Solved Chemistry Questions For University Freshers
Take the atomic weight of elements as follows C =12.011; H =1.00794; O =15.9994; N = 14.01.
Q1 (a) Your friend served you cup of tea. He told you that he used 0.024mol of table sugar (Sucrose C12H22011) in the tea he made. Calculate the mass of sugar he used in making the tea
Q1(a). (Mole) n=Mass (C12H22O11=342gmol-1).
: Mass =nmolar mass
(b)i. If he makes choice to use aspartame C14H18O2N5 , an artificial sweetener instead, in his tea. The content of aspartame is 40mg (measured in two significant figures). Calculate how many moles of aspartame contained in the packet.
Mass=40mg=40 10-3g of sweetener
Molar mass (C14H18O2N5) =288gmol-1
(No of moles) n =
= 1.410-4 moles
No of moles of Aspertame in the packet is 1.410-4 moles.
Q1b(ii) The mass of aspartame that would give 0.0120 mol is ? How many packets is this?
Mass = No of moles Molar mass
Xpacket=86.4 86 packets.
Q1c. From the equation below, derive the equation from first principle (half- life of radioactive materials)
Q1c. It is a first order reaction
r = K[A]1---(1) Rate of reaction
r1= d[A]--- (2)instantaneous rate
d[A] =-kdt (integrate both sides) [A]t
ln[A]t –ln[A]0 =-K(t-0)
Kt = ln[A]0 –ln[A]t
(During half time t= t) [A]t =0
(Q1d) list and discuss any five (5) differences between nuclear reactions and chemical reactions
Terms Nuclear reaction Chemical reactions
Released absorbed large amount of energy
Released or absorbed small amount of energy
Tsotopes of the element
Show unidentical behavior
Show identical behaviour
Nucleus of the atoms are affected
Only the electronic structures of the atoms are affected
Results in conversion of one element to another
Does not result in the formation of new element
Its not a function of its state of chemical combination
It’s a function of its state of chemical combination.
Q1e. Applications of radio isotopes
Radio carbon dating – It is widely used by archaeologists to date articles composed of organic material e.g wood. Radio carbon dating of archaeological artifacts depends on the slow and constant production of radioactive C-14 in the upper atmosphere by neutron bombardment of nitrogen atoms
Food preservation-Foodstuffs are irradiated by a beam of -rays which kill any bacteria present without imparting heat that could denature the food . However, there are concerns of food safety.
Blood flow monitoring-Sodium -24 (used as Nacl solution) is used to discover blood flow obstructions (blood clot) and other circulation disorders
Diagnosis/Treatment of thyroid disorders. Iodine -131 is used in the diagnosis ad treatment of disorders of the thyroid gland. Here, the patient is given low dose of the radioactive Iodine as Na. The radioactive iodine concentrates in the thyroid gland and activity measured.
Q2a. Having far spent your feeding money, you considered ‘smoking garri’ with your 3 roommates by ‘soaking’ 960g of garri in a bowl with only 60 milligrams of sugar (sucrose, C12H22O11) left in the room, Assuming the garri was mixed properly with the sugar before water was added, calculate the concentration of sugar used in ppm (weight per weight on dry weight basis)
Q2a. Solution: C =
= 1.83 10-6
= 183 ppm
(2b) An ancient wood artifact has a specific activity of 9.14d/min-g how old is the artifact? Assume the ratio of 12C/14C in a living plant has specific activity of 15.3d/min-g
(2b) solution: =
M = M1(15.31)
(2d) A bottle of wine of volume 750ml is labeled “ 10.5 % alcohol by volume , what is the volume of alcohol in the wine?
(2d) Solution: Volume of alcohol =
(2e) The explosive trinitrotoluene (TNT) has the composition 37.1% C, 2.22% H, 18.50% N and 42.42% O what is the empirical formula of TNT?
(2e) Solution: C H N O
2.33 1.68 1 2
T N T Empirical Formula C2H2N1O2