NCEA Level 1 Chemistry (90934) 2013 Assessment Schedule



Assessment Schedule – 2013

Chemistry: Demonstrate understanding of aspects of chemical reactions (90934)

Evidence Statement

|Q |Evidence |Achievement |Merit |Excellence |

|ONE |In test tube A, a white precipitate / solid / |Describes ONE observation |Links ONE correct |All observations are correct and |

| |deposit forms (or the solution turns cloudy |correctly. |observation to the correct |linked to the chemical species |

| |white). The precipitate / solid / deposit is lead| |chemical species / |involved for both reactions. |

| |sulfate. |Identifies the white |substance for one reaction.| |

| |In test tube B, a yellow precipitate / solid / |precipitate as lead sulfate. | | |

| |deposit forms (or the solution turns cloudy | | | |

| |yellow). The precipitate / solid / deposit is |Identifies the yellow | | |

| |lead iodide. |precipitate as lead iodide. | | |

| |The type of reaction occurring in each test tube | | | |

| |is a precipitation reaction (or exchange |Identifies the type of | | |

| |reaction) because when the two solutions are |reaction as precipitation or | |Identifies and justifies the |

| |added together an insoluble substance called a |exchange. |Identifies and partially |choice of the type of reaction. |

| |precipitate forms. This settles at the bottom of | |justifies the choice of the| |

| |the test tubes, so they are both precipitation | |type of reaction. | |

| |reactions. | | | |

| |(OR … because when the two solutions are added | | | |

| |together ions from each substance are swapped or |Writes a correct word | |BOTH balanced ionic equations are|

| |exchanged and an insoluble substance forms, so |equation OR writes the |ONE ionic equation has been|correct. |

| |they are both exchange reactions.) |formula for ONE product |written with correct |(States are not required.) |

| |Candidate could provide an ionic or a molecular |correctly. |formulae, but is not | |

| |balanced symbol equation. | |balanced. | |

| |A: Pb2+(aq) + SO42–(aq) → PbSO4(s) OR | |OR | |

| |Pb(NO3)2(aq) + K2SO4(aq) → | |Writes ONE molecular | |

| |PbSO4(s) + 2KNO3(aq) | |equation (balanced or | |

| |B: Pb2+(aq) + 2I–(aq) → PbI2(s) | |unbalanced) with the | |

| |OR | |correct formulae. | |

| |Pb(NO3)2(aq) +2KI(aq) → | | | |

| |PbI2(s)+ 2KNO3(aq) | | | |

|NØ |N1 |N2 |A3 |A4 |

|TWO |When white calcium carbonate solid, CaCO3, is | | | |

| |strongly heated it releases a colourless gas, | | | |

| |carbon dioxide, CO2, and forms another white |Describes ONE observation |Links ONE observation to |ALL observations are linked to |

| |solid calcium oxide, CaO. |correctly. |the correct chemical |the chemical species involved for|

| |CaCO3(s) → CaO(s) + CO2(g) | |species / substance for one|both reactions. |

| |When white calcium hydroxide solid, Ca(OH)2, is| |reaction. | |

| |strongly heated it releases a colourless gas, | | | |

| |water, H2O, and also forms the white solid | | | |

| |calcium oxide, CaO. | |Identifies and partially | |

| |Ca(OH)2(s) → CaO(s) + H2O(g) |Identifies the type of |justifies the choice of the|Identifies and justifies the |

| |Comparisons: |reaction as thermal |type of reaction. |choice of the type of reaction. |

| |Both calcium carbonate and calcium hydroxide |decomposition. | | |

| |are undergoing thermal decomposition since a | | | |

| |solid is decomposing to form more than one | | | |

| |substance when heated. Both are white solids | | | |

| |and when strongly heated, they both form |Describes a test for one of | | |

| |another white solid, calcium oxide. During |the products. | | |

| |heating, both of the solids break up because | | | |

| |gas escapes from them. | | | |

| |Contrast: | | | |

| |The difference in these reactions is in the | |Explains how one gaseous | |

| |gases released. | |product can be identified. |Explains how both gaseous |

| |Calcium carbonate releases carbon dioxide, so a| | |products can be identified. |

| |loop of limewater (calcium hydroxide in |Writes a word equation OR |Compares or contrasts the | |

| |solution) will turn milky (or cloudy white) |writes the correct formulae |two reactions. |Compares and contrasts the two |

| |when held in the gas / carbon dioxide will |for the reactant or the | |reactions. |

| |extinguish a burning splint. |products for ONE reaction. |Writes ONE symbol equation | |

| |Calcium hydroxide releases steam or water as a | |(balanced or unbalanced) | |

| |gas / vapour. A piece of cobalt chloride paper | |with the correct formulae. |Writes BOTH balanced equations. |

| |held in this gas will turn from blue to pink. | | |(States are not required.) |

|NØ |N1 |N2 |A3 |A4 |

|THREE |Shiny grey metal sodium reacts with yellow /|Links ONE observation to |Links ALL observations to | |

|(a) |green chlorine gas to form white crystals of|correct reactant or product. |correct reactants and | |

| |sodium chloride. | |product. | |

| |Sulfur dichloride or disulfur dichloride or |Identifies product as sulfur | | |

|(b)(i) |sulfur chloride. |dichloride / disulfur | | |

| | |dichloride / sulfur chloride | | |

|(ii) |This is a combination reaction because two | | | |

| |elements, sulfur and chlorine combine to |Identifies the type of | | |

| |form a new substance / compound, (di)sulfur |reaction as combination. | | |

| |dichloride. | |Identifies and partially | |

|(c) | |Writes a correct word |justifies the choice of |Identifies and justifies the |

| |2Na(s) + Cl2(g) → 2NaCl(s) |equation OR writes the |the type of reaction. |choice of the type of reaction. |

| |S(s) + Cl2(g) → SCl2(s) or |correct formulae for the | | |

| |2S(s) (or S2 (s)) + Cl2(g) → S2Cl2(g) |reactants OR the product of |Writes ONE symbol equation| |

| | |ONE reaction. |(balanced or unbalanced) |Writes BOTH balanced equations. |

|(d) |Sodium is a metal element and when it reacts| |with the correct formulae.|(States are not required.) |

| |with chlorine gas, both elements form ions. |Identifies the type of | | |

| |Each sodium atom loses 1 electron to each |electron transfer for ONE | | |

| |chlorine atom / each chlorine atom gains 1 |reaction. |Explains ONE reaction in | |

| |electron. Sodium ions and chloride ions | |terms of electron | |

| |combine to form the (ionic) compound sodium | |transfer. |Explains BOTH reactions in terms |

| |chloride, NaCl. | | |of electron transfer (or lack |

| |Sulfur is a non-metal element and when it | | |thereof). |

| |reacts with chlorine gas, electrons are | | | |

| |shared. Sulfur and chlorine atoms combine to| | | |

| |form the (covalent) compound sulfur | | | |

| |dichloride, SCl2. | | | |

|NØ |N1 |N2 |A3 |A4 |

|FOUR | | | | |

|(a) |Zn |Completes the table | | |

| |Mg |correctly. | | |

| |Cu | | | |

| |Pb | | | |

|(b) | | | |Observations are linked to the |

| |Cu(NO3)2 | |Links ONE observation to |chemical species involved for the|

| |⎫ |Describes ONE observation |the correct chemical |selected reaction for one |

| |⎫ |correctly. |species / substance for the|reactant and one product. |

| |⎦ | |selected reaction. | |

| |⎫ | | | |

| | |Identifies reaction as |Identifies and partially |Identifies and justifies the |

| |Pb(NO3)2 |displacement / redox |justifies the choice of the|choice of the type of reaction. |

| |⎫ |reaction. |type of reaction. | |

| |⎫ | | | |

| |⎦ | | | |

| |⎦ | | | |

| | | |Writes unbalanced molecular|Writes a balanced equation. |

| | |Writes a correct word |/ ionic equation with the |(States are not required.) |

| |For example: In the reaction between magnesium |equation OR writes the |correct formulae. | |

| |metal and copper nitrate solution, the grey |correct formulae for the | | |

| |magnesium metal would (slowly) disappear and an|reactants or the products of | | |

| |orange / brown deposit / solid / precipitate of|ONE reaction OR writes two | | |

| |copper would form. The blue copper nitrate |balanced half equations. | | |

| |solution’s colour would fade to colourless as | |Explains why Zn, Cu and Pb | |

| |magnesium ions displace the blue copper ions |Identifies Mg as more |do not react with Mg(NO3)2 | |

| |from the solution resulting in a magnesium |reactive than any one of Zn, |solution. | |

| |nitrate solution. Since the magnesium has |Cu and Pb. | | |

|(c) |displaced the copper ions (copper in solution) | | | |

| |from the solution, this is a displacement | | | |

| |reaction (redox). | | | |

| |Balanced equation: Either | | | |

| |Mg(s) + Cu2+(aq) → | | | |

| |Cu(s) + Mg2+(aq) | | | |

| | | | | |

| |Mg(s) + Cu(NO3)2(aq) → | | | |

| |Cu(s) + Mg(NO3)2(aq) | | | |

| | | | | |

| |Zinc, copper and lead do not react with | | | |

| |magnesium nitrate because magnesium is higher | | | |

| |on the activity series, so is more reactive | | | |

| |than the other metals. Therefore none of zinc, | | | |

| |copper, or lead can displace magnesium ions | | | |

| |from solution, so no reaction will occur. | | | |

|NØ |N1 |N2 |A3 |A4 |

|Score range |0 – 10 |11 – 19 |20 – 25 |26 – 32 |

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