Science Buddies: "Ask an Expert"

Hello

I am making this experiment for my science project. I have completed all the steps as mentioned in the procedure. Until step 11 it works fine. the pump starts running as soon as I put the conductivity sensor in the neutralized solution. I then adjusted the potentiometer to stop the vinegar flow to normalize the model. I only used 1 MΩ (1,000,000 ohms) potentiometer to adjust the flow and normalize (it this a problem?). Few facts - when check the ph level for all 2 solutions it comes out be for Vinegar - 2, Baking Soda - 6 and netutralize - 4 (not sure if this is correct)

The problem starts after this step as when put the sensor in base solution (baking soda) along with one end of pump tube (outlet) the pump does not run to flow vinegar into baling soda solution to neutralize. I can hear a faint sound of pump trying to run but nothing flows. I made sure all circuits is a shown and no short circuit is occurring. I tried changing batteries but no luck. Does this model uses too much battery to run the motor only once?

My project is due next week and I want this to work at least once and I am lost as to what is the issue. I used the exact measurements of baking soda, water and vinegar to make solutions.

Any help/ guidance will be really helpful.

Thanks

Hi,

Thanks for the detailed description of the problem. I don't know what is wrong, but maybe we can brainstorm some possibilities. It sounds like you have checked everything, but it can't hurt to go over it again: https://www.sciencebuddies.org/science- ... #procedure

Here's my checklist of suspects--

1. make sure all wire and component connections on the breadboard are correct and tight

2. make sure the batteries are installed in the correct orientation and are making good contact.

3. make sure your solutions were prepared and labeled correctly

4. make sure your conductivity sensor is connected securely and the wires are not touching

5. make sure the wires to the alligator clips are tight and the jaws make good contact with the sensor wires

6. make sure all the other alligator clips are making good contact


Make the neutralized solution again, but this time add the bromothymol blue to the baking soda solution and add vinegar until it turns green as it shows in the picture in the Procedure. That gives a solution of about 7, which is neutral pH, neither acidic nor basic. You said the pH of the neutralized solution you made was 4 which means that you overshot the neutralization by adding too much vinegar. If you set the pots to turn the pump off at this pH then too much vinegar will be added.

Having three potentiometers (pots) allows you to adjust the resistance (R) more exactly, so you should be using all three. Are you sure you are turning the pot knob in the right direction? One way increases R and the other decreases it, but the direction depends on which way you connected the pot on the breadboard.

Set up the neutralization step as you described it with the inlet tubing in vinegar and the outlet in baking soda and the sensor in the baking soda. Turn the 1M-ohm pot until the pump starts. Is this what you did already? Try turning each pot's knob back and forth. Maybe the pump is not getting enough voltage (V) to run. Do you have a digital multimeter? You could measure the V across the pump leads and see what it is. Eight AA batteries should give about 12 V DC.

Did you get any extra MOSFETs? This component can fail, although it is unlikely. The pump could also fail, but again that is unlikely.

Get back to us after you have tried again. Hopefully you will find the problem.

Good luck!

Sybee

Thanks Sybee for your response.

As you advised, I rechecked my model according to the steps in the procedures. Everything is in accordance with the steps. Verified all wire contacts and looked OK.

Now you advised to use bromothymol blue but the biggest problem is I don't have that as I am in Canada and I couldn't find it here. Even amazon US does not have this in supply. I am using ph testing strips to check the acid/ base levels. Is there any other way to make the neutralized solution? And the main problem I faced here none of the required products are available in Canada and not everyone in US ships to Canada.

I even tried to use just plain distilled water as a neutralized solution and test the ph level. Even the plain water is giving me ph 4.

I think MOSFET and pump is working fine as when I run by putting sensor in neutralized solution and both tubes in vinegar, it is working i.e. vinegar flows in from one tube and comes out of another. When I tried used all 3 Pots to stop the flow, it stops but does not turn back on when turn back slightly. I think I am turning it Ok as I am able to stop the flow by turning clockwise?

I don't have digital multimeter but when pump is working for one solution I think it is getting enough V (12V) to run via 8 batteries. It should work for the last step as well.

The main problem is the final step when I put the sensor in base solution to run the vinegar into base solution to neutralize it, the pump doesn't work. Can I use different sensors to normalize and to run vinegar to base solution? Is cleaning of the sensor the issue as if I am not cleaning the sensor properly when moving from neutralized solution to base solution?

Appreciate your feedback and guidance.

Thanks

Yo are welcome! Wish I had a good solution to your problem.

You don't have to use bromothymol blue. Test strips work fine for measuring pH of solutions, but not water alone.

Make sure you weighed out the correct amount of baking soda and dissolved it completely in the correct volume of water:
https://www.sciencebuddies.org/science- ... #procedure

The neutralized solution that you made by following the procedure should be close to 7. If your pH paper says otherwise I would suspect that it may be wrong. Get some new test strips if possible. Just be sure they have a wide range of pH 0 to 11.

You should rinse the conductivity sensor with distilled water before putting it into a different solution. Just make sure the leads are still tightly contacted by the alligator clips.

So, when you put the sensor into the neutralized solution the pump runs. That's good. Then you did this, right:

Procedure - Step 11
"If the pump is not running, slowly and gently turn the white knob on the 1 MΩ potentiometer until the pump turns on. Try turning it all the way clockwise and all the way counter-clockwise find out which way turns the pump on (which way you need to turn it will depend on which way you put the potentiometer into the breadboard).

Once the pump is running, very slowly turn the potentiometer's knob in the opposite direction to turn the pump off. Stop turning the knob when it reaches the point that makes the pump very slow and almost turn off. Then move on to the 100 kΩ potentiometer and turn the knob until the pump just switches off. You can also use the 1 kΩ potentiometer for fine-tuning to find the right setting that just turns the pump off. Play around with adjusting the knobs of all three potentiometers until you are satisfied that the pump does not run in the neutralized solution (but will still run if turned slightly)."

Then, you were not able to get the pump to turn back on? Try it again and maybe put a piece of tape on each pot to indicate which direction you have to turn the knob to increase resistance. Also, be sure you know which pot is which!

If the pump was running then it should turn back on using the fine-control pot (1000 ohm, 1 kO). If you used the 1 million ohm (1 MO) coarse control, you may have overshot the R so far that you could not turn the other pots far enough to get the pump back on.

Try this and let us know what happens.

Good luck!

Sybee