Chemical Changes

1) How does a gas dissolve in water ?
Gas molecules do not float, they are moving at high speed in straight lines.
When they hit something they cannot penetrate they bounce off in a different direction.
Gases dissolve into water through a physical process of intermolecular attraction.
Because liquid molecules have spaces between them, some of these gas molecules can penetrate the surface and enter the liquid.
Once the gas molecule is inside the liquid, there is a natural attraction between the molecules (intermolecular forces).
For non reactive gases the water molecules have a weak attraction to the gas.
For reactive gases (Hydrogen Chlorine) the water molecules can actually break down the gas molecule into ions.

2) Why do we always dissolve in water ?
Water is a "universal solvent" that can dissolve solids, liquids and gases.
Water can dissolve more substances that any other liquid.
Solids - Salt in water (creates ions). Sugar in water (no ions).
Liquids - Food colouring in water.
Gases - Carbon Dioxide in water creates the fizz in soda and sparkling water.

3) What is the chemical formula for Chlorine ?
This is a gas. It is highly reactive and is a neutral element.

C l_{2}

4) What is the chemical formula for Chloride ?
This is either solid or aqueous. This is chemically stable.
It must always be bound to a positive ion (like a metal) to balance its charge, or be dissolved in water.
Chloride refers specifically to the chlorine atom after it has gained an electron to become a negatively charged ion.

C l^{-}

5) What is the chemical formula Hydrogen Chloride ?

H C l

Hydrogen Chloride (gas)

Hydrogen(g) + Chlorine(g) = Hydrogen Chloride(g)

The water is just acting as a solvent to dissolve the gas, not as a chemical reactant.

Hydrogen Chloride(g) + H2O(l) = Hydrogen Chloride(aq) 
Hydrogen Chloride(g) + H2O(l) = Hydrochloric Acid(aq)

6) What is the name changing rule for Pure Element vs Compound ?
When a non-metal element forms a chemical bond with another element to make a new compound, its suffix changes to "-ide".
Whenever you see a name ending in "-ide", you instantly know it is a combination of elements, not a pure element by itself.
The best example is chlorine and chloride.

7) What is the pH Scale ?
The "p" stands for power or potential and the "H" stands for Hydrogen.
The pH scale measures the concentration of hydrogen ions in a solution.
Although the scale measures the concentration, it is actually inverted.
More hydrogen ions = more acidic = lower pH number
Less hydrogen ions = more alkali = higher pH number

8) What do the pH numbers represent ?
For every decrease in 1 on the pH scale, the concentration of the Hydrogen ions increases by a factor of 10.
If the pH increases from 3 to 6, the hydrogen ion concentration has fallen by 1000.

9) How can you measure the PH of a solution ?
pH Meter - A digital instrument with a glass probe that you dip into the liquid.
Indicator Strips / Litmus Paper - Small paper strips treated with chemical dyes that change color when dipped in liquid.
Liquid Indicator Solutions - You add a few drops of a liquid chemical directly into your solution.

10) How is the pH Scale connected to Water ?
Without water, there is no pH scale.
The entire scale is based on the unique properties of pure water.
Water is so chemically active that it constantly breaks itself apart.
In pure water, a tiny fraction of the water molecules naturally split apart (dissociate) into two types of ions:
In pure water, the number of Hydrogen ions = the number of Hydroxide ions = Neutral (pH 7).
Hydrogen ions = acidic
Hydroxide ions = alkaline

H_{2} O = H^{+} + O H^{-}

11) What happens when you dissolve Acids and Alkalis in Water ?
When you add an acid or an alkali to water, you upset the balance of these ions:
Acid - a substance that releases Hydrogen ions when dissolved in water to make a solution with PH<7
Alkali - a substance that releases Hydroxide ions when dissolved in water to make a solution with a PH>7
An alkali is a BASE that dissolves in water.

12) What is the range of the scale used to measure how Acid or Alkaline a substance is ?
The PH scale ranges from 0 to 14.
Substances with a PH less than 7 are called acids.
Substances with a PH more than 7 are called alkaline.

13) What happens to the pH of an acid, when it is diluted with water ?
By adding water you increase the volume without increasing the number of hydrogen ions.
Therefore the concentration drops and the pH increases towards neutral.

14) What are the two most important elements in the periodic table ?
Hydrogen and Oxygen are the most important elements for life and our planet.
Oxygen is a diatomic element, meaning oxygen atoms always travel in pairs bonded together as a molecule

15) What is a SALT ?
This is the name of a substance made in a neutralisation reaction.
Do not confuse this with Table Salt (NaCl = sodium chloride)
"SALTS" is a broad family name for any ionic compound made from positive and negative ions.
Sodium chloride is just one type of salt. Not all salts contain sodium chloride.

16) What is Table Salt ?
Table salt is 97% to 99.9% pure sodium chloride (NaCl)

17) What is the difference between Table Salt and Sea Salt ?
Sea salt has tiny amounts of extra minerals like magnesium and potassium.
Table salt is heavily processed, mixed with anti-caking agents, and fortified with iodine.

18) What is the difference between Table Salt and Epson Salt ?
These are completely different chemical compounds with different molecular structures, tastes, and uses.
Table salt is sodium chloride (NaCl)
Epsom salt is magnesium sulfate (MgSO4 7H2O)

19) Can you give a list of the different types of SALTS ?
One way of organising the SALTS is by the name of the acid used.
Chloride Salts - Potassium chloride
Sulfate Salts - Copper sulfate, Calcium sulfate
Nitrate Salts - Potassium nitrate, Silver nitrate
Carbonate Salts - Calcium carbonate, Sodium bicarbonate

20) Which SALTS are soluble and which are insoluble ?
Soluble Salts
All Nitrates: Every single nitrate salt dissolves perfectly.
All Common Sodium, Potassium, and Ammonium Salts: These are always soluble.
Most Chlorides: Except for Silver Chloride and Lead Chloride
Most Sulfates: Except for Lead Sulfate, Barium Sulfate and Calcium Sulfate.
Insoluble Salts
Most Carbonates: Except for Sodium, Potassium, and Ammonium Carbonates.
Most Hydroxides: Except for Sodium, Potassium, and Ammonium Hydroxides (calcium hydroxide is slightly soluble).

21) What is a BASE ?
A base is any substance that will react with an acid to form a SALT.
A base is a substance that neutralises an acid.
Bases can be both soluble and insoluble in water.

22) How many different types of BASEs are there ?
A BASE is only alkali if it dissolves in water.
All Alkalis are Bases.
Not all Bases are Alkali.

23) Which BASES are soluble and which are insoluble ?
Soluble Bases
A small number of bases dissolve perfectly in water to form clear solutions.
Soluble bases are given a special chemical name: alkalis. All alkalis are bases, but not all bases are alkalis.
When they dissolve, they release free-moving hydroxide ions into the water, raising the pH above 7.
Sodium hydroxide, Potassium hydroxide and Calcium hydroxide.
Insoluble Bases
The vast majority of bases do not dissolve in water. When you mix them into a liquid, they remain as a solid powder at the bottom.
Even though they don't dissolve, they will still completely react with and neutralise an acid if you stir them into the solution.
Copper(II) oxide, Copper(II) hydroxide, Iron(III) oxide, Iron(III) hydroxide, Aluminium Hydroxide, Magnesium oxide, Copper(II) carbonate, Zinc oxide.

24) What is a Strong Acid ?
These ionise completely in water.
These have a lower pH.
All the acid particles dissociate to release H+ ions

H C l = H^{+} + C l^{-}

Hydrochloric Acid = Hydrogen + Chloride

H_{2} S O_{4} = 2 H^{+} + S O_{4}^{2 -}

Sulfuric Acid = Hydrogen + Sulfur + Oxygen

H N O_{3} = H^{+} + N^{3 -} + 3 O^{2 -}

Nitric Acid = Hydrogen + Nitrogen + Oxygen

25) What is a Weak Acid ?
These do not ionise fully in the solution
These have a higher pH.
Only a small proportion of acid particles dissociate to release H= ions

C H_{3} C O O H = H^{+} + C H_{3} C O O^{-}

Ethanoic Acid = Hydrogen + Ethanoate

H_{2} C O_{3} = 2 H^{+} + C^{4 +} + 3 O^{2 -}

Carbonic Acid = Hydrogen + Carbon + Oxygen

C_{6} H_{8} O_{7} = 3 H^{+} + C_{6} H_{5} O_{7}^{3 -}

Citric Acid = Hydrogen + Carbon + Oxygen

26) What is a Metal Oxide ?
All metal oxides are BASEs.
When a metal chemically reacts with oxygen.
This process is called oxidation = gaining oxygen, losing electrons.

2 M g + O_{2} = 2 M g O

Magnesium(s) + Oxygen(g) = Magnesium Oxide(s) 
Mg(2,8,2) + O(2,6) = Mg(2,8) + O(2,8)

4 F e + 3 O_{2} = 2 F e_{2} O_{3}

Iron(III)(s) + Oxygen(g) = Iron (III) Oxide(s)

2 C u + O_{2} = 2 C u O

Copper(s) + Oxygen(g) = Copper Oxide(s)

4 A l + 3 O_{2} = 2 A l_{2} O_{3}

Aluminium(s) + Oxygen(g) = Aluminium Oxide(s)

4 K + O_{2} = 2 K_{2} O

Potassium(s) + Oxygen(g) = Potassium Oxide(s)

O_{2} + 4 N a = 2 N a_{2} O

Sodium(s) + Oxygen(g) = Sodium Oxide(s)

27) What is it called when oxygen is removed from an Oxide ?
The reverse of this is called reduction = losing oxygen, gaining electrons.

P b O_{2} + C = P b + C O_{2}

Lead(IV) Oxide(s) + Carbon(s) = Lead(s) + Carbon Dioxide(g)

F e_{2} O_{3} (s) + 3 C O (g) = 2 F e (s) + 3 C O_{2} (g)

Iron(III) Oxide(s) + Carbon Monoxide(g) = Iron(s) + Carbon Dioxide(g)

28) What is a Metal Hydroxide ?
All metal hydroxides are BASEs.
When a metal chemically reacts to one or more hydroxide ions.
A metal hydroxide is an ionic compound containing a positive metal ion bonded to negative hydroxide ions
They are usually formed when a metal oxide dissolves in water or reacts with a water molecule.

2 N a + 2 H_{2} O = 2 N a O H + H_{2}

Sodium(s) + Water(l) = Sodium Hydroxide(aq) + Hydrogen(g)

C a + 2 H_{2} O = C a (O H)_{2} + H_{2}

Calcium(s) + Water(l) = Calcium Hydroxide(aq) + Hydrogen(g)

M g + 2 H_{2} O = M g (O H)_{2} + H_{2}

Magnesium(s) + Water(l) = Magnesium Hydroxide(s) + Hydrogen(g)

2 A l + 6 H_{2} O = 2 A l (O H)_{3} + 3 H_{2}

Aluminium(s) + Water(l) = Aluminum Hydroxide(s) + Hydrogen(g)

2 K + 2 H_{2} O = 2 K O H + H_{2}

Potassium(s) + Water(l) =  Potassium Hydroxide(s) + Hydrogen(g)

29) What is a Carbonate ?
A carbonate is a SALT of carbonic acid,
Carbonates are compounds containing CO32 ions.
Carbonates react with dilute acids to form a salt, carbon dioxide, and water.
example - calcium carbonate + hydrochloric acid = calcium chloride + carbon dioxide + water
example - copper2 carbonate = copper2 oxide + carbon dioxide

30) What are Metal Carbonates ?
All metal carbonates are BASEs.
When a metal chemically reacts to a carbonate ion.
Calcium Carbonate
Copper Carbonate
Magnesium Carbonate
Zinc Carbonate

31) What is a REDOX Reaction ?
REDuction and OXidation always happen at the same time.
If electrons are transferred, its a redox reaction.

32) How many different types of Chemical Reactions are there that involve hydrogen and oxygen ?
Combination (REDOX)
Displacement (REDOX)
Neutralisation
Combustion (REDOX)
Thermal Decomposition (REDOX)
Precipitation

33) What can these chemical reactions be used for ?
Generating Electricity
Medical Uses
Food Production and Cooking
Manufacturing and Industry
Heavy Duty Cleaning

34) Can you name the four factors that affect the rate of reaction ?
Temperature
Surface Area
Concentration / Pressure
Any Catalysts

35) What is a Combination Reaction ?
Also called a synthesis reaction.
This is when two seperate elements combine to form a single product.

2 N a + C l_{2} = 2 N a C l

Sodium + Chlorine = Sodium Chloride

2 N a + H_{2} = 2 N a H

Sodium + Hydrogen = Sodium Hydride

2 H_{2} + O_{2} = 2 H_{2} O

Hydrogen(g) + Oxygen(g) = Water(l)

2 H_{2} + C = C H_{4}

Hydrogen(g) + Carbon = Methane(g)

36) What is a Displacement Reaction ?
When a metal or the element Carbon (C) comes into contact with a metal in a compound that is lower in the reactivity series there will be a reaction.
A more reactive metal displaces a less reactive metal.
A more reactive metal forms stronger bonds with non-metals.

37) How many different types of Displacement Reactions are there ?
Metal-Metal Displacement

M g + C u S O_{4} = C u + M g S O_{4}

Magnesium(s) + Copper Sulfate(aq) = Copper(s) + Magnesium Sulfate(aq)

4 N a + T i C l_{4} = 4 N a C l + T i

Sodium + Titanium Chloride = Sodium Chloride + Titanium

2 A l + 3 C u C l_{2} = 2 A l C l_{3} + 3 C u

Aluminium + Copper Chloride = Aluminium Chloride + Copper

F e + C u S O_{4} = F e S O_{4} + C u

Iron + Copper Sulfate = Iron Sulfate + Copper

\ce{Zn + CuSO4 = ZnSO4 + Cu}

Zinc + Copper Sulfate = Zinc Sulfate + Copper

3 C + 2 F e_{2} O_{3} = 3 C O_{2} + 4 F e

Carbon + Iron(III) Oxide = Carbon Dioxide + Iron

\ce{Zn (s) + 2AgNO3 (aq) = Zn(NO3)2 (aq) + 2Ag (s)}

Zinc(s) + Silver Nitrate(aq) = Zinc Nitrate(aq) + Silver(s)

zinc is more reactive than silver, zinc loses electrons, silver gains electrons

Carbon(s) + Iron(III) Oxide(s) = Carbon Dioxide(g) + Iron(s)

C + 2 C u O = 2 C u + C O_{2}

Carbon + Copper(II) Oxide = Copper + Carbon Dioxide 
This is the chemical equation for the extraction of copper from copper oxide using carbon 
where Cu = (Cu2 + 2e- = Cu)

C + 2 Z n O = 2 Z n + C O_{2}

Carbon + Zinc Oxide = Zinc + Carbon Monoxide 
Chlorine + Potassium Bromide = Potassium Chloride + Bromine

Metal-Acid (Hydrogen) Displacement

H_{2} S O_{4} + Z n = Z n S O_{4} + H_{2}

Sulfuric Acid + Zinc = Zinc Sulfate + Hydrogen

H_{2} S O_{4} + F e = F e S O_{4} + H_{2}

Sulfuric Acid + Iron = Iron(2) Sulfate + Hydrogen

2 H C l + Z n = Z n C l_{2} + H_{2}

Hydrochloric Acid + Zinc = Zinc Chloride + Hydrogen

2 H C l + 2 N a = 2 N a C l + H_{2}

Hydrochloric Acid + Sodium = Sodium Chloride + Hydrogen

2 H C l + M g = M g C l_{2} + H_{2}

Hydrochloric Acid + Magnesium = Magnesium Chloride + Hydrogen

Halogen-Halogen (both Non-Metals) Displacement

C l_{2} + 2 K B r = 2 K C l + B r_{2}

Chlorine(g) + Potassium Bromide(aq) = Potassium Chloride(aq) + Bromine(aq)

38) What is a Neutralisation Reaction ?
When an acid and a BASE are mixed together, they react and the solution is neutral (pH 7).
acid + BASE (metal oxide) = SALT + water
acid + BASE (metal hydroxide) = SALT + water
acid + BASE (metal carbonate) = SALT + water + carbon dioxide
All (Acid + Alkali) are neutralisation reactions, because all Alkalis are BASEs.
Acid + Metal Oxide

2 H C l + C u O = C u C l_{2} + H_{2} O

Hydrochloric Acid(aq) + Copper Oxide(s) = Copper Chloride(aq) + Water(l)

H_{2} S O_{4} + Z n O = Z n S O_{4} + H_{2} O

Sulfuric Acid(aq) + Zinc Oxide(s) = Zinc Sulfate(aq) + Water(l)

2 H N O_{3} + M g O = M g (N O_{3})_{2} + H_{2} O

Nitric Acid(aq) + Magnesium Oxide(s) = Magnesium Nitrate(aq) + Water(l)

Acid + Metal Hydroxide

H C + N a O H = N a C l + H_{2} O

Hydrochloric Acid(aq) + Sodium Hydroxide(aq) = Sodium Chloride(aq) + Water(l)

H N O_{3} + K O H = K N O_{3} + H_{2} O

Sulfuric Acid(aq) + Calcium Hydroxide = Calcium Sulfate + Water(l)

H_{2} S O_{4} + C a (O H)_{2} = C a S O_{4} + 2 H_{2} O

Sulfuric Acid(aq) + Potassium Hydroxide = Potassium Sulfate + Water(l)

H_{2} S O_{4} + 2 K O H = K_{2} S O_{4} + 2 H_{2} O

Nitric Acid(aq) + Potassium Hydroxide(aq) = Potassium Nitrate(aq) + Water(l)

2 H N O_{3} + C u (O H)_{2} = C u (N O_{3})_{2} + 2 H_{2} O

Nitric Acid(aq) + Copper Hydroxide(s) = Copper Nitrate(aq) + Water(l)

Acid + Metal Carbonate

2 H C l + N a_{2} C O_{3} = 2 N a C l + H_{2} O + C O_{2}

Hydrochloric Acid(aq) + Sodium Carbonate(s) = Sodium Chloride + Water(l) + Carbon Dioxide(g)

H_{2} S O_{4} + C a C O_{3} = C a S O_{4} + H_{2} O + C O_{2}

Sulfuric Acid(aq) + Calcium Carbonate(s) = Calcium Sulfate + Water(l) + Carbon Dioxide(g)

H_{2} S O_{4} + C u C O_{3} = C u S O_{4} + H_{2} O + C O_{2}

Sulfuric Acid(aq) + Copper(II) Carbonate(s) = Copper(II) Sulfate(aq) + Water(l) + Carbon Dioxide(g)

39) Can you have a neutralisation reaction that is not acid or alkali ?
Neutralisation can involve insoluble BASEs as well.
So not all neutralisation reactions are acid + alkali

40) What is a Combustion Reaction ?
A combustion reaction is a specific, fast type of oxidation known as burning, which always produces a noticeable amount of heat and light.

C_{25} H_{52} + 38 O_{2} = 25 C O_{2} + 26 H_{2} O

Wax(s) + Oxygen(g) = Carbon Dioxide(g) + Water(g)

41) What is a Thermal Decomposition Reaction ?
When a substance is heated and breaks down

C a C O_{3} = C a O + C O_{2}

Calcium Carbonate(s) + Heat = Calcium Oxide(s) + Carbon Dioxide(g)

42) What is a Precipitation Reaction ?
This is a chemical reaction that occurs in an aqueous solution when two clear, soluble ionic solutions are mixed together and react to form an insoluble solid.

43) What is the Reactivity Series of metals ?
The more reactive a metal is, the more vigorous the reactions with acid and water are, and the more the temperature increases.
Potassium (K) - most reactive
Sodium (Na)
Lithium (Li)
Calcium (Ca)
Magnesium (Mg)
Aluminimum (Al)
Carbon (C) (GAS)
Zinc (Zn)
Iron (Fe)
Tin (Sn)
Lead (Pb)
Hydrogen (H) (GAS)
Copper (Cu)
Silver (Ag)
Gold (Au)
Platinum (Pt) - least reactive

44) What is the Reactivity Series of non-metals ?
Fluorine (F) - most reactive - Gas at room temperature this is a toxic, pale yellow gas.
Chlorine (Cl) - Gas at room temperature this is a toxic, pale green/yellow-green gas.
Bromine (Br) - Liquid - red brown
Iodine (I) - least reactive - Solid - Grey/dark grey

45) How can metals be extracted ?
Reduction
Displacement
Electrolysis (below)
Photomining
Bioleaching

46) Why do metals conduct electricity ?
Delocalised electrons can move freely and carry charge

47) What are Reacting Volumes ?
This refers to the exact amounts of gases or solutions that react together completely according to a balanced chemical equation.

48) What is the Haber Process ?
It produces Ammonia from Nitrogen and Hydrogen

49) What is Electrolysis ?
At the negative electrode positively charged ions gain electrons.

50) What is an Exothermic Reaction ?
This is a chemical reaction that transfers energy to the surroundings
rusting, camp fires, water evaporation, water + acid reacting, nuclear fusion

51) What is an Endothermic Reaction ?
This is a chemical reaction that takes energy from the surroundings
water to ice, cooking an egg, photosynthesis, dissolving salt in water, baking bread

52) What is an Enzyme ?
This is a biological catalyst

Questions

53) The "ide" suffix
Chlorine = Chloride
Bromine = Bromide
Iodine = Iodide
Halogens have 7 in their outer shell
so the ions all have a -1 charge
Any single non-metal atom that gains electrons to form a negative ion gets the "ide" suffix.
Nitrogen = Nitride
Oxygen = Oxide
Sufur = Sufide

54) What is an Ore ?
A natural rock containing valuable minerals with metals and metal compounds.

55) Are all substances either Acid, Alkali or Neutral ?
Yes, when dissolved in water, all aqueous solutions are classified as acidic, alkaline (basic), or neutral on the pH scale.
However, this only applies to solutions or substances that can interact with water.
Many solid materials and pure chemical compounds do not fit neatly into these categories until they are placed in a liquid solvent.

56) What happens when you mix an acid with an alkali ?
Hydrogen ions from the acid react with the hydroxide ions from the alkali to make water.
The extra hydrogen ions react with the extra hydroxide ions to make water.
The left over bits of the acid and alkali make a SALT.

57) Do all Acids contain Hydrogen ions ?
No. A hydrogen ion is a proton

58) Do all Alkalis contain Hydroxide ions ?
No, but they all produce Hydroxide Ions when dissolved in water.
The most common alkalis are metal hydroxides
Amonia (NH3) is an alkali that does not have hydroxide in its formula.

59) What name is given to BASEs that dissolve in water ?
Alkalis

60) Is Water an Alkali ?
Pure water is neutral

61) What is Wax ?

62) What are Alkanes ?
general formula is CnH2n + 2

63) What is limewater ?

64) What is Ionisation ?
This involves covalent molecules (that do not have ions)
But they dissolve into water and then react to form ions.

65) Define the term Hydrocarbon ?

66) What would you observe if Sodium and Potassium are reacted with water ?

67) Explain how crude oil is seperated into fractions ?

68) How many metals can form ions with different charges ?
The vast majority (80 of the 95 metals) can form ions with different charges.
Iron (II) Oxide = FeO
Iron (III) Oxide = Fe2O2
Copper (I) Oxide = CuO
Copper (II) Oxide = Cu2O

69) Will an insoluable BASE react with an acid ?
Yes. All bases react with an acid.

70) Can all the different types of metals be found in the ground ?
False.

71) How can solid salt be obtained from a salt solution ?
By Crystallation of the salt solution.

72) What is the rock salt experiment / seperation
(use warm water)

73) In the reactivity series which elements react with water ?
Potassium, Sodium, Lithium + Water
observations - float, fizzes, moves around, hydrogen produced
Calcium + Water
observations - fizzes, hydrogen produced, cloudy solution forms
Magnesium + Water
observations - bit of bubbling
(metals below Magnesium do not react)

74) What is the colour of these when dissolved in water ?
Fluorine (F) -
Chlorine (Cl) - pale green
Bromine (Br) - orange/yellow
Iodine (I) - brown

75) Why does Calcium react more vigorously than Magnesium with Hydrochloric acid of the same concentration ?
A Calcium atom is larger than a Magnesium atom
Calcium has more electron shells than magnesium so its outer electrons sit further away from the positive nucleus.
The nuclear pull on those outer electrons is weaker because extra inner electrons layers block the pull.
Therefore calcium gives up its outer electrons faster during the reaction.

76) In the reactivity series which elements react with dilute acid (hydrochloric acid / sulfuric acid) ?
Potassium, Sodium, Lithium, Calcium, Magnesium
observation - lots of fizzing, fast reaction, hydrogen produced
Aluminium, Zinc, Iron, Tin, Lead
observation - some fizzing, gradual dissolving
Copper, Silver, Gold, Platinum
observation - no visible change

77) How does the atomic radius of atoms change throughout the periodic table and why ?
Atomic radius increase going DOWN - as there are more overall no of electrons
Atomic radius decreases going ACROSS - the increase of effective nuclear charge pulls electrons closer

78) How does the ionization energy change throughout the periodic table and why ?
Ionization energy increases going ACROSS - stronger nuclear attraction to harder to remove
Ionization energy decreases going DOWN - there is now an increase of the atomic radius and more inner shells making it easier to lose electrons

79) What happens to the pH of an acid when diluted with water ?
The pH increases and moves closer to 7 because adding water increases the total volume of the liquid.
The number of acid particles stays the same but they spread out. This lowers the concentration of hydrogen ions.

80) Barium (Ba) is an element in Group 2 of the periodic table.
Barium reacts with hydrochloric acid. Suggest 2 observations made during / after the reaction.
Fizzing
Test tube or mixture feels warm because of the exothermic change