Group 2 and Group 7 Elements

Question 1

Group 2 elements ____ two electrons when they react

Answer 1

lose

Question 2

What happens to the atomic radius as you go down group 2 ?

Answer 2

increases

Question 3

What happens to the first ionisation energy as you go down group 2?

Answer 3

decreases

Each element down group 2 has an extra electron shell compared the the one above

The extra shell shields the outer electrons from the attraction of the nucleus and means outer electrons are further away from the nucleus

Question 4

What happens to the reactivity as you go down group 2 ?

Answer 4

Increases as the more reactive the element the easier it is to lose electrons (linked to first ionisation)

Question 5

Melting points generally ________ down group 2

Answer 5

Decrease
The larger the ionic radius, the further away the delocalised electrons are from the positive nuclei and the less attraction they feel. So it takes less energy to break the bonds

However magnesium has a drop as the arrangement of metallic ions changes.

Question 6

show oxidation of Ca

Answer 6

Ca –> Ca2+ + 2e-

Question 7

When group 2 metals react with water, what are the products formed?

show example Ca

Answer 7

products = metal hydroxide and hydrogen

Ca(s) + 2H2O(l) –> Ca(OH)2 (aq) + H2(g)

water is the oxidising agent in this reaction

Question 8

Generally compounds of group 2 elements that contain singly charged negative ions (e.g. OH-) _______ in solubility whereas compounds that contain doubly charged negative ions (e.g. SO4 2- ) ________ in solubility

Answer 8

increase

decrease

Question 9

Most sulfates are soluble in water but ______ _______ is insoluble

Answer 9

barium sulfate (BaSO4)

Question 10

Test for sulfate ions

Answer 10

If acidified barium chloride (BaCl2) is added to a solution containing sulfate ions then a white precipitate of barium sulfate is formed.

Ba2+(aq) + SO4 2- (aq) –> BaSO4 (s)
e.g. BaCl2 (aq) + FeSO4 (aq) –> BaSO4 (s) + FeCl2 ( aq)

Question 11

Group 2 elements are known as the alkaline earth metals and many of their common compounds are used for _________ acids.

Answer 11

neutralising

examples
calcium hydroxide is used in agriculture to neutralise acid soils.
magnesium hydroxide is used in some indigestion tablets as an antacid

H+(aq) + OH-(aq) –> H2O(l)

Question 12

Use of barium sulfate

Answer 12

it is opaque to x rays so can help diagnose problems with oesophagus, stomach etc

Question 13

Halogens are the highly reactive ________ of group 7

Answer 13

non metals

Question 14

What happens to electronegativity of group 7 as you go down the group?

Answer 14

decreases

electrons are further from the nucleus and are shielded by more electrons

Question 15

Why do the boiling points of group 7 increase as you go down the group?

Answer 15

increasing strength of van der Waals as the size and relative mass of molecules increases. This trend is shown in the changes in physical state from fluorine (gas) to iodine (solid)

Question 16

Halogens ______ less reactive halide ions from solution

Answer 16

displace

Question 17

Why are group 7 less oxidising as you go down the group?

Answer 17

When the halogens react, they gain an electron. They get less reactive down the group, because the atoms become larger. The outer shell is further from the nucleus so less strongly attracted to it.

Question 18

If you mix chlorine gas with cold, dilute, aqueous sodium hydroxide you get sodium chlorate solution which is ____
give equation
What are the uses of this?

Answer 18

bleach

2NaOH(aq) + Cl2(g) –> NaClO(aq) + NaCl(aq) + H2O(l)

used in water treatment to bleach paper and textiles , cleaning toilet etc

Question 19

When you mix chlorine with water you get chloride ions and ______ ions

Answer 19

chlorate
chlorate ions kill bacteria so makes water safe to drink or swim in.

Question 20

Why is chlorine an important part of water treatment?

Answer 20

kills disease causing microorganisms
some chlorine persists in the water and prevents reinfection
prevents the growth of algae , eliminates bad smells and tastes, removes discolouration

Question 21

What are the risks of using chlorine to treat water?

Answer 21

chlorine gas is very harmful if breathed in
liquid chlorine can cause chemical burns
water contains a variety of organic compounds ie from decomposition of plants. chlorine reacts with these compounds to form chlorinated hydrocarbons which can be carcinogenic

Question 22

To reduce something, the halide ions needs to lose an electron from its outer shell. How easy this is depends on the attraction between the nucleus and the outer electrons. As you go down the group, the attraction gets _____ because:
the ions get bigger so electrons are further away from the positive nucleus
there are extra inner electron shells so there is a greater shielding effect

So the further down the group the halide ion is the easier it is to lose electrons and the _______ its reducing power.

Answer 22

weaker

greater

Question 23

What happens when a halide reacts with concentrated sulfuric acid?

Answer 23

gives a hydrogen halide but what happens next is dependent on which halide

check page 106

Question 24

Test for halide ions?

Answer 24

First add dilute nitric acid to remove ions which may interfere with the test.
Then add a few drops of silver nitrate solution ( AgNO3(aq))
A precipitate is formed (of the silver halide)

Ag+(aq) + X-(aq) –> AgX(s)

Question 25

What colour precipitate is formed for
chloride
bromide
iodide
in the silver nitrate test?

Answer 25

Cl- = white ppt
Br- = cream ppt
I- = yellow ppt

Question 26

When testing silver halide ppt in ammonia, what happens?

Answer 26

Cl- = soluble in dilute ammonia
Br- = soluble in conc ammonia
I- = insoluble in conc ammonia

Question 27

Describe flame test and NaOH to identify group 2 ions

Answer 27

Flame test
1) dip a wire loop into conc HCl
2) dip the wire look in unknown compound
3) hold the look in the clear blue flame
4) observe colour change
Ca2+ = brick red
Sr2+ = red
Ba2+ = pale green

NaOH
add NaOH in dropwise and observe change and ppt
keep adding until it is in excess and record any change

Mg2+ = slight white ppt –> white ppt
Ca2+ = slight white ppt –> slight white ppt
Sr2+ = slight white ppt –> slight white ppt
Ba2+ = no change –> no change

Question 28

How to test for ammonium ions?

Answer 28

use damp red litmus paper - if present it will turn blue

You can also add hydroxide ions to a solution containing ammonium ions and they will react to produce ammonia gas and water
NH4 + (aq) + OH- (aq) –> NH3(g) + H2O(l)
add some dilute sodium hydroxide solution and gently heat
If ammonia gas is given off ammonia gas must be present

Question 29

How to test for sulfates?

Answer 29

Add a little dilute hydrochloric acid followed by barium chloride solution
If a white ppt of barium sulfate forms it means original compound contained a sulfate

Question 30

How to use pH indicator to test for hydroxides

Answer 30

dip a piece of red litmus paper into the solution
if hydroxides are present the paper will turn blue

Question 31

How can hydrochloric acid help to detect carbonates?

Answer 31

when you add hydrochloric acid to a solution containing carbonate ions it will effervescence and carbon dioxide is created

to test for the CO2
bubble gas through limewater - if present the limewater will go from colourless to cloudy