2.6_Reactivity_AS9116

= 2.6 AS 91166 Demonstrate understanding of chemical reactivity (4 credits) =

== NCEA PAST EXAM QUESTIONS on Rates of Reaction == ====The table below provides an overview of the specify factor affecting the Rate of a Reaction and the year that this question appeared in the NCEA Exam paper ====  ====(a) Hydrochloric acid was reacted with calcium carbonate in the form of marble chips (lumps) and powder (crushed marble chips) in an experiment to investigate factors affecting the rate of a chemical reaction.====

A student carried out this reaction between solution X and solution Y in a conical flask. Over time, the cross on the piece of paper under the flask disappeared when viewed from above.
The following experiments were carried out, and the times taken for the cross to disappear recorded. ====Elaborate on why the reactions in Experiment 2 and Experiment 3 occur faster than the reaction in Experiment 1. In your answer, include the following words or terms: **//collisions activation energy temperature effective catalyst//**==== 

When dilute hydrochloric acid, HCl(aq), is added to sodium thiosulfate, Na2S2O3(aq), in a conical flask, the following reaction occurs:
2HCl(aq) + Na2S2O3(aq) → 2NaCl(aq) + SO2(g) + S(s) + H2O(ℓ)

**Experiment 3** compared to **Experiment 1:**


The equation for this reaction is represented by:
2HCl(//aq//) + Na2S2O3(//aq//) --> S(//s//) + SO2(//g//) + 2NaCl(//aq//) + H2O(//ℓ //)

(b) Explain how decreasing the concentration of sodium thiosulfate and decreasing the temperature of the reactants affects the reaction rate. In your answer, you should refer to:

 * ====particle collision====
 * ====activation energy====
 * ====the reaction between hydrochloric acid and sodium thiosulfate====

(a) Zinc foil reacts with dilute sulfuric acid to produce zinc sulfate and hydrogen gas.
Zn(s) + H2SO4(aq) → ZnSO4(aq) + H2(g) ====Two experiments were carried out using the same mass of zinc foil and excess sulfuric acid of concentrations 0.500 mol L–1 and 1.00 mol L–1. The reactions were carried out at 25°C. A graph showing the results of the two experiments is shown below. ==== ==== (i) Write down the letter of the experiment which was carried out using the 1.00 mol L–1 sulfuric acid. Justify your answer in terms of the collision of particles. ==== ==== (ii) Experiment A was repeated, using the same mass of zinc granules instead of zinc foil. The rate of reaction increased. Explain this effect on the reaction rate, in terms of the factor investigated and the collision of particles. ==== ==== (iii) Experiment A was repeated again; this time the reaction was carried out at a temperature of 15°C. Discuss the effect of this temperature change. ====

Your answer must include reference to:
<span style="font-family: Arial,Helvetica,sans-serif;">(a) An experiment to investigate the rate of reaction between a 5 cm strip of magnesium ribbon and 20 mL of 1.00 mol L–1 hydrochloric acid was carried out at 25°C. The hydrochloric acid was in excess.
 * ====<span style="color: #221e1f; font-family: Arial,Helvetica,sans-serif;">reaction rate ====
 * ====<span style="color: #221e1f; font-family: Arial,Helvetica,sans-serif;">collision of particles ====
 * ====<span style="color: #221e1f; font-family: Arial,Helvetica,sans-serif;">Activation Energy ====

<span style="font-family: Arial,Helvetica,sans-serif;">Complete the table below for EACH change, by:

 * ====<span style="font-family: Arial,Helvetica,sans-serif;">stating the factor being investigated ====
 * ====<span style="font-family: Arial,Helvetica,sans-serif;">describing how the reaction rate would be affected by using the word **"increase"** or **"decrease"** in your answer ====

<span style="color: #221e1f; font-family: 'Arial','sans-serif';">The equation for this reaction can be represented by:
<span style="color: #221e1f; font-family: 'Arial','sans-serif';">CaCO <span style="font-family: 'Arial','sans-serif'; font-size: 10.6667px;">3 <span style="color: #221e1f; font-family: 'Arial','sans-serif';">(//s//) + 2HCl(//aq//) → CaCl <span style="font-family: 'Arial','sans-serif'; font-size: 10.6667px;">2  <span style="color: #221e1f; font-family: 'Arial','sans-serif';">( //<span style="color: #221e1f; font-family: 'Arial','sans-serif';">aq //<span style="color: #221e1f; font-family: 'Arial','sans-serif';">) + CO <span style="font-family: 'Arial','sans-serif'; font-size: 10.6667px;">2  <span style="color: #221e1f; font-family: 'Arial','sans-serif';">(//g//) + H <span style="font-family: 'Arial','sans-serif'; font-size: 10.6667px;">2  <span style="color: #221e1f; font-family: 'Arial','sans-serif';">O(//ℓ//)

<span style="color: #221e1f; font-family: 'Arial','sans-serif';">The equation for this reaction can be represented by:
<span style="color: #221e1f; font-family: 'Arial','sans-serif';">Mg(//s//) + 2HCl(//aq//) → MgCl <span style="font-family: 'Arial','sans-serif'; font-size: 10.6667px;">2 <span style="color: #221e1f; font-family: 'Arial','sans-serif';">(//aq//) + H <span style="font-family: 'Arial','sans-serif'; font-size: 10.6667px;">2  <span style="color: #221e1f; font-family: 'Arial','sans-serif';">(//g//) ====<span style="color: #221e1f; font-family: 'Arial','sans-serif';">The beakers drawn below show particle representations of magnesium metal and hydrochloric acid just before the reaction is about to begin. ==== ====<span style="color: #221e1f; font-family: 'Arial','sans-serif';">The rate of reaction can be followed by recording the volume of hydrogen, H <span style="font-family: 'Arial','sans-serif'; font-size: 10.6667px;">2 <span style="color: #221e1f; font-family: 'Arial','sans-serif';">, produced. The graph below shows the volume of hydrogen produced during the **initial** part of the reaction. ====

<span style="color: #221e1f; font-family: 'Arial','sans-serif';">Explain your answers in terms of
====<span style="color: #221e1f; font-family: 'Arial','sans-serif';">(c) An experiment was carried out by reacting bromine, Br <span style="font-family: 'Arial','sans-serif'; font-size: 10.6667px;">2 <span style="color: #221e1f; font-family: 'Arial','sans-serif';">, and methanoic acid, HCOOH, in a beaker. The equation for this reaction can be represented by: ==== Br2(aq) + HCOOH(aq) → 2Br–(aq) + 2H+(aq) + CO2(g)<span style="font-family: Arial,Helvetica,sans-serif;">brown colourless all colourless
 * ====<span style="color: #221e1f; font-family: 'Arial','sans-serif';">particle collision ====
 * ====<span style="color: #221e1f; font-family: 'Arial','sans-serif';">concentration of the particles present ====

Your answer must include reference to
<span style="color: #221e1f; display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">Hydrogen peroxide decomposes to form water and oxygen gas. <span style="color: #221e1f; font-family: 'Arial','sans-serif';">2H <span style="font-family: 'Arial','sans-serif'; font-size: 10.6667px;">2 <span style="color: #221e1f; font-family: 'Arial','sans-serif';">O <span style="font-family: 'Arial','sans-serif'; font-size: 10.6667px;">2  <span style="color: #221e1f; font-family: 'Arial','sans-serif';">(//aq//) → 2H <span style="font-family: 'Arial','sans-serif'; font-size: 10.6667px;">2  <span style="color: #221e1f; font-family: 'Arial','sans-serif';">O(//l//) + O <span style="font-family: 'Arial','sans-serif'; font-size: 10.6667px;">2  <span style="color: #221e1f; font-family: 'Arial','sans-serif';">(//g//) ====<span style="color: #221e1f; font-family: 'Arial','sans-serif';">The rate of decomposition is changed with the addition of manganese dioxide, MnO <span style="font-family: 'Arial','sans-serif'; font-size: 10.6667px;">2 <span style="color: #221e1f; font-family: 'Arial','sans-serif';">. ==== ====<span style="color: #221e1f; font-family: 'Arial','sans-serif';">The rate of the reaction can be followed by recording the volume of oxygen produced. The graph below shows the volume of oxygen produced with, and without, manganese dioxide. ====
 * ====particle collision====
 * ====reaction rate====
 * ====Activation Energy====

<span style="color: #221e1f; font-family: 'Arial','sans-serif';">Your answer must include reference to:

 * ====<span style="color: #221e1f; font-family: 'Arial','sans-serif';">particle collision ====
 * ====Activation Energy====

[[image:NCEA2007.jpg]]
An experiment was carried out by reacting zinc metal with excess dilute sulfuric acid. All the zinc was used up in the reaction. The equation for this reaction is: Zn(s) + H2SO4(aq) → ZnSO4(aq)+ H2(g) ====<span style="font-family: 'Arial','sans-serif';">(a) The experiment was repeated, but this time 2 mL water was also added to the beaker. Again the zinc was all used up. Explain why: when water is added, the rate of reaction will decrease. ====

<span style="font-family: 'Arial','sans-serif';">Discuss how this claim could be tested by experiment.
====<span style="font-family: 'Arial','sans-serif';">In an experiment, a sample of large marble chips (CaCO3) is added to 200 mL of dilute hydrochloric acid in an open conical flask. The reaction that occurs is shown below. ==== <span style="font-family: 'Arial','sans-serif';">2HCl(//aq//) + CaCO3(//s//) → CaCl2(//aq//) + H2O( //<span style="font-family: 'Arial','sans-serif';">ℓ //<span style="font-family: 'Arial','sans-serif';">) + CO2(//g//) ====<span style="font-family: 'Arial','sans-serif';">As the carbon dioxide gas escapes from the flask, the total mass of the flask and contents decreases. The loss in mass is recorded at 5 minute intervals until the reaction has stopped. The experiment is repeated, using the same mass, but different sized, marble chips. ====

<span style="font-family: 'Arial','sans-serif';">(c) Explain the change in reaction rate that occurs, with reference to the collisions of particles.
<span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">(1) Hydrogen peroxide decomposes at room temperature (25'C) according to the following equation. 2H2O2(aq) → 2H2O(l) + O2(g)

As the decomposition reaction occurs, bubbles of gas are produced.
====<span style="font-family: 'Arial','sans-serif';">(a) On addition of a very small amount of solid manganese dioxide, the rate at which the bubbles of gas are produced is increased so that rapid fizzing is observed. Further observation indicates that manganese dioxide remains after reaction has stopped. With reference to the collisions of particles, explain why the reaction rate has increased. ====

<span style="font-family: 'Arial','sans-serif';">(b) Hydrogen peroxide is stored at a low temperature. Discuss this statement in terms of reaction rate.
(2) The concentration and pH of three acids, HA, HB and HC, are shown in the table below. ====<span style="font-family: Arial,Helvetica,sans-serif;">(a) A small piece of magnesium is added to a 20 mL sample of each of the acid. Name the acid that would be expected to react most rapidly with the magnesium. Explain why this acid will react the fastest. ==== <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">The reaction between 20.0 mL of 0.500 mol L–1 hydrochloric acid and 20.0 mL of 0.250 mol L–1 sodium thiosulfate solution at room temperature (25°C) produces a precipitate of sulfur that makes the solution go cloudy after about 5 minutes. ====<span style="font-family: Arial,Helvetica,sans-serif;">(a) How would the time taken for the solution to go cloudy be affected if the reaction were carried out in a water bath at a temperature of 50°C? ====

<span style="font-family: Arial,Helvetica,sans-serif;">(b) With reference to the collisions of particles, explain why the reaction is affected in this way.
====<span style="font-family: Arial,Helvetica,sans-serif;">Attempt all of the previous NCEA Rate of Reaction exam questions - shown above and available to download on a word document below. Ideally get your answer corrected by either your teacher or email them to the email link on the sidebar, we'll email you back with feedback in a couple of days. It is essential that you have personal feedback on your answers so as to ensure you have phrased your answer correctly and not left out any key points. ==== <span style="font-family: Arial,Helvetica,sans-serif; line-height: 0px; overflow: hidden;">

[[image:crystalball.gif]]
<span style="color: #000000; display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">There is no set of Crystal Ball questions for Rates of Reaction, once you have completed all above you'll be very comfortable answering a question on rates of reaction.



<span style="color: #f95725; font-family: Arial,Helvetica,sans-serif;">NCEA EXAM QUESTION:Write the Equilibrium constant expression for the following reactions
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==<span style="color: #f95725; font-family: Arial,Helvetica,sans-serif;"> NCEA EXAM QUESTION: Interpreting information using equilibrium constant values == <span style="color: #f95725; font-family: Arial,Helvetica,sans-serif;">

1) For the reaction below, the values of //K// c at different temperatures are shown in the table. N 2 (//g//) + 3H  2  (//g//) <span style="font-family: 'Cambria Math','serif';">⇄ 2NH  3  (//g//)
====<span style="font-family: Arial,Helvetica,sans-serif;">Use this information to determine whether the formation of NH3(g) is endothermic or exothermic. Justify your reasoning using equilibrium principles. ==== ====<span style="font-family: Arial,Helvetica,sans-serif;">2) For the reaction below, the //K//c value is 46.8 at 491°C H2(//g//) + I2(//g//) <span style="font-family: 'Cambria Math','serif';">⇄ 2HI(//g)// Calculate the concentration of HI(//g//), at equilibrium, at 491°C, if the concentration of H 2(//g//) is 0.0190 mol L–1 and the concentration of I 2(//g//) is 0.210 mol L –1 . ==== <span style="color: #f95725; font-family: Arial,Helvetica,sans-serif;">

<span style="color: #f95725; font-family: Arial,Helvetica,sans-serif;">[[image:2012sample.jpg]]
The reaction between sulfur dioxide gas and oxygen gas at a particular temperature to make sulfur trioxide gas can be represented as: 2SO2(g) + O2(g) --> 2SO3(g)

The following reaction can be used to produce gaseous methanol, CH3OH, from carbon monoxide and hydrogen.
<span style="color: #221e1f; font-family: 'Arial','sans-serif';">CO(//g//) + 2H <span style="font-family: 'Arial','sans-serif'; font-size: 10.6667px;">2 <span style="color: #221e1f; font-family: 'Arial','sans-serif';">(//g//) → <span style="color: #221e1f; font-family: 'Arial','sans-serif';">CH <span style="font-family: 'Arial','sans-serif'; font-size: 10.6667px;">3  <span style="color: #221e1f; font-family: 'Arial','sans-serif';">OH(//g//) Δ <span style="font-family: 'Arial','sans-serif'; font-size: 10.6667px;">r  //<span style="color: #221e1f; font-family: 'Arial','sans-serif';">H //<span style="color: #221e1f; font-family: 'Arial','sans-serif';">= –90.7 kJ mol <span style="font-family: 'Arial','sans-serif'; font-size: 10.6667px;">–1 ====<span style="color: #221e1f; font-family: 'Arial','sans-serif';">At 25°C, the equilibrium constant, //K// <span style="font-family: 'Arial','sans-serif'; font-size: 10.6667px;">c <span style="color: #221e1f; font-family: 'Arial','sans-serif';">= 2.20 × 10 <span style="font-family: 'Arial','sans-serif'; font-size: 10.6667px;">–4 <span style="color: #221e1f; font-family: 'Arial','sans-serif';">. Explain what this indicates about the relative amounts of reactants and product at equilibrium. ==== <span style="color: #221e1f; font-family: 'Arial','sans-serif';"> ====<span style="color: #221e1f; font-family: 'Arial','sans-serif';">Hydrogen gas and iodine vapour are placed in a sealed container at 445°C. These gases combine to form hydrogen iodide gas. This equilibrium can be represented by: ==== <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: center;">H2(g) + I2(g) → 2HI(g)colourless purple colourless

<span style="color: #221e1f; font-family: 'Arial','sans-serif';">(a) Describe how an observer would know that the system had reached equilibrium.
====<span style="color: #221e1f; font-family: 'Arial','sans-serif';">(b) At 445°C, the equilibrium constant //K// <span style="font-family: 'Arial','sans-serif'; font-size: 10.6667px;">c <span style="color: #221e1f; font-family: 'Arial','sans-serif';">= 49.5. ==== ====<span style="color: #221e1f; font-family: 'Arial','sans-serif';">(i) Name the species that will be in the highest concentration at this temperature. You may name one, or more than one species in your answer. ====

<span style="color: #221e1f; font-family: 'Arial','sans-serif';">(ii) Explain your answer.
====<span style="color: #221e1f; font-family: 'Arial','sans-serif';">(c) When the temperature of the equilibrium system is raised from 445°C to 1000°C (at constant pressure), the value of //K// <span style="font-family: 'Arial','sans-serif'; font-size: 10.6667px;">c <span style="color: #221e1f; font-family: 'Arial','sans-serif';">decreases. ==== ====<span style="color: #221e1f; font-family: 'Arial','sans-serif';"> Use this information to determine whether the reaction between hydrogen and iodine is exothermic or endothermic. Justify your reasoning. ==== <span style="color: #221e1f; font-family: 'Arial','sans-serif';">

<span style="color: #221e1f; font-family: 'Arial','sans-serif';">(a) Nitrogen monoxide gas reacts with oxygen gas to form nitrogen dioxide gas. The equilibrium reaction can be represented by:
<span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: center;">2NO(g) + O2(g) → 2NO2(g)colourless colourless brown ====<span style="color: #221e1f; font-family: 'Arial','sans-serif';">At 230°C the equilibrium constant for this reaction has a value of 6.44 × 10 <span style="font-family: 'Arial','sans-serif'; font-size: 10.6667px;">5 <span style="color: #221e1f; font-family: 'Arial','sans-serif';">. ==== ====<span style="color: #221e1f; font-family: 'Arial','sans-serif';"> (ii) State which gas will be in the highest concentration at 230°C. Explain your answer in terms of //K// <span style="font-family: 'Arial','sans-serif'; font-size: 10.6667px;">c <span style="color: #221e1f; font-family: 'Arial','sans-serif';">and the colour seen. ====

<span style="color: #221e1f; font-family: 'Arial','sans-serif';">[[image:NCEA2005.jpg]]
<span style="font-family: Arial,Helvetica,sans-serif;">Ag+(aq) + 2NH3(aq) → <span style="font-family: Arial,Helvetica,sans-serif;">Ag(NH3)2+(aq) <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">(i) At 25°C the value of Kc is 1.70 ´ 107. Name the species that would be present in the higher concentration in the equilibrium mixture at this temperature. Choose either Ag+(aq) or Ag(NH3)2+(aq) Justify your choice. <span style="font-family: Arial,Helvetica,sans-serif;">2NO2(g) →<span style="font-family: Arial,Helvetica,sans-serif;"> 2NO(g) + O2(g) <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">(ii) At 200°C the value of Kc is 1.10 ´ 10–5. Name the species that would be present in the higher concentration in the equilibrium mixture at this temperature. Choose either NO2(g) or NO(g). Justify your choice. <span style="color: #000000; display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">

<span style="color: #f95725; display: block; font-family: Arial,Helvetica,sans-serif; font-size: 0px; text-align: left;">NCEA EXAM QUESTION: Describing and Explaining equilibrium constant reactionsNC <span style="color: #000000; font-family: Arial,Helvetica,sans-serif;">

<span style="color: #f95725; font-family: Arial,Helvetica,sans-serif;">NCEA EXAM QUESTION: Describing and Explaining equilibrium constant reactions
<span style="color: #f95725; font-family: Arial,Helvetica,sans-serif;">

<span style="font-family: Arial,Helvetica,sans-serif;">[[image:2013explainequil.jpg width="528" height="105"]]
<span style="color: #221e1f; font-family: Arial,Helvetica,sans-serif;">Compare and contrast the effect of increasing the pressure on both reactions, with reference to the equilibrium positions. <span style="color: #f95725; font-family: Arial,Helvetica,sans-serif;">

<span style="font-family: Arial,Helvetica,sans-serif;">The pressure is decreased.
====<span style="font-family: Arial,Helvetica,sans-serif;"> 2) When the temperature of the equilibrium system is increased from 200°C to 350°C (at constant pressure), the value of Kc increases, as shown in the table ==== ====<span style="font-family: Arial,Helvetica,sans-serif;">Use this information to determine whether the decomposition of PCl5 is endothermic or exothermic. Justify your reasoning using equilibrium principles. ==== <span style="color: #f95725; font-family: Arial,Helvetica,sans-serif;">

(a) Two oxides of nitrogen exist in an equilibrium system represented by the following equation. N2O4 is a colourless gas and NO2 is a brown gas.
N2O4(//g//) → 2NO2(//g//) <span style="font-family: 'Lucida Sans','sans-serif';">∆ r//H// = + 57 kJ mol–1

For each of the following changes applied to this equilibrium system in (i) and (ii) below:

 * ====describe the expected observation====
 * ====use equilibrium principles to explain this observation.====

(i) The pressure is **decreased.**
====<span style="color: #221e1f; font-family: 'Arial','sans-serif';">The following reaction can be used to produce gaseous methanol, CH <span style="font-family: 'Arial','sans-serif'; font-size: 10.6667px;">3 <span style="color: #221e1f; font-family: 'Arial','sans-serif';">OH, from carbon monoxide and hydrogen. ==== <span style="color: #221e1f; font-family: 'Arial','sans-serif';">CO(//g//) + 2H <span style="font-family: 'Arial','sans-serif'; font-size: 10.6667px;">2  <span style="color: #221e1f; font-family: 'Arial','sans-serif';">(//g//) → <span style="color: #221e1f; font-family: 'Arial','sans-serif';">CH <span style="font-family: 'Arial','sans-serif'; font-size: 10.6667px;">3  <span style="color: #221e1f; font-family: 'Arial','sans-serif';">OH(//g//) Δ <span style="font-family: 'Arial','sans-serif'; font-size: 10.6667px;">r  //<span style="color: #221e1f; font-family: 'Arial','sans-serif';">H //<span style="color: #221e1f; font-family: 'Arial','sans-serif';">= –90.7 kJ mol <span style="font-family: 'Arial','sans-serif'; font-size: 10.6667px;">–1

<span style="color: #221e1f; font-family: 'Arial','sans-serif';">Below are three possible factors that could be changed to alter the amount of methanol produced in this reaction.
====<span style="color: #221e1f; font-family: 'Arial','sans-serif';">Discuss the changes which could be made to **increase** the amount of **methanol** produced. Your answer should relate each of the factors in the table above to equilibrium principles. ==== <span style="color: #221e1f; font-family: 'Arial','sans-serif';">

<span style="color: #221e1f; font-family: 'Arial','sans-serif';">The following equilibrium system is formed when hydrogen gas is mixed with iodine gas.
<span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: center;">H2(g) + I2(g) → 2HI(g)colourless purple colourless ====<span style="color: #221e1f; font-family: 'Arial','sans-serif';">The reaction has a negative value for Δ <span style="font-family: 'Arial','sans-serif'; font-size: 10.6667px;">r //<span style="color: #221e1f; font-family: 'Arial','sans-serif';">H //<span style="color: #221e1f; font-family: 'Arial','sans-serif';">. For each of the following changes applied to this system: ====
 * ====<span style="color: #221e1f; font-family: 'Arial','sans-serif';">describe the expected observation ====
 * ====<span style="color: #221e1f; font-family: 'Arial','sans-serif';">use equilibrium principles to discuss the reason for this observation. ====

 <span style="color: #221e1f; font-family: Arial,Helvetica,sans-serif;">(iii) <span style="color: #221e1f; font-family: 'Arial','sans-serif';"> The pressure is increased.
<span style="color: #221e1f; font-family: 'Arial','sans-serif';"> ====<span style="font-family: Arial,Helvetica,sans-serif;">(1) One step in the production of sulfuric acid involves forming sulfur trioxide from sulfur dioxide. The equilibrium reaction can be represented by ==== 2SO2(g) + O2(g) → 2SO3(g) ΔrH = –196 kJ mol–1

<span style="font-family: Arial,Helvetica,sans-serif;">(ii) Explain why this will increase the amount of SO3(g) present at equilibrium.
====<span style="font-family: Arial,Helvetica,sans-serif;">(2) <span style="color: #221e1f; font-family: 'Arial','sans-serif';">Carbon dioxide is added to drinks to make them fizzy. The following equilibria are involved: ==== ====<span style="font-family: Arial,Helvetica,sans-serif;">The drink is fizzy when there is dissolved carbon dioxide, CO2(aq). The drink stops being fizzy when the carbon dioxide escapes from the drink as a gas. ====

<span style="font-family: Arial,Helvetica,sans-serif;">Your answer must include reference to:
<span style="color: #221e1f; font-family: 'Arial','sans-serif';">
 * ====<span style="font-family: Arial,Helvetica,sans-serif;">equilibrium shift in Equation One and Equation Two ====
 * ====<span style="font-family: Arial,Helvetica,sans-serif;">changes in the fizziness of the drink ====
 * ====<span style="font-family: Arial,Helvetica,sans-serif;">any change in pH. ====

<span style="font-family: Arial,Helvetica,sans-serif;">For each of the following changes applied to this system:

 * ====<span style="font-family: Arial,Helvetica,sans-serif;">describe the expected observation ====
 * ====<span style="font-family: Arial,Helvetica,sans-serif;">use equilibrium principles to discuss the reason for this observation. ====

<span style="font-family: Arial,Helvetica,sans-serif;">(iii) Solid iron(III) chloride is added to the reaction mixture.
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<span style="font-family: 'Arial','sans-serif';">An equilibrium system is shown below.
3H2(//g//) + N2(//g//) --> 2NH3(//g//) ====<span style="font-family: 'Arial','sans-serif';">The pressure of the system is increased, while maintaining a constant temperature. The percentage of NH3 in the reaction mixture is recorded and graphed. ==== ====<span style="font-family: 'Arial','sans-serif';">(b) On the above graph, identify the line that shows the correct relationship between the percentage of NH3 in the reaction mixture, and increasing pressure**.** Explain your answer by applying knowledge of equilibrium principles. ====

<span style="font-family: 'Arial','sans-serif';">(b) The enthalpy change (∆r//H//) for this reaction as written above, has a negative value.
====<span style="font-family: 'Arial','sans-serif';"> **N**ame the ion that would be present in the higher concentration when the equilibrium mixture is heated, choose either [CoCl4]2–(//aq//) or [Co(H2O)6]2+(//aq//) Explain your answer. ==== <span style="font-family: 'Arial','sans-serif';">

<span style="font-family: 'Arial','sans-serif';">[[image:NCEA2004.jpg]]
==== (a) The following equilibrium system is established when thiocyanate ions (SCN) are added to iron (III) ions (Fe3+). The resulting aqueous solution is a dark red colour. The equation representing the equilibrium system and the colours of each species involved are given below. ==== <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">When iron (III) ions (Fe3+) are removed from the equilibrium mixture (by adding sodium fluoride), a colour change is observed. Describe the colour change you would expect to see and explain why it occurs.(ii) <span style="display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">The pressure of the system at equilibrium is increased (by decreasing the total volume of the system). Describe the effect of this change on the amount of NH3 in the system. Explain your answer.The percentage of NH3 present in equilibrium mixtures at different temperatures and at constant pressure is shown in the table below.

Justify whether the reaction in which NH3 is formed, is endothermic or exothermic.
<span style="color: #000000; display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;"> <span style="color: #000000; display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">

Complete the table showing the hydronium ion concentration, hydroxide ion concentration and pH for these solutions. **Kw = [H3O+] [OH-] = 1.00 x 10-14**
<span style="font-family: Arial,Helvetica,sans-serif;"> <span style="font-family: Arial,Helvetica,sans-serif; line-height: 0px; overflow: hidden;">

[[image:crystalball.gif]]
<span style="color: #000000; display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">There is no Crystal Ball Activity for this task as once you have completed all the above calculations you will be sweet with them.

<span style="color: #000000; display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;"> <span style="color: #f95725; font-family: Arial,Helvetica,sans-serif;">NCEA PAST EXAM QUESTIONS on writing equations on conjugate acid/base pair <span style="color: #f95725; display: block; font-family: Arial,Helvetica,sans-serif; text-align: left;">

(ii) HPO42–(aq) is a species that can act as an acid or a base. Write equations for the reactions of HPO42– with water: one where it acts as an acid, and one where it acts as a base.
<span style="color: #f95725; display: block; font-family: Arial,Helvetica,sans-serif; line-height: 0px; overflow: hidden; text-align: left;">

<span style="font-family: Arial,Helvetica,sans-serif;">ii) HF(aq) + H2O -->
====<span style="font-family: Arial,Helvetica,sans-serif;">The bicarbonate ion, HCO3–, can both accept and donate hydrogen ions (protons). Write the equations below. When sodium bicarbonate, NaHCO3, dissolves in water the solution is basic. ====

<span style="font-family: Arial,Helvetica,sans-serif;"> Circle Reaction A or Reaction B to show which reaction predominates. Justify your answer.
<span style="font-family: 'TimesNewRomanPSMT','sans-serif'; font-size: 14.6667px;">

<span style="font-family: Arial,Helvetica,sans-serif;">iii) A solution of sodium hypochlorite, NaOCl, is basic. Discuss the above statement, including appropriate chemical equation(s) in your answer.
====Chickens make egg shell, CaCO3, using carbon dioxide gas from the air. The carbon dioxide forms carbonic acid (H2CO3), which then reacts to form the carbonate ions (CO32–) needed to make egg shell. Two equations showing part of this process are given below.====

Specify which equation above (1 or 2) shows HCO3− acting as an acid. Give a reason for your answer.










<span style="color: #f95725; font-family: Arial,Helvetica,sans-serif;">NCEA PAST EXAM QUESTIONS on Explaining properties of aqueous solutions
<span style="color: #f95725; font-family: Arial,Helvetica,sans-serif;">

<span style="font-family: Arial,Helvetica,sans-serif;">Some properties of three aqueous solutions A, B and C, of equal concentration are shown in the table below.
====<span style="font-family: Arial,Helvetica,sans-serif;">The labels of the three solutions have been removed. It is known that the solutions are NH3(aq), HCl(aq) and NH4Cl(aq). Use the information in the table above to identify each of the three solutions. Justify the identification of all three solutions. In your answer you should: ====

(a) Place the following solutions in order of increasing pH,

 * ====0.01 mol L–1 CH3COOH====
 * ====0.01 mol L–1 HCl====
 * ====0.1 mol L–1 HCl====
 * 0.1 mol L–1 NaOH

• equations for reactions.
====<span style="font-family: Arial,Helvetica,sans-serif;">Methyl orange can be used as an acid-base indicator. It is pink in solutions with a pH less than 3 and yellow in solutions with a pH greater than 4. ====

<span style="font-family: Arial,Helvetica,sans-serif;">a) Write down the pH and colours of each of the four solutions if methyl orange is added to them.
====<span style="font-family: Arial,Helvetica,sans-serif;">b) Using only the methyl orange indicator, additional water, test tubes and a measuring cylinder, discuss how a student could identify each of the four solutions. ====

The concentration and pH of three acids, HA, HB and HC, are shown in the table below.
====<span style="font-family: Arial,Helvetica,sans-serif;">a) A small piece of magnesium is added to a 20 mL sample of each of the acids. Choose acid that would be expected to react most rapidly with the magnesium. ====

<span style="font-family: Arial,Helvetica,sans-serif;">b) Choose the weakest acid, Explain why this acid is the weakest
====<span style="font-family: Arial,Helvetica,sans-serif;">c) A solution of sodium ethanoate (NaCH3COO) is tested and found to have a pH of 8.50. Discuss why the pH of the solution is greater than 7. Include appropriate equation(s) in your answer. ====

Two acids of the same concentration, hydrochloric acid (HCl) and propanoic acid (CH3CH2COOH), have properties as shown below:
====(b) Consider the properties described in the table above. Explain the differences in the **conductivity** and **pH** of the two acids. In your explanation include reference to the species present in each solution.====

an increase in pH indicates a decrease in hydrogen concentration [H3O+] or [H+]
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=<span style="color: #f95727; font-family: Arial,Helvetica,sans-serif;">Download this FREE preview of a BRILLIANT Level 2 Chemistry workbook = =<span style="color: #f95727; font-family: Arial,Helvetica,sans-serif;">Beginning Chemistry (2012) Anne Wignall and Terry Wales, Pearson Publishers = =<span style="color: #f95727; font-family: Arial,Helvetica,sans-serif;">Answers included at the back of the book too (Thank you!) = =<span style="color: #f95727; font-family: Arial,Helvetica,sans-serif; text-align: center;">Download this FREE live preview of an INCREDIBLY student friendly Level 2 Chemistry workbook = =<span style="color: #f95727; font-family: Arial,Helvetica,sans-serif; text-align: center;">and = =<span style="color: #f95727; font-family: Arial,Helvetica,sans-serif; text-align: center;">REALLY student friendly Level 2 Chemistry Revision workbook = =<span style="color: #f95727; font-family: Arial,Helvetica,sans-serif; text-align: center;">//SciPAD// (2015) Jason Rendle, Silverback Academic Media = <span style="color: #211d1e; display: block; height: 1px; left: -40px; overflow: hidden; position: absolute; top: 10677px; width: 1px;">(i) Complete the table below to show the conjugate acid-base pairs.
 * = [[image:l2scipadexternal.jpg width="226" height="318" link="@http://www.scipad.co.nz/Digital/Year%2012%20Chemistry%20Externals%20digital/Level%202%20Chemistry%20%28Ext%29.html"]] ||= [[image:l2scipadrevision.jpg width="226" height="327" link="@http://www.scipad.co.nz/Digital/Level%202%20Chemistry%20Revision%20Digital/Level%202%20Chemistry%20Revision.html"]] ||