Objective: Determination of the percent mass of copper in a brass screw via Gravimetric analysis.
1. What is gravimetric analysis?
2. How will gravimetric analysis apply to my objective?
Overview:
The screws we are using are brass screws. Brass is an alloy made up of Copper and zinc. Copper is much more expensive then zinc and the consistency of the alloy is what makes the product profitable and appealing to the customer. Therefore the composition of the alloy is of the utmost concern for the company manufacturing the brass screws. Your objective will be to determine the percent mass of the copper in a brass screw.
What is gravimetric analysis?
The term gravimetric analysis obviously includes the word "gravity". This is likely due to the fact that gravity filtration was used to separate an insoluble substance from a soluble substance. This last detail is what really makes gravimetric analysis. Soluble verses insoluble. If we can convert an unknown quantity into a known substance that is insoluble, then we can collect it, dry it, and weigh it. Use its known composition to determine (stoichiometrically) how much stuff is there. In our case we are tracking copper, so all the copper that is in the screw afterwards is all the copper in there in the beginning and obviously the copper that was in the screw.
Chemical process
Copper alloy to copper ions: The copper alloy needs to be dissolved to release the copper ions into a dissolved solution. We will do this with nitric acid, typically concentrated.
Copper ions to Copper hydroxide: We will neutralize and make the substance insoluble in one step. We are going to add fairly concentrated NaOH to the solution. How much base will be required to neutralize? Think proportions... This will create a blue slushy substance called copper hydroxide (Cu(OH)2). We could use this substance as our known but it is very unstable. It decomposes down to Copper oxide relatively quickly. This sample would decompose overnight. We will use heat to speed up this process.
Collection of Copper oxide via suction filtration: After heating the substance it will turn dark brown, you will want to filter this substance with a buchner funnel. please watch the video on how to complete this task.
How to use a buchner funnel?
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