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Practice acids and bases test 2

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Date Shared: 1 September 2022

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You are given the ions table and the periodic table also, you can access them at this link: https://www.nzqa.govt.nz/ncea/assessment/search.do?query=Science&view=exams&level=01  

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QUESTION ONE: ALUMINIUM AND OXYGEN Aluminium has an atomic number of 13. Oxygen has an atomic number of 8. (a) State the electron arrangement of the aluminium atom and the oxygen atom. Aluminium: Oxygen :
2.8.3 and 2.6
(b) Discuss the type of ions aluminium and oxygen form. In your answer: • State the electron arrangement of the ions formed • List the symbols of both ions • Explain the charge on the ions formed
Aluminium _ion_ has the electron arrangement _2,8_ it loses _3_ electrons to now have a full _outer/valence_ shell and to become _stable._ It becomes _Al3+,_ a _positive_ ion/cation. The _oxide_ ion has the _electron_ _arrangement_ 2,8 it _gains_ 2 electrons to have a full outer/valence shell and become stable. It becomes _O2-,_ a _negative_ ion.
(c) When aluminium and oxygen react together they form a compound. Discuss the type of bonding occurring when they react together. In your answer: • State the formulae of the compound formed • Explain the ratio of the ions in the compound formed • Discuss the type of bonding occurring in the compound
Al2O3. Ratio _2:_ 3 Aluminium _loses_ _3_ electrons, it has _2_ atoms which does this and it gives a total of _6_ electrons to _oxygen,_ each of the _3_ atoms receiving _2_ of these. The type of _bonding_ that occurs is _ionic_ bonding. This is the _attraction_ between a _positive_ metal ion and a _negative_ non-metal ion.
QUESTION TWO: CALCIUM HYDROXIDE AND HYDROCHLORIC ACID Calcium hydroxide and hydrochloric acid reacted together to form a salt and water. (a) State the approximate pH of both the calcium hydroxide and hydrochloric acid.
Calcium hydroxide: pH _11-14 _ Hydrochloric acid : pH _0-2_
(b) Explain the type of reaction occurring between the calcium hydroxide and the hydrochloric acid.
_Neutralisation_ reaction as it is a _base_ and acid reacting together to produce a neutral _salt_ + water
(c) Write a word and balanced symbol equation for calcium hydroxide reacting with hydrochloric acid.
_Calcium_ hydroxide + _hydrochloric_ acid → _Calcium_ _chloride_ + water _ Ca(OH)2_ + _2_ HCl → _CaCl2_ + _2_ H2O
(d) The calcium hydroxide is in a beaker. To this is added hydrochloric acid until there are equal amounts of both. • Explain how universal indicator could be used to determine if a reaction has occurred between the calcium hydroxide and hydrochloric acid. • Discuss the changes in pH as the reaction occurs and link this to the different amount of hydrogen and hydroxide ions.
Universal indicator will go _green_ if a neutral _salt_ is produced. If there is too much _acid_ it will be red, orange or yellow. If there is too much _base_ it will be either _blue_ or purple. At the start the pH would be high _(11-14)_ there would be lots of _OH-_ ions as the calcium hydroxide is a _base._ As the _acid_ is added the pH would _lower_ towards _7_ as you are adding _H+_ ions from the _acid_ and the H+ reacts with _OH-_ to make _H2O._ When there are _equal_ amounts of both the acid and base the pH should be _7_ and the _OH-_ ions and H+ ions would have reacted to form _H2O._
QUESTION THREE: REACTION RATES A piece of copper metal reacts with concentrated nitric acid to form a brown gas nitrogen oxide. The following data was obtained from the experiment: (The same sized piece of copper was used in each experiment).
(a) Compare and contrast the rate of reaction in the three reactions using the collision theory. Experiment 1: This experiment produces the _least_ amount of gas as the concentration is _lower_ (as is the temperature compared to experiment 3) Experiment 2: This produces _more_ gas per minute as the concentration of acid is _greater,_ this means there are more _acid_ particles per volume which means more _successful_ collisions can occur per _second._ Experiment 3: This produces even _more_ gas per _minute_ as the temperature is _warmer_ for this experiment so the acid particles will have more _kinetic_ _energy._ So the reaction will occur at a _faster_ rate as more _successful_ collisions will occur per _second._
Explain how diluting the acid may affect the rate of reaction
Diluting the acid will _slow_ _down_ the reaction rate. As there are now _less_ acid particles per unit _volume_ there are _less_ particles available to react and therefore _less_ successful _collisions_ per _second,_ slowing down the _reaction_ _rate_
The graph opposite was plotted for experiment 1. (c) Explain the above graph in terms of the slope of the line and why it eventually flattens out.
The reaction occurs _quickly_ at first as there are _lots_ of _reactant_ _particles._ The reaction begins to _slow_ as _more_ particles are _used_ _up._ The reaction eventually _stops_ as one or _both_ reactants are _used_ _up._
(d) Discuss TWO ways the reaction rate between the copper metal and concentrated nitric acid could become faster. Relate your answer to the collision theory.
Ways to speed up the reaction include: _ Cut_ up the _metal:_ this increases the _surface_ _area_ available to _react_ Use a _catalyst:_ this _speeds_ up the reaction but the _catalyst_ is not _used_ up. _ Heat_ up the reaction: this increases the _kinetic_ _energy_ of the particles Use even more _concentrated_ acid to provide _more_ acid _particles_ to react

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1 September 2022

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