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SUTD Chemistry Problem Set #1
st
Due date: 21 May by noon
This problem set will be graded out of 54 points. Question
Points
Question 1 (out of 10 points)
1
/10
Do you remember the Systeme International d’Unites” (SI) units and
2
/10
3
/12
4
/5
5
/3
(a) Length
6
/8
(b) Mass
7
/6
Total
/54
symbols we use for chemistry? Fill in the following chart. Quantity
Unit
(c) Time
Symbol
(d) Temperature (e) Chemical Amount of Substance Question 2 (out of 10 points)
Fill in the following chart with the correct prefix and symbol Fraction -2
Example: 10
103 10-6 10-9 10-3 1012
Prefix
Symbol
Answer: centi-
Answer: c
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Question 3 (out of 12 points)
Do you remember your units and conversions? Answer the following (each one is worth 2 points): (a) Convert 220 K into C (b) Convert 42.4C into K (c) Convert 1.28 10-7 m into nm (d) Convert 0.566 Å3 to m3 (e) Convert 4.41 × 10-19 J into eV (f) Convert 0.12 moles into number of atoms Question 4: (out of 5 points)
The poisonous gas hydrogen cyanide (HCN) is produced by the high-temperature reaction of ammonia (NH3) with methane (CH4). Hydrogen is also produced as a byproduct. (a) Write a balanced chemical equation for the reaction that occurs (b) Suppose 500.0 g of methane is mixed with 200.0 g of ammonia. Identify the reactant in excess.
(c) Calculate masses of the substances present after the reaction is allowed to proceed to completion. Question 5: (out of 3 points)
An unknown compound weighing 100.0 mg contains only C, H, and O. It is burnt in an excess of O 2. The only products are 239.9 mg of CO 2 and 49.0 mg of H 2O. What is the empirical formula of the unknown compound? The atomic masses of H, C, and O are 1.00794, 12.0107, and 15.9994. Question 6 (out of 8 points)
Automatic doors open when a beam of infra-red radiation is directed onto a photoelectric cell. The beam is arranged so that it breaks when someone approaches the door and stops the radiation from hitting the photoelectric cell. A signal is sent to the door opener by a sensor when the current in the circuit stops. The infrared radiation has frequency of 1.32 × 10 13 Hz. (a) Calculate the energy of the infrared photons.
(2 points)
(b) One of the materials for the emitter plate has a work function of 8.94×1021J. Calculate the threshold frequency for this plate. Use the value of the threshold frequency to explain whether this material would be suitable to function as an emitter. (2 points)
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(c) The material that is finally chosen for the emitter plate has a threshold frequency of 9.85×1012 Hz. Calculate the maximum kinetic energy of the photoelectrons that are ejected using the infrared radiation. (2 points) (d) the maximum velocity of the ejected electrons from part (c).
(2 points)
Question 7 (out of 6 points)
You have a piece of tungsten metal that has a work function ( ) equal to 4.55 eV. What is the maximum number of photoelectrons that can be ejected from the metal surface when it is illuminated with a 10.0 mW laser operating at the following wavelengths? (a) (b)
