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90944
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SUPERVISOR'S USE ONLY
NEW ZEALAND QUALIFICATIONS AUTHORITY
MANA TOHU MATAURANGA 0 AOTEAROA
Level 1 Science, 2014
90944 Demonstrate understanding of aspects
of acids and bases
9.30 am Monday 10 November 2014
Credits: Four
Achievement
Demonstrate understanding of aspects
of acids and bases.
Achievement with Merit
Demonstrate in-depth understanding of
aspects of acids and bases.
Achievement with Excellence
Demonstrate comprehensive
understanding of aspects of acids and
bases.
Check that the National Student Number (NSN) on your admission slip is the same as the number at the
top of this page.
You should attempt ALL the questions in this booklet.
Pull out Resource Booklet 90944R from the centre of this booklet.
If you need more space for any answer, use the page(s) provided at the back of this booklet and clearly
number the question.
Check that this booklet has pages 2-1 0 in the correct order and that none of these pages is blank.
YOU MUST HAND THIS BOOKLET TO THE SUPERVISOR AT THE END OF THE EXAMINATION.
Excellence
TOTAL
31
ASSESSOR' S USE ONLY
©New Zealand Qualifications Authority, 2014. All rights reserved.
No part of this publication may be reproduced by any means without the prior permission of the New Zealand Qualifications Authority.
2
QUESTION ONE: ATOMS, IONS, AND FORMULAE
(a)
ASSE$S4
U$EONI
Write the formulae for the following ionic compounds.
Use the Table of Ions in ym~~~~SJC-W:~~okletto help you.
(1)
Calcium chloride
(ii)
Sodium nitrate
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..
...
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\~~ C.~O.?.)~ ..
(iii) Zinc nitrate
(b)
,®£: J <f
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Complete the table below for the ions fom1ed by magnesium, aluminium, and oxygen.
Use the periodic table in your Resource Booklet to help you.
Atom
(c)
The formula for magnesium oxide is MgO. The formula for aluminium oxide is Al2 0 3 .
Explain why the two formulae are different.
In your answer:
•
consider the ratio of ions in each formula and explain how the ratio is related to the
charge on the ions
relate the ratio of ions in the formula to the number of electrons lost or gained by each
atom .
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Question One
E8- Explains correctly the number of electrons that
magnesium, aluminium, and oxygen gain or lose in
order to gain a full valence shell.
Candidate goes on to explain that the ratio of magnesium ions to oxide ions in magnesium oxide is one-toone, as the +2 charge on the magnesium ion cancels out
the -2 charge on the oxide ion, giving a neutral compound overall.
For aluminium oxide, the candidate explains that the
ratio of aluminium ions to oxide ions is two to three, as
the +6 charge of the two aluminium ions cancels out the
-6 charge of the three oxide ions, giving a neutral compound overall.
4
QUESTION TWO: BALLOONS
(a)
ASSESS;:
U$EON
Calcium carbonate pieces are placed in a flask and hydrochloric acid is added, Immediately a
balloon is placed over the top of the flask The balloon then starts to inflate.
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inflating balloon
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calcium carbonate
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pieces
~
(-
(i)
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\
~ hydrochloric acid
D.-
/
Explain why the balloon inflates.
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In a second experiment, the same mass
(ii)
~1m carbonate in a powdered fom1 is used.
Explain why the balloon inflates faster when powdered calcium carbonate is used.
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(b)
Using the same chemical substances (calcium carbonate and hydrochloric acid), discuss a
different way to make the balloon inflate faster.
In your answer you should refer to rates of reaction and particle collisions.
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Write a word equation AND a balanced symbol equation for the reaction between calcium
carbonate and hydrochloric acid.
BaTanced symbol equation:
~ct(O~-~i.~t(\
7
-- ·· .. --.. .._ ..
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--------Science 90944, 2014
u
Question Two
E7- Candidate has a correct balanced symbol equation.
Candidate explains that heating the acid causes the particles
to move faster, hence there will be more collisions occurring
more regularly (per unit time), and therefore the reaction is
faster (1 E point).
Candidate has explained the surface area correctly in part
a(ii), but is prevented from gaining an E8, as they have not
indicated more collisions per unit time.
6
QUESTION THREE: INDICATORS AND pH
A student has three unlabelled beakers each containing a colourless liquid. One contains water, one
contains a solution of baking soda (sodium hydrogen carbonate), and one contains white vinegar
(a solution of ethanoic acid).
To work out which liquid is which, the student put a drop from each beaker onto a piece of blue
litmus paper and a piece of red litmus paper. She then added universal indicator to each beaker.
The following results were obtained:
I Colour
ofT
I blue litmus
:
paper
stays blue
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·-·-·-+-
Beaker 2
turns red
i Beaker 3
stays blue
L____
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//
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Beaker 1
Colour of ) Colour with
: red litmus
universal
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paper
i indicator
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tums blue
-
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(a)
Complete the last column of the table above to identify the tl;?;;eligmds.
(b)
Use the information in the table to show how each of the liquids can be identified.
L
In your answer you should:
I
•
use all of the observations for each beaker
•
state the approximate pH from the colour of the universal indicator.
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c) · Another student was given two beakers (Beaker 4 and Beaker 5) each containing different
liquids. The liquid in Beaker 4 had a pH of 1. The liquid in Beaker 5 had a pH of 6.
ASSESSOR'S
USEONl.Y
Discuss which liquid is more acidic and how you know this.
In your answer you should:
•
use the pH to determine which liquid is more acidic
•
compare the amount of hydrogen ions AND hydroxide ions in Beaker 4 (pH 1) with the
amount of hydrogen ions AND hydroxide ions in Beaker 5 (pH 6).
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Science 90944, 2014
Question three
E8- Candidate correctly identify all three liquids with reference to litmus paper, universal indicator, and pH (1 E point).
Correctly explains that both beaker 4 and 5 have an excess
of hydrogen ions compared to hydroxide ions (1 E point).
Correctly explains that the excess of hydrogen ions to hydroxide ions in beaker 4 compared to beaker 5 is greater (1
E point).
8
QUESTION FOUR: ADDING SULFURIC ACID TO SODIUM HYDROXIDE
A beaker contains sodium hydroxide solution and 5 drops of universal indicator.
Sulfuric acid was added to the beaker until no more changes were observed.
(a)
Write a word equation Al'.'D a balanced symbol equation for the reaction between sulfuric
acid and sodium hydroxide.
!
I
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(b)
Describe how the indicator colour changes as the sulfuric acid is added to the beaker, AND
explain what this tells you about the changing pH of this solution.
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Science 90944.2014
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(c)
I ASSES~R'$_
Explain the relationship betvveen the changing pH of the solution and the ions in the solution
·
as the sulfuric acid is added to the beaker.
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Question four
E8- Correct balanced symbol equation.
In part (c), the candidate explains that at the beginning, there
is a large excess of hydroxide ions compared to hydrogen
ions (linked to pH and colour), and that at the point where the
solution becomes green (ph= 7) the number of both ions is the
same, and the solution is neutral.
At the end, when the solution becomes red (linked to pH),
there is now a large excess of hydrogen ions compared to hydroxide ions.
Some of the evidence for this was taken from part (b), ie evidence can be taken across the whole of the question.
In part (c), the candidate has also compared the amount of hydroxide ions to hydrogen ions at a point to the start, neutral, or
end point as the acid is added, and linked this to pH and
colour.