Science Buddies: "Ask an Expert"

Oh and another thing- should I consider grinding up the shavings somehow? They haven't exactly become "jelly".

I’m glad you asked about what exactly the ‘wood extract’ was since that is a key point in your experiment. If you look back at one of my early posts, I said to filter out whatever was undigested and use the LIQUID part. You want the acid-digested part of the wood, NOT the undigested fibers. If the digest was successful, you should have some carbohydrates in the liquid that the algae can use as food. This culture will grow faster than the one without the extract and result in a greater mass of algae at the end of the experiment—at least that is the hypothesis. You won’t know if this all works until you do the experiment. I was hoping you could use the Diastix to show that some glucose was produced in the digest.

Note: If you use a coffee filter to filter the digest solution, be sure to rinse it thoroughly BEFORE you use it in case there is something in the paper that might be harmful to algae.

If the pH is still 1 after adding NaOH solution it means you diluted the NaOH too much. As I said before, the NaOH solution should be more concentrated than the HCl so that you don’t have to add too much NaOH to bring the pH to 8.0-8.5. I would go ahead and filter the wood extract and then carefully add NaOH solution to it until you get the pH to 8.0-8.5. If the solution becomes too alkaline you can add some HCl to bring the pH down to what it should be. Don’t add the extract to the algae until you are absolutely certain that the pH is correct!

Go back over my previous posts and follow the instructions for preparing the growth medium and starting the cultures. Remember to take photos of the cultures at the same time every day and under the same lighting.

I think that’s everything I need to tell you, but if you have any doubts about anything, don’t assume it will be OK—ASK! Everything has to be done right because you don’t have time to repeat it.

Good luck!

Sybee

Hi Sybee,
What is the absolute soonest I can pipet the algae from the starter bottle into the six other bottles? I am really crunched for time and am trying to avoid cramming all my conclusions and data anlysises the night before the fair. The algae has been growing with the 16/8 hr cycle since the evening of the twelveth. There is little change; if I scrutinize the photos so far, the liquid seems slightly darker green, but that's it. I'm getting kind of stressed. Could you explain the purpose of the starter bottle? Would it ruin the experiment to just pipet equal amounts into the control and experimental bottles?
Thanks so much (again).

The purpose of the starter bottle is just that-- to get the algae growing well so you can get the experimental cultures off to the best possible start. If you dilute the culture too much it will take longer to grow back. Growing algae quickly requires lots of carbon dioxide, light and some nutrients. You did add the fertilizer, right?

You are providing enough light and hopefully warm enough temperatures to get the algae growing as rapidly as possible. Are you shaking the bottle occasionally? This will help to aerate it better because the more CO2 the algae has the faster it will grow. Some companies actually bubble CO2 through their algae cultures to promote faster growth but this can make the solution acid and the pH has to be monitored and corrected.

Speaking of pH. Did you finally succeed in getting the pH of your wood extract to 8.0? If that wasn't successful then it isn't going to work.

Since you are strapped for time what you can do is reduce the volume of medium in the control and experimental bottles by 1/4. Then you can divide the starter culture among all the bottles and you won't be diluting the cells so much. You have to do three controls and three experimentals so you can run a statistical test on your data. Otherwise you won't be able to prove that there is a significant difference in algae mass with the wood extract compared to controls without wood extract.

So, set up your bottles, add the starter and let the algae grow for as long as you can before you end the experiment. If your hypothesis is correct you should see an increase in the amount of algae in the bottles with the extract. However, it may be that acid digestion does not produce any carbohydrates that Chlorella can use. In that case there won't be any difference. That's ok. Disproving your hypothesis is just as valid as proving it. Did you ever succeed in getting any accurate glucose measurements on the extract?

Good luck!

Sybee

Sybee,
This is not going well. Is 2M NaOH really diluted or something? That is what I have and it is making no difference whatsoever on the filtered HCI solution. I feel bad because I am using up my teacher's acid supply seemingly for naught. I even tried taking just 1/2 L of the HCI and neutralizing that, but still no change with...let's see...265 ml NaOH and 35 ml water (at first I was diluting the acid but stopped when I realized it was weak enough already).

I guess my main question is how much of the HCI do I actually need so it will impact the algae growth? I suppose this depends on the glucose readings, which of course I cannot get until I'm able to neutralize the acid. If it doesn't, though, I could use just how much HCI I need instead of trying to raise the pH of larger than necessary quantities.

OK. When we have problems like this in the lab we always ask WHO made the solutions and did they make them correctly. Errors in making percent and molar solutions are VERY common. I can't be there to see exactly how you are doing the dilutions and what the pH paper looks like, but it is not possible that a strong NaOH solution will not neutralize an HCl solution to give a pH of 8. Are you saying that you have been adding more and more NaOH and your pH is still acidic?

Equal volumes of equimolar solutions of a strong acid like HCl mixed with a strong base like NaOH will give a pH around 7--that's a law of chemistry. So, if that does not happen it means that either your pH paper is not working properly or the concentration of the HCl or NaOH is wrong.

Tell me exactly how the HCl solution was made that you used to digest the wood shavings and also how the NaOH solution was made. Did you make the solutions?

In answer to your "main question", it is NOT HCl that you are looking at! The purpose of the HCl is only to digest the cellulose in the wood to provide some sugars for the algae. Once the HCl acid has done this you have to GET RID OF IT by neutralizing it with NaOH! I thought you understood this. What you have to add to your algae is a solution of about pH 8 that hopefully contains some glucose or other sugar that the Chlorella can use, not HCl.

Post again right away with the answers to my questions and I'll try to help you get your experiment started.

Sybee

Sorry, I do understand about the neutralization but used the wrong terminology. So after I dilute the HCI with NaOH, it cannot be called HCI anymore? I'll make note of that--really wishing my chemistry unit would come faster!

Yes, I am saying that I have been adding NaOH and the pH is still 1. I tested my strips with water and got a pH of 6, so it's not the paper. As for the solutions...I am positive about the NaOH as it is from a previously unopened container that specifically says 2.0 molarity on it. A teacher at the lab made the 10% HCI solution for me while I was getting the equipment set up and ready, so unfortunately I did not see it made. This was a very experienced professor, however, and I have confidence that she did it correctly. The error is likely my own.

I am thinking now that I shouldn't have added NaOH to the entire solution (can we go back to calling this solution WD? ). Perhaps my next course of action should be taking 100 ml or so from the 1/2 L solution I have started and just working with that? Calculating the amounts of water/NaOH/HCI that are in that smaller solution would not be a problem. And I would be able to adjust the proportions of NaOH to WD without using so much NaOH.

Thank you!!!

In science, the one thing that you ALWAYS have to do is use the correct terminology!

OK. You didn't tell me how much 2M NaOH you added to the WD or what the resulting pH was so it's a little hard for me to make suggestions. It would be helpful if you would give specific volumes when there's a problem like this so maybe i can see better how to correct the problem. If I had known the concentration of NaOH was only 2M I would have said there was going to be a problem. That's why I suggested using a concentrated NaOH solution so you would not have to add so much.

The reason that it matters how the HCl solution was made is because there are two ways to make a % solution--by volume or by weight. If the person made 10% HCl by volume (the most common method) then the molarity would be about 1.2 because concentrated HCl has a molarity of 12.1. But if they made a 10% solution by weight the molarity would be about 3.2 because conc HCl is 37%. Can you ask the teacher how they made the HCl solution exactly and let me know?

Is there a chemistry lab at your school? If so then they must certainly have either solid NaOH or a more concentrated solution. Also, a chemistry lab HAS to have a pH meter. Take your WD and tell someone you need to get the pH to 8 without increasing the volume too much. The problem with taking a smaller volume of your WD is that you are also reducing the amount of sugars that you will be adding to the algae. You can do this if you have absolutely no other possibility of using a more concentrated NaOH solution, but it may limit the effect of your digest.

Let me know when you find out how the 10% HCl was made. It is important that you know that, regardless of the neutralization problem for your lab report.

Good luck!

Sybee

How is your project going? Did you complete it ok?

Any feedback or suggestions that you can give us would be very helpful for dealing with similar projects in the future.

Thanks,

Sybee