chemistry aspects of acids and bases 4 credits (90944) … · the electron arrangement 2,8 is the...

CHEMISTRY

There are 4 ways to change the rate of reaction (to increase the number of successful collisions):1. Temperature (speeds up movement of particles)2. Surface Area (more area available for collisions)3. Concentration (more particles are put in the same space to collide)4. Catalyst (sets up the molecules for more successful collisions)

Note: Problems may rely on knowledge from earlier chemistry sections

• There is a pH scale going from 1 (acidic) to 7 (neutral) to 14 (basic)

• Universal indicator shows pH with a colour: From red (acid), to green(neutral), to blue/purple (base)

pH AND INDICATORS p 42

• This is where a positive ion is attracted to a negative ion, and they combine to make a neutral compound

• The positive charges must be balanced by the negative charges

• Use the “swap and drop” method to write the compound

• Positive ions are writen first. Negative ions end in -ide. Negative ions with oxygen end in -ate

COMPOUNDS p 38

• Election Configuration: This is how electrons are arranged within their shells. This can be written as a row of numbers: E.g. Calcium, Ca, is 2, 8, 8, 2

• Atomic Structure is the number of protons, neutrons and electrons within an atom

• Ions have gained or lost electrons to get a FULL OUTER SHELL, this gives them a charge

• Isotopes are elements that have a differing number of neutrons

• Rows (horizontal) indicate which electron shell is being filled

• Groups or columns (vertical) indicate how many electrons exist in the valence shell

PERIODIC TABLE p35ATOMS & IONS p 30

CHEMISTRY

• Acids always give Hydrogen• Bases give (usually) Hydroxide or

Carbonate• Neutralisation reactions are an acid

base reaction where the acid and the base balance each other to form a neutral solution of pH around 7 (not all acid-base reactions are neutralisation reactions)

ACID - BASE REACTIONS p 48

RATES OF REACTION p 51

• Reactants are the starting materials• Products are the final materials• In a word equation reactants and products are

written as words:Magnesium+Oxygen Magnesium Oxide→

• For chemical (or symbol) equations use the chemical symbols as the products and reactants.

• These are balanced by adding numbers in front of the products and reactants so that there is the same number of atoms on both sides of the arrow: 2 22Mg O MgO+ →

WORD & CHEMICAL EQUATIONS p 45

THE SKILLS YOU NEED TO KNOW:

ASPECTS OF ACIDS AND BASES4 CREDITS (90944)

ATOMS, IONS & ISOTOPES

OLD NCEA QUESTIONS1. Explain why the ions formed by sodium and oxygen

both have the same electron arrangement. In your answer you should:• Describe an ion• Describe the atomic structures of a sodium ion

and an oxide ion• State the charge on the sodium ion and the

oxide ion• Explain the charges on both ions in terms of

electron arrangement and number of protons

2. Sodium and beryllium atoms form ions with different charges. Complete the table below.

Element Electron arrangementof the atom

Charge on the atom that the ion

formsSodium

Beryllium

3. Lithium atoms can exist in different forms called isotopes. Two of these isotopes are Lithium-6 (

36Li

) and Lithium-7 (37 Li ).

a. Explain why 36Li and

37 Li are both neutral

atoms. In your answer, you should fully describe their atomic structure and state their electron configuration.

b. Beryllium can exist as an isotope in the form of Beryllium-7 ( 4

7Be ).Discuss how the mass of 4

7Be compares with 36Li AND 3

7 Li . In your answer, you should:• Consider the atomic structure of each atom• Consider the meaning of the numbers ‘6’

and ‘7’ in terms of the atomic structures• Explain how the particles within an atom

contribute to its overall massYou may draw labelled diagrams to support your answer.

•

• Election Configuration: This is how electrons are arranged within their shells. There are 2 in 1st shell; 8 in 2nd shell; 8 in 3rd shell (the rest are in 4th shell). This can be written as a row of numbers: E.g. Calcium, Ca, is 2, 8, 8, 2

• Atomic Structure is the number of protons, neutrons and electrons within an atom

• Ions have gained or lost electrons to get a FULL OUTER SHELL. This gives them a charge

• Isotopes are elements that have a differing number of neutrons. This means that different isotopes will have a different masses

• Electrons do not count toward the atomic mass as their mass is very much smaller than the protons and neutrons and doesn’t make a difference

For a complete tutorial on this topic visit www.learncoach.co.nz

SUMMARY

CHEMISTRY

4. a. The electron arrangement for Oxygen (O) is 2,6. Write the electron arrangement for Be and S.

b. The element calcium can be represented as

2040Cli. Name the two particles found in the

nucleus.ii. The electron arrangement for the element

boron can be written 2, 3. Write the electron arrangement for the element calcium.

5. Oxygen atoms are made of protons, neutrons, and electrons. One type of oxygen atom can be represented as 8

16O . a. Draw a diagram to show the arrangement of

the electrons, protons, and neutrons within the above oxygen atom.

b. Explain, with reference to the diagram, why the atom is neutral.

6. An aluminium atom has an atomic number of 13.a. How many electrons does an aluminium atom

have in its outer most shell or energy level?b. How many electrons does the aluminium ion

have in its outermost shell or energy level?

7. The element sodium is a metal. Give TWO physical properties of sodium.

8. The diagram below represents a model of an aluminium atom, 13

27 Al .

The symbols in the diagram above represent the protons, electrons and neutrons. a. Write the appropriate symbol for the diagram to

complete the key.

Particle SymbolProton

ElectronNeutron

b. Using the key above, draw a diagram that shows a magnesium atom

1224Mg .

c. Discuss the similarities and differences between a magnesium atom and a magnesium ion. You should consider the number of protons, electrons and neutrons, and the charge of each particle.

9.

a. The diagram above can be used to represent the arrangement of electrons in levels around the nucleus of a sulphur atom.i. The atomic number of sulphur is 16. How

many protons are there in the nucleus of the neutral atom?

ii. How many electrons does a sulphur atom gain to form a sulphur ion?

b. A neutral chlorine atom has 17 electrons in the arrangement 2,8,7.i. What is the atomic number of chlorine? ii. How many electrons does chlorine gain to

form a chloride ion?iii. Draw a diagram like the one above for

the arrangement of electrons around the nucleus of a chloride ion.

10. Some elements have isotopes. Isotopes of an element have different numbers of neutrons. Carbon-12 ( 6

12C ) and carbon-14 ( 614C ) are isotopes of carbon.

a. Explain why 612C and

614C are neutral atoms.

You should describe their atomic makeup, and state their electron configuration.

b. Explain how the particles within an atom contribute to its mass.

c. Nitrogen can exist as an isotope in the form of Nitrogen-13 ( 7

13 N ). Discuss how the mass

of 713 N compares with 6

13C . In your answer consider:• The atomic structure of each atom• The relevance of the numbers ‘12’ and ‘13’

in terms of atomic structureDiagram(s) may be used to support your discussion.

11. The element carbon can be represented as 614C .

How many protons, electrons and neutrons are in this carbon atom?

12. Lithium can exist in a number of different forms called isotopes. Two of these isotopes are 3

6Li and 37 Li . Lithium can also exist as the ion Li+. In terms of the atomic structure, discuss the similarities and differences between 3

6Li and 37 Li and Li+.

PRACTICE QUESTIONS

NCEA1. An ion is an atom which has lost or gained electrons.

It will have a positive or negative charge. Sodium atoms have the electron arrangement 2,8,1. The atom loses 1 electron to form an ion with 2,8 with a charge of +1 because there is 1 less electron than protons, Na+. Oxygen atoms have the electron arrangement 2,6 and will gain 2 electrons to form the electron arrangement 2,8. Because the oxide ion has 2 more electrons than protons it will have a -2 charge, O2-. The electron arrangement 2,8 is the stable electron arrangement of Na atoms. (Excellence)

2.

Element Electron arrangement

Ion Charge

Sodium 2,8,1 +1Beryllium 2,2 +2

(Merit)

3. a. The atomic structure of the isotopes are as follows:

36Li – 3p, 3n, 3e

37 Li – 3p, 4n, 3eBoth have an electron configuration of 2,1Both 3

6Li and 37 Li have equal numbers of

protons and electrons, i.e. 3p and 3e. An atom is neutral when it has equal numbers of protons and electrons. The number of neutrons doesn’t matter. (Merit)

b. The atomic structure of beryllium is:

47Be – 4p, 3n, 4eSee (a) for the structure of 3

6Li and 37 Li .

The numbers 6 and 7 refer to the total mass of the elements.The overall mass of an atom is made up of protons and neutrons, as the mass of electrons is negligible.

47Be will have the same atomic mass as 3

7 Li because the total number of protons and neutrons is the same AND 4

7Be is heavier than

36Li as it has one more proton. (Excellence)

PRACTICE4.

a. Be: 2,2 S: 2,8,6 (Achieved) b.

i. Neutrons and protons (Achieved)ii. 2,8,8,2 (Achieved)

5. a.

b. Electrons have a negative charge and protons have a positive charge. The oxygen atom has eight protons and eight electrons. The equal number of protons and electrons means that there this is the same amount of negative and positive charge within this oxygen atom. The positive an negative charges cancel making an atom that is neutral overall. (Merit - a or b)

(Excellence - a and b)

6. a. 3 valence electrons. (Achieved)b. 8 valence electrons. (Achieved)

7. Two of the following are required:• Shiny• Malleable• Ductile• Conductor• Grey colour• Soft• Solid at room temperature (Achieved)

8. a.

Particle SymbolProton +

ElectronNeutron o

b.

ANSWERS

CHEMISTRYc. The magnesium atom has its electrons

configured as 2, 8, 2 (12 electrons total), with 12 protons and 12 neutrons. The charge on the atom is zero because the number of protons and electrons are equal. The magnesium ion has lost its two valance electrons to give a 2, 8 configuration (10 electrons total). The number of protons and neutrons are the same in both cases, however the magnesium atom has two more electrons than the magnesium ion. Therefore, the magnesium ion’s charge is +2.

(Achieved - a or b) (Merit - AND c) (Excellence - a, b and c)

9. a. i. 16 (Achieved)ii. 2 (Achieved)

b. i. 17 (Achieved)ii. 1 (Achieved)iii.

(Achieved)

10. a. 6

12C and 614C are neutral atoms because they

contain equal numbers of positive protons and negative electrons. The charges cancel and so the atom is neutral overall. Both atoms have the same number of electrons and the configuration 2, 4. Also, both atoms have the same number of protons (six). However, carbon-12 has six neutrons in the nucleus, whereas carbon-14 has eight neutrons in the nucleus. This means that carbon-14 is heavier than carbon-12 due the weight of the extra two neutrons.

b. The mass of an atom is almost completely due to the neutrons and protons in the nucleus. Electrons don’t have an effect on the mass as they are very light.

c. 713 N has the same mass number as 6

13C . This ‘13’ refers to the total mass of the elements. A 7

13 N atom will have 7 protons and 6 neutrons in its nucleus, whereas a 6

13C atom will have 6 protons and 7 neutrons in its nucleus, both totalling 13. This means that both atoms will have similar masses. However,

612C has a mass number of 12, therefore, it is a lighter isotope of Carbon than 6

13C because it has 6 neutrons.

(Achieved - b correct) (Merit - a or c correct) (Excellence - a and c correct)

11. Protons: 6Electrons: 6Neutrons: 8 (Achieved)

12. 36Li has 3 protons, 3 electrons and 3 neutrons.

37 Li has 3 protons, 3 electrons and 4 neutrons.

These are isotopes because they have the same atomic number but different mass number (i.e. different number of neutrons). 3

7 Li is heavier than

36Li .Li+ is an ion because it has lost an electron. It has 3 protons, 2 electrons and 3/4 neutrons. The electron configuration of Li : 2, 1 and Li+ : 2 (more stable because it has a full shell). (Excellence)

PER

IOD

IC T

AB

LE

OF

TH

E E

LE

ME

NT

S

18

12

Ato

mic

Num

ber

1H

1314

1516

17

2H

e

3L

i4

Be

5B

6C

7N

8O

9F

10N

e

11N

a12

Mg

34

56

78

910

1112

13A

l14

Si15

P16

S17

Cl

18A

r

19K

20C

a21

Sc22

Ti23

V24

Cr

25M

n26

Fe27

Co

28N

i29

Cu

30Z

n31

Ga

32G

e33

As

34Se

35B

r36

Kr

37R

b38

Sr39

Y40

Zr

41N

b42

Mo

43Tc

44R

u45

Rh

46Pd

47A

g48

Cd

49In

50Sn

51Sb

52Te

53I

54X

e

55C

s56

Ba

71L

u72

Hf

73Ta

74W

75R

e76

Os

77Ir

78Pt

79A

u80

Hg

81T

l82

Pb83

Bi

84Po

85A

t86

Rn

87Fr

88R

a10

3 Lr

104 R

f10

5 Db

106 Sg

107 B

h10

8 Hs

109 M

t11

0 Ds

111 R

g

57L

a58

Ce

59Pr

60N

d61

Pm62

Sm63

Eu

64G

d65

Tb

66D

y67

Ho

68E

r69

Tm

70Y

b

89A

c90

Th

91Pa

92U

93N

p94

Pu95

Am

96C

m97

Bk

98C

f99

Es

100 Fm

101 M

d10

2 No

3

CHEMISTRY

• Rows (horizontal) indicate which electron shell is being filled• Groups or columns (vertical) indicate how many electrons exist in the valence shell.• This knowledge is almost always combined with knowledge from the previous section on

‘atoms and ions’• There will be a periodic table provided for you in your exam (and on the back page of this

book) For a complete tutorial on this topic visit www.learncoach.co.nz

PERIODIC TABLE

OLD NCEA QUESTIONS1. Magnesium and calcium atoms both form ions with

a charge of +2.Magnesium atoms form Mg2+ ions, and calcium atoms form Ca2+ ions.Explain why magnesium and calcium atoms form ions with the same charge of +2.

In your answer, you should:• Define an ion• Explain why atoms form ions• Identify the group on the periodic table where

the two atoms are found• Explain why both magnesium and calcium ions

have a charge of +2

SUMMARY

2. Sulphur and Chlorine appear near each other on the periodic table. Discuss how they are related to each other.In your answer you should:• Refer to their relative locations in the periodic

table• Mention their atomic structure• Discuss how the ions they form are related• Discuss how their electron arrangements are

similar

PRACTICE QUESTIONS

NCEA1. An ion is an atom or group of atoms that have lost

or gained electron(s) and therefore carry a charge. If the outer shell (valence) of an atom is not filled, the atom is unstable. It will react to gain a full outer shell to become more stable, by either losing or gaining electrons and making it into an ion.Magnesium and Calcium are in the same group on the periodic table (Group 2). The atoms have the same number of electrons (two) in their outer shell. Their electron arrangements are Mg 2,8,2 and Ca 2,8,8,2.Both Mg and Ca need to lose two outer electrons to become stable by having a full outer shell. Each ion (Mg2+ and Ca2+) ends up with two less electrons than there are protons in its nucleus, so the ion has a charge of +2. (Excellence)

PRACTICE2. Sulphur and chlorine are in the same row of the

Periodic Table. This means that they both gain electrons to form ions with the same number of electrons (18). Sulphur and Chlorine are also in neighbouring groups in the Periodic Table, so the charges on their ions differ by only one electron (S2- and Cl-). The electron arrangement of their atoms also differ by one electron, a sulphur atom has 16 electrons (arrangement 2,8,6), a chlorine atom has 17 electrons(arrangement 2,8,7). (Excellence)

ANSWERS

Study Tip:

Believe in YourselfSelf belief is the biggest indicator of achievement:Set yourself a goal that you really want• Then understand and genuinely believe it is possible to pass

(or get Excellence)• Stop worrying, just patiently follow the steps outlined for you• When you meet barriers, don’t be discouraged, simply find a

way throughIf you can’t make progress yourself, just ask for help.

CHEMISTRY

Study Tip:

Study LocationChoose an ideal study place:• Can be the library, your room, anywhere quiet• Should have none of the distractions that could slow you

down• Should have all the resources you need • Should enable more effective study and give better results

• A positive ion is attracted to a negative ion, and they combine to make a neutral compound• The positive charges must be balanced by the negative charges• Use the “swap and drop” method to write the compound (E.g. Fe3+ and O2- make Fe2O3)• Use your periodic table and table of ions (back page of this book) to work out ion charges• Positive ions are writen first. Negative ions end in -ide. Negative ions with oxygen end in -ate• There will be a list of ions provided for you in your exam (and on the back page of this book)


COMPOUNDS

OLD NCEA QUESTIONS1. Element X is between numbers 11 and 18 on the

Periodic Table. An atom of element X forms an ion. This ion combines with the hydroxide ion to form a neutral compound, X(OH)3.Determine what element X is and justify your answer.In your answer you should:• Name element X • Consider the ratio of X ions to hydroxide ions• Use the formula X(OH)3 to determine the charge

of the X ion• Explain how you would use the Periodic Table to

find out which group element X is in

2. Explain why the ions in sodium hydroxide combine to give the formula NaOH but the ions in beryllium hydroxide combine to give the formula Be(OH)2.In your answer, you should:• Compare the charges on the individual ions

found in the compounds sodium hydroxide and beryllium hydroxide

• Explain why the ions combine in the ratios the way they do to form the compounds NaOH and Be(OH)2

SUMMARY

3. a. How many atoms of oxygen are there in the

formula Mg(HCO3)2?b. What is the total number of atoms in the formula

from (a)?

4. Write a formula for the following: a. Calcium oxideb. Copper hydroxidec. Sodium carbonate

5. Name each of these compounds:a. MgOb. Na2Sc. Ca(NO3)2

6. Give the formula of:a. Zinc oxideb. Potassium sulphatec. Calcium hydrogen carbonate

7. Name the following compounds: a. Cu(OH)2b. PbS c. MgCI2

8. State the charge on the iron ion in the compounds below: a. Fe2O3b. FeCI2c. Fe2(CO3)3

9. Write the formula for magnesium hydroxide.

10. Fill in the missing parts of the table below:

Scientific Name Formula(i) FeSO4

Ammonium nitrate (ii)(iii) KNO3

Calcium hydrogen carbonate (iv)

PRACTICE QUESTIONS

CHEMISTRY11. Give the formula of copper (II) carbonate.

12. Give the chemical names of:a. Na2CO3b. Mg(OH)2

13. Name these compounds:a. CuCl2b. Zn(OH)2c. KF

14. Work out the formulae for the following compounds:a. Potassium oxideb. Magnesium nitratec. Calcium sulphided. Ammonium sulphate

15. The formula of copper chloride is CuCl2. Explain why the formula has TWO chloride atoms for each copper atom. It would be helpful to discuss how the compound is formed.

16. a. How many atoms are there in Ca(HCO3)2?b. How many atoms are there in Cu(OH)2?

17. Name the compound Pb(NO3)2.

18. Write the formula for potassium sulfide.

19. What is the formula for calcium oxide?

Table of Ions

+1 +2 +3 -3 -2 -1NH4

+ Ca2+ Al3+ O2- OH-

Na+ Mg2+ Fe3+ S2- Cl-

K+ Cu2+ CO32- NO-

Ag+ Pb2+ SO42- HCO3

-

H+ Fe2+

Ba2+

Zn2+

NCEA1. Each hydroxide ion has gained 1 electron to form

OH-. With ionic compounds the charges must balance. Hydroxide ions have a charge of -1 and so since 3 OH- combine with one X ion, the X must have a 3+ change so that the charges on the ions cancel. Element X must be aluminium with the electron arrangement 2,8,3. Its atomic number is 13 and it is in group 13 of the periodic table. Al will lose its three outermost electrons to form Al3+. It is the only one within that range to form an ion that is 3+. (Excellence)

2. When these elements react, Na loses one electron and forms a +1 ion, while Be loses two electrons and forms a +2 ion in order to adopt the stable electron configuration. The hydroxide carries a charge of -1. An ionic compound is electrically neutral therefore all the positive charges must balance the negative charges. Therefore it requires one OH- for each Na+ ion but two OH- ions for each Be2+ ion to form a neutral compound/ balance the charges. (Excellence)

PRACTICE3.

a. 6 (Achieved)b. 11 (Achieved)

4. a. CaO (Achieved)b. Cu(OH)2 (Achieved)c. Na2CO3 (Achieved)

5. a. Magnesium Oxide (Achieved)b. Sodium Sulphide (Achieved)c. Calcium Nitrate (Achieved) (Merit - a, b and c)

6. a. ZnO (Achieved)b. K2SO4 (Achieved)c. Ca(HCO3)2 (Achieved) (Merit - a, b and c)

7. a. Copper hydroxide (Achieved)b. Lead Sulfide (Achieved)c. Magnesium Chloride (Achieved) (Merit - a, b and c)

8. a. 3+ (Achieved)b. 2+ (Achieved)c. 3+ (Achieved) (Merit - a, b and c)

9. Mg(OH)2 (Achieved)

10.

Scientific Name Formula(i) Iron sulfate FeSO4

Ammonium nitrate (ii) NH4NO3

(iii) Pottasium nitrate KNO3

Calcium hydrogen carbonate (iv) Ca(HCO3)2

(Merit)

11. CuCO3 (Achieved)

12. a. Sodium Carbonate (Achieved)b. Magnesium hydroxide (Achieved)

13. a. Copper chloride (Achieved)b. Zinc hydroxide (Achieved)c. Potassium fluoride (Achieved) (Merit - a, b and c)

14. a. K2O (Achieved)b. Mg(NO3)2 (Achieved)c. CaS (Achieved) d. (NH4)2SO4 (Achieved) (Merit - a, b, c and d)

15. Copper loses 2 electrons to form the copper ion (charge 2+) while chlorine gains 1 electron to form the chloride ion (charge 1-). In copper chloride, chlorine gains its electrons from copper which is why the charges must balance. As the copper has a change of 2+ it needs to give two electrons away, the chlorine atoms only want one electron each (charge of 1-) and so it requires two of them to take the electrons and to form a neutral compound. (Excellence)

16. a. 11 (Achieved)b. 5 (Achieved)

17. Lead nitrate (Achieved)

18. K2S (Achieved)

19. CaO (Achieved)

ANSWERS

CHEMISTRY

Study Tip:

MotivationBored?If you do feel bored, spend some time focusing on what you want to achieve.If a grade isn’t enough, think of a reward that you will treat yourself to if you reach your target grade.

• There is a pH scale going from 1 (acidic) to 7 (neutral) to 14 (basic)• Universal indicator shows pH with a colour:

From red (strong acid), to yellow (weak acid), to green(neutral), to blue (weak base), to purple (strong base)


pH AND INDICATORS

OLD NCEA QUESTIONS1. A student put 10 ml of dilute nitric acid in a boiling

tube with five drops of universal indicator. Sodium hydroxide of the same concentration was added. The following observations were recorded:

Amount of Sodium Hydroxide Added (ml)

Colour of Solution

0 Red10 Green20 Purple

Discuss the reaction occurring as sodium hydroxide is added to the nitric acid.In your answer you should:• Explain the relationship between the colours

observed and the pH of the solution• Explain which ions cause the different colours

of the solution

2. A student puts 5 mL of dilute hydrochloric acid into a boiling tube and adds five drops of universal indicator to the solution. The student then takes a solution of sodium hydroxide of the same concentration as the acid and adds it one drop at a time to the acid until the colour stops changing.a. Describe the colour of the universal indicator

solution:• In the hydrochloric acid before any sodium

hydroxide was added• When the sodium hydroxide was added and

the colour of the solution stopped changingb. As the sodium hydroxide is added several colour

changes occur.Explain how the colour changes relate to pH AND what ions are present in the solution when the colour changes.

SUMMARY

Note: These questions may require some knowledge of Acids and Bases (following section)

CHEMISTRY

3. In the table below, write the pH value that best represents the pH of each of:

Substance pHWater

Sodium Hydroxide Solution

Hydrochloric Acid

4. Shelly wanted to make as many different colours as she could with universal indicator. She started with 10 ml of dilute hydrochloric acid in a flask and added 10 drops of universal indicator. The solution turned red. Shelly then added dilute sodium hydroxide to the boiling tube, a drop at a time, until the solution turned purple.a. Shelly obtained three other colours as she added

the sodium hydroxide to the acid. These colours were green, blue and yellow. Write the colours in the correct places on the chart below.

Universal Indicator ChartAcid BaseRed Purple

b. Which colour on the chart corresponds to a pH of 13 - 14?

5. Describe what will happen to the pH value of the contents of a container when the concentration of acid in the container is increased.

6. What colour would red litmus paper turn when it is immersed in sodium hydrogen carbonate? Give a reason for your answer.

7. The pH values of three substances are given below:• Hydrochloric acid pH = 1• Potassium carbonate solution pH = 9 • Sodium hydroxide solution pH = 14When Universal Indicator solution is added to these substances, what colour would result? a. Hydrochloric acid b. Potassium carbonate solution c. Sodium hydroxide solution

8. Sodium hydroxide solution is added slowly to the hydrochloric acid in which Universal Indicator solution is already present. Describe the colour changes as the sodium hydroxide solution is added. Discuss how the colour changes relate to the substances present in the solution. Use the following substances - water, sodium chloride, sodium hydroxide, hydrochloric acid.

9. State the colour seen if red and blue litmus are added to samples of the following:

Solution Red litmus added

Blue litmus added

WaterSodium HydroxideHydrochloric Acid

10. Complete the table to show the characteristics of the solutions listed in the table below.

Solution Estimated pH

Universal Indicator

ColourHydrochloric Acid 1Sodium Hydrogen

CarbonateBlue

Aluminium Sulfate 5Water Green

11. Below is the pH scale.

An unknown chemical turns yellow when a few drops of universal indicator are added.a. What would be the predicted pH?b. Give a reason for your predicted pH.

PRACTICE QUESTIONS

NCEA1. Universal indicator is red in acidic solutions (low pH).

As the base is added, the OH- from the base reacts with the H+ from the acid. As the concentration of H+ decreases, the solution is less acidic and the indicator changes from red to green when the solution is neutral at pH 7. As more OH- ions are added the pH increases as the solution becomes more basic and the indicator changes to blue then purple. The H+ from the acid make the indicator red and the OH- from the base make the indicator purple. (Excellence)

2. a. Red/pink to start with, then Blue/purple/violet

at the end. (Achieved)b. At the beginning the red indicated a low (acidic)

pH.As the NaOH (base) was added, the colour changed to yellow, then to green, indicating a pH of around 7. As more NaOH was added the pH kept increasing and the blue/purple colour indicated a pH of at least 11. (Merit)

PRACTICE3.

Substance pHWater 7

Sodium Hydroxide Solution 14Hydrochloric Acid 1

(Achieved)

4. a.

Universal Indicator ChartAcid BaseRed Yellow Green Blue Purple

(Achieved)

b. Purple (Achieved)

5. The pH would decrease. (Achieved)

6. Blue, because sodium hydrogen carbonate is a base and bases turn (or keep) litmus paper blue. (Achieved)

7. a. Redb. Bluec. Purple (Achieved - two of a, b or c)

8. At the beginning there is only hydrochloric acid. This is a strong acid and so the solution appears red. When the acid is finally neutralised (i.e. all the hydrochloric acid has been neutralised by the sodium hydroxide) the universal indicator will change to green. When more sodium hydroxide is added, the solution becomes basic and the universal indicator turns purple. (Merit)

9.

Solution Red litmus added

Blue litmus added

Water Red (no change)

Blue (no change)

Sodium Hydroxide Turns Blue Blue (no change)

Hydrochloric Acid Red (no change)

Turns Red

(Achieved)

10.

Solution Estimated pH

Universal Indicator

ColourHydrochloric Acid 1 RedSodium Hydrogen

Carbonate8-10 Blue

Aluminium Sulfate 3-5 Yellow/Orange

Water 7 Green

(Achieved - 5 correct) (Merit - all 8 correct)

11. a. Any number between 3 – 5b. Yellow is between orange/red and green. From

the scale shown, green has a pH of 7 and orange/red of about 2. Yellow will be somewhere between those two values. (Merit - a and b)

ANSWERS

CHEMISTRY

• Reactants are the starting materials• Products are the final materials• In a word equation reactants and products are written as words:

Magnesium+Oxygen Magnesium Oxide→• For chemical (or symbol) equations use the chemical symbols as the products and reactants.• These are balanced by adding numbers in front of the products and reactants so that there is

the same number of atoms on both sides of the arrow:2 22Mg O MgO+ →


WORD AND CHEMICAL EQUATIONS

OLD NCEA QUESTIONS1. Write a word equation AND a balanced symbol

equation for the reaction between hydrochloric acid and magnesium oxide

2. Sodium hydroxide is added to nitric acid. Write a word equation AND a balanced symbol equation for the reaction.

SUMMARY

3. Reacting Sulfuric acid with magnesium hydroxide is used to create Epsom Salt (MgSO4). Write the word equation for the preparation of MgSO4.

4. Calcium oxide reacts vigorously with water to form calcium hydroxide. Write a word equation for this reaction.

5. Write a word equation AND a balanced symbol equation for the reaction between magnesium and oxygen gas

6. Write the word equation AND a balanced symbol equation for the reaction of hydrochloric acid with copper carbonate.

7. Write a word equation for the reaction of copper oxide and sulphuric acid.

8. Write a balanced chemical equation for the reaction between sodium and water.

9. Write a balanced chemical equation for the reaction between copper carbonate and hydrochloric acid.

10. Write a balanced chemical equation for the reaction between potassium carbonate and hydrochloric acid.

11. A student reacted zinc oxide with sulphuric acid and wrote the following incorrect equation to represent the reaction:ZnO H SO H O ZnSO H2 2 4 2 4 22+ + +→ This equation contains THREE errors.a. Rewrite the equation so that it is a correctly

balanced chemical equation.b. Discuss the reasons for the three changes made

to correctly balance the chemical equation.

12. Write a fully balanced symbol equation for the reaction of sulphuric acid with sodium hydrogen carbonate.

PRACTICE QUESTIONS

NCEA1. Hydrochloric Acid Magnesium Oxide Magnesium Chloride Water + → +

22 2 2HCl MgO MgCl H O+ → +

(Excellence)

2. Nitric Acid Sodium Hydroxide Sodium Nitrate WaterHNO NaOH

+ → ++3 →→ +NaNO H O3 2

(Excellence)

PRACTICE3. Sufuric Acid Magnesium Hydroxide Magnesium Sulfate Water+ → + (Achieved)

4. Calcium Oxide Water Calcium Hydroxide+ → (Achieved)

5. Magnesium Oxygen Magnesium OxideMg O MgO

+ →+ →2 22

(Excellence)

6. Hydrochloric Acid Copper Carbonate Copper Chloride Carbon + → + DDioxide WaterHCl CuCO CuCl CO H O

++ → + +2 3 2 2 2 (Excellence)

7. Copper Oxide+Sulphuric Acid Copper Sulphate Water→ + (Achieved)

8. 2 2 22 2Na H O NaOH H+ +→ (Merit)

9. 2 3 2 2 2HCl CuCO CuCl CO H O+ → + + (Merit)

10. 2 22 3 2 2HCl K CO KCl CO H O+ → + + (Merit)

11. a. ZnO H SO ZnSO H O+ +→2 4 4 2

b. 1. Zinc Oxide is ZnO not ZnO2 since zinc forms an ion with a charge of +2 and oxygen forms an ion with a -2 charge. For the compound to be neutral they need to be in equal quantities.2. Hydrogen is not the product of an acid and a metal.3. The equation is not balanced because the number or each type of atom on each side of the equation is not equal. (Excellence - a and b)

12. H SO NaHCO Na SO CO H O2 4 3 2 4 2 22 2 2+ → + + (Merit)

ANSWERS

Study Tip:

Make it Colourful Colours help you remember!Use highlighters to mark the important points.Use different colours for different categories.

CHEMISTRY

Study Tip:

Make Sure You UnderstandUnderstanding is important.Wait until you have a clear understanding of the topic before moving on to the next section.When you get stuck, ask for clarification (see your teacher the next day).

ACID & BASE REACTIONSSUMMARY

• Acids and bases react together. They give or receive ions.• Acids always give Hydrogen• Bases give (usually) Hydroxide or Carbonate• Neutralisation reactions are an acid base reaction where the acid and the base balance each

other and form a salt (or precipitate). This leaves the pH around 7 (not all acid-base reactions are neutralisation reactions)


3. Epsom salt (MgSO4) can be prepared by reacting an acid with magnesium hydroxide.a. Name the acid used in this reaction.b. This reaction is described as a neutralisation

reaction. Explain what is meant by the term neutralisation.

4. a. What would you observe when calcium carbonate and acid react together?

b. Discuss why the reaction between magnesium hydroxide and hydrochloric acid (HCl) can be called a neutralisation reaction.

5. Potassium carbonate solution is added slowly to the hydrochloric acid (without indicator) in a beaker until no further change is seen.Describe what you would see happening when potassium carbonate is added to the acid.

6. Tom has an unknown acid. He decided to react black copper oxide with the acid to determine what it is. It could be either hydrochloric acid or sulphuric acid. He filtered the resulting solution and got a clear blue liquid. He knew that barium chloride would react with a metal sulphate to form a precipitate but that wouldn’t happen with a metal chloride.When barium chloride was added to the blue copper salt solution a precipitate formed.a. What acid did Tom use in the reaction with the

black copper oxide? b. Explain your answer to (a) above.

7. Hydrochloric acid is added to a sodium carbonate solution. Describe the observation(s) that would be made when this reaction occurs, and explain the reason for them.

PRACTICE QUESTIONS

1. A student wanted to make the salt magnesium chloride.Discuss how the student would make magnesium chloride salt from hydrochloric acid and magnesium oxide. In your answer you should:• State what type of reaction occurs• Write a word equation AND a balanced symbol

equation for the reaction between hydrochloric acid and magnesium oxide

• Explain how you would make magnesium chloride in a school lab from hydrochloric acid and solid magnesium oxide (this can be done by drawing labelled diagrams)

2. A student combines equal volumes of nitric acid solution and sodium carbonate solution. Both solutions have the same concentration.Discuss what happens in this reaction. In your answer, you should:• Name the type of reaction involved and the ions

involved• Describe what the student would observe• State the products of the reaction and link these

to the observations made• Write a word equation for the reaction• Write a balanced symbol equation for the

reaction.

OLD NCEA QUESTIONS

CHEMISTRY8. Copper (II) carbonate powder will react with dilute

sulfuric acid to form a neutral blue solution and a colourless gas.a. Explain why copper (II) carbonate could be

described as a base in this reaction.b. Give the symbol of the ion that is responsible

for the blue colour of the final solution in the reaction.

c. Name the gas that is formed in the reaction.d. How could the gas from this reaction be

collected, and identified?e. What is the positive test result for this gas being

produced?

9. Jo was carrying out an investigation on chemicals involved in the test for carbon dioxide.

The test for carbon dioxideWhen carbon dioxide is bubbled through limewater

(calcium hydroxide), the solution goes milky (Solution 1). If more carbon dioxide is then bubbled

through the milky solution, the milky solution eventually goes clear again (Solution 2).

Most carbonates are insoluble, and most hydrogen carbonates are soluble.

a. Give the chemical formula of calcium hydroxide. b. Describe what Jo would observe if 10 drops of

hydrochloric acid are added to Solution 1.c. Describe what Jo would observe if 10 drops of

hydrochloric acid are added to Solution 2.

10. Hydrochloric and sulphuric acids both react with carbonates and hydrogen carbonates to produce a gas.a. Name the gas.b. Explain why the reactions of acids with

carbonates and hydrogen carbonates are called neutralisation reactions.

11. Copper sulphate is a salt. Copper sulphate crystals can be prepared in the laboratory by adding copper oxide to an acid.Name the acid that would be used to make copper sulphate crystals and explain your choice.

Exam Tip:

Read the TestScanning the test before you start can help by:• Giving an overview • Is essential for time planning• Helps prevent basic errors (e.g. not staying on topic)

NCEA1. This is a neutralisation reaction.

Hydrochloric Acid Magnesium Oxide Magnesium Chlori

+ →dde Water

HCl MgO MgCl H O+

+ → +2 2 2

Place some HCL in a test tube with a few drops of universal indicator or litmus. Add small amounts of MgO until the solution is neutral (Universal Indicator = green, Litmus = purple).Filter to remove any remaining magnesium oxide, put solution in evaporating basin and evaporate the water leaving the magnesium chloride. (Excellence)

2. The reaction is a Acid-base (or acid-carbonate) neutralisation reaction (the carbonate ions react with the H+ ions of the acidic solution and neutralise the solution).The student would observe bubbling in the solution / fizzing / effervescence / frothing / foaming as the Na2CO3 disappears. The products are CO2, H2O and a salt. The CO2 gas causes the bubbles / fizzing / etc. Nitric Acid SodiumCarbonateSodium Nitrate Water Carbon Di

+ →+ + ooxide

2HNO Na CO 2NaNO H O CO3 2 3 3 2 2+ → + + (Excellence)

PRACTICE

3. a. Sulphuric Acidb. Neutralisation is a reaction between a base (pH

> 7) and an acid (pH < 7). The acid and base neutralise each other to form a salt and water (pH = 7). Water is neutral which is why it is called a neutralisation reaction. (Merit - a and b)

4. a. A salt, water and carbon dioxide would be produced. The carbon dioxide would appear as bubbles in the liquid.

b. Neutralisation is a reaction between a base and an acid. The acid and base neutralise each other to form a salt and water. In this instance magnesium hydroxide is the base and hydrochloric acid the acid. They combine to form magnesium chloride and water. The products are neutral (pH=7) and so it is a neutralisation reaction.

(Merit - a or b) (Excellence - a and b)

5. The potassium carbonate would fizz when the acid is added. (CO2 being released) (Achieved)

6. a. Sulphuric acid (Achieved) b. The precipitate wouldn’t have formed if the

other acid had been used. (Achieved)

7. When hydrochloric acid is added to a sodium carbonate solution bubbles would be observed. This is the creation of carbon dioxide gas.

(Achieved)

8. a. It is a base because it neutralises the sulphuric acid.

b. Cu2+

c. Carbon dioxide (CO2)d. Seal the container except for a tube for the gas

to go through. Put the other end of the tube into lime water and the gas will bubble through the limewater.

e. If the gas is carbon dioxide then the limewater will go cloudy or milky.

(Achieved - two of a, b, c, d or e correct) (Merit - four of a, b, c, d or e correct) (Excellence - all of a, b, c, d and e correct)

9. a. Ca(OH)2b. Bubbles of gas would be given off (Carbon

dioxide, because when a metal carbonate reacts with an acid it produces water, salt and carbon dioxide)

c. A white precipitate would form. (Calcium chloride made from calcium hydroxide and hydrochloric acid)

(Merit - two of a, b or c correct) (Excellence - a, b and c correct)

10. a. Carbon dioxide.b. A neutralisation reaction is a reaction between

an acid and a base where the acid neutralises the base and a salt and water are produced. In an acid and carbonate (or hydrogen carbonate) reaction the carbonate (or hydrogen carbonate) acts as a base, and water and a salt are formed.

(Merit - a and b)

11. Sulphuric acid would be used to make copper sulphate crystals because when bases react with sulphuric acid, the salt is always a sulphate. Sulphuric acid has a sulphate group and two hydrogen ions. When the acid reacts with the copper oxide, the sulphate ions and copper ions will bond and the reaction will give copper sulphate. (Merit)

ANSWERS

CHEMISTRY

RATES OF REACTION

OLD NCEA QUESTIONS1. Calcium carbonate (marble chips) and hydrochloric

acid react together in a conical flask. The word equation for this reaction is:Calcium Carbonate Hydrochloric Acid

Calcium Chloride Water+ →

+ ++Carbon Dioxide Gas

a. Describe an observation you would make when this reaction occurs

The mass of the flask and contents is measured on a scale over time and recorded on the graph shown below.

b. Explain why the mass decreases with time. In your answer you should:• Consider all the products being formed• Explain what is happening, in terms of

particles AND the rate of reaction, in each section of the graph.

c. When more concentrated hydrochloric acid is used, the reaction is faster. Explain the difference in the rate of reaction.In your answer you should refer to: • Particles• Collisions• Reaction rate

2. Marble chips (calcium carbonate) are added to dilute hydrochloric acid in a conical flask. The flask is connected to an inverted measuring cylinder in a trough of water, as shown in the diagram below. The volume of gas produced is measured over a few minutes, and the results used to sketch a graph.

a. The slope of the graph is steep at the beginning and then levels off over time. Explain what is happening, in terms of particles, during the reaction.

b. Complete the word and symbol equations below to show the reaction in the experiment. Word Equation:Hydrochloric Acid Calcium Carbonate+ →

+________________ ____________________________+

Balanced Symbol Equation:HCl CaCO+ →

++

3

_______________ __________________________

c. The experiment is repeated but this time the same mass of marble chips is crushed into a powder before it is added to the flask.Discuss the effect on the reaction rate of using powdered marble with hydrochloric acid compared with using marble chips. In your answer, you should:• Compare the rates of reaction• Explain the differences in the reaction rate

by discussing how crushing the marble chips affects the number of particle collisions

SUMMARYThere are 4 ways to change the rate of reaction (i.e. change the number of successful collisions)1. Temperature (speeds up the movement of particles)2. Surface Area (more area available for collisions)3. Concentration (more particles are put in the same space to collide)4. Catalyst (sets up the molecules for more successful collisions)


NCEA1. a. Fizzing, amount of marble chips decreases.

(Achieved)b. The mass decreases with time because the gas

being produced from the reaction is escaping into the air. Since there are fewer particles in the flask its mass is decreasing.In section X there is a high concentration of acid particles. There will be lots of collisions and a rapid production of CO2.In section Y the reaction is slowing down as the HCl or CaCO3 particles are used up. There will be fewer collisions and a lower rate of CO2 production.In section Z the HCl or CaCO3 particles have all be used up, so there will be no more collisions. The reaction has stopped and CO2 is being produced. (Excellence)

c. The higher concentration means more particles per unit volume. There will be more collisions between the acid particles and the calcium carbonate particles, so the rate of reaction will be faster. (Excellence)

2. a. As the reactant particles collide, they are converted into product particles. Initially many gas molecules are produced, but as the reaction proceeds there are fewer and fewer reactant particles available to collide, so the volume of gas produced decreases and eventually no gas is produced. (Most likely the supply of H+ ions in the solution will be exhausted before the marble chips disappear.) (Excellence)

b. Hydrochloric Acid Calcium CarbonateCalcium Chloride Water

+ →+

++Carbon Dioxide

2HCl CaCO CaCl H O CO3 2 2 2+ → + + (Merit)c. The reaction rate will be faster with the powdered

marble than when the chips were used. More gas will be produced each minute. The reaction itself will be completed in a shorter period of time. There are more reactant particles immediately available to react because the surface area of the powder is greater than that of the chip. There is greater exposure of the marble particles so there are more available for the acid particles / hydrogen ions / H+ ions to collide with.This means there will be more (effective) collisions per second / more frequent collisions between the acid particles and the ions in the calcium carbonate powder, leading to an increase in the rate of the reaction and the reaction will be completed sooner. (Excellence)

ANSWERS

Exam Tip:

Use the CluesBullet points and key words are clues in a question. Use them!If you are unsure about the answer, don’t give up. Find the clues and write about closely related word or ideas.

chemistry aspects of acids and bases 4 credits (90944) … · the electron arrangement 2,8 is the...

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