucleus
2
Charge on positive protons is exactly balanced by same number of negative
electrons.
3
a)
b)
4
Sodium has electron arrangement 2)8)1. This means the first energy level
closest to the nucleus has 2 electrons. The second energy level has eight
electrons and the outer energy level furthest from the nucleus has only 1
electron.
5
a)
b)
c)
6
a) 16p, 16e, 17n
c)
33
S
16
b)
Sulphur 2)8)6
7
a)
8p, 8e, 9n
b)
oxygen, 2)6
c)
17
O
8
8
a)
b)
c)
d)
20p, 20n, 18e
9p, 10n, 10e
8p, 9n, 10e
19p, 21n, 18e
9
Varieties of the same element with different numbers of neutrons. They have
the same atomic numbers but different mass numbers.
10
The average mass of the isotopes measured in atomic mass units (amu).
11
The graph shows that the sodium isotope with mass 23 makes up 90% of all
sodium. Thus the average mass (relative atomic mass) will be between 23 and
24 but closer to 23. Answer= 23.1 amu
Number of protons in nucleus of an atom.
Protons and neutrons added together.
13p, 13e, 15n
Aluminium 2)8)3
28
Al
13
2)8)8
2)8
2)8
2)8)8
Page 3
Standard Grade Chemistry –Topic 3
Credit Work – Questions and Answers
12
Since the relative atomic mass is an average this tells us the lithium isotope
with mass =7 is the more common isotope.
13
Relative atomic masses are not whole number values because they are
averages which are calculated from the masses of the isotopes taking into
account their proportions.
Page 4
Standard Grade Chemistry –Topic 3
Credit Work – Questions and Answers
Topic 5 – Fuels
1
Fractional distillation produces hydrocarbons with varying numbers of carbon
atoms in the different fractions.
How does increasing the numbers of carbon atoms in the molecules affect:
a)
b)
c)
2
boiling point
flammability
viscosity
A compound produces carbon dioxide and water when it is burned in a
plentiful supply of air.
a)
b)
What elements must be present in the compound?
Justify your answer to (a) above.
3
a)
b)
c)
What metals are used as catalysts in catalytic convertors?
What does the catalytic convertor do to harmful gases?
Complete the word equation for the reaction in a catalytic converter:
carbon monoxide + nitrogen oxide 
____ + _____
4
Car exhausts sometimes release unburnt petrol and at other times release
carbon monoxide when petrol is not burned fully.
What measure can be taken to increase the efficiency of combustion of petrol
and so reduce these forms of pollution.
Topic 6
1
What is meant by a homologous series?
2
Give 2 examples of homologous series.
3
What is the general formula of
a)
the alkanes
b)
the alkenes
4
The first three members of a homologous series are:
C2H2, C3H4, C4H6
What is the general formula of this series?
5
Name the first five members of the cycloalkanes.
6
Explain what is meant by isomers.
7
Draw extended structures for 2 isomers with the formula
a) C4H8
b)
C5H12
Page 5
Standard Grade Chemistry –Topic 3
Credit Work – Questions and Answers
8
Explain why the boiling point increases steadily as we go from methane to
octane.
9
In thermal cracking, why does use of a catalyst represent a cost saving?
10
What types of molecules are produced from the cracking of long chain
alkanes?
12
Copy and complete this equation for cracking putting in numbers for x and y
and suggest possible names for all the products.
C10H22 
C4H10 + C3H6 + CxHy
Topic 7 – Properties of Substances
1
When a current is passed through an electrolyte in an electrolysis experiment,
why is a DC current used rather than AC.
(DC – direct current, AC – alternating current)?
2
Explain the following.
Ionic substances and covalent network substances are solids, but covalent
molecular substances can be solid, liquid or gas.
3
Give an example of a covalent molecular substance which is:
a)
solid
b)
liquid c)
gas
4
Name 2 covalent network substances.
5
In the electrolysis of molten lead bromide - Pb2+(Br-)2
a)
b)
c)
d)
e)
What is the product at the negative electrode?
What is the product at the positive electrode?
What has the electricity done to the compound?
What is the ion-electron equation at the positive electrode?
What is the ion-electron equation at the negative electrode?
6
In the electrolysis of copper (II) chloride solution?
a)
b)
c)
d)
e)
What is the product at the negative electrode?
What is the product at the positive electrode?
What has the electricity done to the compound?
What is the ion-electron equation at the positive electrode?
What is the ion-electron equation at the negative electrode?
Page 6
Standard Grade Chemistry –Topic 3
Credit Work – Questions and Answers
Topic 8 – Acids and Alkalis
1
What can you say about the concentration of H+ ions and the concentration of
OH- ions in water?
2
When hydrochloric acid dissolves in water it produces aqueous hydrogen ions
and aqueous chloride ions according as follows:
HCl
-->
H+(aq) +
Cl- (aq)
Write similar equations for a) sulphuric acid
3
b) nitric acid
Copy and complete:
a) An acid solution contains ____ H+(aq) ions than pure water.
b) An alkaline solution contains ____ OH-
(aq)
ions than pure water.
c) When we dilute an acid the concentration of H+(aq) ions ________
d) When we dilute an alkali the concentration of OH4
(aq)
________
Calculate formula masses for the following substances:
a) NaOH
b) MgSO4
c) Na2CO3
d) (NH4)3PO4
5
Explain what is meant by a mole of a substance.
6
What units do we use for the concentration of solutions in chemistry?
In the following questions the formula triangles below should assist you.
n
mg
n
c
fm
n = number of moles
mg = mass given in question
fm = formula mass
7
8
v
n = number of moles
c = concentration (mol l-1)
v = volume (litres)
Find the mass of :
a) 0.1 moles of sodium hydroxide
b) 2 moles of magnesium sulphate
How many moles are contained in:
a) 10.6g of sodium carbonate
b) 1.49g of ammonium phosphate
Page 7
Standard Grade Chemistry –Topic 3
Credit Work – Questions and Answers
9
How many moles of substance are contained in:
a)
b)
500 cm3 of 0.5 mol l-1 hydrochloric acid?
250 cm3 of 0.1 mol l-1 sodium hydroxide?
10
What is the concentration in mol l-1 of a solution containing
a) 2 moles in 500cm3
b) 0.5 moles in 100 cm3
c) 5 moles in 2 litres.
In question 11 you must first write the formula, find the formula mass then
calculate how many moles of substance you have before using the second
triangle.
11
What is the concentration in mol l-1 of a solution containing:
a)
5.6g of potassium hydroxide in 500 cm3 of solution?
b)
13g of lithium fluoride in 250 cm3 of solution?
In question 12, use the second triangle to work out the number of moles, then use
this answer and the formula mass in the first triangle to find the given weight.
12
Find the mass of dissolved substance in the following solutions:
a)
100 cm3 of 0.1 mol l-1 sodium chloride solution.
b)
200 cm3 of 0.5 mol l-1 copper(II) sulphate solution
Page 8