National Chemistry

2000 Credit Almost the right answer

 

1.  (a)  i)  find the number of outer electrons 3, 1, 5, 2 , 6  and 2 respectively

ii) elements with the same number of outer electrons appear in the same   column

 

(b) Without any other information we can assume that the covalent substance is made from non-metals.

The only  non-metals are P and  S!!!!!!!

(c)  the charges on the ions are 3+, 1+, 3-, 2+, 2- and 2+

ionic compounds have a negative ion and a positive ion = boxes A or B or D or   F with C or E

given formula X2Y suggests that X is 1+ and Y is 2-

 

2.  Starch is the polysaccharide - passes the iodine test

In alphabetical order:-

 

fructose and glucose are                                      monosaccharides C6H12O6

fructose and glucose and maltose                     all reducing sugars pass Benedict's

sucrose    disaccharides C12H22O11      fails both tests

 

3.   With hydrocarbon formula in the boxes it is usually useful to write in the  molecular

formula  C4H8;    C3H8;   C4H10;  and   C3H6  respectively

(a)  but = 4 carbon atoms in the molecule

       polymer  means molecule is unsaturated ie. C=C present

(b) isomers have the same molecular formula but different structural formulae

   in this case the given molecule has  C<3H6  which is the same as box

 

4. A.  What is reduction ?  

a gain of electrons - as described in the statement

B. Does gaining electron affect Atomic Number

NO

C. Is the bromide ion negatively charged ?

YES

D. have the energy levels increased  ?

stayed the same - NO

E. are bromine and argon almost the same electronic configuration already ?

NO - bromide would have same electronic configuration as Kr

 

5.  A. Displacement : one substance "kicking" out or swapping with another - all   displacement

reactions are redox

B. Hydrolysis: breaking down an organic molecule using water

C. Fermentation: organic reaction producing alcohol

D. Condensation: organic reaction producing larger molecule and water

E. Addition: occurs at C=C

F. Redox: gain and loss of electrons; ion becomes atom and atom becomes   ion - some

redox reactions are displacement reactions

a) organic small molecule to larger molecule

b) Fe "kicks out " Cu;  iron atom becomes iron ion, copper ion becomes copper  atom

 

6.  Why is the Mg attached to the Fe ?

To protect it.

A. Can Mg be oxidised ?  YES

B. Does this stop magnesium corroding die oxidising   --

A and B are opposites

C. Would this make Fe corrode faster than Mg ?  protecting the Fe ?? NO

D. Mg protects the iron by "sacrificial protection" ?  should know this - YES

E. Electrons move from Fe to Mg. Statement A said that Mg was losing electrons so

A and E are opposites - NO

 

7. (a) acid plus carbonate ----->salt + CO<2   +   H2O

acid plus hydroxide or alkali -----> salt  + H2O

acid plus metal oxide -----> salt  + H2O

acid plus metal-----> salt  + H2

(b) Copper and  silver are the usual examples of unreactive metals

 

8.  (a) Only one correct answer

      C and D cannot both  be correct but certainly  looks like one of them must  be the answer

 

A.   get the formula for each =  HCl and H2SO4- - sulphuric acid has two positive ions to one negative ion

B.   what salts are produced by each acid ? = chlorides and sulphates

      what is a precipitate ? =  insoluble solid formed by reaction

      are the barium salts both insoluble ?  = barium chloride is soluble while barium sulphate is insoluble

C.   does diluting an acid increase or decrease Hydrogen ion concentration ? if true then it   would be true for both =  decreases so FALSE

D.  does electrolysis of an acid produces hydrogen gas ? if true then it would be   true for both  

TRUE

E.  depends on formulae - NaOH neutralised by 0.5 of acid = HCl and  H2SO4 ; the acids have different amounts of Hydrogen ions

 

(b) Can discount C and D as they would be true for both !

A.   get the formula for each =  HCl  and  H2SO4 - sulphuric acid has two   positive ions to one negative ion

Statement is True for HCl

B. what salts are produced by each acid ? = chlorides and sulphates

      what is a precipitate ? =  insoluble solid formed by reaction

      are the barium salts both insoluble ?  = barium chloride is soluble while barium sulphate is insoluble

Statement is true for  H2SO4

 

E.  depends on formulae - NaOH neutralised by 0.5 of acid = HCl and  H2SO4 ; the acids have different amounts of Hydrogen ions

HCl needs same amount of NaOH - one hydrogen ion to one hydroxide ion

H2SO4 has two hydrogen ionsso more NaOH (with one hydroxide) is required.

 

This shows how important it is to know the formula of the common acids    hydrochloric  HCl  ; sulphuric H2SO4 and nitric HNO3

 

Part 2

 

9. (a) Aluminium less dense; less strong; poorer conductor

diagram shows wires being held up high

(b) iron is middle density (no reason to pick a middle value);  strongest; poorest conductor (using for electrical cable !!)

 

10.  (a) Atomic number always the same for the same element.

Number of protons equals atomic number

(b) same atomic number but different mass number is.................

(c)

Average mass is 28.11 - must be associated with the numbers 28, 29 and 30   as these

are  mass numbers.

Most of the atoms must be close to the average

 

11.   (a) Pentane boils at 36<sup>o</sup>C so appears in the fraction 20 - 120oC

(b) The number of carbon atoms in  the molecule affects all of the physical   properties.

(c) What else speeds up reactions ? higher temperature, greater concentration   and

smaller surface area.

 

12. (a) The repeating unit is  

<IMG SRC="methcynrepeat.gif"

(b) Substances burn in oxygen.

The gas produced must contain one or more elements given in the chain (ie   cannot contain chlorine)

Must be toxic so not water or carbon dioxide

 

13.  (a) The element above silicon is carbon - and carbon forms CO2 - silicon oxide   should be similar

(b) silicon + impurities + gas X -----> SiCl4+ dissolved impurities

cancel out impurities since they appear on both sides

What is therefore missing from the reactant side

(c) separating SiCl4(l) and dissolved impurities - ie two liquids

(d) tetrahedral is the shape - CH4 has the same shape

(e) Start by putting  4 in front of HCl to give 4 x Cl on both sides

 

14.  (a) An electrical circuit is needed

     Ions cross an ion bridge

(b) Need a very soluble TIN salt

(c)  Higher voltage requires metals further apart.

Mercury is a liquid.

 

15.  The figures required for the calculation are

- volume of air at start, which is giveen in the box = 60

- reduction in volume of air - which has to be calculated using the figures in the   box  = 60 - 47.5 =

12.5

(b) Is all the oxygen used up in one pass ?

(c) What would coal do when heated ?

 

16. (a) What is normally written beside the electrodes in diagrams ?

What are ions attracted to ?

(b) label both axes - copy the words from the box in the table

first box along the way "time (min)"

second box up and down "volume of gas (cm3)

put on the scale  along the way each large box worth 5

up the way each large box worth 5;

make sure over half the graph paper is used;

make sure it is a line graph.

plot points

join the dots

(c) Remember the units

(d) Copy the ion electron equation from page 7 of the data book which    produces the hydrogen gas. This is found near the middle opposite the word   hydrogen.

Are you copying the right way for producing the hydrogen gas ?

 

17.  (a) Haber or Ostwald ?

(b) At higher temperatures what happens to the ammonia ?

(c) How does ammonia help food production ?

 

18. (a)What do propane and butane have in common to place them in the alkanes?

(b) Underline the chemicals mentioned in the question

 ie propane     C3H8       -----> water    H2O

Write under this the number of moles </center>

                            1 mole ----->   4 mole

Write under this the mass of these moles

                                 44g ----->       4 x 18 = 72g ;                  (1 mole of water = 18 g)

So 44g of propane produces 72 g of water

 

19. (a) How would you test for starch

(b) (i) What happens to starch molecules during digestion ?

(ii) Look at part (a) for help.

Make sure you use everything mentioned - it's there for a reason.

 

20. (a) A process for making ethanol/alcohol

(b) When making a statement about a relationship given in a table you can usually frame your answer as follows "As the data in first column increases   then the data in the second column

 increases or decreases (pick one)"

 

(i)

In this case the first column moves

 methanol--->  ethanol  ---> propanol   ---> butanol  

1 carbon --->    2 carbons --->       3 carbons --->        4 carbons

 

As you move down this column the  number of carbons increase and moving down the

second column  the heat released increases/decreases (pick one)

(ii) Pentanol has 5 carbon atoms ?

     How much did the value increase between each carbon atom ?

 

2000 CREDIT

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                          almost the answers

                          Answers