Knowing the volume and given some other information, it is possible to work out the number of moles of oxygen. What about the nitrogen IV oxide? You can't measure its volume, but you can measure its mass.
If you weigh the tube containing the sodium hydroxide solution before and after the experiment, the increase in mass is due to the nitrogen IV oxide absorbed. If you know its mass, you can easily work out how many moles there are. Note: You have to be able to do these basic mole calculations. Much of this question was based around this sort of sum. There is nothing at all sophisticated in any of this, but if you were faced with it in an exam for the first time, you could easily panic.
Well, that shouldn't happen now! This involves a complex bit of apparatus, which follows on from Example 2, but adds another problem. The questions concerned the electrolysis of potassium butanedioate solution, and you were given the equation. Three gases were produced. Hydrogen at one electrode, and a mixture of carbon dioxide and ethene at the other one - you weren't told which came off which electrode. You were also told that carbon dioxide could be removed by absorbing it in an alkali before the ethene was collected.
This is just like Example 2 as far as the carbon dioxide and ethene is concerned. Your extra problem is keeping the gases produced at the two electrodes separate so that the hydrogen doesn't get mixed in with the carbon dioxide and ethene. There is a standard bit of apparatus that you can use to do this which most students should have come across, but if you haven't then you would have a bit of difficulty with this.
You use a side-armed U-tube fitted with two carbon electrodes. There is then no possibility of the gases from the two electrodes mixing, and the side-arms can be connected easily to whatever you are going to use to collect or absorb the gases.
Don't forget to draw the bungs, otherwise you won't collect anything. Instead you will throw away a mark! Now let's put in the circuit diagram which the question asked for and some labelling. You need to measure the current the question also asked for that and so you need an ammeter.
Some students apparently used a voltmeter, and so threw away a mark. The hydrogen always comes off from the negative electrode the cathode if it is produced during the electrolysis of a solution.
You should know that. This is probably the favoured method of gas collection in schools. Apart from being easy to set up, it is entertaining to watch! However, if the gas is produced too rapidly then readings may be difficult to take accurately. One advantage is that the apparatus can be adapted for greater volumes of gas by substituting the burette for a large measuring cylinder. Collection over water cannot be used when the gas in question is soluble, for example ammonia, or reacts with water.
One of the difficulties in performing rates experiments is the actual beginning of the reaction. If gases are to be collected then the reactants must be mixed with the apparatus already sealed, or gas will be lost. Report abuse.
Page details. Page updated. Google Sites. This site uses cookies from Google to deliver its services and to analyze traffic. Information about your use of this site is shared with Google. By using this site, you agree to its use of cookies. Learn more Got it. For example, when sodium thiosulphate reacts with an acid, a yellow precipitate of sulfur is formed. This reaction is written as follows:. One way to estimate the rate of this reaction is to carry out the investigation in a conical flask and place a piece of paper with a black cross underneath the bottom of the flask.
At the beginning of the reaction, the cross will be clearly visible when you look into the flask. However, as the reaction progresses and more precipitate is formed, the cross will gradually become less clear and will eventually disappear altogether. By using a stopwatch to time how long it takes for the cross to disappear, and then massing the amount of precipitate formed during this time, an average reaction rate can be calculated. Note that it is not possible to collect the SO 2 gas that is produced in the reaction because it is highly soluble in water.
Boundless vets and curates high-quality, openly licensed content from around the Internet.
0コメント