Answers
|
Question |
Answer |
Question |
Answer |
|
27 |
5 |
33 |
1 |
|
28 |
4 |
34 |
3 |
|
29 |
5 |
35 |
3 |
|
30 |
4 |
36 |
2 |
|
31 |
5 |
37 |
3 |
|
32 |
1 |
38 |
5 |
Explanation
You should know your fractions of units now (i.e. mM = 10-3 M). One of the objectives of these MCQs is to make sure you have them at your fingertips. Deci is 10-1 (1 dm = 100 cm)
One of the rules of algebra that you should be familar with is that (10x)y
= 10x.y
So wiith respect to question 27, 1 cm = 10-2 m. Thus 1 cm3
= 1 x (10-2)3 m3 = 10-2x3 m3=
10-6 m3. Likewise, in question 28, 1 cm2 = 1 x
(10-2)2 m2 = 10-4 m2.
For questions 32 and 33, the equation "concentration = amount ÷ volume" has been incorrectly manipulated. It is easy to remember this equation if you think about units. An example of a concentration is moles litre-1 (molar), which is the amount of substance in a known volume. By rearranging the equation, volume = amount ÷ concentration (not volume = concentration ÷ amount as in question 32), and amount = concentration x volume (not amount = concentration ÷ volume as in question 33).
Q (34 & 36) A ml is cm3. A ml is a unit of volume (10-3 litres). Therefore ml3 = cm9 which would require several new dimensions!
Q (35) Acceleration is measured in distance per unit time per unit time, not mass per unit time per unit time.
Q (38) The rates of chemical reactions are usual given in an amount
of product produced per unit of time. Ans 5 is the rate in mmoles
per hour, and so the correct answer. Ans 1 is a unit of speed. Ans
2 nonsensical, as it is a unit of distance (the small m is the abbrevation of
metre) per litre per min. Ans 3 & 4 are concentrations - they have no
time contingent.