SIR MICHELANGELO REFALO SIXTH FORM Half-Yearly Exam 2016

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SIR MICHELANGELO REFALO SIXTH FORM Half-Yearly Exam 2016 Subject: Chemistry Intermediate 1 st Year Time: 2Hrs Name: Useful information: 1 mole of gas occupies 22.4dm 3 at S.T.P Avogadro s constant is 6x10 23.

1 SIR MICHELANGELO REFALO SIXTH FORM Half-Yearly Exam 2016 Subject: Chemistry Intermediate 1 st Year Time: 2Hrs Name: Useful information: 1 mole of gas occupies 22.4dm 3 at S.T.P Avogadro s constant is 6x Universal Gas Constant is 8.314J/K/mol 1atm = 1.05x10 5 Pa Specific heat capacity of water = 4.2kJ/ o C/kg A Periodic Table is attached by the end of this paper. SECTION A: Answer all questions 1. a) Complete the table below: Compound Molar Mass (g/mol) Empirical formula Molecular formula Hydrazine 32 NH 2 Cyanogen 52 CN Benzene 78 CH Nitrogen oxide 92 NO 2 Glucose 180 CH 2 O b. Zinc phosphide is made by heating zinc and phosphorus together. It is found that 9.75 g of zinc combines with 3.10 g of phosphorus. (i) Find the number of moles of: zinc in 9.75 g of the element [5] phosphorus in 3.10 g of the element (ii) Use your answers to question b. to write down the empirical formula of zinc phosphide. (iii) Calculate the percentage mass of phosphorus in zinc phosphide. [5] Page 1 of 7

2 2. 2 g of iron was added to 50 cm 3 of sulfuric acid of concentration 0.5 mol dm -3.After the reaction, when all the hydrogen was evolved, the resulting mixture of iron sulfate solution and unreacted iron was filtered. The unreacted iron was dried and weighed. Its mass was 0.6 g. a. What mass of iron took part in the reaction? [1] b. Change your answer to question a. to moles. [2] c. How many moles of sulfuric acid took part in the reaction? [2] d. Write the equation for the reaction, including state symbols. [2] e. What volume of hydrogen calculated at STP is bubbled off during the reaction? [2] 3. Complete the following table Reaction Substance oxidized Reason to show that named substance has been oxidized 1. Mg + 2HCl MgCl 2 + H 2 2. CuO + H 2 Cu + H 2 O 3. 2Na + Cl 2 2NaCl 4. 2Fe 2+ + Cl 2 Fe Cl - 5. Zn + H 2 SO 4 ZnSO 4 + H 2 4. An oxygen molecule comprises two oxygen atoms held together by a pair of covalent bonds. (i) What do you understand by covalent bonding? [10] [2] Page 2 of 7

3 (ii) Give the name of a substance whose molecule is composed of: two atoms held together by one single covalent bond.. three atoms held together by two single covalent bonds.. (iii) Draw a dot-and-cross diagram showing all electron shells to represent an oxygen molecule. b. Magnesium metal burns in air when ignited to form magnesium oxide which is an ionic compound. Draw a dot-and-cross diagram showing all electron shells to show the bonding in magnesium oxide. [7] [3] c)methane molecules have Van der Waals intermolecular forces. Explain how these are produced.... [3] 5. a) Alpha and beta are two types of radiation. List down their mass, charge if any and relative penetration... [2] b) The atomic number of carbon is 6. An isotope of carbon, of mass number 14 is radioactive by emission of a beta particle. The radioactive decay of the isotope results in the production of element Z. i) What is a radioactive isotope? Page 3 of 7

4 i) Give the number of protons, neutrons and electrons of the isotope 14 C: protons = neutrons =.. electrons =. (3) ii) Write a nuclear equation to show the nuclear decay of 14 C:.. iii) Explain what is meant by the term half-life of a radioactive isotope. Sketch a graph in the space provided next page to back up your reasoning. iv) Explain the use of radioactive isotopes in radiocarbon dating. (5)... (3) 6. a) The atomic number of Br, is 35. Give the full electron configuration (s, p,d) of: Br atom Br - ion. (2). b) Why is Br a p block element?.. (1) c) State whether the following statements are true or false. Give a brief reason for your answer. i) the atomic radius of potassium is greater than that of rubidium.. Page 4 of 7

5 .. (3) ii) the first ionization energy of sodium is greater than that of potassium... (3) iii) the first electron affinity of chlorine is greater that that of iodine... (3) iv) Ca 2+ and Cl - are isoelectronic.. (1) 7. What is mass spectrometry?.. b) Label and annotate (ie write the function of each labeling) the following diagram of a mass spectrometer. [10] Page 5 of 7

6 8. Chlorine gas can be produced by heating calcium hypochlorite, Ca(OCl) 2, in dilute hydrochloric acid. Ca(OCl) 2 (s) + 2HCl(aq) Ca(OH) 2 (aq) + 2Cl 2 (g) a) Calculate the mass of calcium hypochlorite that would be needed to produce litres of chlorine gas at STP. (4) b) Find the number of negative ions needed in calcium hypochlorite to produce litres of chlorine gas at STP. (4) c) List one precaution that must be carried out when heating calcium hypochlorite. (2) d) Give two uses of the chlorine. (2) Section B: Answer ONE question from the following Total: 100 marks 9. The chemical name of washing soda is hydrated sodium carbonate. (Na 2 CO 3.xH 2 O). In a titration experiment to find the value of x, a student found that 2 g of the hydrated compound exactly neutralized 14 cm 3 of hydrochloric acid of concentration 1 mol dm -3. a. Describe how this titration can be conducted in a school lab. Your answer should include: a simple diagram of the apparatus, labeled with 2 main items of lab. equipment required. the name of a suitable indicator. one essential precaution required for accurate titre values. [6] b. Write a balanced equation for the reaction, including state symbols. [2] c. How many moles of hydrochloric acid were neutralized? [2] d. How many moles of sodium carbonate were used for this neutralization? [1] e. Find the mass of sodium carbonate in g equivalent to the answer you found in question d. [3] Page 6 of 7

7 f. What mass of the hydrated sodium carbonate used in this experiment was water? [1] g. Change your answer to question f. to moles of water. [2] h. Calculate how many moles of water are there in 1mole of hydrated sodium carbonate. [2] i. What is the value of x in the formula Na 2 CO 3.xH 2 O? [1] OR 101.a) Distinguish between covalent and dative bonding. Include a diagram as an example for each type of bonding. (5) b) Explain how the VSEPR theory is used to determine the shapes of covalently or datively bonded molecules. In your answer give examples of molecules with three and four bonding pairs of electrons. (15) Total:20 marks Page 7 of 7

2. Relative molecular mass, M r - The relative molecular mass of a molecule is the average mass of the one molecule when compared with

2. Relative molecular mass, M r - The relative molecular mass of a molecule is the average mass of the one molecule when compared with Chapter 3: Chemical Formulae and Equations 1. Relative atomic mass, A r - The relative atomic mass of an element is the average mass of one atom of an element when compared with mass of an atom of carbon-12