 Our world is full of examples of mixtures whose properties we can fine-tune by adjusting the composition of the mixture. Usually when we do this we're trying to get the best of both worlds, achieving the best possible compromise between the properties of the ingredients. For instance, we add antifreeze to the water in car radiators to change the freezing and boiling points of the water. And this means the solution in the car radiators can get colder than 0°C and hotter than 100°C without freezing or boiling. In theory we could use pure antifreeze but the viscosity of this substance is too high to be useful in an engine and it's more expensive than water. So by using a mixture we get the low viscosity and the low cost of the water combined with the wider temperature range of the antifreeze. Gnash is the soft smooth chocolatey mixture used in many desserts or in chocolate centres. It's made by carefully mixing the right proportion of chocolate with cream. The chocolate gives the flavour but it's too hard and brittle for soft fillings. The cream tempers the texture of the chocolate and makes it soft and workable. We used to add lead in the form of a compound called tetraethyl lead to petrol to change its combustion properties. This is an example of using a mixture to fine tune chemical rather than physical properties. The additive raises the temperature at which the petrol ignites, preventing the engine from misfiring or running roughly. When lead and petrol was banned chemists found other less toxic chemicals that could be mixed with petrol in order to change the properties in a similar way. Metal alloys are a very common example of mixtures. Since pure gold is extremely soft it's usually alloyed with silver or other metals to make it stronger and harder. The carrot measurement of gold is an indication of how much gold is in the alloy. Iron is a fantastically useful and relatively cheap metal and is the basis of most modern architecture along with many other uses. However in its pure elemental state iron is too soft for many uses. It can be hardened and strengthened though by mixing it with other elements to give the alloy that we call steel. Carbon or silicon are often added. The steel used for the Harbour Bridge, the Sydney Harbour Bridge, was silicon steel. Steel can also be made resistant to corrosion which is a chemical property by adding a small amount of chromium and nickel and then you have stainless steel. Ok your task for this video is this. I'd like you to look at this question. I've given you the density of silver and the density of gold. Predict what the density of a silver gold mixture and alloy would be and then give me a short explanation of why you think your answer to question one is correct.