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 ?

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