Year 10 Advanced Chemistry Revision -ANSWERS Name: ______1. What are the differences between physical and chemical changes? Physical change Chemical Reaction Change of what? Changes of states Sound, Light, Heat is given Evidences of chemical Changes of shapes out (exothermic), Heat is reactions Temporary changes of colours absorbed (endothermic), New substance formed or No new substance is formed New substances (products) not are formed from reactants Reversible or not Reversible (change back) Irreversible (not changing back) Example Ice becomes water and steam Making a toast; frying an on heating; stepping on a can; egg; lighting up a sparkler Heating iodine to purple vapour (sublimation)
2. Atomic Structures – sub-atomic particles Proton Electron Neutron Where can you it? Inside the nucleus Surrounding the Inside the nucleus Inside nucleus or nucleus surrounding nucleus Charge – neutral, Positive charge Negative charge No charge positive or negative = Neutral Mass – 1 unit or 1 unit 0 (very little mass) 1 unit negligible Function or To attract electrons To exchange and To hold the protrons importance share with other together inside the atoms to form nucleus compounds
3. Different types of metals: Types Examples Remarks Alkali metals Li, Na, K 1 valence electron Alkaline earth metals Be, Mg, Ca 2 valence electrons Transition metals Ni, Fe, Ag, Au, Cu Variable valence electrons Other metals Al, Pb 3 valence electrons
4. a) What is a molecule? A molecule is the smallest part of a substance made of 2 or more atoms chemically bonded together, can be the same kind (like diatomic elements) or different kind forming compounds. b) Can an element exist as molecule? Give all the examples. Yes – those 7 diatomic elements “I Have No Clever Or Bright Friends”
Iodine I2, Hydrogen H2, Nitrogen N2, Chlorine Cl2, Oxygen O2, Bromine Br2, Fluorine F2, 5. c) Why do noble gases exist as atoms only but not molecules? Noble Gases (Group 8 elements) have 8 electrons (except He 2) in the outermost electronic shells – being full shell – have octet rule – very stable, unlikely to bond or react with other elements. 6. Differences between Ionic and Covalent compounds: Ionic compounds Covalent compounds Metal only; Metal and Non-metal bonded Non-metals only Metal & non-metal; together Non-metals only Formation by: By transfer electrons – Metal By sharing electrons between sharing electrons or atom gives away electrons to non-metal atoms transfer of electrons non-metal atom
Examples NaCl, CuSO4 H2O, NH3. CO2, CH4,
CH3OH (methanol), C2H5OH (ethanol) Usually existed as Existed as Solids mainly Existed in all states, including solids, liquids and gases or gases Solubility in water Mostly soluble Insoluble to form ions Those insoluble eg. Lead iodide, Silver Choride, Calcium carbonate etc. Melting point – high High Low or low Conducting Conducting electricity if the Not conducting electricity electricity in solid compounds are in molten EXCEPT Acids H+ or state or in water form or dissolved in water Alkali OH- Others give no free ions.
7. The 6 types of chemical reactions: Types Example Remarks
COMBUSTION Methane + oxygen Hydrocarbon fuel burns Carbon dioxide + Water in oxygen to give CO2
CH4(g) + 2O2(g) CO2(g) + 2H2O (g) and H2O COMBINATION Iron + sulphur Iron sulphide Forming more Fe(s) + S(s) FeS (s) complicated products DECOMPOSITION Calcium carbonate Broken down to simpler Calcium Oxide + Carbon dioxide substances
CaCO3 (s) CaO(s)+ CO2(g) SINGLE Zinc + Copper sulphate Only Stronger metal can DISPLACEMENT Zinc sulphate + Copper displace the weaker one Zn(s) + CuSO4 (aq) ZnSO4(aq) + Cu(s) in the compound PRECIPITATION Lead nitrate + Potassium iodide When a solid (Double Lead Iodide + Potassium nitrate (precipitate) is formed
Displacement) Pb(NO3)2(aq) + 2KI(aq) by mixing 2 solutions
PbI2(s) + 2KNO3(aq) NEUTRALISATION Hydrochloric acid + Sodium hydroxide A salt and water are (Double Sodium chloride + Water formed.
Displacement) HCl (aq) + NaOH NaCl (aq) + H2O (l) H2SO4(aq) + 2NaOH
Na2SO4(aq) + 2H2O (l) Balanced NB: The last 2 are examples of DOUBLE DISPLACEMENT REACTIONS 8. What are the different types of ions? Cation (Positive Ion) Anion (Negative Ion) Simple (one element) Na+, K+, Ag+, Fe3+, Cu2+, Zn2+, O2-, S2-, N3-, Al3+, Mg2+, Polyatomic ion Only 1 6 of them - - - 2- 2- (=Radical) OH , NO3 , HCO3 , CO3 , SO4 , + 3- NH4 PO4
9. Lewis dot diagrams of elements – periodic table:
a) What do the Lewis dot diagrams show? The outermost electrons (valence electrons)
b) What is special about the elements in the same group? Same number of valence electrons
c) Which groups of elements will form Cations? Explain why. Group 1, 2 and 3
d) Which groups of elements will form Anions? Explain why. Group 5, 6 and 7
e) Which groups of elements will not form Ions? Explain why for each group mentioned. Group 4 (4 valence electrons – different to give away and take up another 4) Group 8 – full shell – octet – very stable, not bonding with other atom.
10. Using Lewis Dot diagrams to show the formation of a) Potassium Chloride. b) Aluminium Oxide
11. Using Lewis Dot diagrams to show the formation of Covalent bonds in a) Fluorine, b) Oxygen c) Nitrogen. d) What are the differences between the bonding in nitrogen, oxygen and fluorine gases? (Hint: single, double bond etc. and why it is so?) 12. Using Lewis Dot diagrams to show the formation of
a) Ammonia (NH3) b) Carbon dioxide.
13. a) Explain the differences between the electrical conductivity of Sodium chloride in crystal form and as aqueous solution. Using: Sodium chloride is an ionic compound, consisting of a giant (endlessly repeating) lattice of ions. Both Na+ and Cl- are bonded together in the giant lattice form, not able to move freely, therefore it can’t conduct electricity.
When it is placed in water, it can dissolve easily, releasing free ions – allowing electricity to pass through.
b) Why does Sodium Chloride (Table salt) has a very high melting point at 8010C compared to Sucrose (Table sugar) at 1860C? The giant lattice bonds all the ions together strongly, lots of energy is required to break the bonds between Na+ and Cl-; however, sucrose exists as individual molecules with weak bonds between molecules; therefore having lower melting point.
14. Explain “Sea of electrons” in Metallic Elements. Name 2 properties that are related to this structure. Metals have their atoms in cations form with lots of electrons moving around the cations – this allows electrical conduction.
The atoms can also slide layers by layers – making metal with the property of being malleable,
15. Chemical Reaction – Word equation - State of matter – Chemical formulae – Chemical 16. Equation – Balanced equation
Do the same as above for these reactions: a) Above 50 °C, sodium bicarbonate gradually decomposes into sodium carbonate, water and carbon dioxide.
2NaHCO3(s) Na2CO3(aq) + H2O(l) + CO2(g)
b) Ethane gas C2H6, burns in air (oxygen) and produces carbon dioxide and water.
2C2H6(g) + 7O2(g) 6H2O(l) + 4CO2(g) c) Reaction between Magnesium and dilute Hydrochloric acid ?
Mg(s) + 2HCl (aq) MgCl2(aq) + H2(g) d) Reaction between Zinc metal and Copper sulphate solution ?
Zn(s) + CuSO4 (aq) ZnSO4(aq) + Cu(s) e) Reaction between Iron metal and Aluminium nitrate ? (Tricky) No reaction – as Aluminium is more reactive, can’t be displaced by Iron at all.
17. Metal Reactivity Series Water, Hydrogen, Oxide, Hydroxide, Salt
a) Metal + Oxygen Metal OXIDE
2Mg + O2 2MgO b) Metal + Water Metal HYDROXIDE + HYDROGEN
2Na (s) + 2H2O(l) 2NaOH(aq) + H2 (g) c) Metal + Acid SALT + HYDROGEN
Mg(s) + 2HCl (aq) MgCl2(aq) + H2(g) Compared to d) Acid and Base SALT + WATER HCl (aq) + NaOH NaCl (aq) + H2O (l)
Metals Remarks Stored in Oil K and Na Extremely reactive; reacts vigorously with oxygen (air)) Reacting with water K, Na and Ca Highly reactive metals Reacting with acid All except: Reactive metals Copper, Silver, Lead, Platinum Reaction with oxygen All except: Not reacting with oxygen and other elements GOLD will then exist as NATIVE metals.
18. Factors affecting Rate of Reaction: Increases the Rate when Decreases the Rate when Temperature increases decreases Surface area of reactants increases decreases Concentration of reactants increases decreases Presence of Catalyst Is present Is not present