Group 7

Question 1

Observation during the reaction where br2 is produced

Answer 1

Brown solution SOLUTION is key

Question 2

In terms of electrons state the meaning of the term oxidising agent

Answer 2

Causes another species to lose electrons but accepts electrons itself.

Question 3

In sunlight chlorine can also oxidise water slowly to form oxygen. Write an equation for this reaction

Answer 3

2Cl2+2H2O—->4HCl+O2 or (4h+ +4cl- +o2)

Question 4

Explain why chlorine has a lower bp than bromine

Answer 4

Chlorine is smaller than bromine so has fewer electrons (for my understanding less to create temp dipoles) the van der waals forces BETWEEN chlorine molecules are weaker. (Intermolecular forces)

Question 5

Strontium carbonate reacts with nitric acid to produce a solution of strontium nitrate. Strontium sulfate does not react with nitric acid.
Describe briefly how you could obtain strontium sulfate from a mixture of strontium carbonate and strontium sulfate

Answer 5

Add nitric acid to the mixture until in excess and filter to isolate strontium sulfate.

Question 6

Explain why drinking magnesium sulfate is effective in the treatment of barium poisoning

Answer 6

As insoluble barium sulfate is formed.

Question 7

Medicines for the treatment of nervous disorders often contain calcium bromide. Silver nitrate acidified with dilute nitric acid can be used together with another reagent to test for the prescence of bromide ions in a solution of a med.
describe briefly how you would carry out this test and state observations.

Answer 7

Add silver nitrate and then dilute ammonia. Cream ppt and no visible change precip dissolves slightly in dilute ammonia.

Question 8

Which of these substances reacts most rapidly to produce a silver halide ppt with acidified silver nitrate. (CH3Br, CH3Cl, CH3F, CH3I)

Answer 8

CH3I

Question 9

How to separate and purify something

Answer 9

Filter off remaining ppt. Wash to remove soluble compounds. Dry to remove water.

Question 10

A colourless solution contains a mixture of sodium chloride and sodium bromide.
develop a procedure to prepare a sample of pure silver bromide from this mixture.

Answer 10

Add silver nitrate to form precips pf agcl and agbr

Add excess dilute ammonia to ensure silver chloride dissolves.
Then filter off remaining solver bromide ppt wash to remove soluble compounds and dry to remove water.

Question 11

Reaction between chlorine and cold dilute sodium hydroxide

Answer 11

Cl2+2HO- —> OCl-+Cl- + H2O

Question 12

Other than cost, explain one advantage of using magnesium hydroxide rather than magnesium carbonate to reduce acidity in the stomach.

Answer 12

Does not produce co2 gas which distends stomach. Prevents burping

Question 13

Explain why the precip of silver chloride was washed several times with deionised water

Answer 13

To remove soluble impurities

Question 14

explian why the solution of strontium chloride was filtered to remove insoluble impurities before the addition of silver nitrate

Answer 14

as it would give an incorrect mass of AgCl

Question 15

deduce reasons why the method of extraction from a low grade pre is a low cost process, do not include the cost of the ore

Answer 15

may use scrap metal, single step process, requires less energy

Question 16

explain why chlorine is used to kill bacteria eventhough toxic

Answer 16

used in small amounts, health benefits outweigh the risks

Question 17

what does chlorine do

Answer 17

dissolves in water to make a mixture of hcl and chloric acids. cl2+h20=hcl+hclo and cl2+h20=2h+ +cl- +clo-

Question 18

what happens if you add an acid

Answer 18

more hydrogen ions are formed so the equibrium shifts to the left

Question 19

what happens if you add an alkali, oh-

Answer 19

the ph increases so the equilibrium shifts to the right

Question 20

test for chlorine

Answer 20

damp blue litmus paper, turns white. or pink to white over swimming pools

Question 21

adding conc sulfuric acid to solid potassium chloride- write the simplest ionic equation and what species is responsible for the misty fumes produced

Answer 21

h2s04 + 2cl- –> 2hcl +so42-

and hcl

Question 22

state the role of sulfuric acid and identify the yellow solid

Answer 22

oxidising agent and sulfur

Question 23

give two features of a reaction at equilibrium

Answer 23

the conc of reac and products remains the same, adn the forward and backwards rate stay the same

Question 24

state why the silver nitrate is acified when testing for iodide ions

Answer 24

it reacts with ions that would interfere with the test, for example carbonates

Question 25

in terms of electrons state the meaning of a reducing agent

Answer 25

electron donor

Question 26

state one risk in using hydrogen gas in metal extractikon

Answer 26

not flammable! explosive

Question 27

major cost in the extraction of calcium via electrolysis

Answer 27

electricity

Question 28

why is it not possible to measure the enthalpy change directly for areaction where co is made as a product

Answer 28

because co isnt the only product, co2 may also be formed if further oxidation occurs

Question 29

state why the value quoted in c is the standard enthalpy of formation is the same as the one for carbon

Answer 29

because they both make a mole of co2, only from carbon and oxygen

Question 30

When chlorine gas dissolves in cold water, a pale green solution is formed. In this solution, the following equilibrium is established. Cl2(g) + H2O(l) H+ (aq) + Cl– (aq) + HClO(aq) Give the formula of the species responsible for the pale green colour in the solution of chlorine in water. Use Le Chatelier’s principle to explain why the green colour disappears when sodium hydroxide solution is added to this solution.

Answer 30

``` Cl2 (provides the pale green colour) M1 requires the formula M2 NaOH reacts with the acid(s)/the HCl/the HClO/H+ Ignore “reacts with the products” Ignore “reacts with chloride ion” Ignore “reacts with chlorine” M3 requires a correct answer in M2 Equilibrium shifts (from left ) to right OR wtte ```

Question 31

state what is observed when silver nitrate solution is added to sodium fluoride solution

Answer 31

instead of saying no visible change, say colourless solution. allows nvc

Question 32

the role of cl in nacl making hcl

Answer 32

hcl h - cl | proton acceptor or a base

Question 33

give an equation for the redox reax between solid sodium bromide and conc sulfuric acid

Answer 33

normally nabr and h2so4 is the equation that makes nahso4 but thats not redox remember. the one after that is a redox so tweak it slightly NaBr+ 2H2SO4 -->Na2So4 +Br2 +2H2O the only thign that changed was the extra na added so instead form another so4 to get enough waters and also form na2so4

Question 34

what halide can the scientist not idenitfy

Answer 34

fluoride as it is soluble so would dissolve | so no ppt would form