National Chemistry

2004 Credit First thoughts

Credit  2004     First thought

                            Hints

                            Almost the answers

                            Answers

 

1. (a) B                                     Oxygen and nitrogen in the air react to produce NO2

(b) A and E                               Hydrogen in hydrocarbon forms H2O

                                   carbon in hydrocarbon forms CO2 (not a choice) so CO when

                                                       combustion is incomplete

 

2. Write the molecular formula  C4H8; C5H12; C4H10; C3H8; C2H6 C4H8;

(a) B                             All melt before 25oC but rest boil before 25oC so are gases

(b) A and F                       Both C4H8 but different structures

(c) F                             Alkene has C=C decolourises orange bromine

 

3. (a) C                        Oxides, carbonates and hydroxides

(b) A and C                               magnesium hydroxide

(c) A                               Write the charge on the ions above each name.

                                                  +2; and -1; +1 and -1; +1 and -1; +1 and -1; +1 and -2; +1 and -1

                                                  Notice B, C , D and F are the same so cannot be a correct answer

                                                                    X2+ (Y-)2 = Mg2=(Br-)2

 

4. (a) D and C

Concentration is the only value changed.

 

         2 mole/l               1 mole/l

                               A Zn   B    Mg

                            D Zn   C    Zn

        F    Mg           E    Mg

 

Notice that A and B cannot be correct as metal changes as well.

Now add the temperature

 

                            A   Zn, 30,                B      Mg, 30,

                         D   Zn, 20,                      C      Zn, 20,

     F    Mg, 30,                        E       Mg, 20

 

D and C are possible; so are F and B.

Now look at powder or lump.

                            A   Zn, 30,                B      Mg, 30, lump

                         D   Zn, 20,powder          C      Zn, 20, powder

      F    Mg, 30, powder            E       Mg, 20

 

(b) F                                      Most reactive metal, higher temperature, higher

                                                               concentration and powder

 

5. (a) A and E                            conduct when molten or solution not solid

(b) D                            does not conduct and high melting point

 

6. (a) C and D                                     Same atomic number different mass number

(b) A and F                                          electron arrangement of argon (2.8.8)and for each of the                  

                                                            six boxes. Some are ions and some are atoms. 2,8,8 (ion) ;                                

                                                             2,8 (ion)  ;  2,8,8,1  ;  2,8,8,1 ;  2,8,8,2  ;  2,8,8 (ion)

 

7. A and C                                      no mass, -1 and around nucleus

 

8. A and F                                         Write list of the five carbohydrates (fructose, glucose,

                                                             maltose, sucrose, starch) and match up what they have in

                                                             common.

 

A. Glucose polymerises to form starch and water  T

B. Starch is made from glucose ?

C. Sucrose does not react with benedict's (first three do)  

D. first and fourth are not a pair

E. big starch molecules do not dissolve easily

F. sucrose (number 3) can be broken down T

 

9. B and D

A. +ve ions do NOT move to +ve electrode - opposites attract   F

B. Ni oxidised at +ve electrode - T

C. galvaniSINg   uses zinc    F

D. oxidation  at +ve electrode - Ni loses electrons T

E. electrons along wires F

 

part 2

 

10. (a)   view    triple bond to nitrogen not required  -CN will do

(b) Carbon monoxide or cyanide

 

11. (a) A mixture of metals

(b) (i) 5% of 5.74g   = 0.287g

(ii) Use figure from part (i).

 

moles = mass in question      =    0.287     =    0.01 moles

           mass 1 mole                 27    

 

12.(a) gas escapes from flask (CO2 produced)

(b)Label the axes using the words in the table. Create scales using at least half the graph paper.

Plot and join the dots.

(c) The amount produced is still 0.80g - it is produced faster

(d) calcium chloride

 

13.(a) the negative electrons from one atom are attracted to the positive nucleus (protons) of the other atom

(b) (i) The diagram tells you what the dots are. Draw nitrogen out showing only outer 5 electrons. Three hydrogens are required

(ii) You only know one shape. Formula is NH3. draw bonds between the atoms. view

 

14.

(a)(i) Carbon has double bond to oxygen and two single bonds to two hydrogens. view

(ii)loss of hydrogens

(b) CO

 

15. Read the information above and below the diagram.

(a) iron to carbon (ferroxyl told you Fe2+ was formed therefore electrons lost).

(b) pH indicator turns blue

 

16. (a) Ionic solution broken down to elements using electricity

(b) Aluminium to reactive to break compound using heat and carbon

(c)     2Cl-  ---> Cl2     +  2e

(d) Tin is less reactive than iron

So iron sacrificially protects the tin

 

17. (a) (Ag+)2HCO32-

(b) (i)

                 3Ag2S    +  2Al  --->  6Ag    +   Al2S3

 

 working     Ag2S    +   Al   --->  Ag    +   Al2S3

                  Ag2S         Al Ag          

     Ag2S Ag

                               Ag

                 Ag

                 Ag

 

(ii) Redox                                 silver ion reduced; alumionium metal oxidised

or displacement                                 aluminium 'kicks out' silver

 

(c)  Mass is mentioned so need mass of 1 mole.

Al2S3 = (2 x Al) + (3 x S) for 1 mole.

= (2 x 27) + (3 x 32) = 150 for 1 mole.

 

54 g of aluminium in 150g 54     x 100 (for percentage)  = 36%

                150

 

18. (a) ammonia has dissolved in the water

(b) above 7 (ammonia is alkali)

 

19. (a) gas

(b) -5oC

 

20.Write out molecular formulae - C4H6; C5H8; C6H10 -for each molecule.

(a) Group of molecules with similar chemical properties/same general formula

(b) CnH2n-2

(c) C5H8Br4

(d) cyclo with 4 carbons one pair having a double bond. each carbon has enough hydrogens to make it have 4 bonds.

 

21.Titration. Circle figures from the diagram ie  0.20 mol/l and 20cm3

(a) indicator changes colour

(b)(i) 20.6  (average of 20.5 and 20.7)

 

(ii) You now have two figures. 0.20 mol/l from diagram and 20.6 from part (i(0.0206 litres)

concentration =  mol       

            litre

 

 therefore    mole = conc x litre  

 

       = 0.2  x  0.0206   =    0.004

   

 

(iii) H2SO4      +      2KOH    ---->  K2SO4   +   2H2O

       1 mole    with    2 moles

               0.004     with    2 x 0.00

 

= 0.008 mol

 

 

END