National Chemistry

1999 Credit Hints

1999 credit HINTS

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 yes/no ?

conduct when molten yes/no ?

melting/ boiling points high/low

(b) covalent compound: conduct when solid yes/no ?

conduct when molte yes/no ?

melting/ boiling points high/low

A substance will not be covalent and ionic

2. There are two small monosaccharide
two larger disaccharide
and one large polysaccharide.
Identifying these may help.
(a) The single one
(b) C12 - a mid sized pair
(c) The single one

(b) cannot be hydroylesd -ie broken down

3. Get to page 5 - the solubility table
(a) identify one of these as a precipitate
(b) Mixing two of the boxes will give a precipitate
A + B; A + C; A + D; B + C; B + D and C + D must all be tried

4. A time consuming question but should be easy to get correct.
(a) What conditions increase reaction rate ?<
(b) Changing temperature - place the letter of the box under the appropriate temperature
  20oC 30oC 40oC
A C E
B D F

MUST be boxes from different columns ie not C and D

Write the concentrations beside each box letter
  20oC 30oC 40oC
A 1 C 2 E 2
B 2 D 1 F 2

This eliminates some more pairs - cannot be A and C as although different temperatures
they also have different concentrations.
Write the metal beside each letter to eliminate some combinations.

5. (a) definition of isotopes.
At least select two boxes with something in common.
(b) Look in data book for electron arrangement of argon
Then write down the electron arrangement of the six atoms/ions in question.
(c) Calculate the neutrons using the figures in the boxes

6. Lot of information
One of the metals corrodes -
Electrons flow from metal B to metal A - what does this tell you ?
What does 'Fe'rroxyl indicator test for ?
Use page 7 of data book.
(a) Blue colour around metal B due to Ferroxyl indicator.
Which metal is more reactive A or B ?
On question paper circle the most reactive of each pair of metals
(b) Use page 7 of data book

7. TWO correct answers.
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.
Watch for statements that are the opposite of each other - both cannot be correct
and one usually is.
During distillation fractions are separated due to boiling points.
Fraction 6 is darkest deliberately .
A. "most easily" is an extreme - either 6 or 1
B. is fraction 4 bigger than fraction 3 ?
C. is flammability less at 1 ?
D.  fraction 1 is collected first then fraction 4 has lower boiling point than fraction 5
E. Are the smallest molecules collected first ?

8. TWO correct answers.
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.
Watch for statements that are the opposite of each other - both cannot be correct and one usually is.

(a) Each statement must be TRUE for both
Always worthwhile knowing formula of common acids
A. do all acids react with magnesium ?
B. do all acids have a pH less than 7 ?
C. do acids not conduct electricity ?
D. do all acids produce Cl2(g) ? Must have Cl present
E. do acids have equal numbers of H+and OH- ions

(b) Each statement must be TRUE for Na+Cl- and FALSE for H+Cl-
Use information gathered for part (a) to help.
A. do all both react with magnesium ? Acids do.
B. acids and salts have different pH
C. Ionic solutions conduct electricity ? yes
D. do both produce Cl2(g) ? Must have Cl- present.
E.. both have equal numbers of H+ and OH- ions. Acids excess H+

part 2

9. (a) When making a statement about a relationship given in a graph you can usually
frame your answer as follows "As the data along the way increases then the data up the way
 increases or decreases (pick one)"
In this question you need to isolate a "group " ie all group 1 elements
(b) When making a statement about a relationship given in a graph you can usually
frame your answer as follows "As the data along the way increases then the data up the way
 increases or decreases (pick one)"
In this question you need to isolate a "Li to F" in the graph.
(c) In this question you need to identify where calcium will appear.
Page 1 of the data book would help.

10. (a) Electronic configurations on page 1 may help concentrate your mind.
(b) What occurs during oxidation. Try page 7 of data book.

11. (a) count up the atoms from the structural formula.
(b) What is the definition of an isomer.
Write the molecular formula for B
(c) Must be something, present in the compound, with oxygen.

12. Read the question underlining chemicals mentioned so you can then position them
appropriately.

13. (a) Create the repeating unit be changing the C=C to single bond
3 monomer units would be 6 C joined together
(b) Reaction which releases heat (heat is always "therm")
(c) Write the molecular formula C5O2H8
  How much C = mass of carbon   x 100 %
mass of C5O2H8

14. (a) Migration of ions obviously requires potassium nitrate in gel.
(b) Red, green and purple/blue colours should suggest something
Hydrochloric acid and sodium hydroxide should suggest something

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.
(b) (i) Ion electron equations should be copied from page 7 of the data book.
Ag+ ions present at start
This one should make Ag
(ii) Top of page Page 7 shows what type of reactions.

16. (a) How does the structure of the five molecules given affect density.
Effect of more carbons =
(b) Similar question to (a) working in reverse BUT must have 4 carbon atoms and
at least one -OH group.

17. (a) Must be a reason that it is impossible.
(b) ammonia comes from ammonium chloride heated with .
(c) Heat is required at start but not after reaction has started.
(d) Answer must come from diagram.

18. (a) Look at page 6 for the boiling points and write them on the diagram in the
  correct places.
(b) One of them is liquid at -25oC while two are gases.

19. (a) Easy to make hard to break - platinum ore easy to break.
(b) Underline the chemicals mentioned in the question
ie copper sulphide CuS and sulphur dioxide SO2<
Write under this the number of moles ie 2 mole of CuS and 2 mole of SO2
Write under this the mass of these moles
(c) Catalytic converter is found in the exhaust.

20. (a) Notice that the enzyme does not appear in the chemical equation.
(b) Needs to be measurable to get a concentration
(c) When making a statement about a relationship given in a graph you can usually
frame your answer as follows "As the data along the way increases then the data up the way
 increases or decreases (pick one)"

21. (a) What gas is indicated by lime water turning milky.
What ion would produce this gas ?
(b) The blue solution contains Cu2+

22. To calculate the concentration of sodium hydroxide you need the volume of sodium
hydroxide used and both the volume and the concentration of hydrochloric acid.

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