Practice Chemistry Induction day test questions 2016

Transcription

1 Practice Chemistry Induction day test questions 206 Q.Magnesium oxide nanoparticles can kill bacteria. The figure below shows the percentage of bacteria killed by different sized nanoparticles. Size of nanoparticles in nanometres (a) (i) Give two conclusions that can be made from the figure above. (2) (ii) Points are plotted for only some sizes of nanoparticles. Would collecting and plotting data for more sizes of nanoparticles improve the conclusions? Give a reason for your answer. () Page

2 Magnesium oxide contains magnesium ions (Mg 2+ ) and oxide ions (O 2 ). Describe, as fully as you can, what happens when magnesium atoms react with oxygen atoms to produce magnesium oxide. (4) (Total 7 marks) Q2. Aluminium is a useful metal. (a) The atomic number (proton number) of aluminium is 3. Complete the diagram to show the electronic structure of an aluminium atom. Use crosses (x) to represent the electrons. () Aluminium is used as the electrical conductor for overhead power cables. Page 2

3 Explain why metals are good conductors of electricity (2) (Total 3 marks) Q3. The diagram represents the structure of graphite. Use your knowledge and understanding of the structure of graphite to explain why graphite can be used: (a) in the leads of pencils; Page 3

4 as an electrical conductor (Total 5 marks) Q4. Scientists have recently developed a method to produce large sheets of a substance called graphene. Graphene is made from carbon and is a single layer of graphite just one atom thick. The properties of graphene include: it conducts electricity it is transparent since it is only one atom thick it is strong and durable. These properties make it suitable to overlay a monitor screen to make it a touchscreen. The photograph below shows the structure of graphene. Photographs supplied by istockphoto/thinkstock Page 4

5 Use your knowledge of the bonding in graphite and the photograph of the structure to help you to explain, as fully as you can: (a) (i) why graphene is strong; (3) (ii) why graphene conducts electricity. (2) Suggest why a sheet of graphite which has a large number of carbon layers would not be suitable for the touchscreen. () (Total 6 marks) Q5. Diamonds are used as abrasives. Page 5

6 Model of part of the diamond structure Diamonds are very hard. Explain why. A good answer will include information on the structure and bonding in diamonds Q6.A Bunsen burner burns natural gas. Natural gas is mainly methane. (3) (Total 3 marks) By Kingsway School [CC BY 2.0], via Flickr (a) Name and describe the bonding in methane (CH4) To gain full marks you must include details of the electronic structure of the atoms involved in the bonding. Page 6

7 (5) Explain, in terms of forces, why methane is a gas at room temperature. (2) (Total 7 marks) Q7.Ammonia is produced from nitrogen and hydrogen. The equation for this reaction is: (a) (i) A company wants to make 6.8 tonnes of ammonia. Calculate the mass of nitrogen needed. Relative atomic masses (Ar): H = ; N = 4 Mass of nitrogen =... tonnes (3) Page 7

8 (ii) The company expected to make 6.8 tonnes of ammonia. The yield of ammonia was only 4.2 tonnes. Calculate the percentage yield of ammonia. Percentage yield of ammonia =... % (2) (iii) Use the equation above to explain why the percentage yield of ammonia was less than expected. () Complete the diagram to show the arrangement of the outer shell electrons of the nitrogen and hydrogen atoms in ammonia. Use dots ( ) and crosses (x) to represent the electrons. (2) (c) Ammonia dissolves in water to produce an alkaline solution. (i) Which ion makes ammonia solution alkaline? () Page 8

9 (ii) Name the type of reaction between aqueous ammonia solution and an acid. () (iii) Name the acid needed to produce ammonium nitrate. () (iv) The reaction of ammonia with sulfuric acid produces ammonium sulfate. Use the formulae of the ions on the Chemistry Data Sheet. Write the formula of ammonium sulfate. () (Total 2 marks) Q8. Lead compounds have been used for thousands of years as colours in paint. Johannes Vermeer [Public domain], via Wikimedia Commons (a) A sample of a red oxide used in paint was found to contain 6.2 g of lead and 0.64 g of oxygen. Calculate the empirical (simplest) formula of this compound. You must show all your working to gain full marks. Relative atomic masses: O = 6; Pb = 207. Page 9

10 (4) A problem with lead compounds is that they slowly react with hydrogen sulfide in the air. This produces lead sulfide which is black. (i) Hydrogen sulfide has the formula H2S. The bonding in a molecule of hydrogen sulfide can be represented as: H S H Complete the diagram below to show the arrangement of the outer electrons of the hydrogen and sulfur atoms in hydrogen sulfide. Use dots ( ) and crosses (x) to represent the electrons. You need only show the outer shell electrons. (Atomic numbers: H = ; S = 6.) () (ii) Hydrogen sulfide has a low boiling point. Explain why. Page 0

11 (2) (iii) Lead white is also used in paint. The white colour slowly darkens when lead sulfide is produced. The painting can be restored with hydrogen peroxide. This converts the black lead sulfide into white lead sulfate. Balance the equation for the reaction between lead sulfide and hydrogen peroxide (H2O2). PbS(s) +...H2O2(aq) PbSO4(s) + 4H2O(l) () (Total 8 marks) Q9. The following steps show how to use a type of glue. Step Measure out equal amounts of the liquids from tubes A and B. Step 2 Mix the liquids to make the glue. Put a thin layer of the glue onto each of the surfaces to be joined. Page

12 Step 3 Assemble the pieces to be joined and then hold them together with tape. Step 4 Leave the glue to set. (a) When liquids A and B are mixed a chemical reaction takes place. (i) This reaction is exothermic. State how the temperature of the mixture will change as the glue is mixed () (ii) When the glue sets it forms a giant covalent structure. Explain why substances with giant covalent structures have high melting points (2) The time taken for the glue to set at different temperatures is given in the table below. Temperature in C Time taken for the glue to set 20 3 days 60 6 hours 90 hour Page 2

13 Explain, in terms of particles, why increasing the temperature changes the rate of the reaction which causes the glue to set (2) (Total 5 marks) Page 3

14 Markscheme M.(a) (i) any two from: ignore any conclusion drawn referring to data below 7.5 nm or above 20 nm 00% of (type and type 2) bacteria are killed with a particle size of 7.5 to 8.5 nm accept nanoparticles in the range of 7.5 to 8.5 nm are most effective at killing (type and type 2) bacteria as the size increases (beyond 8.5 nm), nanoparticles are less effective at killing (type and type 2) bacteria type shows a linear relationship or type 2 is non-linear type bacteria more susceptible than type 2 (at all sizes of nanoparticles shown on the graph) allow type 2 bacteria are harder to kill 2 (ii) (yes) because you could confirm the pattern that has been observed allow would reduce the effect of anomalous points / random errors allow would give better line of best fit ignore references to reliability / precision / accuracy / reproducibility / repeatability / validity or (no) because trend / conclusion is already clear magnesium loses electron(s) oxygen gains electron(s) two electrons (per atom) gives full outer shells (of electrons) or eight electrons in highest energy level reference to incorrect particles or incorrect bonding or incorrect structure = max 3 or (electrostatic) attraction between ions or forms ionic bonds accept noble gas structure [7] Page 4

15 M2. (a) on diagram as Xs / dots or e accept paired or unpaired any two from: electrons in highest energy level or electrons in outer shell electrons are delocalised or sea of electrons electrons are free or electrons move around / flow electrons carry charge / current ignore carry electricity 2 [3] M3. (a) made of layers of carbon atoms weak forces of attraction between layers (owtte) / weak vertical bonds i.e. candidate refers to the diagram layers can slide over each other layers peel off each for mark because there are electrons which are free (to move) reason for free electrons / each carbon atom has 3 covalent bonds each for mark to max 5 [5] Page 5

16 M4. (a) (i) ionic / molecules / metallic / (inter)molecular = max 2 because graphene / it has a giant structure / lattice / macromolecular accept all / every / each atom is bonded to 3 other atoms because graphene / it has covalent bonds / is covalent because in graphene / the bonds are strong or a lot of energy needed / hard to break the bonds (ii) there are delocalised / free electrons because one (delocalised / free) electron per atom linked to first marking point accept because three electrons per atom used (in bonding) accept because one electron per atom not used (in bonding) opaque (owtte) eg could not see through them or layers slide or layers not aligned ignore thick [6] M5. any three from: any reference to incorrect bonding = max 2 giant structure / lattice / macromolecule covalent (bonds) bonds are (very) strong Page 6

17 allow bonds difficult to break or takes a lot of energy to break bonds each atom / carbon joined to four others accept each atom / carbon forms four bonds 3 [3] M6.(a) covalent (bonding) do not accept ionic / metallic / intermolecular (bonding) any four from: C 2, 4 and H accept carbon has 4 electrons in outer shell and hydrogen has electron in outer shell shared (pair of) electrons 4 (shared) pairs of electrons a correct dot and cross diagram gains bullet points 2, 3 and 4 all atoms now have a complete outer shell accept in methane the electronic structure of carbon is 2, 8 and hydrogen is 2 forms strong bonds 4 (because methane) has weak forces do not accept intramolecular forces / covalent bonds are weak between molecules / intermolecular do not accept intramolecular do not accept reference to ions do not accept intermolecular forces between atoms accept it is made of small / simple molecules with weak forces of attraction for 2 marks Page 7

18 allow weak bonds between molecules for 2 marks if no other marks awarded allow for mark made of small / simple molecules [7] M7.(a) (i) Mr of NH3 = 7 correct answer with or without working gains 3 marks accept correct rounding of intermediate answers can be credited from correct substitution from step 2 or 2 (moles of) NH3 = 34 or 4 7 or (28/34) 6.8 allow ecf from step or (4/7) 6.8 = 5.6 allow ecf from step (ii) 6.8 accept 6.76 or 62 or 6.76 correct answer with or without working gains 2 marks if answer is not correct evidence of 4.2 / gains mark if answer not correct 0.68 or 0.62 gains mark 2 Page 8

19 (iii) reaction is reversible accept reaction reaches equilibrium allow reaction does not reach completion ignore some is lost 3 bonding pairs do not accept extra electrons on hydrogen lone pair accept 2 non-bonding electrons on outer shell of nitrogen (c) (i) hydroxide / OH accept phonetic spelling (ii) neutralisation accept acid-base allow exothermic (iii) nitric (acid) allow HNO3 ignore incorrect formula (iv) (NH4 )2 SO4 allow (NH4 + )2 SO4 2 [2] M8. (a) Page 9

20 mark for dividing mass by A r max 2 if Ar divided by mass = 0.03 = 0.04 mark for correct proportions 3 4 mark for correct whole number ratio (allow multiples) can be awarded from correct formula Pb3O4 mark for correct formula ecf allowed from step 2 to step 3 and step 3 to step 4 if sensible attempt at step correct formula with no working gains 2 marks (i) allow all dots or all crosses or e or e ignore inner shells and any inner electrons allow 4 non-bonded electrons anywhere on shell as long as not in overlap need not be paired (ii) forces of attraction / bonds between molecules are weak (owtte) do not accept intramolecular forces / covalent bonds are weak do not accept reference to ions or intermolecular forces / bonds are weak (owtte) Page 20

21 or it is made of small molecules with weak forces of attraction if 2 marks not awarded made of small molecules / simple molecular gains mark forces of attraction are weak (without specifying between molecules / intermolecular) gains mark (accept easily broken / not much energy needed to break instead of weak) bonds are weak without specifying intermolecular would not gain a mark and would be ignored 2 (iii) 4 [8] M9. (a) (i) increase (owtte) or gets hotter ignore gives out heat / takes in heat (ii) any two from: bonds are strong accept hard to break a lot of energy needed to break bonds allow heat for energy all atoms are joined by (covalent bonds accept forms lattice a large number of bonds would need to be broken reference to ionic / metallic = mark intermolecular forces /forces between molecules = max mark ignore electrostatic many strong bonds need to be broken = 2 marks accept double bonds as equivalent to bonds 2 Page 2

22 any two from: particles have more energy ignore more vibrations particles move faster ignore move more particles collide more often or more collisions accept answers such as hit / bump more particles / particle collisions have the activation energy or more of the particles / particle collisions have enough energy to react or collisions are more energetic / harder (owtte) or more of the collisions are successful if electrons rather than particles stated then max mark there are more collisions and more of the collisions are successful = 2 marks accept more collisions per second / unit of time for 2 marks accept more successful collisions for mark 2 [5] Page 22