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Georges chem > reactivity trends chp 8 > Flashcards

reactivity trends chp 8 Flashcards

1
Q

what is the test for a carbonate

A

1) in a test tube add dilute nitric acid to the solid or solution to be tested
2) if you see bubbles, the unkown compound could be a carbonate
3) to prove that the gas is carbon dioxide, bubble the gas through lime water and if it is CO2 the lime water will turn cloudy

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2
Q
  • what is the test for sulfate
  • whats the equation for it
  • what should you not use in the test
A
  • add aqueous barium nitrate to the solution in question
  • barium sulfate is insolube & forms a white precipitate
    Ba 2+ (aq) + SO4 2- (aq) => BaSO4 (s).
  • do not use barium chloride as chloride ions could give false results in future tests
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3
Q

what are the halide tests, explain the method

A
  • most halides are soulble in water, but silver halides are insoluble
    1)Add aqueous silver nitrate (AgNO3), to an aqueous soultion of a halide
    2)silver chloride is white, silver bromide is cream-coloured and silver iodide is yellow
    3) Add aqueous ammonia to test the solubility of the precipitate. this stage is very useful as silver chloride and bromide are soluble in ammonia solution and silver iodide is insoluble
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4
Q

Which silver halide is insoulable in ammonia (aq)

A

silver iodide is insoluble in aqueous ammonia and silver chloride and bromide are soluble

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5
Q

what sequence should you test substances in

A

1)carbonate test
2)sulfate test
3)halide test

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6
Q

why should the carbonate test be first in the sequence

A

Because carbonate ions can interfere with further tests and can give you a false result.

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7
Q

why should the sulfate test be 2nd in the testing sequence

A
  • BaNO3 is used in the sulphate test and so if you test for sulphates first while there could potentially be carbonate ions within the unknown solution you could get a false result
    ^BaCO3 forms a white precipitate
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8
Q

why should the halide test be last in the testing sequence

A
  • In this test you add AgNO3 to a solution and are looking for a precipitate,
  • silver carbonate(Ag2CO3) and silver sulfate (Ag2SO4)both form precipitates
    ^carbonates and sulfates both tested for in previous tests
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9
Q

what is the ammonium ion test

A
  • add aq sodium hydroxide (NaOH) to solution maybe containing ammonium ions
  • ammonia gas produced but not seen as very soluble in water
  • warm mixture, ammonia gas released
  • use most pH indicator paper to test for ammonia gas, if turns blue ammonia gas present as is alkaline
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10
Q

what are the chemical properties of group 2 metals

A

the elements are reactive metals and do not occur in their elemental form naturally, on earth they are found in stable compounds such as calcium carbonate, CaCO3.

also called the alkaline metals due to the alkaliine properties of their metal hydroxides

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11
Q

what are the physical properites of group 2 metals

A

they have low boiling points, low melting points, and low densities.

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12
Q

what sub shell is the outer electrons of a group 2 metal in

A
  • each group 2 element has 2 outer shell electrons.
  • both are in the s sub-shell
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13
Q

what are the most common types of reactions that group 2 metals are involved in

A
  • Redox reactions
  • Each metal atom is oxidised, losing 2 electrons to form a 2+ ion
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14
Q

what is a defintion of a redox reaction

A

An oxidation-reduction (redox) reaction is a type of chemical reaction that involves a transfer of electrons between two species.

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15
Q

what does the group 2 element act as during a redox reaction

A

-A reducing agent.
-another species will gain the electrons that the group 2 metal will lose and therfore be reduced.
-the group 2 metal has reduced another species and is therfore a reducing agent.

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16
Q

How will group 2 metals react with oxygen

A

The group 2 elements all react with oxygen to form a metal oxide, with the general formula MO, made up of M(2+) and O(2-) ions.

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17
Q

what are the changes in oxidation numbers during group 2 metals reactions with oxygen

A
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18
Q

how do group 2 metals react with water

A

The group 2 elements react with water to form an alkaline hydroxide, with the general formula M(OH)2 and hydrogen gas.

19
Q

what is the trend in reactivity for group 2 metal + water reactions

A

the reactions get more vigours as your go down the group

20
Q

what is reduced and what is oxidised during a reaction between group 2 metals and water

A

Sr represents any alkaline metal

21
Q

how do group 2 metals react with dilute acids

A

Group 2 metals react with dilute acids to from a salt and hydrogen gas, the reactivity increases down the group.

22
Q

what is the trends in reactivity of group 2 in redox reactions

A

The reactivity increases down the group

23
Q

what is the trend in ionisation energy for group 2 and why

A

It decreases as you go the group

-attraction between the nucleus and the outer electrons decreases as a result of increasing atomic radius and increasing shielding.
-The energy needed to form 2+ ions decreases

24
Q

how do the atoms of group 2 atoms react

A
  • oxidised to from 2+ ions
  • the first and second ionisation energies make up most of the energy input.
25
Q

What is the trend in the ability to reduce in group 2

A

they become stronger reducing agents as you go down the group

26
Q

what are the reactants and products in a reaction between an alkaline metal oxide and water

A
27
Q

what is the trend in solubility in alkaline metal hydroxides

A
28
Q

what is the experiment to show the trend in alkilinity of group 2 metal hydroxides

A

1) Add a spatula of each group 2 metal oxide to water in a test tube
2)Shake the mixture. You will have a saturated solution of each metal hydroxide with some white solid undissolved at the bottom of the test-tube
3) Measure the PH of each solution, the alkalinity will be seen to increase down the group

29
Q

what is one common use for group 2 compounds in agriculture

A

Calcium hydroxide, Ca(OH)2, is added to fields as lime by farmers to increase the PH of acidic soil

30
Q

What is one common use of group 2 compounds in medicine

A

-Group 2 compounds are often uses as antacids fro treating acid indigestion.
-Many tablets use calcium/magnesium carbonate
-milk of magnesia is a suspension of white magnesium hydroxide, Mg(OH)2, in water

HCL= stomach acid

31
Q

What are the characteristics of the halogens

A

-Most reactive non-metal group
-The elements do not occur in their elements form in nature
-They occur as stable halide ions, dissolved in sea water or combined with a sodium or potassium as solid deposits, such as in salt mines (NaCl) or in diatomic ions.

32
Q

What is the trend in the boiling point in group 7

A
33
Q

what is the structure of the halogens when solid

A

-At RTP all the halogens exists as diatomic molecules(X2)
-They form lattices with the simple molecular structures

34
Q

what sub-shell is the outer-most electron in, in group 7 elements

A

there are 2 in the s sub-shell and 5 in the p sub-shell(-s2p5)

35
Q

what is the most common type of reaction that halogens are involved in

A

Redox reactions

  • each halogen atom is reduced, gaining 1 electron to from a 1- halide
  • another species loses electrons to halogen atoms, so are oxidised
    ^ the halogen is called the oxidising agent as it oxidises another species
36
Q

What can you do to show that the reactivity of halogens decreases down the group

A
  • halogen-halide displacement reaction
  • can be carried out on a test-tube scale
37
Q

What is the process of the halogen-halide displacement reaction

A
  • Add solution of one halogen to a solution of another halogen
  • if the halogen added is more reactive than the halogen present a displacement reaction takes place
    ^the solution changes colour
  • if the halogen added is less reactive there will be no colour change
38
Q

How would you tell the difference between iodine and bromine solutions

A

-solutions of iodine and bromine in water can appear a similar orange-brown colour, depending on the concentration
-An organic non-polar solvent such as cyclohexane can be added and the mixture shaken, the non-polar halogens dissolve more readily in cyclohexane than water and the colours of the solutions of halogens can be more easily told apart

39
Q

What is the trend in reactivity in group 7

A
40
Q

what is a oxidising agent

A

An atom/compound that accepts electrons from other species

41
Q

what is a reducing agent

A

An atom/compound that donates electrons to other species

42
Q

What is a disproportionation reaction

A

A redox reaction in which the same element is both oxidised and reduce

43
Q

what are some examples of disporportionation reactions involving halogens

A

The reaction of chlorine with water and with cold, dilute sodium hydroxide

44
Q

why is chlorine used in the purification of water

A
  • chlorine reacts with water to produce acid solution (HClO-, HCl)
  • bacteria killed by acids
  • chloric acid acts as weak bleach

Georges chem (29 decks)

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