BronxNerd Posted February 17, 2011 Report Share Posted February 17, 2011 Hye! I need to know of a way to control the amount of pressure exerted on the pipette, because it's one of my control variables for my design lab due tomorrow! I would also like to know if there is a website that features the ingredients/chemical compounds in household items, like Drano, Honey, Ketchup, and Olive Oil? Thanks in advance! Reply Link to post Share on other sites More sharing options...
Keel Posted February 17, 2011 Report Share Posted February 17, 2011 You would simply state that the experiment would be carried out at a constant atmospheric pressure, that of the lab (1 atm). (Unless of course the pressure in your lab constantly changes ) As for the chemical compounds for household items, I think it would be very hard to find a source that will tell you that, as the chemical compounds can vary from product to product. Reply Link to post Share on other sites More sharing options...
BronxNerd Posted February 17, 2011 Author Report Share Posted February 17, 2011 No I mean I have to find a way to control the pressure used to produce a drop from the pippette. Reply Link to post Share on other sites More sharing options...
Keel Posted February 17, 2011 Report Share Posted February 17, 2011 I’m not sure I follow, maybe I'm misunderstanding you. You would normally use a pipette bulb or pump to suck up the liquid, the liquid will then drop out when the pressure in the bulb or pump returns to normal (ie you let air into the bulb). Why this counts as a control variable I’m not sure. Reply Link to post Share on other sites More sharing options...
BronxNerd Posted February 17, 2011 Author Report Share Posted February 17, 2011 My teacher wants the pressure used to be constant so that it doesn't screw up the experimental results. Reply Link to post Share on other sites More sharing options...
Keel Posted February 17, 2011 Report Share Posted February 17, 2011 Hmm...well the pressure will definitely be constant because the pressure exerted on the pipette is the same as the atmospheric pressure. When you say the 'pressure used' what do you mean? How are you using pressure? To me the only control variable valid to a pipette is the volume used, same pipette ect. What experiment are you doing by the way, maybe that will help? Reply Link to post Share on other sites More sharing options...
dessskris Posted February 17, 2011 Report Share Posted February 17, 2011 did you mean a dropper? if yes, maybe you should try using pinch clamp, the thing at the bottom in the figure belowI think it can help a little bit to control the pressure in a dropper.the pressure exerted when using the pipette filler bulb does not affect the volume of solution in the pipette as long as your reading is exactly on the line thing and there is no parallax error. 1 Reply Link to post Share on other sites More sharing options...
Daedalus Posted February 17, 2011 Report Share Posted February 17, 2011 Depends on his experiment.. if he's testing how much liquid is sucked up by a certain (constant) pressure then all your answers are completely useless. If you want to keep pressure exerted rather than the amount of liquid pulled up constant, you probably need one of these: how much pressure is exerted is logically proportionate to the amount of air removed, which you can regulate, most easily, by always removing the maximum amount of air (in the diagram you pull the white bit at the top all the way up). Controlling it with a bulb filler is harder but you can try to "press" it exactly the same number of times with the same intensity -- if the manual controller isn't available, this will be a source of uncertainty.But like I said, it depends on the experiment. Most common experiments, Desy's answer would be correct.. Reply Link to post Share on other sites More sharing options...
BronxNerd Posted February 17, 2011 Author Report Share Posted February 17, 2011 I mean the pressure placed on the bulb filler of the pipette. It's one of my control variables. Desy answered my question. Thanks everyone for helping me figure this out! I really appreciate this! You guys are life-savers. Reply Link to post Share on other sites More sharing options...
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