Homework for Week 3

Dear Sec3A,

Things to be done over the weekend:

1. Discussion thread on blog.
2. Worksheet 1 in Chemistry Matters Workbook
   
3. Part of worksheet 2 in Chemistry Matters Workbook(since I haven't finished the topic)

Make sure that at least you do the "test it" section. I will not upload the answers unless everyone has completed the worksheets. To be checked next week during theory lessons. Please help to inform your friends who do not have Macbook.

Chapter 3: Solid, Liquid and Gases

Dear Sec3A,

Please spend sometime to browse through the online resources that I've listed:

A Closer Look: Scientific Models
http://www.learner.org/courses/essential/physicalsci/session2/closer1.html

Three States of Matter at Molecular Level
http://mutuslab.cs.uwindsor.ca/schurko/animations/phasesofmatter/phasesofmatter.html

Phases of Matter in Container
http://mutuslab.cs.uwindsor.ca/schurko/animations/phasescontainers/phasescontainer.html

Videos on Changes of States
http://cwx.prenhall.com/petrucci/medialib/media_portfolio/text_images/031_ChangesState.MOV
http://www.educationusingpowerpoint.org.uk/Animations/change%20state.html

Discussion Thread: Pure Water for Singapore (Chapter 2)

Singapore is dependent on other countries for water. However, should these countries decide to stop their supply to Singapore, we would have inadequate supply of drinking water available.

With that in mind, the government has built a desalination plant in Tuas in 2005 which uses the cutting edge technology "reverse osmosis" instead of desalination to obtain drinking water from seawater. This plant supplies about enough water to meet around 10% of the national demand. The production of NEWwater from wastewater also uses the process of reverse osmosis.

Refer to textbook page 25 for the process of reverse osmosis.

Thinking questions:

1. Suggest possible reasons why Singapore decided to use reverse osmosis and not distillation to obtain pure water from seawater.
2. What are some of the strategies that Singapore has taken to diversify Singapore's water resources?

Note: Remember to end your comments with your names. Those (scholars) who do not have a MacBook, please pair up with your peers.

Online Resource:
http://en.wikipedia.org/wiki/Water_resources_of_Singapore
http://en.wikipedia.org/wiki/NEWater

Answers to Practice Questions in Textbook (chapter 1)

Structured Questions (Textbook pg16)

1.(a) Burette
(b) Beaker
(c) Test tube
(d) Measuring cylinder

2. (a) (i) Cubic metre, m3
(ii) It is a very large unit and so is less
convenient for the smaller volumes of
liquids usually encountered in Chemistry
experiments.

(b) (i) Cubic centimetre
(ii) cm3

(c) (i) Burette
(ii) To 0.1 cm3

3. (a) 53 cm3

(b) To the nearest cm3
(At ‘O’ Level, the volume in a 100 cm3
measuring cylinder is measured to the nearest
cm3 though more accurate readings may be
possible, e.g. 53.4 cm3.)

(c) In a burette, the gradations are reversed. The
zero is at the top of a burette, whereas it is at
the bottom of a measuring cylinder.

4. Balance, gram(g)
Thermometer, degree celsius(oC)
Measuring cylinder, cubic centimetre (cm3)
stopwatch, seconds (s)

5. (a) X – temperature sensor/probe.
Y-connector/interface/data logger.
Z – computer.
(b) (i) To measure the temperature of the reaction
mixture
(ii) To display the data on the monitor/screen,
often in the form of a graph
(c) (ii) Vertical axis – temperature. Horizontal  axis – time.

6. (a) During the reaction, the (carbon dioxide) gas
produced escapes from the flask.

(b) (i) Vertical axis – mass. Horizontal axis – time.

(iii) As the speed of the reaction decreases with time,
the gradient of the graph decreases. When the
reaction ends, the graph is flat/horizontal.

Free Response Question (Textbook pg17)

Place a bag of silica gel on a balance connected to a computer to record its mass over a period of time. The mass increases as water is absorbed. Plot a graph of mass against time. When the mass stops increasing, the silica gel is no longer absorbing wate