C4.1 Predicting chemical reactions
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C4.1 Predicting chemical reactions
Mathematical learning outcome:
CM4.1i arithmetic computation and ratio when determining empirical formulae, balancing equations
Assessable content statements:
C4.1a recall the simple properties of Groups 1, 7 and 0 to include physical and chemical properties
C4.1b explain how observed simple properties of Groups 1, 7 and 0 depend on the outer shell of electrons of the atoms and predict properties from given trends down the groups to include ease of electron gain or loss; physical and chemical properties
C4.1c predict possible reactions and probable reactivity of elements from their positions in the periodic table to include melting point, density, reactivity, formation of coloured ions with different charges and uses as catalyst
C4.1d explain how the reactivity of metals with water or dilute acids is related to the tendency of the metal to form its positive ion
C4.1e deduce an order of reactivity of metals based on experimental results
This resource contains all the necessary teacher notes for performing the demonstration of properties of Group 1 and their reaction with water.
If possible a camera should be used here to enable better vision for the learners. This links to C4.1a and C4.1b.
The reactions of Group 1 are extended to include those with oxygen and chlorine. The close ups allow better observation of the reactions.
This video allows further discussion relevant to C4.1b.
Complete teacher notes and worksheets for a practical investigating the properties and reactions of aqueous solutions of the halogens/halides.
Trends in reactivity and differences in colour of the halogens can be discussed C4.1a and b. The different colours in different solvents link to differences in the particles involved (ions or diatomic molecules).
Learners should already be aware of the periodic table and the fact that the elements are grouped according to certain similarities. The greater detail required to be given here provides the learner with a greater understanding of why the periodic table is of fundamental importance in predicting whether materials will react and to what extent.
The differences in physical properties and relative reactivity of the elements in Group’s 1, 7 (IUPAC 17) and 0 (IUPAC 18) are directly linked to their atomic structure and this should be a route to the learners’ understanding of the reasons for differences seen in reactivity and as a means to support predictions regarding possible reactions (specification statements C4.1a and C4.1b).
Learners are then to look at metals in general and should have previous knowledge from KS3 of the differences in reactivity observed between metals, particularly Group 1. Practical work is invaluable here in allowing learners to discover more of these differences, from which it is possible to deduce an order of reactivity. C4.1c, d and e.
Common misconceptions or difficulties learners may have
Learners rely most on what they are able to see therefore they are unable to differentiate between the nature of particles or bulk materials. Changes of state and dissolving are confused with chemical reactions. This reliance on what they can see rather than appreciating the role of what they might not leads to ignoring the role of oxygen in open system reactions such as corrosion and combustion. Thus the increase in mass of oxidised materials is not realised.
Learners often find it difficult to maintain the idea that the Halogens are found only as diatomic molecules.
Conceptual links to other areas of the specification – useful ways to approach this topic to set learners up for topics later in the course
The development of the reactivity series for metals forms the basis for later understanding of the choice between smelting and electrolysis. The practical work required for PAG C4 and C5 in the practicals listed in this section give the required data for learners to develop their own reactivity series. Research into the extraction methods used for some of these metals would place carbon and hydrogen in the series and give the opportunity for an early introduction to the idea of electrolysis.
Approaches to teaching the content
The physical properties of elements should, wherever possible, be demonstrated in order to give a reality to the information being given. Gas jars containing chlorine, bromine and iodine give access to the fact that there is a clear change in physical state, which can lead to discussions regarding the differing strengths of the intermolecular forces within each one and what cause these. The relative inertness of the Group 0 gases can be discussed in terms of full outer electron rings, while the idea of xenon compounds might be opened up for the more able.
Learners may not have any overt previous knowledge of transition metals and relating their properties to common uses (iron in steel for building and as a catalyst, tungsten in incandescent lamps and dart shanks, copper for pipework and cables, and platinum as a catalyst) makes it easier for them to assimilate the knowledge. Instrumental analysis, involving spectroscopy, brings the ability to identify (qualitative) and quantify (quantitative) substances in a matter of minutes to extremes of precision. At this point it might be useful to discuss nanogram and ppm quantities.
Instructions and worksheets are provided for a practical to investigate the different reactions of a variety acids and metals. There are also details for extension into producing the relevant salts.
Learners can use the results, in conjunction with the work on Group 1, to build a reactivity series for the metals.
Setting up some magnesium in water with an inverted funnel and a boiling tube over the previous week enables it’s positioning in the reactivity series.
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