Cocaine Effects Involve Changes In The Activity Of What Chemical?

This focus thought is explored through:

Contrasting student and scientific views
Disquisitional teaching ideas
Teaching activities

Contrasting student and scientific views

Student everyday experiences

Students have difficulty distinguishing between physical and chemical change, despite formal teaching, and the distinction is somewhat capricious. Withal an agreement of the differences betwixt purely physical processes such every bit melting, evaporation and boiling and the changes that have identify in chemical reactions, peculiarly the idea that new substances are formed, is important to an understanding of chemistry and students very frequently confuse the two. The following conversations are typical:

Student adding universal indicator to various solutions to rack of 6 test tubes.

Pat (recording the group's notes about a prac): What happened?
Kim: It went fizzy.
Pat: Did yous see whatever new substances?
Kim: Nope.

Sam: What shall I write down was formed?
Chris: A blue colour.

Research: Loughran, Mulhall & Berry (2002)

Research shows that students frequently use the term chemical change to draw changes in physical state. Freezing and boiling are considered to exist examples of chemical reactions. This depends on their conception of substance. If students regard ice as a different substance from liquid water they are likely to classify the melting of water ice equally a chemical change. 1 study constitute that fourscore% of students considered a deviation in color betwixt the reactant and product show of chemic change. Students can consider potassium permanganate (Condy's crystals) dissolving in water to be a chemical change because of the intense difference in colour. Melting and expansion on heating were also considered to be prove of chemical change past some students.

Enquiry: Driver, Rushworth & Wood-Robinson (1994)

Many students did not appreciate that a chemical change is characterised past the formation of a substance having different properties from the original substance and a considerable proportion of students who did were unable to offer suitable reasons for distinguishing a 'new' substance.

Enquiry: Driver, Rushworth & Wood-Robinson (1994)

Students may believe that beer frothing is an instance of a chemic change or an apple ripening is a physical modify.

Research: Tsaparlis (2003)

Students commonly believe that physical changes are reversible while chemic changes are not. Students also frequently believe that the original substance in a chemical reaction vanishes completely and forever. A common everyday application of a reversible chemical reaction is the charging and discharging of rechargeable batteries – including car batteries; however students may believe that batteries are a container of stored electricity, rather than of chemicals that react in ways that convert chemical energy into electrical free energy.

Other unremarkably held views are that chemical changes are caused by the mixing of substances/reactants or that oestrus (which is considered to be some form of fabric) has to exist added.

Scientific view

In a physical change the advent or form of the matter changes but the kind of affair in the substance does not. However in a chemical change, the kind of matter changes and at least i new substance with new properties is formed.

The distinction between concrete and chemical change is not clear cutting. Frequently students are led to believe that a alter is either physical or chemic. In fact this should be considered more than of a continuum. For case salt dissolving in water is usually considered to be a physical modify, however the chemical species in salt solution (hydrated sodium and chlorine ions) are different from the species in solid table salt. Dissolving of instant coffee in water seems to be a concrete modify merely in most cases dissolving is accompanied by an energy change and is probably better considered to be a chemical process even though it is possible to recover the original components by physical means. Many examples of materials dissolving (for example, an Alka Seltzer in water, metal in acid and the effect of acid pelting on marble and physical) involve both chemic and physical processes.

– Research: Fensham (1994)

Most chemical reactions are reversible although this tin exist difficult in practise. Many junior schoolhouse science texts state that chemical changes are irreversible while physical changes can be reversed. Cut paper into tiny pieces or burdensome a stone are obvious physical changes but to restore the original piece of newspaper or rock is difficult. Rechargeable batteries employ ane chemical reaction when discharging and recharging involves driving that reaction backwards, turning the products back into the original reactants. The electrical generator (alternator) on a car recharges the car bombardment constantly while the auto engine is running.

Critical teaching ideas

In a physical alter the nature of the substance, the particles of which it is composed and the numbers of particles remain unchanged.
In a chemical change the properties of the new substances are different from the original, the particles are dissimilar and the number of particles can change.
While the distinction between concrete and chemical alter is a useful ane it should exist seen as more than of a continuum.
Chemical reactions can be reversed but this can be difficult in practise.

Explore the relationships betwixt ideas about physical and chemical change in the Concept Development Maps - (States of Matter, Chemical Reactions)

When instruction virtually physical and chemical changes it is important to let students to see the nomenclature as a continuum. They should be able to observe a number of changes and formulate their views on the kind of change and problems with the nomenclature process. Students should come to see that chemic reactions produce new chemicals distinct from the starting materials but that chemical processes can be reversed. Examining examples of reversible chemical reactions and considering why information technology is difficult to opposite many chemical changes can be very useful.

Teaching activities

Promote reflection on and clarification of existing ideas
The following activities are intended to become students identifying and and then refining their ideas virtually concrete and chemical change. Information technology is important for students to observe a number of changes and to record their opinions on what is happening. They could tape this in a booklet where they write about and depict results and observations. They should exist encouraged to formulate and tape hypotheses about what is happening with the knowledge that their opinions volition not be assessed at this stage.

For an example of this technique see: Using logbooks in year 10 electricity.

This can help bring out their existing ideas and help them challenge and extend their existing beliefs.

Students could investigate:

Heating steel wool in air and collecting the black pulverisation that results, then weighing the reactant and product (there should exist an increase). This could be done as a POE (Predict-Observe-Explain): students are asked to predict what will happen to the weight of the steel wool when it burns. What has been added to the steel wool during combustion?
Dissolving sugar and salt in water and comparing what happens to the electrical conductivity of the ii solutions as the dissolving takes place. Recovering the salt by evaporation shows the table salt is still in that location but the conductivity is indicating something new is forming.
Comparing boiling water with mixing vinegar and baking soda - both produce bubbles but what's the difference? The baking soda and vinegar tin can be mixed in a Ziploc sandwich bag to show the production of a new substance which blows the bag up.
Precipitation reactions, particularly ones that produce an obvious color change, such as Epsom salts and ammonia solution. This can be compared with calculation potassium permanganate to water. What are the differences?
Acid - base reactions tin exist illustrated through the use of indicators both natural (cabbage juice) and synthetic. The colour changes help illustrate that new materials could be forming.

Practise using and build the perceived usefulness of a scientific model or thought
It is of import that examples of changes are not confined to only the materials and chemicals students are exposed to in the classroom. Every bit a homework activity students could be asked to collect examples of changes they see effectually them and classify these on their scale of physical and chemical changes. Some examples they may collect are combustion of fuels, cooking and processes such as digestion, respiration and photosynthesis.

Clarify and consolidate ideas for/past advice to and with others
To consolidate their views students in groups could be asked to choose 2 changes, one which is on the physical end of the continuum and one on the chemic terminate and explain to the class what the differences are. Communicating their ideas to others tin can help students clarify and consolidate new and existing ideas about changes.

Practise using and build the perceived usefulness of a scientific model or idea
Science is an area where deeper significant for a number of key ideas is built gradually by using them in a range of situations and stressing how the same idea helps brand sense of many situations. This is particularly the case with primal ideas in the chemical sciences that cannot be 'discovered', 'proved' or even demonstrated by classroom experiments. Both elements and compounds (a key idea at the macro level) and atoms and molecules (which involve the same thinking at the micro level) are examples of this, but their usefulness tin can be developed by showing (among many other things) how they can help make sense of physical versus chemical changes. These ideas may exist introduced hither, or referred dorsum to if they have been introduced earlier. Writing chemical equations in word and symbolic form can be introduced as a useful style of describing some of the changes students accept seen and also to evidence the advantages of chemical symbols in keeping track of the elements (or atoms) in ways that words do not. If the exact chemical formulae cannot be written (as is the instance with most biochemicals) a desperate simplification tin still be useful. For example wood is mostly cellulose, a polymer of glucose, and a representation such as (C₆H_xO₅)_north can be used to track changes in processes like combustion.

Models and diagrams can help here. For instance, nigh schools have molecular modelling kits which tin exist adapted to show how molecules have contradistinct and atoms have rearranged equally a outcome of changes. Affiche size diagrams can too exist drawn by students to assist with their explanations.

Challenge some existing ideas
Although it is difficult to demonstrate the reversibility of chemical changes, students are very familiar with the need to recharge their mobile phones, cameras and other rechargeable devices. This could be simply discussed, although investigating the chemical reactions that power these devices could be a useful inquiry project. A caveat here is that much of the available information tin can exist very technical.

Promote reflection on how students' ideas have changed
Re-examining their original journal entries can promote reflection on how students' views have changed. Students can then use their new ideas to more examples of change. Activities such equally the following can be used to promote discussion of the kinds of change taking place and of the difficulties of classifying some changes as concrete or chemical:

Dissolving metals in acid (magnesium and zinc) and testing the resultant gas.
Investigating limestone and acid reactions (the production of limestone caves - what sort of change is this?)
Calculation zinc to copper sulfate solution and observing the colour changes that accept place.
Comparing the setting of h2o-based glues such every bit Clag and Aquadhere with two pack adhesives such as Araldite. The sometime works past evaporation of the solvent (water) and is reversible; the latter involves a chemical reaction (a thermosetting polymerisation reaction) between the two components and is not reversible.