Crystal Clear
Look-a-likes
Surely, if you know what elements are in something, you know all about it?
Dorothy Hodgkin looked at how atoms fit together into very complicated molecules. She used X-ray crystallography to find out what penicillin and insulin look like. Knowing what the molecules look like has helped other scientists understand how these molecules work, and to make new medicines.
This resource looks at how the same atoms can bond together to create very different molecules.
In theory, a can of diet drink will float, while a can of regular, sugary drink will sink. The sugar in the drink makes the can and drink more dense than water. The diet drink floats, as its average density (the metal can, the liquid and the gas that gives it its fizz) is less than water. There are times when this doesn't work, for instance if there is more gas in the regular drink can!
Curriculum Links
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Science: |
QCA Unit 7G |
Particle model of solids, liquids and gases |
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QCA Unit 8A |
Food and digestion |
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QCA Unit 8E |
Atoms and elements |
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QCA Unit 8F |
Compounds and Mixtures |
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Key Concepts 1.1 Scientific thinking a) using scientific ideas and models to explain phenomena and developing them creatively to generate and test theories Key Processes 2.1 Practical and enquiry skills a) use a range of scientific methods and techniques to develop and test ideas and explanations c) plan and carry out practical and investigative activities, both individually and in groups Curriculum Opportunities h) explore contemporary and historic scientific developments, and how they have been communicated APP Links AF2 Understanding the implications and applications of science (e.g. exploring how understanding of crystallography/atomic structure allowed scientists to answer and pose further questions) |
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History: |
Unit 21 |
Scientific discoveries |
Scottish Curriculum Links
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Science
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SCN 2-08a |
Forces, electricity and waves - Forces I have collaborated in investigations to compare magnetic, electrostatic and gravitational forces and have explored their practical applications. [Note: level 2] |
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SCN 3-08a |
Forces, electricity and waves - Forces I have collaborated in investigations into the effects of gravity on objects and I can predict what might happen to their weight in different situations on Earth and in space. |
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SCN 3-15b |
Materials - Properties and uses of substances Having contributed to a variety of practical activities to make and break down compounds, I can describe examples of how the properties of compounds are different from their constituent elements. |
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SCN 4-15a |
Materials - Properties and uses of substances Through gaining an understanding of the structure of atoms and how they join, I can begin to connect the properties of substances with their possible structures. |
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Technologies
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TCH 4-10b |
Food and textiles contexts for developing technological skills and knowledge |
Look-a-likes
Scientists in the 1700s began to understand
that everything around us is made of tiny particles called
atoms. By the end of the century Antoine Lavoisier had
discovered that water was made of hydrogen and oxygen and that air
was a mixture of gases: he did this by carefully weighing different
elements and compounds (where more than one element is bonded
together).
Another scientist, John Dalton, used models to show how some elements bonded together to make compounds: have a look at his drawings in the 1826 trailblazing entry(http://trailblazing.royalsociety.org/). By the 1900s, chemists were able to describe what many simple compounds, or molecules, looked like.
Larger molecules were a different matter. It was harder to work out their bonds, and two different molecules could even have the same number and type of elements in them.
| Key fact: Molecules are made up of different atoms - or elements - bonded together. |
Surely, if you know what elements are in something, you know all about it?
A lot of the sugar we eat
is made up of three different types of sugar:
glucose; fructose; and
galactose. Fructose is the sweetest, while
galactose is not very sweet at all. When we eat these
different sugars, our body treats them differently.
However, if we just look at the elements which make them
up, they each have six carbon atoms, six oxygen atoms and twelve
hydrogen atoms.
You can see the range of sugars found in foods by looking at the ingredients list on the back of the packet.
Have a look at some food packaging yourself. You may want to choose food like chocolate biscuits and breakfast cereals. You will probably find sucrose, common sugar (made of fructose and glucose bonded together), as well as lactose or maltose.
Types of sugar:
Sucrose - a glucose and fructose molecule
bonded together
Maltose - two glucose molecules bonded
together
Lactose - a galactose and glucose molecule bonded
together
Honey - 20% water, 40% fructose, 30% glucose, 7%
maltose, 1% sucrose.
Dextrose - this is a form of glucose
Maltodextrin - a chain of glucose molecules bonded
together
Invert sugar syrup - a mixture (not bonded) of
glucose and fructose
| Key fact: Molecules with the same number and types of elements can have different properties. |
Artificial sweeteners
You can
test food to find out how much sugar each contains by using
Benedict's Test. However, two foods with the same amount of
sugar in them will not necessarily taste equally sweet, and there
is no test for sweetness. Instead, many people have to taste
a substance and scientists compare their perception of how sweet it
is with something of known sweetness (like a gram of sugar).
Artificial sweeteners are hundreds or thousands of times more sweet
than glucose.
Use the information below to help you find some
artificial sweeteners in the ingredients lists on your food
packets. How do they compare to sugar in terms of
sweetness?
Acesulfame K - 200 times sweeter than
sucrose
Aspartame - 200 times sweeter than sucrose
Neotame - this is a new sweetener and is 8000
times sweeter than sucrose
Saccharin - about 400 times sweeter than sucrose -
the oldest artificial sweetener discovered 100 years ago.
Sucralose - made from sucrose, but it is 600
times sweeter than sucrose
Diet drinks - the lighter option
Take a closed can of soft drink and a diet version of the same soft drink, and place them both in a basin of water. Does one of the cans float while the other one sinks?
Can you work out what is happening here?
You will need to think about the density of the each of the cans. Take a look at these pictures - there is the same amount of liquid in each of the cans.
You need much less sweetener than you need
sugar, so which can will have a greater mass?
Both cans have exactly the same volume... by using the density equation
Density = Mass / Volume
can you work out which can will have the highest density?
Whether something sinks or floats depends on how its density compares with the density of water. Something with a lower density than water, such as wood, will float. Something with a higher density than water will sink.
Did the cans do what you expected?