mid year exam chemistry form 4

Section A [60 marks] Answer All questions in this section. The time suggested to complete Section A is 90 minutes. 1. Figure 1 shows a graph of temperature againt time of subtance Z when it is heated until it boils.

Figure 1 (a) state the physical state of Z at the region (i) PQ : _________________ (ii) QR : _________________ (iii) RS : _________________ (iv) ST : _________________ (v) TU : _________________ [3 marks] (b) Describe the movement of the particles of the pure substance at stage PQ of the curve ? ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ [2 mark] (c) Draw a diagram to show the arrangement of particles of the subtance at stage QR in the box below.

[2 marks] (d) What is the time when the Z begins to boil ? ______________________________________________________________ [1 mark] (e) What is the melting point of Z ? ______________________________________________________________ [1 mark] (f) Explain why the temperature of Z remains constant from time t 1 to t2 ? ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ [2 marks] (g) Sketch the graph obtained when molten Z is cooled from 460 0C to room temperature.

[2 marks] 2. Particle V W X Y Z

Proton number 6 8 8 11 16

Nucleon number 12 16 18 23 32

Electron arrangement

Table 1 Table 1 shows the proton number and nucleon number of five particles represented by the letters V, W, X, Y and Z. (a) Write the electron arrangements of all the particles in Table 1.

[2 marks] (b) What is the number of valence electrons in particle V? ______________________________________________________________ [1 mark] (c) Draw the atomic structure of particle Y.

[2 marks] (d) State the number of electron shells in particles Z. ______________________________________________________________ [1 mark] (e) Explain the meaning of nucleon number. ______________________________________________________________ ______________________________________________________________ [1 mark] (f) What is the number of neutrons in particle Y ? ______________________________________________________________ [1 mark] (g) (i) Explain the meaning of the term ‘isotope’ ______________________________________________________________ ______________________________________________________________ [2 marks] (ii) State a pair of isotopes from the particles in Table 1. ______________________________________________________________ [1 mark]

3.

Figure 2 The figure 2 shown above is used to determine the empirical formula of lead oxide. Lead oxide is reduced using hydrogen gas in the experiment. [Relative atomic mass : O, 16; Pb, 207] (a) State two precautions that must be taken when carrying out this experiment. ______________________________________________________________ ______________________________________________________________ [2 marks] (b) How would you make sure that all the lead oxide has been reduced ? ______________________________________________________________ ______________________________________________________________ [1 mark] (c) The table below shows the result of the experiment. Mass of heating tube + asbestos paper Mass of heating tube + asbestos paper + contents before heating Mass of heating tube + asbestos paper + contents after heating

24.27 g 68.87 g 65.67 g

(i) Determine the empirical formula of lead oxide.

[2 marks] (ii) Write a chemical equation for the reduction of lead oxide to lead.

______________________________________________________________ [1 mark] (d) Write an equation for the burning of excess hydrogen gas at the end of the heating tube. ______________________________________________________________ [1 mark] (e) Can the empirical formula of magnesium oxide be determined using the same arrangement of figure 2 as above ? Explain your answer. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ [2 marks] 4. Figure 3 shows the set-up of apparatus for an experiment to determine the empirical formula of magnesium oxide.

Figure 3 Result : Mass of crucible + lid Mass of crucible + lid + magnesium ribbon Mass of crucible + lid + magnesium oxide

24.0 g 26.4 g 28.0 g

(a) What is meant by empirical formula ? ______________________________________________________________ ______________________________________________________________ [1 mark]

(b) Based on the above results,

(i) calculate the mass of magnesium and the mass of oxygen that have reacted.

[1 mark] (ii) calculate the mole ratio of magnesium atoms to oxygen to atoms. [Relative Atomic Mass : O, 16; Mg, 24]

[1 mark] (iii) determine the empirical formula of magnesium oxide.

[1 mark] (iv) write the chemical equation for the reaction in the experiment ______________________________________________________________ [1 mark] (c) Why was the crucible lid opened once in a while during the experiment ? ______________________________________________________________ ______________________________________________________________ [1 mark] (d) Metal X is places below hydrogen in the reactivity series. You are required to carry out an experiment to determine the empirical formula of the oxide of metal X. The apparatus provided are combustion tube, glass tube, cork, Bunsen burner, and porcelain dish. (i) Draw a labelled diagram of the set-up of the apparatus for the experiment. [2 marks]

(ii) Describle the steps that should be taken to ensure that all the air in the combustion tube has been expelled. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ [3 marks] 5. Figure 4 shows part of the Periodic Table of the Elements. Q, R, T, X and Y do not represent the actual symbol of the elements.

Figure 4 (a) Using the letters in the Periodic Table of the Elements in Figure 4, answer the following questions. (i) Choose an element that is a halogen. ___________________________________________________________ [1 mark] (ii) Which element is monoatomic ? ___________________________________________________________ [1 mark] (iii) Which elements forms an amphoteric oxide ? ___________________________________________________________ [1 mark] (b) Arrange Q, R, T, X and Y according to the increase in size of the atoms. ______________________________________________________________ [1 mark] (c) Write the electron arrangement for an atom of element Q ______________________________________________________________ [1 mark] (d) Write the formula for the ion formed from an atom of element Y. ______________________________________________________________

[1 mark] (e) Why are elements Q and R placed in the same period ? ______________________________________________________________ [1 mark] (f) When a small piece of element T is put into water, TOH solution is formed and hydrogen gas is released. State one observation when red litmus paper is put into the solution. ______________________________________________________________ [1 mark] (g) State the common name of the elements between group 2 and group 13. ______________________________________________________________ [1 mark]

3. Figure 2 shows part of the Periodic Table of Elements.

Figure 2 Based on Figure 2, answer the following questions (a) What is the element represented by the symbol Fe ? ________________________________________________________________ [1 mark]

(b) In Figure 2, mark ‘X’ in the boxes for all the transition elements. ________________________________________________________________ [1 mark] (c) Write the electron arrangement for the Mg and Al atoms. Mg : ___________________ Al : ______________________ [2 mark] (d) (i) Write the chemical equation for the reaction between Magnesium and oxygen gas. ______________________________________________________________ [1 mark]

4

Helium Gas  light  not reactive  colourless

Hydrogen Gas  light  flammable  colourless

(e) Based on the above informations, which gas is more suitable to be used in meteorological ballons ? Give one reason. ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ [2 marks] (f) What is the proton number of element O?. ________________________________________________________________ [1 mark] (g) State one element that are same group as element Helium. ________________________________________________________________ [1 marks] (h) State the elements that are: (i) Metal __________________________________________________ (ii) Non metal __________________________________________________ [2 marks]

5 Section B [20 marks] Answer any one question

The time suggested to answer this section is 30 minutes. 7 (a) Compare the three physical states of matter in terms of particle arrangements, forces of attraction between the particles, kinetic energy of the particles and compressibility. [9 marks] (b) Using

16 8

O and

17 8

O as example, explain what is meant by the terms proton

number, nucleon number and isotopes. [7 marks] (c) (i) The chemical equation below shows the reaction between calcium carbonate and hydrochloric acid. CaCO3 + 2HCl → CaCl2 + CO2 + H2O Given that the relative atomic mass of C=12, O=16, Ca=40 and the molar volume of any gas is 24 dm3 mol-1 at room temperature and pressure. [4 marks]

8. The relative atomic mass of four elements W, X, Y and Z are 23, 40, 35.5 and 16 respectively. Elements W and X are metals whereas elements Y and Z are nonmetals. [Avogadro constant = 6x10 23 mol-1]. Based on the above information, answer the following question. (a) What is meant by the relative atomic mass of an elements ?

[2 marks]

(b) If the molecule of element Y is diatomic, what is the mass of 3.0 x 10 23 molecules of Y ? [2 marks] (c) Calculate the number of atoms in (i) 4.60 g of element W. (ii) 8.00 g of element X. (iii) 14.20 g of element Y

[2 marks] [2 marks] [2 marks]

(d) If the molecule of element Z is also diatomic, calculate the number of molecules in (i) 3.55 g of element Y. [2 amrks] (ii) 4.0 g od element Z. [2 marks] (h) What is the similarity between 40g of element X and 32g of element Z ? [ 2marks]

(g) For each of the following, determine the empirical formula of the compaund formed. (i) 0.1 mole of the compound formed from W and Z has a mass of 6.2 g. [2 marks] (ii) 0.1 mole of the compound formed from X and Z has a mass of 7.20 g. [2 marks]

Section C [20 marks] Answer any one question The time suggested to answer this section is 30 minutes.

9. (a) With a suitable example, explain the following terms : (i) Relative molecular mass (ii) One mole of a subtance (iii) Molar mass (iv) Molecular formula [8 marks] (b) Group 1 elements are known as the alkali metals. Using lithium, sodium and potassium as example, explain how to carry out an experiment to determine the reactions of alkali metal with oxygen. State the precautions that should be taken during experiment and write the observation and balance chemical equations. [12 marks]

10. (a) Explain why the reactivity of Group 17 elements descrease down the group. [5 marks] (b) Using a suitable period in the Periodic Table as an example, explain why the electro-negativity of the elements increase across a period from left to right. [5 marks] (c) Using chlorine, bromine and iodine, explain how to carry out an experiment to determine the reactions of halogens with iron wool. State the precautions that should be taken during experiment and write the observation and balance chemical equations. [10 marks]