Spm Che3 Q&a (n9)

CHEMISTRY PAPER 3 2008 NEGERI SEMBILAN 1. There are two different experiments : A and B in this question. Experiment A is used to determine the empirical formula of an oxide of copper, which is reduced in a stream of dry hydrogen gas. Diagram 1 shows the steps used to carry out experiment A.

(a) Based on Diagram 1, complete Table 1. Item Combustion tube + porcelain dish Combustion tube + porcelain dish + oxide of copper Combustion tube + porcelain dish + copper Copper Oxygen Table 1

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[3] Mass / g

(b) Based on Table 1, calculate the empirical formula of this oxide of copper. [relative atomic mass: Cu=64; O=16] [3]

(c) Complete colour change of the oxide of copper requires 10 minutes of heating. State the colour change. [3] ………………………………………………………………………………………. (d) State the inference based on the answer in 1(c) [3] ………………………………………………………………………………………. (e) Write the chemical equation for the reaction in Experiment A. [3] ………………………………………………………………………………………. (f) The oxide of copper is reduced to copper in step B. State the operational definition for the reduction. [3] ………………………………………………………………………………………. ………………………………………………………………………………………. ………………………………………………………………………………………. Experiment B is carried out to determine the position of hydrogen in the reactivity series of metals. Only step 3 of experiment A is carried out using different metal oxides to replace the oxide of copper. The oxides used are • • •

Lead(II) oxide Iron (II) oxide Magnesium oxide

(g) State the variables used in Experiment B.

[3]

(i)

Manipulated variable:………………………………………………

(ii)

Responding variable :………………………………………………

(iii)

Fixed variable :…………………………………………………….

(h) Write the hypothesis for Experiment B.

[3]

……………………………………………………………………………………….

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(i) Based on the inferences given, state the colour change for each part of Experiment B, in the table below. [3] Experiment B 1. between hydrogen gas and lead(II) oxide 2. between hydrogen gas and iron(II) oxide 3. between hydrogen gas and magnesium oxide

Colour change [if any]

Inference Hydrogen reduced lead(II) oxide to lead Hydrogen reduced iron(II) oxide to iron Magnesium oxide is not reduced

(j) Metal Q is placed below magnesium but above iron and lead in the reactivity series of metals towards oxygen. Predict whether the oxide of Q can react with hydrogen gas. Suggest a metal for Q. [3] ………………………………………………………………………………………. ………………………………………………………………………………………. (k) Classify the following metal ions in the oxides below according to their oxidation number. [3] • • • •

Copper(II) oxide Lead(II) oxide Iron(II) oxide Magnesium oxide

Oxidation number +2

+3

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2. Diagram 2 shows two pieces of oil-stained cloths soaked in two separate beakers. Beaker I is filled with 100 cm3 of soap dissolved in hard water. Beaker II is filled with 100 cm3 of detergent dissolved in hard water. Both pieces of cloth are identical in size and stained with five drops of oil each.

You are required to plan an experiment to investigate the effectiveness of the cleansing action of two types of cleaning agents in hard water. Your planning should include the following: (i) (ii) (iii) (iv) (v) (vi)

Aim of experiment All the variables Hypothesis List of materials and apparatus Procedure Tabulation of data

END OF PAPER

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[17]

ANSWERS 1. (a) 195.0265 197.0572 196.6362 1.6097 0.421 (b) Cu 1.61 1.61/64 0.025 1

O 0.42 0.42/16 0.025 1 CuO

(c) Black turns to brown (d) oxide of copper becomes copper (e) CuO + H2 Æ Cu + H2O (f) Hydrogen gas is passed over the heated black oxide of copper until it turns brown. (g) (i) types of metal oxides (ii) colour change of product /flame or glow of product (iii) hydrogen gas (h) different types of metal oxides react differently with hydrogen gas (i) yellow to grey brown to grey remain unchanged/ no colour change (j) no reaction zinc/ Zn or aluminium/ Al (k) +2 Cu2+ Pb2+ Mg2+

+3 Fe3+

2. (i)

Aim of experiment To compare/ investigate the effectiveness of the cleansing action of soap and detergent in hard water

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(ii)

All the variables Manipulated variable: type of cleansing agents Responding variable : effectiveness of cleansing action in hard water Fixed variable : volume of water / amount of oil/ type of cloth

(iii)

Hypothesis Detergent is more effective as cleaning agent than soap in hard water.

(iv)

List of materials and apparatus Materials : detergent, soap, hard water , oil , cloths, dropper Apparatus : beaker, glass rod,

(v)

Procedure 1. Add 5 drops of oil on a piece of cloth 2. Add soap to a beaker containing hard water. 3. Put the piece of oil-stained cloth into the beaker. 4. Stir the solution with a glass rod. 5. Record the observation 6. Repeat steps 1-5 using detergent to replace soap.

(vi)

Tabulation of data Type of cleansing agent Soap Detergent

Observation

END OF MARKING SCHEME

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