National Chemistry

1999 Credit     Almost the answers

 

1.  There is not a lot of point reading this complete table. Note the headings and

then look at the question.

(a) Ionic compounds :  conduct when solid no

conduct when moltenyes

 

melting/ boiling points high

</CITE>

<CITE>remember to pick 2 boxes<BR>

</CITE>

<BR>

(b) covalent compound: conduct when solid <CITE>no </CITE>

<BR>

conduct when molten<CITE> no <BR>

</CITE>

<CITE> </CITE>

melting/ boiling points <CITE>molecule low; network high<BR>

</CITE>

 

A substance will not be covalent and ionic<BR>

<BR><BR>

2.  In alphabetical order:-<BR>

fructose<BR>

glucose both monosaccharide C<sub>6</SUB>H<sub>12</SUB>O<sub>6</SUB><BR>

maltose     first 3 reducing sugars pass Benedict's<BR>

sucrose both disaccharide C<sub>12</SUB>H<sub>22</SUB>O<sub>11</SUB> last one fails all tests<BR>

<BR>

starch is a large molecule    turns iodine blue black<BR>

<BR>

(a) The single one (C<sub>6</SUB>H<sub>10</SUB>O<sub>5</SUB>)<sub>n</SUB><BR>

<BR><BR>

(b) C<SUB>12</SUB> - a mid sized pair<BR>

<CITE>remember to pick 2 boxes<BR>

</CITE>

<BR>

(c) The single one<BR><BR>

(b) cannot be  broken down so  small<BR>

<CITE>remember to pick 2 boxes<BR>

</CITE>

<BR><BR>

3.  Get to page 5 - the solubility table<BR>

(a) identify one o f these as a precipitate - ie insoluble<BR><BR>

(b) Mixing two of the boxes will give a precipitate<BR>

A + B - produces copper sulphate and barium nitrate - both check in table;<BR>

A + C - produces copper carbonate and lithium nitrate - check both in table<BR>

 A + D; B + C; B + D and C + D must all be tried<BR>

<BR><BR>

4.. A time consuming question but should be easy to get correct.<BR>

(a) higher temperature; smallest particles; more concentrated acid; most   reactive

metal all  increase reaction rate ?<BR>

So pick slowest reaction.<BR><BR>

(b) Changing temperature - place the letter of the box under the appropriate temperature <PRE>

<EM> <U>20<SUP>o</SUP>C</U>   <U>30<SUP>o</SUP>C</U> <U>40<SUP>o</SUP>C</U> </EM>

A        C       E

B        D       F</PRE><BR>

 

MUST be boxes from different columns ie not C and D<BR>

 

Write the concentrations beside each box letter<BR><PRE>

<EM> <U>20<SUP>o</SUP>C</U>   <U>30<SUP>o</SUP>C</U> <U>40<SUP>o</SUP>C</U> </EM>

A   1 mol/l   C    2     E   2

B   2          D    1     F   2</PRE><BR>

This eliminates some more pairs - cannot be A and C as although different temperatures

they also have different concentrations.<BR>

Write the metal beside each letter to eliminate some combinations.<BR><PRE>

<EM> <U>20<SUP>o</SUP>C</U>   <U>30<SUP>o</SUP>C</U> <U>40<SUP>o</SUP>C</U> </EM>

A   1 mol/l   iron   C    2   Mg     E   2   Mg

B   2        Mg      D    1   iron     F   2   iron</PRE><BR>

 

possibilities A &amp; D; B &amp; C; C &amp; E; B &amp; E<BR>

Now add in particle size to identify correct pair<BR>

 

<CITE>remember to pick 2 boxes<BR>

</CITE>

<BR><BR>

5. (a) Same atomic number but different mass number <BR><BR>

At least select two boxes with something in common.<BR>

<CITE>remember to pick 2 boxes</CITE>

<BR><BR>

(b) argon is 2,8<BR>

Then write down the electron arrangement of the  six atoms/ions in question.<BR>

eg A is 2,8,1 &#160&#160&#160&#160&#160 B is 2,8,8  etc.<BR>

<CITE>remember to pick 2 boxes</CITE>

<BR><BR>

(c) Mass number - (number of protons) <BR>

number of protons =atomic number<BR>

<BR><BR>

6. Lot of information :-<BR>

One of the metals corrodes - <BR>

Electrons flow from metal B to metal A - what does this tell you ?<BR>

<EM>fe</EM>

rroxyl indicator shows Fe<SUP>2+</SUP> Use page 7 of data book.<BR>

(a) Blue colour around metal B due to<EM> fe</EM>

rroxyl indicator.<BR>

Electrons move down electrochemical series<BR>

On question paper circle the most reactive of each pair of metals<BR>

B, C &amp; E have metal A the more reactive metal.<BR><BR>

(b) Use page 7 of data book<BR>

Biggest gap or smallest gap ?<BR>

<BR><BR>

7.   "statement(s)" in the credit paper usually means TWO correct answers.<BR>

<BR>

In this style of question then there are TWO correct answers and three wrong   answers

- work through each statement individuaally deciding if it is True/ False.<BR>

Watch for statements that are the opposite of each other - both cannot be   correct

and one usually is.<BR>

During distillation fractions are separated due to boiling points - lower boiling

  points coming off first.<BR>

Fraction 6 is darkest  deliberately  as it has the biggest molecules<BR>

The bigger the molecule the darker, more viscous, heavier, harder to ignite the   substance

is.<BR><BR>

<STRONG>A</STRONG>

. "most easily" is an extreme - either 6 or 1<BR>

<STRONG>B</STRONG>

. is fraction 4 bigger than fraction 3 ?<BR>

<STRONG>C. is</STRONG>

 flammability less at 1 ?<BR>

<STRONG>D. f</STRONG>

 fraction 1 is collected first then  fraction 4 has lower boiling point than     fraction

5<BR>

<STRONG>E</STRONG>

. Are the smallest molecules collected first ?<BR>

<CITE>remember to pick 2 boxes</CITE>

<BR><BR>

<BR>

8. "statement(s)" in the credit paper usually means TWO correct answers.<BR>

<BR>

In this style of question then there are TWO correct answers and three wrong   answers

- work through each statement individuaally deciding if it is True/ False.<BR>

Watch for statements that are the opposite of each other - both cannot be   correct

and one usually is.<BR>

<BR>

(a) Each statement must be TRUE for both<BR>

Always worthwhile knowing formula of common acids <BR>

hydrochloric acid H<SUP>+</SUP>Cl<SUP>-</SUP>  ; sulphuric acid H<SUP>+</SUP>2SO<SUB>4</SUB><SUP>2-</SUP>  ;  nitric acid    H<SUP>+</SUP>NO<SUB>3</SUB><SUP>-</SUP> <BR>

<STRONG>A</STRONG>

. do all acids react with magnesium ? <BR>

If one does both do<BR>

<STRONG>B</STRONG>

. do all acids have a pH less than 7 ?<BR>

If one does both do.<BR>

<STRONG>C. do</STRONG>

 acids not conduct electricity ?<BR>

If one does not  both do not.<BR>

<STRONG>D.</STRONG>

 do all acids produce Cl<SUB>2</SUB>(g) ?  Cl<SUP>-</SUP> present in only one.<STRONG><BR>

</STRONG>

<STRONG>E.</STRONG>

 do acids have equal numbers of H<SUP>+</SUP> and OH<SUP>-</SUP> ions - this is a neutral    substance<BR>

<CITE>remember to pick 2 boxes</CITE>

<BR><BR>

(b)  Each statement must be TRUE for Na<SUP>+</SUP>Cl<SUP>-</SUP> and  FALSE for H<SUP>+</SUP>Cl<SUP>-</SUP><BR>

Use information gathered for part (a) to help.<BR>

<BR>

<STRONG>A</STRONG>

. do all both react with magnesium ?<BR>

<STRONG>B</STRONG>

. acids and salts have different  pH .<BR>

<STRONG>C. do</STRONG>

 ionic solutions conduct electricity ?<BR>

<STRONG>D.</STRONG>

 do both produce Cl<SUB>2</SUB>(g) ?  Must have Cl<SUP>-</SUP> present.<STRONG><BR>

</STRONG>

<STRONG>E.</STRONG>

 both have equal numbers of H<SUP>+</SUP> and OH<SUP>-</SUP> ions <BR>

<BR><BR>

<EM>part 2</EM>

<BR>

<BR>

9. (a) When making a statement about a relationship given in a graph you can   usually

frame your answer as follows "As the <CITE>data along the way</CITE>

 increases   then the <CITE>data up the way</CITE>

 increases or decreases (pick one)"<BR>

In this question you need to isolate a "group "  ie all group 1 elements Li, Na K

  etc<BR>

As it moves Li, Na, K the atom size inreases/decreases <CITE>pick one</CITE>

<BR><BR>

(b) When making a statement about a relationship given in a graph you can   usually

frame your answer as follows "As the <CITE>data along the way</CITE>

 increases   then the <CITE>data up the way</CITE>

 increases or decreases (pick one)"<BR>

In this question you need to isolate a "Li to F" in the graph<BR>

As you move along group Li (3), Be (4) B (5) ...etc the atom size increases/   decreases

<CITE>pick one</CITE>

 <BR><BR>

(c) Look up the atomic number of calcium.<BR>

Page 1 of the data book would help.<BR>

<BR><BR>

10. (a) Electronic configurations on page 1 may help concentrate your mind.<BR>

Na moves from 2,8,1 to Na<SUP>+</SUP> 2,8<BR><BR>

(b) Oxidation is loss of electrons therefore Fe<SUP>2+</SUP> becomes  ....<BR>

 Try page 7 of data book.<BR>

<BR><BR>

11. (a)3 C , 1 S and 8 H<BR><BR>

(b) Write the molecular formula for B<BR><BR>

(c) Must be something, present in the compound,  with oxygen. ie C, S  and H   but

 not chlorine oxide.<BR>

<BR><BR>

12. bubbled through water<BR>

 

bubbled through concentrated sulphuric acid<BR>

 

Make sure the test tubes are connected<BR>

<BR>

<BR><BR>

13.  (a) The repeating unit is<BR>

<IMG SRC="perspexrepeat.gif"><BR>

3 monomer units would be 6 C joined together<BR><BR>

(b) Reaction which releases heat (heat is always "therm")<BR>

releasing is indicated by "exo" as in exit<BR><BR>

(c)  Write the molecular formula C<SUB>5</SUB>O<SUB>2</SUB>H<SUB>8</SUB> <BR>

<PRE>How much C   = <U>mass of carbon</U> x 100 %

 mass of C<SUB>5</SUB>O<SUB>2</SUB>H<SUB>8</SUB>

 

= <U>5 carbons </U>    x  100

    100</PRE><BR><BR><BR>

14.  (a) Migration of ions obviously requires potassium nitrate in gel.<BR>

d.c. power supply for electricity; electrodes<BR><BR>

(b) Red, green and purple/blue colours should suggest pH numbers<BR>

 acid and sodium hydroxide (alkali) have pH numbers<BR>

<BR><BR>

15. (a) Remember that you can only put figures in front of the formulae - you    CANNOT

change any of the formula you have been given.<BR>

1 Ag on left hand side but 2 Ag on right hand side so place a 2 in front of Ag<BR>

2 oxygens on left hand side  but only one on right hand side so place 2 in front   of

H<SUB>2</SUB>O<BR>

Check the rest in a similar manner<BR><BR>

(b) (i)  Ag<SUP>+</SUP> ions present at start ----&gt; this one should make Ag<BR>

Ag<SUP>+</SUP> ions  ----&gt;  Ag<BR>

(ii)  Top of page Page 7 shows what type of reactions.<BR>

gain of electrons or loss of electrons<BR>

<BR><BR>

16.  (a)  How does the structure  of the five molecules given affect density.<BR>

Effect of more carbons = increasing density<BR>

Effect of increasing number of -OH groups =<BR><BR>

(b) Similar question to (a) working in reverse BUT must have 4 carbon atoms   and

some -OH groups. Only one OH group only gives a density of 0.8<BR>

<BR><BR>

17.  (a) Nitrogen in the air is N<SUB>2</SUB>(g)<BR><BR>

(b) ammonia comes from ammonium chloride heated with ... ?<BR>

A salt and water is also produced<BR><BR>

(c) Heat is required at start but not after reaction has started.<BR>

But reaction needs heat. Where is it coming from ?<BR><BR>

(d) Answer must come from diagram.<BR>

Each diagram has 1N  and 2 H in common, and one other thing.<BR>

<BR><BR>

18.  (a) nitrogen dioxide at 21; sulphur dioxide at  -10; ammonia at -33<BR><BR>

(b) One of them is liquid at -25<SUP>o</SUP>C while two are gases.<BR>

Where will -25<SUP>o</SUP>C fit in between  these three figures.<BR>

There is only one answer.<BR><BR>

<BR>

19. (a) Easy to make hard to break  <BR>

Reactive metals make compounds easily.<BR>

<BR>

(b) Underline the chemicals mentioned in the question <BR>

ie copper sulphide <U>CuS</U>    and  sulphur dioxide <U>SO<SUB>2</SUB><BR></U>

<center> Write under this the number of moles </center>

<BR>&#160&#160&#160ie 2 mole of CuS ------&gt; 2 mole of SO<SUB>2</SUB><BR>

<center>Write under this the mass of these moles </center>   <BR>

&#160&#160&#160&#160&#160&#160&#160&#160&#160&#160 2 x (64+32)  ------&gt; 2 x  64<BR>

&#160&#160&#160&#160&#160&#160&#160&#160&#160&#160&#160&#160&#160&#160&#160&#160&#160&#160&#160 192 g  ------&gt; 128 g<BR>

<BR>

(c) What is wrong with exhaust gas ?<BR><BR>

<BR>

20.  (a) Notice that the enzyme does not appear in the chemical equation.<BR>

It has taken part in the reaction but has not been changed by it.<BR><BR>

(b) What experiment measures concentration ?<BR><BR>

(c) When making a statement about a relationship given in a graph you can   usually

frame your answer as follows "As the <CITE>data along the way</CITE>

 increases   then the <CITE>data up the way</CITE>

 increases or decreases (pick one)"<BR>

As temperature increases the enzyme activity  .....   <CITE>does what </CITE>

?<BR>

<BR><BR>

21. (a) Carbon dioxide indicated by lime water turning milky. <BR>

An ion containing C is needed to produce this gas ?<BR><BR>

(b) The blue solution contains Cu<SUP>2+</SUP> <BR>

Changing these to copper atoms would convince.<BR>

<BR><BR>

22.  To calculate the concentration of sodium hydroxide  you need the volume of   sodium

hydroxide (20cm<SUP>3</SUP>) used and the volume (15cm<SUP>3</SUP>) and concentration   (0.1 mol/litre) of hydrochloric acid.

Credit  1999      Hints

                           Almost the answers

                           Answers