CONTEST19

ROUND 1
1. Endothermic reactions are not meant to occur spontaneously. Why?

ANSWER: The products of endothermic reactions are thermodynamically less stable

than the reactants

2. Exothermic reactions are supposed to occur spontaneously but some do not. Why?

ANSWER: In such cases the activation energy is high and external assistance is
required to initiate the reaction.

3. Define enthalpy of formation of a substance.

ANSWER: Is the enthalpy change when a mole of a substance is formed from its
constituent elements in their standard states at 298K and 100 kPa.

4. The eggs of female toads are surrounded by a jelly substance as they are laid. Give one function of
the jelly substance.

ANSWERS:

a. It protects the eggs from infection by bacteria

b. It enables the eggs to float on the water surface.

c. The unpleasant and slippery nature prevents predators from grasping and
eating them

d. It prevents overcrowding of the eggs thus making room for development

and better circulation of oxygen

5. What is the distinction between gauge pressure and absolute pressure?

ANSWER: Gauge pressure is the difference between absolute pressure and atmospheric
pressure
6. What does a negative gauge pressure signify?

ANSWER: The pressure is lower than atmospheric pressure

7. Which of the following is usually gauge pressure: blood pressure, atmospheric pressure, tire pressure?

ANSWER: Blood pressure and tire pressure

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
8. A circle of radius 7 cm is cut from a square of side 15 cm. Find the remaining area. [ Take 7

ANSWER: 71 cm2 [Area = 152 – (22/7)72 = 225 – 22(7) = 225 – 154 = 71]

9. Find the area of a sector of a circle of radius 7 cm that subtends an angle of 3 radians at the center.
ANSWER: (77/3) cm2 [ Area = ½ 72 x (22/7)(1/3) = 7 x 11 x(1/3) = 77/3]

radians
10. Find the perimeter of a sector of a circle of radius 21 cm and sectoral angle 3 .
22
P 2r  r 2 21  21 42  22 64
ANSWER: 64 cm [ 3 7 ]
11. If a substituent in an organic compound is ‘decyl’ what is the formula of the substituent?

ANSWER: C10H21—

12. If a substituent in an organic compound is ‘benzyl’ what is the formula of the substituent?

ANSWER: C6H5CH2—

13. If a substituent in an organic compound is ‘oxo’ what is the formula of the sustituent?

ANSWER: --C=O

14. State the symbol that is used to describe a superior ovary in a floral formula.

ANSWER: (capital G with a bar below the G)

15. State the symbol used to describe a female flower in a floral formula.

ANSWER:

16. State the symbol used to describe a bisexual flower in a floral formula.

ANSWER:

17. What is the relationship between force and displacement for an object undergoing simple harmonic
motion?

ANSWER: : force is the negative product of displacement and spring constant

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 18. What is the relationship between acceleration and displacement for an object undergoing simple harmonic
motion?

ANSWER: : acceleration is the negative product of angular frequency squared and

displacement

19. What is the relationship between angular frequency and spring constant for an object of mass
undergoing simple harmonic motion?

ANSWER: : angular frequency is square root of the ratio of spring constant to mass

Solve the quadratic equation

20. 3x2 + 19x – 14 = 0

ANSWER: x = 2/3, x = -7 [3x2 + 21x – 2x – 14 = 3x(x + 7) – 2(x + 7) = (3x – 2)(x + 7)

= 0, x = -7, 2/3 ]

21. 8x2 – 22x + 15 = 0

ANSWER: x = 3/2, x = 5/4 [8x2 – 12x -10x + 15 = 4x(2x – 3) -5(2x – 3) = (4x - 5)(2x
– 3) = 0, x = 3/, 5/4]

22. 3x2 – 13x – 10 = 0

ANSWER: x = -2/3, x = 5 [3x2- 15x + 2x – 10 = 3x(x – 5) + 2(x – 5) = (3x + 2)(x – 5)

= 0, x = -2/3, 5]

23. Give the products of decomposition when solid Li2CO3 is heated.

ANSWER: Li2O and CO2

24. Li2O is formed when solid is Li2CO3 heated, why?

ANSWER: Higher lattice energy in Li2O than in Li2CO3 because of the smaller O2- ion.

25. Why is NaOH ionic but Al(OH)3 is partly ionic and partly covalent?

ANSWER: Al3+ ion quite small and polarizes the OH- ion

26. The adult male lizard differs from the female lizard in a number of ways. State one difference
between the adult male lizard and the female lizard.

ANSWERS:

a. The male is bigger and more brightly coloured.

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 b. The male has more prominent nuchal crest and gular fold.

c. The cloacal opening of the male is surrounded by a row of hard rounded

scales (Pre-anal pads)

d. The male has bright orange head, dark blue or black trunk and a tail
which is blue at the base and orange in the middle and black at the tip/

e. The female’s head is light brown with green spots; her trunk and tail are
light brown and the sides of the trunk have large yellow patches.

27. Oil flows through a pipe of cross-sectional area at an average velocity of . What is the
volume flow r ate in ?

ANSWER:

28. What is the average fluid velocity in a pipe of cross-sectional area which discharges of
fluid in ?

ANSWER:

29. What is the cross-sectional area of a pipe which discharges of fluid in when the average
fluid velocity is ?

ANSWER:

Find the domain of the function

30. f ( x)  1  2 x

ANSWER: {x : x ½ } [1  2 x 0  2 x 1, x 1 / 2]

x 1
f ( x) 
31. x2  x  6

ANSWER {x : x 2, x  3} [ x2 + x – 6 = (x – 2)(x + 3) , denominator not zero

hence result]

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 1
f ( x) 
32. x 1

ANSWER: {x : x > 1} [denominator should be positive hence (x – 1) > 0 and x > 1]

33. Calculate the volume of 0.75 moldm=3 solution of HCl that will be required to neutralize 25 cm3 of
0.06 moldm-3 of Na2CO3 in a titration using phenolphthalein as indicator.

ANSWER: HCl + Na2CO3 → NaHCO3 + NaCl

0.075, V? 25, 0.06

(25 x0.06)/0.075 x V = 1/1

Hence V = 20 cm3

34. Calculate the volume of 0.16 moldm-3 solution of HCl that will be required to neutralise 20 cm3 of
0.10 moldm-3 Na2CO3 in a titration using methyl orange as indicator.

ANSWER: 2HCl + Na2CO3 → 2NaCl + CO2 + H2O

0.16, V? 20, 0.10

(0.16 x V)/0.10 x 20 = 2/1

Hence V = 25cm3

35. A solution containing a mixture of Na2CO3 and NaHCO3 is analysed as follows: 20 of the solution
requires an average 10.5 cm3 of 0.10 moldm-3 HCl solution using phenolphthalein as indicator. A
second set of titrations using 20 of the solution requires an average of 25.6 cm3of the same HCl
solution, using methyl orange as indicator. Calculate the volume of the HCl solution that
neutralises the NaHCO3 alone.

ANSWER: Volume required to neutralize all Na2CO3 = 2 x 10.5 cm3

Volume required to neutralize only NAHCO3 = 25.6 – 21 cm3

= 4.6 cm3

36. The distribution of organic compounds in plants is called

ANSWER: Translocation

37. Which cells of the phloem tissue is responsible for the flow of organic compounds?

ANSWER: Sieve tube

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 38. Name the cells that help load organic compounds into the sieve tubes.

ANSWER: Companion cell

39. A object is released from a height of . What is the speed of the object just before it strikes the
ground if acceleration due to gravity is and air resistance is negligible?

ANSWER:

40. What is the greatest height attained by a object projected upward with speed if acceleration
due to gravity is and air resistance is negligible?

ANSWER:

41. What is the initial speed of a object thrown vertically upward which attains a maximum height of
if acceleration due to gravity is and air resistance is negligible?

ANSWER:

42. A car is sold for GHc 46,000 at a profit of 15%. Find the cost price of the car.

ANSWER: GHc 40,000 [ Cx115/100 = 46,000, hence C = 46000 x 100/115 = 40,000 ]

43. A laptop is listed at GHc1,000. It is sold at a discount of 16%. Find the sales price

ANSWER: GHc 840 [ 1000 x 84/100 = 840 ]

44. A television is sold for GHc 800 at a loss of 20%. Find the loss in GHc.

ANSWER: GHc GHc 200 [ Cost price C = 800 x 100/80 = 1000, hence loss =
1000 – 800 = 200 ]

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 PROBLEM OF THE DAY

A block of iron at a temperature of is immersed in an ice-water bath

containing of ice and of water. The specific heat capacity of iron is
, the specific heat capacity of water is and the specific heat
of fusion of ice is .

a. Determine the final temperature of the bath.

b. Determine the minimum quantity of ice at that must added to the bath
before immersion of the block to maintain the bath temperature.

SOLUTION:

a. The heat released when the iron cools to ,

, is larger than the heat
required to melt all the ice, which is . So the ice melts
and the additional water warms with the water already present to a final temperature .
Conservation of energy demands

from which one gets

b. To maintain the bath temperature, there must at least enough which just takes up all the heat
from the block. The heat from the block is . This is just enough to melt
. The bath already contains of ice so at
least must be added.

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ROUND 3 – True or False

1. In the Mass Spectrometer ions are produced in the ionization chamber by an electron beam’

ANSWER: True

2. In the Mass Spectrometer, ions are separated according to mass-charge ratio by a magnetic field

ANSWER: True

3. Neon has three natural isotopes and so its mass spectrum will show 3 peaks.

ANSWER: True

4. Whereas chlorine forms several oxides iodine forms only one oxide.

ANSWER: True

5. Chlorine IV oxide should be a paramagnetic compound

ANSWER: True There is odd number of electrons

6. One important industrial use of chlorine is preparation of chloroalkanes.

ANSWER: True e.g. vinyl chloride

7. Viruses are bigger than bacteria

ANSWER: False
8. Viruses have nuclei
ANSWER: False
9. Some viruses can be crystallized like non living chemicals
ANSWER: True
10. Seeds are mature stamens
ANSWER: False
11. Fruits are mature ovaries
ANSWER: True
12. Pollen grains are male gametophytes
ANSWER: True

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13. The function f(x) = x3 – 3x is an odd function

ANSWER: TRUE

14. A quadratic function is an even function

ANSWER: FALSE

15. For an even function, f(-x) = f(x)

ANSWER: TRUE

16. (a – b)3 = a3 – 3a2b + 3ab2 – b3

ANSWER; TRUE

17. a3 + b3 = (a + b)(a2 + ab +b2)

ANSWER: FALSE [ (a +b)(a2 – ab + b2) ]

18. a3 - b3 = (a – b)(a2 + b2)

ANSWER: FALSE [ (a – b)(a2 + ab + b2) ]

19. A Wheatstone bridge can be used to compare electrical resistances.

ANSWER; TRUE
20. At the balance point, the current through any part of the Wheatstone bridge is zero.
ANSWER: FALSE
21. If all the resistances in a Wheatstone bridge are equal, the galvanometer gives maximum deflection.
ANSWER: FALSE
22. The thermal coefficient of superficial expansion is half the thermal coefficient of linear expansion.
ANSWER: FALSE
23. The thermal coefficient of volume expansion is larger than the thermal coefficient of superficial
expansion.
ANSWER; TRUE
24. The thermal coefficient of volume expansion is three times the thermal coefficient of linear expansion.
ANSWER; TRUE

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ROUND 4 – Riddles

Riddle #1

1. I have atomic number96 and atomic weight 247.

2. I was discovered in Chicago in the United States of America in 1944.
3. I have 13 known isotopes.
4. I was formed by helium bombardment of a certain nuclide.
5. In the Periodic Table I come after the element americium.
6. I was named after a French couple who made a name in radiochemistry.
WHO AM I?
ANSWER: CURIUM//Cm

Riddle #2

1. You may call me a smaller division of a family.

2. My members have very similar features and are closely related.

3. In spite of that, they cannot interbreed to produce offspring..

4. In fact, I am one of the seven major ranks into which taxonomists classify living organisms.

WHO AM I?

ANSWER: Genus/Genera

Riddle #3
1. I am a phenomenon associated with waves.

2. I am associated with the frequency of a wave.

3. Because of me, the pitch of the horn of an approaching car appears to drop as the car passes you.

4. I am named after Christian Doppler.

WHO AM I?

ANSWER: Doppler effect

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Riddle #4

1. I am composed of various horizontal arrays of numbers but I am not a sequence.

2. Each array begins and ends with 1.

3. I am triangular but not in a strict geometric sense.

4. My name suggests I am a special triangle.

5. My numerical components are the coefficients in a binomial expansion.

6. Remember, 1, 2, 1 ; 1, 3, 3, 1; etc.
WHO AM I?
ANSWER: PASCAL’S TRIANGLE

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