NCEA Level 1 Chemistry (90934) 2013 — page 1 of 4

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 / • Describes ONE • Links ONE • All observations are solid / deposit forms (or the solution observation correct correct and linked to turns cloudy white). The precipitate / correctly. observation to the the chemical species solid / deposit is lead sulfate. correct chemical involved for both In test tube B, a yellow precipitate / • Identifies the white species / reactions. solid / deposit forms (or the solution precipitate as lead substance for one turns cloudy yellow). The precipitate sulfate. reaction. / solid / deposit is lead iodide.

The type of reaction occurring in • Identifies the

each test tube is a precipitation yellow precipitate reaction (or exchange reaction) as lead iodide. because when the two solutions are

added together an insoluble • Identifies and justifies substance called a precipitate forms. • Identifies the type the choice of the type This settles at the bottom of the test of reaction as • Identifies and of reaction. tubes, so they are both precipitation precipitation or partially justifies exchange. reactions. the choice of the (OR … because when the two type of reaction. solutions are added together ions from each substance are swapped or • BOTH balanced ionic exchanged and an insoluble substance equations are correct. forms, so they are both exchange • Writes a correct • ONE ionic (States are not reactions.) word equation OR equation has been required.) writes the formula Candidate could provide an ionic or a written with for ONE product correct formulae, molecular balanced symbol equation. correctly. 2+ 2– but is not A: Pb (aq) + SO4 (aq) → PbSO4(s) balanced. OR OR Pb(NO3)2(aq) + K2SO4(aq) → PbSO4(s) + 2KNO3(aq) Writes ONE 2+ – molecular B: Pb (aq) + 2I (aq) → PbI2(s) equation OR (balanced or Pb(NO3)2(aq) +2KI(aq) → unbalanced) with PbI2(s)+ 2KNO3(aq) the correct formulae.

NØ N1 N2 A3 A4 M5 M6 E7 E8

No response 1a 2a 3a 4a 2m 3m 2e 3e or no Including relevant the evidence. balanced equations.

NCEA Level 1 Chemistry (90934) 2013 — page 2 of 4

Q Evidence Achievement Merit Excellence

TWO When white calcium carbonate solid, CaCO3, is strongly heated it releases a colourless gas, carbon • Describes ONE • Links ONE • ALL observations are dioxide, CO2, and forms another observation observation to the linked to the chemical white solid calcium oxide, CaO. correctly. correct chemical species involved for

CaCO3(s) → CaO(s) + CO2(g) species / both reactions. substance for one When white calcium hydroxide reaction. solid, Ca(OH)2, is strongly heated it releases a colourless gas, water, H2O, and also forms the white solid calcium oxide, CaO. • Identifies the type • Identifies and • Identifies and justifies Ca(OH) (s) → CaO(s) + H O(g) of reaction as partially justifies the choice of the type 2 2 thermal the choice of the of reaction. Comparisons: decomposition. type of reaction. Both calcium carbonate and calcium hydroxide are undergoing thermal decomposition since a

solid is decomposing to form more than one substance when heated. • Describes a test for one of the products. Both are white solids and when strongly heated, they both form another white solid, calcium oxide. During heating, both of the solids

break up because gas escapes from • Explains how one • Explains how both

them. gaseous product gaseous products can

Contrast: can be identified. be identified. • Writes a word The difference in these reactions is equation OR writes in the gases released. the correct • Compares or • Compares and Calcium carbonate releases carbon formulae for the contrasts the two contrasts the two dioxide, so a loop of limewater reactant or the reactions. reactions. (calcium hydroxide in solution) will products for ONE turn milky (or cloudy white) when reaction. • Writes ONE held in the gas / carbon dioxide will symbol equation • Writes BOTH balanced extinguish a burning splint. (balanced or equations. Calcium hydroxide releases steam unbalanced) with (States are not or water as a gas / vapour. A piece the correct required.) of cobalt chloride paper held in formulae. this gas will turn from blue to pink.

NØ N1 N2 A3 A4 M5 M6 E7 E8

No response 1a 2a 3a 4a 3m 4m 3e 4e or no Including relevant both evidence. balanced equations.

NCEA Level 1 Chemistry (90934) 2013 — page 3 of 4

Q Evidence Achievement Merit Excellence

THREE Shiny grey metal sodium reacts • Links ONE • Links ALL (a) with yellow / green chlorine observation to observations to gas to form white crystals of correct reactant or correct reactants sodium chloride. product. and product.

Sulfur dichloride or disulfur (b)(i) dichloride or sulfur chloride. • Identifies product as sulfur dichloride

This is a combination reaction / disulfur dichloride

(ii) because two elements, sulfur / sulfur chloride

and chlorine combine to form a • Identifies and justifies new substance / compound, • Identifies and • Identifies the type the choice of the type (di)sulfur dichloride. partially justifies of reaction as the choice of the of reaction. combination. type of reaction. (c) 2Na(s) + Cl2(g) → 2NaCl(s)

S(s) + Cl (g) → SCl (s) or • Writes a correct 2 2 • Writes ONE • Writes BOTH 2S(s) (or S2 (s)) + Cl2(g) → word equation OR symbol equation balanced equations. S2Cl2(g) writes the correct (balanced or (States are not formulae for the unbalanced) with required.) reactants OR the Sodium is a metal element and the correct (d) product of ONE when it reacts with chlorine gas, formulae. reaction. both elements form ions. Each

sodium atom loses 1 electron to each chlorine atom / each • Identifies the type • Explains ONE chlorine atom gains 1 electron. of electron transfer reaction in terms • Explains BOTH Sodium ions and chloride ions for ONE reaction. of electron reactions in terms of combine to form the (ionic) transfer. electron transfer (or compound sodium chloride, lack thereof).

NaCl. Sulfur is a non-metal element and when it 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 M5 M6 E7 E8

No response 1a 2a 3a 4a 3m 4m 2e 3e or no Including relevant the evidence. balanced equations.

NCEA Level 1 Chemistry (90934) 2013 — page 4 of 4

Q Evidence Achievement Merit Excellence

FOUR Zn Mg Cu Pb (a) • Completes the table Cu(NO3)2     correctly. Pb(NO )     3 2

Observations are linked (b) For example: In the reaction • Links ONE to the chemical species between magnesium metal and • observation to the involved for the copper nitrate solution, the grey • Describes ONE correct chemical selected reaction for magnesium metal would (slowly) observation species / one reactant and one disappear and an orange / brown correctly. substance for the product. deposit / solid / precipitate of copper selected reaction. would form. The blue copper nitrate solution’s colour would fade to • Identifies reaction colourless as magnesium ions as displacement / • Identifies and • Identifies and justifies displace the blue copper ions from redox reaction. partially justifies the choice of the type the solution resulting in a the choice of the of reaction.

magnesium nitrate solution. Since type of reaction.

the magnesium has displaced the

copper ions (copper in solution)

from the solution, this is a displacement reaction (redox). • Writes a correct word equation OR • Writes • Writes a balanced Balanced equation: Either writes the correct unbalanced equation. Mg(s) + Cu2+(aq) → formulae for the molecular / ionic (States are not Cu(s) + Mg2+(aq) equation with the required.) reactants or the correct formulae. products of ONE Mg(s) + Cu(NO3)2(aq) → reaction OR writes Cu(s) + Mg(NO3)2(aq) two balanced half

(c) equations. Zinc, copper and lead do not react

with magnesium nitrate because • Explains why Zn, magnesium is higher on the activity • Identifies Mg as more reactive than Cu and Pb do not series, so is more reactive than the react with other metals. Therefore none of any one of Zn, Cu and Pb. Mg(NO3)2 zinc, copper, or lead can displace solution. magnesium ions from solution, so no reaction will occur.

NØ N1 N2 A3 A4 M5 M6 E7 E8

No response 1a 2a 3a 4a 3m 4m 2e 3e or no Including relevant the evidence. balanced equation.

Judgement Statement

Achievement with Achievement Not Achieved Achievement Merit with Excellence

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