CHEMISTRY QUESTIONS HELP (1 Viewer)

[sunshine_c22]

Hi,
I need help with these questions, i've tried doing them mutliple times but I feel that I am not getting anywhere. Also if you could please provide me with tips on how to improve on questions like these it would be greatly appreciated

 

[carrotsss]

For question 3, you first need to convert from grams/Litre to mols/L. This is just like converting from gram to mols normally, you just need to divide the grams by the molar mass, as always. Once you’re done, you can use the pH formula, you don’t need pOH so don’t worry about it.

For question 4, follow the exact same process, but you will need to use the pOH formula, and then use pH=14-pOH

For question 5, remember that [H3O+]=10^(-pH), you can find this using the equation by rearranging the pH equation.

For question 6, you’ll need to convert from pH to pOH using pOH=14-pH and then you can use the formula [OH-]=10^(-pOH) - alternatively you could use Kw but it isn’t really necessary

For question 7, divide the mass by the molar mass (n=m/MM) and then convert the moles to concentration using c=n/v (always remember to keep volume in litres, so 0.3L!) and then you can use the pH formula

For question 8, two aspirin tablets mean we double the mass, getting 1g (remember, mg are 10^-3g), then convert to moles using n=m/MM, and then finally convert to concentration using c=n/v, giving us [acid]. Then, you have to convert the pKa to Ka, which is just using the formula Ka=10^(-pKa), just like pH. Once you’ve found these two, you just need to use the provided formula and you’ll get [H3O+], and so you just need to use pH=-log[H3O+] to find your answer.

For question 9, you’ll first need to convert pKa to pKb using pKb=14-pKa, and then you can convert this pKb value to Kb using the same Kb=10^(-pKb) formula as usual. Then, you can find [OH-] using the formula given, after which you just need to convert it to pOH using pOH=-log[OH-], and then convert that to pH using pH=14-pOH.

For question 10, you’ll first need to find [base]. To do this, just find the moles using n=m/MM (the mass and molar mass are given), and then convert to concentration using c=n/v, the volume being 100mL (0.1L) as there is no volume from the sodium acetate, only the vinegar. The rest of the values are given, so you can just formula sub after this.

In the future it would be good if you provided your answers/working so I could provide more specific advice and figure out where you’ve gone wrong.

Hope this helps!

 

[sunshine_c22]

For question 3, you first need to convert from grams/Litre to mols/L. This is just like converting from gram to mols normally, you just need to divide the grams by the molar mass, as always. Once you’re done, you can use the pH formula, you don’t need pOH so don’t worry about it.

For question 4, follow the exact same process, but you will need to use the pOH formula, and then use pH=14-pOH

For question 5, remember that [H3O+]=10^(-pH), you can find this using the equation by rearranging the pH equation.

For question 6, you’ll need to convert from pH to pOH using pOH=14-pH and then you can use the formula [OH-]=10^(-pOH) - alternatively you could use Kw but it isn’t really necessary

For question 7, divide the mass by the molar mass (n=m/MM) and then convert the moles to concentration using c=n/v (always remember to keep volume in litres, so 0.3L!) and then you can use the pH formula

For question 8, two aspirin tablets mean we double the mass, getting 1g (remember, mg are 10^-3g), then convert to moles using n=m/MM, and then finally convert to concentration using c=n/v, giving us [acid]. Then, you have to convert the pKa to Ka, which is just using the formula Ka=10^(-pKa), just like pH. Once you’ve found these two, you just need to use the provided formula and you’ll get [H3O+], and so you just need to use pH=-log[H3O+] to find your answer.

For question 9, you’ll first need to convert pKa to pKb using pKb=14-pKa, and then you can convert this pKb value to Kb using the same Kb=10^(-pKb) formula as usual. Then, you can find [OH-] using the formula given, after which you just need to convert it to pOH using pOH=-log[OH-], and then convert that to pH using pH=14-pOH.

For question 10, you’ll first need to find [base]. To do this, just find the moles using n=m/MM (the mass and molar mass are given), and then convert to concentration using c=n/v, the volume being 100mL (0.1L) as there is no volume from the sodium acetate, only the vinegar. The rest of the values are given, so you can just formula sub after this.

In the future it would be good if you provided your answers/working so I could provide more specific advice and figure out where you’ve gone wrong.

Hope this helps!

I have tried them again, and got these as the answers, can you tell me if they are right?
3) -0.53
4) 13.93
5) 0.98 mol/L
6) 0.13 mol/L
7) 13.85
8) 1.85 (I'm not so confident with these answers onwards...)
9) 13.69
10) 4.47

 

[carrotsss]

3) yes
4) yes
5) I got 0.95, double check your working and any rounding/calculator entry
6) I got 0.10, double check your working and make sure you don’t round until the end
7) yes
8) I got 3.17, make sure you’re multiplying by Ka and not pKa, and including both tablets
9) I got 12.22. Make sure you convert pKa into pKb and then Kb.
10) I got 4.36. I accidentally wrote 100mL instead of 10mL in my previous post, but either way, I get a different answer so idk why that is, just make sure you used the exact values from the question and don’t round during working

Just wondering, do your quizzes tell you which questions you got wrong or just say the entire thing is wrong? It seems like a strange system

 

[sunshine_c22]

3) yes
4) yes
5) I got 0.95, double check your working and any rounding/calculator entry
6) I got 0.10, double check your working and make sure you don’t round until the end
7) yes
8) I got 3.17, make sure you’re multiplying by Ka and not pKa, and including both tablets
9) I got 12.22. Make sure you convert pKa into pKb and then Kb.
10) I got 4.36. I accidentally wrote 100mL instead of 10mL in my previous post, but either way, I get a different answer so idk why that is, just make sure you used the exact values from the question and don’t round during working

Just wondering, do your quizzes tell you which questions you got wrong or just say the entire thing is wrong? It seems like a strange system

They tell us the question we got wrong, but the question changes when you take another attempt, and I think I only have 2 attempts on this quiz! Thank you so much for your help. I will redo the ones I got wrong, and try to see where I went wrong