2.10  Identification Tests

 

Section A

 

For each of the questions only one of the lettered responses (A – D) is correct.

 

Select the correct response in each case and mark its code letter by connecting the dots as illustrated on the answer sheet.

 

1.       An element, Q, is a silvery-grey solid  which conducts electricity.  It burns in oxygen with a dazzling white light.  When heated in a restricted supply of air, the principal product is a yellowish mass (sometimes white), Z, which on moistening with water evolves a gas with a pungent odour, both gas and wet solid turning neutral litmus blue.

          The identities of Q and Z are

 

                   Q       Z

              A  Li       LiNO2

              B   S       SO2

              $C     Mg     Mg3N2

              D  P        P4O6 

 

2.            An inorganic salt dissolves in water to form a colourless solution. The solution reacts with barium chloride solution to form a dense white precipitate but with sodium hydroxide solution a colourless gelatinous precipitate is formed which re-dissolves in excess of alkali.  The salt is

 

               A   ZnCO3

               $B   Al2(SO4)3

               C   AgF

               D   CuCl2

 

3.           An inorganic salt Q dissolves in water to form a colourless solution. The solution reacts with aqueous sodium fluoride to form a white precipitate.  With silver nitrate in dilute nitric acid a yellow precipitate results.  A flame test on Q produces a red coloration.

               The formula of Q is probably

               A   LiCl

               $B   CaI2

               C   MgCO3

               D   BaBr2

4.    A substance X was dissolved in water and silver nitrate solution added.  A precipitate formed which dissolved immediately in a few drops of concentrated ammonia solution.  When a solution of X was sprayed into a flame, a red colour was observed.  Which one of the following is X?

 

A         Calcium iodide

B         Lithium iodide

C         Potassium chloride

D         Strontium chloride

 

5.       An inorganic salt dissolves in water to form a colourless solution. With silver nitrate solution a curdy pale yellow precipitate is deposited and a flame test on the salt produces a green coloration.  The salt is

 

     A   KBr

     B   NaI

     C   FeCl3

     $D   BaBr2

 

6.          A coloured solid dissolves in water to form a green solution.  On addition of aqueous ammonia to this solution a green precipitate is formed, which dissolved on addition of excess ammonia.  On addition of silver nitrate solution a white precipitate is formed.  The solid is most likely to be:

          A   iron(II) chloride

          B   iron(III) bromide

          C   nickel(II) bromide

     $D   nickel(II) chloride

 

 

7.          A green powder was added to dilute sulphuric acid and a blue solution X was formed together with a gas Y which gave a white precipitate with calcium hydroxide solution.  When ammonia solution was added to X, a pale blue precipitate Z resulted which dissolved in excess to form a deep blue solution.

 

Which one of the following correctly identifies the lettered compounds?

 

                    X                                                  Y                                        Z

A   copper carbonate        sulphur dioxide        calcium carbonate

$B     copper sulphate        carbon dioxide        copper hydroxide

C     nickel carbonate        sulphur dioxide        nickel hydroxide

D     nickel sulphate        carbon dioxide        nickel hydroxide

8. A chemical plant emits traces of different gases on different days of the week.  It emits chlorine and hydrogen chloride each Friday.  Gas samples are taken and tested daily using the reagents listed.  The results are shown below.  Which one of the following samples comes from the plant on Friday?

 

 

Sample

Reagent

KI(aq)/H+ (aq)

NH3 (g)

Ca(OH)2 (aq)

A

unchanged

unchanged

white precipitate

B

goes dark

unchanged

unchanged

$C

goes dark

white smoke

unchanged

D

unchanged

white smoke

white precipitate

 

9. Two compounds are dissolved in water and the resultant solutions X and Y analysed with the results shown.

Reagent

Observation with solution X

Observation with solution Y

NaOH (aq)

Blue precipitate insoluble in excess

White precipitate soluble in excess

NH3 (aq)

Blue precipitate soluble in excess

White precipitate insoluble in excess

AgNO3 (aq) followed by dilute NH3 (aq)

White precipitate soluble in NH3 (aq)

Cream precipitate insoluble in NH3 (aq)

 

     Which one of the following responses correctly identifies the ions in the two solutions?

          Solution X            Solution Y

     A  Cu2+     Br-              Al3+     Cl-

     B     Ni2+     I-                 Zn2+     Cl-

     C     Ni2+     Cl-                    Mg2+     Br-

     $D     Cu2+     Cl-                    Al3+     Br-

 

10·  A substance X was dissolved in water and silver nitrate solution added.  A precipitate formed which dissolved immediately in a few drops of concentrated ammonia solution.  When a solution of X was sprayed into a flame, a red colour was observed.  Which one of the following is X?

 

A     Calcium iodide

B     Lithium iodide

C     Potassium chloride

D     Strontium chloride

 

 

Section B

 

Answer all questions in the spaces provided.

 

1     Several cannon were discovered from the wreck of the Girona, the Spanish galleon wrecked off the Antrim coast. If a fragment of a cannon is dissolved in concentrated nitric acid, and a student attempts to show the presence of  (i) manganese and (ii)  cobalt, describe what tests should be used, and state what would be observed if the metals were present.

 

(a)(i)          manganese ions

 

                                                                                                                                                          

 

                                                                                                                                                          

 

                                                                                                                                                          

 

                                                                                                                                                          

                                                                                                                                                           [3]

(ii)   cobalt ions

 

                                                                                                                                                          

 

                                                                                                                                                          

 

                                                                                                                                                          

 

                                                                                                                                                          

                                [3]

 

(b)   Iron is the predominant metal present and can be identified by adding a solution of thiocyanate ions. State the formula of the complex formed.

 

                                                                                                                                                          

    [1]

                                                                      CHM3J8

 

13 Beryllium occurs to a small extent in the earth's crust.  It is a steel-grey metal, which is extremely light. 

Hydrated beryllium chloride dissolves in water to give beryllium ions and chloride ions.  Describe how you would show the presence of chloride ions using a silver salt and aqueous ammonia.

(Up to two marks may be obtained for the quality of language in this part.)

 

 

 

 

 

 

 

 

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