GChem question

[n2o*]

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Which of the following pH values are possible for an acid?

The answer was -1 AND 4. I know 4 is a possible value, but I tot the pH range was from 1 to 14. Is this a mistake? I don't understand. Pls do explain.

Here is the second question:

In a reaction between 6.0 grams of oxygen gas, 4g of Hydrogen gas, and 5g of S(s) at standard temperature and pressure to make H2SO4, which of hte following is the limiting reagent?

THe answer is oxygen gas, but when I did my calculations it was sulfur. Could a solid not be a limiting reagent?

Pls explain ur calculations. THanks a lot in advance.

 

[howui3]

The -1 is not a mistake. You know that the conversion from molarity (concentration) to pH is -log(concentation). So what if you have a 10M HCl acid, what is the pH?

Though in high school we learn the pH range going from 1-14, there are cases like a very strong concentrated acid that will have a pH lover then 1.

Good luck.

 

[hopesremix]

Here is the second question:

In a reaction between 6.0 grams of oxygen gas, 4g of Hydrogen gas, and 5g of S(s) at standard temperature and pressure to make H2SO4, which of hte following is the limiting reagent?

THe answer is oxygen gas, but when I did my calculations it was sulfur. Could a solid not be a limiting reagent?

Pls explain ur calculations. THanks a lot in advance.

Make sure you don't forget to look at the equation with the correct stoichiometric coefficients:
H2 + 2 O2 + S --> H2SO4

You need 2 moles of O2 per mole of S to produce H2SO4. You have .18 moles of O2 and .15 moles of S. At first glance you might assume that sulfur is the limiting reagent. But since you need 2:1 radtio of 02 to Sulfur, 02 is actually your limiting reagent.

I'm taking the DATs this tuesday and gchem is by FAR my worst subject. DAT achiever is kicking my butt. I just took a practice test and I only scored like a 15 in chem, but a 21 in ochem. go figure.

 

[howui3]

For question 2, you first must convert each element into moles. Then look how many moles you start of the element and how many moles of the product you make. The one that makes the least product is the limiting reagent.

This is a pretty simple gchem problem, have u taken gchem yet?

 

[tinman831]

The -1 is not a mistake. You know that the conversion from molarity (concentration) to pH is -log(concentation). So what if you have a 10M HCl acid, what is the pH?

Though in high school we learn the pH range going from 1-14, there are cases like a very strong concentrated acid that will have a pH lover then 1.

Good luck.

hmm... never knew that. i guess i learn something new every day 🙂

 

[EyeAmCommi]

This is a pretty simple gchem problem, have u taken gchem yet?

Ouch 😱

 

[714guy]

The -1 is not a mistake. You know that the conversion from molarity (concentration) to pH is -log(concentation). So what if you have a 10M HCl acid, what is the pH?

Though in high school we learn the pH range going from 1-14, there are cases like a very strong concentrated acid that will have a pH lover then 1.

Good luck.

Could you give an example of when the pH would be negative?

thanks

 

[beastmaster]

Could you give an example of when the pH would be negative?
thanks

Any acid concentration above 1M gives a negative pH calculation. But here's you're entering the concept of super-acids which are beyond the bronsted-lowry explanations of acid behavior in aqueous solvent. Here's a scenario. You have a HCl and H2O at negative pH. The acid will fully dissociate, but the water picks up the proton to form the hydronium cation (more acid). But now this newly formed acid wants to dissociate, but it's can't. Imagine 2 people playing hot-potatoe. As a group, they can't get rid of the potatoe because they're tossing it back to each other without the option of throwing it on the ground. That's what happens in a super-concentrated acid. It's a theoretical scenario which electrodes don't do a good job calculating. I suspect you can make an acid that would eat the friggin electrode. How's that for negative pH.

 

[howui3]

Could you give an example of when the pH would be negative?

thanks

I did in my answer. What is the pH of 10M HCl? answer: -1.

 

[714guy]

Any acid concentration above 1M gives a negative pH calculation. But here's you're entering the concept of super-acids which are beyond the bronsted-lowry explanations of acid behavior in aqueous solvent. Here's a scenario. You have a HCl and H2O at negative pH. The acid will fully dissociate, but the water picks up the proton to form the hydronium cation (more acid). But now this newly formed acid wants to dissociate, but it's can't. Imagine 2 people playing hot-potatoe. As a group, they can't get rid of the potatoe because they're tossing it back to each other without the option of throwing it on the ground. That's what happens in a super-concentrated acid. It's a theoretical scenario which electrodes don't do a good job calculating. I suspect you can make an acid that would eat the friggin electrode. How's that for negative pH.

Thanks Beastmaster and Thanks Howie. I got it now. 👍

 

[howui3]

no problem. good luck with the DAT.

 

[kimsaekyu]

no problem. good luck with the DAT.

Good luck