x Turn on thread page Beta
 You are Here: Home >< A-levels

# Chemistry ionisation question watch

1. Kw of water at 10 degrees is 3x10-^15 mol 2 Dom-6 and at 50 degrees it is 5.50 x 10-^14 mol dm-6. Calculate pH of water at both temps and state if it's acid, alkali or neutral.
For 10 degrees I got 14.5
For 50 I got 13.3
Don't think it's right. Can someone explain how to do this question and what the right answer is? Thank you
2. Sorry you've not had any responses about this. Are you sure you’ve posted in the right place? Posting in the specific Study Help forum should help get responses.

I'm going to quote in Tank Girl now so she can move your thread to the right place if it's needed.

Spoiler:
Show
(Original post by Tank Girl)
x
3. (Original post by AqsaMx)
Kw of water at 10 degrees is 3x10-^15 mol 2 Dom-6 and at 50 degrees it is 5.50 x 10-^14 mol dm-6. Calculate pH of water at both temps and state if it's acid, alkali or neutral.
For 10 degrees I got 14.5
For 50 I got 13.3
Don't think it's right. Can someone explain how to do this question and what the right answer is? Thank you
10 degrees: (3 x 10-15/1.0x 10-7)= 3 x 10-8
50 degrees: (5.50x 10-14/ 1.0 x 10-7) = 5.5x 10-7

-Log [H+] = pH

10 degrees: 7.52 therefore neutral
50 degrees: 6.25 therefore acidic
10 degrees: (3 x 10-15/1.0x 10-7)= 3 x 10-8
50 degrees: (5.50x 10-14/ 1.0 x 10-7) = 5.5x 10-7

-Log [H+] = pH

10 degrees: 7.52 therefore neutral
50 degrees: 6.25 therefore acidic
Thanks so much!!

Why did u divide it by 1.0x10--7 thoo??
5. (Original post by AqsaMx)
Thanks so much!!

Why did u divide it by 1.0x10--7 thoo??
Because Kw is [H+][OH] So half of 1.0 x 10-14 is 1.0 x 10-7. Btw I gave you the wrong determination above, they are both neutral tions as in pure water the conc of H+ and OH- is always equal
Because Kw is [H+][OH] So half of 1.0 x 10-14 is 1.0 x 10-7. Btw I gave you the wrong determination above, they are both neutral tions as in pure water the conc of H+ and OH- is always equal
I don't get how they're both neutral?

I got 7.3 for 10
And 6.6 for 50
7. (Original post by AqsaMx)
I don't get how they're both neutral?

I got 7.3 for 10
And 6.6 for 50
Because if the concentration of [H+] and [OH-] is equal they cancel out. Remember that this is pure water we are talking about.

Some variation is expected depending on your calculator model; examination mark schemes usually have an accepted range on it to account for this. Your answers look alright to me.
8. 10 DEGREES I got pH= 7.26 ( ALWAYS TO 2.D.P CHEM OCR A )
50 DEGREES i got pH= 6.63

kW= [ H+]2

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: November 15, 2015
Today on TSR

### Ask the House of Commons anything

The digital outreach team is online until 4pm!

Poll

## All the essentials

### Student life: what to expect

What it's really like going to uni

### Essay expert

Learn to write like a pro with our ultimate essay guide.

### Create a study plan

Get your head around what you need to do and when with the study planner tool.

### Resources by subject

Everything from mind maps to class notes.

### Study tips from A* students

Students who got top grades in their A-levels share their secrets