National Chemistry

2000 Credit HINTS

1. Obviously you turn to page 1 of the data book
(a)The symbols are for atoms with Atomic Number 13, 11, 15, 12, 8, and 56 respectively.
Find these in your data book page 1
remember to pick 2 boxes

(b) What type of elements form covalent bonds ?
 Where in the Periodic table do elements that form covalent bonds come from ?
 remember to pick 2 boxes

(c) Ionic compounds - write the charges for each ion into each box - find these in the data book
The ions for boxes A, B and D can be found on page 7
The ion for box F should be obvious if you compare its position in the Periodic table - could help with Q1(a)
The ions for boxes C and E need to be worked out from the electronic configuration on page 1 or from the position in the Periodic Table
You then need to look at the given formula X2Y and fit all of your information together.
remember to pick 2 boxes

2. (a) C12H22O11 is a carbohydrate - monosaccharide, disaccharide or polysaccharide ?
remember to pick 2 boxes

(b) Does not react with iodine therefore not ?
Does not react with Benedicts therefore not ?
The carbohydrate that fails both tests ?

3. With hydrocarbon structural formula in the boxes it is usually useful to add in the molecular formula
(a)but = ? how many carbon atoms in the molecule
  polymer means molecule is -------?------
(b) Definition of isomer required - compare molecular formulae

4. "statement(s)" in the credit paper usually means TWO correct answers
In this style of question then there are TWO correct answers and three wrong answers
- work through each statement individuaally.
Watch for statements that are the opposite of each other - both cannot be correct and one usually is.

A. What is reduction ? try page 7 of data book
B. Does gaining electron affect Atomic Number ?
C. Is the bromide ion negatively charged ? try page 7 of the data book
D. have the energy levels increased ? try page 1 of the data book
E. are bromine and argon almost the same electronic configuration already ?
remember to pick 2 boxes

5. You need to be able to recognise chemical reactions . This is an deal question where eliminating wrong answers is a great help. For example hydrolysis, fermentation and condensation are reactions found in Organic Chemistry (Carbon compounds to you).
(a) Is "glucose to starch " a carbon compound reaction ?
(b) Actual equations can help identify the reaction. Look carefully at what changes have occurred.
"statements" suggests TWO answers - are there any boxes which describe the same reaction ?
remember to pick 2 boxes

6. Corrosion question.
 "statement(s)" in the credit paper usually means TWO correct answers<BR>
In this style of question then there are TWO correct answers and three wrong answers - work through each statement individuaally.
Watch for statements that are the opposite of each other - both cannot be correct and one usually is.
Why is the Mg attached to the Fe ? To protect it.

A, Can Mg be oxidised ? try page 7 of Data Book
B. Does this stop magnesium corroding ?
C. Would this make Fe corrode faster than Mg
D. Mg protects the iron by "sacrificial protection" ?
E. Electrons move from Fe to Mg

7. A common question used to cover many parts of the syllabus.
Worthwhile identifying
 (i) that acids appear in boxes A, B, C and F
(ii) that metals appear in boxes A and C - then check if all metals used actually react
(iii) carbonates in E and F - may indicate CO2

(a) "pairs(s)" in the credit paper usually means TWO correct answers
  water often produced when acids react
(b) one of these pairs do not react - look for unreactive metal (use page 7 of data book)

8. (a) In this style of question then there are TWO correct answers and three wrong
answers - work through each statement individually for each of the acids (hydrochloric
and sulphuric acids looking for TRUE for each acid.

A. get the formula for each - use page 4 of data book to help
B. what salts are produced by each acid ?
  what is a precipitate ?
  are the barium salts both insoluble ? - try page 5 of data book
C. does diluting an acid increase or decrease pH ? if true then it would be true for both
D. does electrolysis of an acid produces hydrogen gas ? if true then it would be true for both
E. depends on formulae - NaOH neutralised by 0.5 of acid

(b) In this style of question then there are TWO correct answers and three wrong answers
- work through each statement individuaally for each of the acids (hydrochloric and sulphuric acid)
Watch for statements that are the opposite of each other - both cannot be correct
and one usually is.

Can discount C and D as they would be true for both !
A. get the formula for each - use page 4 of data book to help
B. what salts are produced by each acid ?
  What is a precipitate ?
  Are the barium salts both insoluble ? - try page 5 of data book
E. depends on formulae - NaOH neutralised by 0.5 of acid

Part 2

9. (a) Use the information in the table comparing aluminium and copper - something that aluminium is better for ?
(b) Use the information in the table selecting something that iron is best for.

10. (a) You should have had plenty of practice at these. the figures to put in the table must bare some relationship to those already being used in the question.
(b) Well known definition - the question tells that all Si and 14 but different top number !
(c) Average is 28.1 - must be associated with the numbers 28, 29 and 30

This might remind us that the top number is the mass number

11. (a) Obviously turn to page 6 of the data book
Look up boiling point of pentane and position in the correct range

(b) Fractions separated by boiling point because of ........?
(c) (i) Why is crude oil refined ? What use is made of crude oil after refining ?
  (ii) Another important definition. What else can it allow if it speeds up the reaction ?

12. (a) Isolate the repeating unit.
A monomer will have two carbon atoms joined by a double bond and must look similar to part of the chain shown.
(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) Use the data book page 1 to help construct the formula
(b) The boxes at the top right contain the reactants and products - Make up a word
equation.
Gas X must be an element(s) present in the process later on - ie not gold
(c) Again look at the boxes what is happening.
(d) You only know one shape - it must contain 1 x Si and 4 x Cl bonded together
(e) Remember that you can only put figures in front of the formulae - you CANNOT change any of the formula you have been given.

14. (a) Straight forward KU
Electricity being produced.
The name tells you.
(b) Turn to page 5 of the data book
Need a TIN compound to make a solution
(c) Look at page 7 of the data book.
To get a higher voltage -is it a metal closer to magnesium or a metal further away in the electrochemical series
Do not pick a very reactive metal (eg sodium) as it would react violently when put
into solution. Why would you not select mercury ?

15. (a) The figures required for the calculation are
- volume of air at start, which is giveen in the box
- reduction in volume of air - which has to be calculated using the figures in the box
(b) Why does it seem the chemical reaction is repeated by passing the AIR back and forward over the hot copper ?
(c) What would carbon do in hot air that copper does not ?

16. (a) d.c. is direct current - what does this means happens ?
(b) label both axes; put on the scale; make sure over half the graph paper is used; make sure it is a line graph.
(c) Read off the figure on your graph for volume produced in ten minutes
(d) Copy the ion electron equation from page 7 of the data book which produces the hydrogen gas

17. (a) You probably only know a few industrial processes and certainly only two associated with nitrogen chemistry.
(b) Higher temperatures cannot be good or needed if they are not used.
(c) What does the world need ammonia for ?
 What was nitrogen chemistry about ?

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 and water H2O
Write under this the number of moles ie 1 mole of propane and 4 mole of water
Write under this the mass of these moles<

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
try to make at least 4 points

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 thedata in the second column increases or decreases (pick one)"
(i) In this case the first column moves methanol---> ethanol ---> propanol ---> butanol  which in fact is not a value. You have to translate this into the number of carbon atoms in each molecule to satisfy the question. As you move down this column (increase or decrease ?) then the heat released increases/decreases

(ii) Where would pentanol appear in the first column ?
You would usually be adding a substance to the column at the top or bottom - so moving below 726 or above 2665 would seem the possible answers.

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