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Year 9 Chemistry Final Exam Answers 1
Year 9 Chemistry Final Exam Answers
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Year 9 Chemistry Final Exam Answers
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16. The diagrams below show the arrangement of atoms or molecules in five
different substances A, B, C, D and E.
Each of the circles , and represents an atom of a different element.
Give the letter of the diagram
which represents:
(i) a mixture of gases;
B [1]
(ii) a single compound.
D [1]
17. The diagram below shows a model of a chemical reaction between two
substances.
How can you tell from the diagram that a chemical reaction took place between
substance P and substance Q?
any one from * a compound or a new substance has been formed * R or the product is a new substance
accept ‘the ratio is always 1P to 2Qs’
accept ‘the atoms or particles have joined’
accept ‘the elements have joined’
[2]
Year 9 Chemistry Final Exam Answers
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18. The particles in a solid cannot spread out
Tick () two reasons why particles in a solid cannot spread out. [2]
The particles are already too far apart.
The particles in a solid do not move around.
Solids have a fixed shape.
Solids can only take on the shape of a container.
The pressure in a solid is too great.
19. ATOMOS: means
a. Invisible b. Indivisible c. Untouchable d. Unfavorable
20. In the 18th Century, scientists had different ideas about how particles
react.
Imagine you want to investigate the ideas of Dalton and Mendeleev. Write your
plan.
In your plan you must give:
• the one factor you would change as you carry out your investigation (the
independent variable); [1]
* the metal
• one factor you would observe or measure to collect your results (the
dependent variable); [1]
any one from
* the change in the mass of the metal after burning
* the change in the mass of the metal after burning
accept ‘whether the mass of metal increases or decreases or stays the same’
accept ‘weight before and after burning’
Dmitri Mendeleev (1834-1907) John Dalton (1766-1844)
When metals burn in air,
they gain something to the
air and a powder is formed.
When metals burn in air,
they lose something to the
air and a powder is formed.
Year 9 Chemistry Final Exam Answers
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• one of the factors you would keep the same as you carry out your
investigation (the control variable); [1]
* make sure all the product is weighed
accept ‘starting mass of metal’
accept ‘mass of the metal’
accept ‘enough time for the reaction to occur’
accept ‘sufficient heat for burning to occur’
accept ‘burn the metals for the same length of time’
award a mark for any suitable rigour in the procedure or identification of any
control variable ‘the atmosphere it is heated in’ is insufficient
• the evidence that would support Mendeleev’s idea. [1]
* an increase in the mass following burning for all three metals
accept ‘mass will increase’
accept ‘weight increase’
21. This question is about elements.
(a) Draw straight lines to match the element with its correct chemical
symbol.
[3]
(b) Chlorine gas, salt water and sodium chloride all contain chlorine.
Draw lines from these substances to the correct type of substance.
Year 9 Chemistry Final Exam Answers
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[3]
22. Solids can change state to become gases.
Look at the diagram to show the changes in state.
Name the common factor in processes A and B.
Accept: increase in heat/ energy/ temperature
[1]
23. Look at the information about different atoms.
Use the information above to answer the following questions.
Which two atoms have 10 neutrons in their nuclei?
Flourine and Neon [1]
24. Ernest Rutherford’s work showed that [1] a. substances exist as atoms.
b. atoms contain electrons.
c. atoms have a nucleus.
Year 9 Chemistry Final Exam Answers
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25. A nucleus with 86 protons and 126 neutrons undergoes alpha decay (breakdown). What does it form? [1]
a. A nucleus with 90 protons and 124 neutrons
b. A nucleus with 84 protons and 124 neutrons
c. A nucleus with 82 protons and 128 neutrons
26. What do we call atoms with the same atomic number but different mass numbers? [1]
a. Ions
b. Isotopes
27. Most of the volume of an atom is occupied by [1] a. the nucleus
b. nuclides
c. empty space or the electron cloud
d. protons
28. Choosing from the following list of words, assign the appropriate labels [A, B, C, D, E, F, G, or H] to the Figure (can be more than one). The first one is done for you. [9]
A. Atom B. Molecule C. Compound D. Matter
E. Substance F. Element G. Organic H. Inorganic
Add [A, B, C, D, E, F, G, or H] to the pictures:
A. Atom, B. Molecule, C. Compound, D. Matter,
E. Substance, F. Element, G. Organic, H. Inorganic
B, D, G, E
D, A, F, [G] D, B, [C, E, H] D, B, [C, E, G]
See next page
+1[1.5] +2[0.5] +1[1.5]
Year 9 Chemistry Final Exam Answers
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29. Determine the mass of each reactant needed to give the indicated amount of product. Be sure that the chemical equations are balanced. [9] Reactants Products
Pb(s) + PbO2(s) + 2H
2SO
4(aq) → 2PbSO4(s) + 2H
2O(l); 3.8 g of PbSO
4
3.8g PbSO4 X 1 mole PbSO4 = 0.013 moles PbSO4 303.27g PbSO4
Mass of Pb (reactant):
0.013 moles PbSO4
X 1 mole Pb
X 207.2g Pb
= 1.35 g Pb 2 moles PbSO
4 1 mole Pb
Mass of PbO2 (reactant):
0.013 moles PbSO4
X 1 mole PbO
2
X 239.2g PbO
2 = 1.55g PbO
2
2 moles PbSO4 1 mole PbO
2
Mass of H2SO
4 (reactant):
0.013 moles PbSO4
X 2 mole H
2SO
4
X 98.09g H
2SO
4 = 1.28g H
2SO
4
2 moles PbSO4 1 mole H
2SO
4
Mass of water H2O (product):
0.013 moles PbSO4
X 2 mole H
2O
X 18.02g H
2O
= 0.23g H2O
2 moles PbSO4 1 mole H
2O
1.35 g Pb + 1.55g PbO2 + 1.28g H
2SO
4 = 3.8 g PbSO
4 + 0.23g H
2O
4.18 g of reactants = 4.03 g of product (0.15 g margin of error?)
Mass of reactants = Mass of Products
Law of conservation of Mass
Continued from previous page
Year 9 Chemistry Final Exam Answers
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30. Chlorine dioxide (ClO₂) is a bleaching agent used in the paper industry. It can be prepared by the following reaction: [6]
2NaClO2(s) + Cl
2(g) → 2ClO2(aq) + 2NaCl(aq)
a. What mass of chlorine is needed for the complete reaction of 30.5 g
of NaClO2?
30.5 g NaClO2
X 1 mole NaClO
2
= 0.34 moles NaClO2
90.44 g NaClO2
Mass of chlorine Cl2 (reactant):
0.34 moles NaClO2
X 1 mole Cl
2
X 70.9 g Cl
2
= 12.05 g Cl2
2 mole NaClO2 1 mole Cl
2
b. Give a general equation for the conversion of ‘x’ grams of sodium
chlorite to chlorine dioxide.
x g NaClO2
X 1 mole NaClO
2
= x
moles NaClO2
90.44 g NaClO2 90.44
Mass of chlorine dioxide ClO₂ (reactant):
x moles NaClO
2 X
2 mole ClO₂ X
67.45 g ClO₂ =
x ⨯ 2 ⨯ 70.9 g ClO₂ 90.44 2 mole NaClO
2 1 mole ClO₂ 90.44 ⨯ 2
16. The figure below models a famous discovery in the history of the atom. In a few sentences describe the figure and its significance. Be sure to include:
a. What was this discovery b. Who made this discovery c. What was the experiment d. What was the expected result and the observed result e. And Label the figure
. [6]
Rutherford's scattering experiment: A scientist called Ernest Rutherford designed an experiment to test the plum pudding model. A beam of alpha particles was aimed at very thin gold foil and their passage through the foil detected. The scientists expected the alpha particles to pass straight through the foil, but some of the alpha particles emerged from the foil at different angles, and some even came straight back. The scientists realised that the positively charged alpha particles were being repelled [repel: Push apart] and deflected [deflect: To cause an object to change direction. The object is 'deflected'.] by a tiny concentration of positive charge in the atom. As a result of this experiment, the plum pudding model was replaced by the nuclear model of the atom.
Alpha particles electrons
Concentration of positive charge
Year 9 Chemistry Final Exam Answers
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Crossword Key Questions 1-15:
Bonus: Describe the exercise done in class with the objects shown here. Name six skills that were used in the exercise. Describe the relationship to the scientific method.
a. Learning outcomes i. Skills used: discussion, developing an argument, observation,
negotiation and teamwork ii. ■ Scientists generate scientific theories based on evidence, but they
do not find definitive answers. iii. ■ Scientific knowledge and ideas change over time and are open to
further revision as our understanding of the world around us evolves. ■ Science is a social and creative activity.
Bonus:
DNA is composed of Nucleic acids that basepair together. The monomers of nucleic acids, called nucleotides, are formed from these units: A phosphoric acid molecule, H3PO4; A five-carbon sugar; One of 4 nitrogen-containing
organic bases: Adenine: C5H5N5 Guanine: C5H5N5O Cytosine: C4H5N3O Thymine: C5H5N2O2
Phosphate: PO4 2-deoxyribose: C5H9O4
Calculate the average atomic weight of a DNA basepair: calculated 717.49 amu Average weight of a DNA basepair (sodium salt) = 650 daltons (amu or u)
If the human genome is 3.3 x 109
basepairs long, what is the mass of the human genome in grams? Molecular weight of a double-stranded DNA molecule = (# of basepairs x 650 daltons) Total weight of the human genome = 3.3 x 109 bp x 650Da = 2.15 X 1012 Da. One Dalton is 1.67 x 10-24grams, so the human genome weighs 3.59 x 10-12 grams (10-12 grams is also known as a picogram)
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