8/8/2019 Sec 1E Revision WS Answer Scheme

1/5

Ngee Ann Secondary SchoolSecondary One Express

Science Revision Worksheet

Name: . ( ) Class:Sec ..

Topics: Structure of Atoms / Elements & Compounds /Mixtures & Separating Techniques

1 (a) Sodium reacts with chlorine to form sodium chloride as shown in the followingchemical word equation:

sodium + chlorine sodium chloride

Give two ways in which sodium chloride differs from its constituent elements.

Thought process:Sodium chloride is a compound. You need to think of how properties ofcompounds are different from the constituent elements.

Suggested answer:o Sodium chloride is a solid at room temperature, while one of its

constituent elements, chlorine is a gas at room temperature.o Sodium chloride is a edible but both of its constituent elements are

inedible.o Sodium chloride is a non-conductor of electricity or heat but its

constituent element, sodium is a good conductor of heat and

electricity.

(b) Hamid is given four substances W, X, Y and Z.

W blue crystals; X a silvery strip; Y a clear liquid; Z black filings

He combines W, X, Y and Z in different ways and records the results in thetable below. Study his results and answer the questions that follow.

Combination of substances Results

W + Z No heat is given off. The result is a mixture of blue and black.

X + Y Heat and light is given off. A gas is produced.The silvery strip disappears and the result is aclear liquid.

W + Y No heat is given off. The blue crystalsdisappear. The result is light blue, clear liquid.

1

8/8/2019 Sec 1E Revision WS Answer Scheme

2/5

(i) Which substances will likely produced a compound when combinedtogether?

X and Y new product, which is a gas, is formed.

(ii) Which combination will likely result in the formation of a mixture?

W and X

(iii) Which combination will likely result in the formation of a solution?

W and Y

(c) Name the methods used to separate the underlined components in thefollowing mixtures:

(i) Red dye from a mixture of red dye and blue dye.

Chromatography

(ii) Obtaining pure H2O from seawater.

Distillation

2 An extract of the periodic table is shown below. Use the table to answer the followingquestions.

H HeLi Be B C N O F NeNa Mg Al Si P S Cl Ar K Ca Ga Ge As Se Fr Kr

(a) Write the chemical symbols of two other elements in the same period asLithium

Thought process:

Period is a horizontal row in the Periodic Table.

Be and B (Choose any element which is on the same row as Li)

(b) Write the chemical symbols of two other elements in the same group as

2

8/8/2019 Sec 1E Revision WS Answer Scheme

3/5

Lithium.

Thought process:Group is the vertical column in the Periodic Table.

Na and K

(c) Name the element used for the following:(i) killing bateria in swimming pools.

Ans:Chlorine [1]

(ii) making the frame of tennis rackets.

Ans: Aluminium [1](iii) Making fertilisers for farms.

Ans: Nitrogen / Phosphorus [1]

3 State with reasons, whether there is any chemical reaction when the followingsubstances are mixed together. Write down the name(s) of the product(s)formed if there is a chemical reaction taking place.

(a) Magnesium heated in air

When magnesium is heated in air, a bright light is observed. The productobtained is a white powder. Hence, there is a chemical reaction.

Products formed: magnesium oxide[3]

(b) Sodium chloride and water

When sodium chloride is mixed with water, it will dissolve to form saltsolution. Only a physical change has taken place. No new productsformed.

[3]

3

8/8/2019 Sec 1E Revision WS Answer Scheme

4/5

4 Complete the table given below.

Compound Elements present

(a) Nitrogen dioxide

(b) sodium chloride

(c) Calcium carbonate

(d) iron sulfide

nitrogen and oxygen

Sodium and chlorine

calcium, carbon and oxygen

Iron and sulfur

[4]

5 Suggest a method of separation in each of the cases given below.

(a) Tea leaves from tea Filtration [1]

(b) Producing pure water from seawater Distillation [1]

(c) Separating iron from the junkyard Magnetic separation [1]

(d) Separating salt from seawater Evaporate to dryness [1]

(e) Separating petrol from crude oil Fractional Distillation [1]

6

(a) What difference in property allows the pigments in the dye to be separated bythis method?

The difference in solubilities of the pigments in the solvent.

4

8/8/2019 Sec 1E Revision WS Answer Scheme

5/5

(b) The dyes in two food colourings, X and Y were analysed usingchromatography. Five pure dyes (labelled A to E) were tested at the sametime. The final chromatogram is shown.

(i) Which pure dye is present in both X and Y?

D

(ii) Which pure dye is not present in X and Y?

C

(iii) Which dyes could be mixed to make X?

B and D

(iv) What is the total number of dyes which had been used to make X andY?

4 dyes

(c) Besides analyzing food dyes, name one otherapplication ofchromatography.

o Detect the type of ink used in forged cheques

o

In urine analysiso In blood analysis

--- End of Paper ---

5