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OCR GATEWAY CHEMISTRY B 16th June C4 C5 C6

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Reply 80
in that question about co2 and h2o there were both opposites
i think they gave water a high boiling point and u needed to work out co2 which has a low boiling point because its a gas.
Sodium Carbonate gets added and the carbonate ions react with the calcium ions to form calcium carbonate.

Yes you can have both temporary and permanent hardness, your friend was correct.
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(edited 9 years ago)
Reply 82
Original post by George Bristowe
Sodium Carbonate gets added and the carbonate ions react with the calcium ions to form sodium carbonate.

Yes you can have both temporary and permanent hardness, your friend was correct.
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sodium carbonate? do you mean sodium hydrogen carbonate?
Original post by geekygeek
sodium carbonate? do you mean sodium hydrogen carbonate?

No, I'll quote you this from the ocr gcse revision guide, 'both types of hardness are removed by adding washing soda - sodium carbonate, the carbonate ions join onto the calcium ions and make an insoluble precipitate of calcium carbonate' you are probably mistake for calcium hydrocarbonate causes temperary hardness.
Original post by mikyyyyy
in that question about co2 and h2o there were both opposites
i think they gave water a high boiling point and u needed to work out co2 which has a low boiling point because its a gas.

i wrote that it had a low boiling point because it had weak intermolecular forces between its molecules (because i remember reading in the revision guide that things with covalent bonds in them have weak intermolecular forces between its molecules but i'm not sure if this was relevant to the question ???)
how many marks was that question?
Reply 85
2 marks
in the CO2 question you needed to talk about the intermolecular bonds being weak between covalent molecules, its not on the syllabus but you could of gone on to say electrons dont move freely between covalent molecules leading to a weak van der waals force.
Original post by Darcy1
Thats wrong unfortunately, they asked for 3 significant figrues and your answer is only 2, I got 0.0595


Sorry wrong again - although the first person was wrong with 0.059, yours is wrong with 0.0595 because after the decimal point every 0 counts as a sig fig. If you forget about that 0, it changes the number to ten times bigger. So 0.059 is 3 sig fig, however the next number was 5 meaning you has to round it so the answer was 0.060 :smile:
Reply 88
i wrote because it has free electrons and has weak bonds between the molercules
Reply 89
Original post by Simonium1010
Sorry wrong again - although the first person was wrong with 0.059, yours is wrong with 0.0595 because after the decimal point every 0 counts as a sig fig. If you forget about that 0, it changes the number to ten times bigger. So 0.059 is 3 sig fig, however the next number was 5 meaning you has to round it so the answer was 0.060 :smile:


Na I'm right, because the number before the decimal point is 0 therefore 3 significant figures means the first 3 values after the point that aren't zero. If you don't believe me check this site: http://www.ausetute.com.au/sigfig.html

Look at example 'e', 0.005 is one significant figure, but your logic would mean it is 3 significant figures, therefore your answer of 0.060 is wrong as it is one significant figure because theres one value after the decimal point that isn't zero :smile:. I remember the value on my calculator to be about 0.059523.... , so it would be 0.0595 to 3s.f :wink:
(edited 9 years ago)
arr man oh well, other marks for workings out are going to be counted, anyway im sure i wrote the whole answer that was displayed on my calculator so who knows really..


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Reply 91
can someone tell me the answers to the first quistion
Reply 92
can someone also tell me the empirical formulae quistion
Reply 93
Original post by mikyyyyy
can someone also tell me the empirical formulae quistion


i think i got CH4
because when i did the mass over Mr i got 0.1 and 0.4.. so i times them both by 10 and got 1 and 4

What was the first question?
Reply 94
Original post by heench
i think i got CH4
because when i did the mass over Mr i got 0.1 and 0.4.. so i times them both by 10 and got 1 and 4

What was the first question?

can someone tell me the actual question for the empirical formulae please. i got ch3 its the simplest form of the equation i kept dividing them both by 2 until i got the simplest one for each one do u think ill get any marks it was 2 marks.
also in the movement of electrons the one where we had to draw the bonds i drew it properly but didn't add the brackets nor the charge just wrote the number of atoms and put arrows next to it. also the question where u had to draw the displayed formulae i drew it but had 3 carbons only 4 hydrogen and one oxygen when it was supposed to be 7 hydrogen s would i at least get 1 mark for each question?
(edited 9 years ago)
Reply 95
Original post by heench
i think i got CH4
because when i did the mass over Mr i got 0.1 and 0.4.. so i times them both by 10 and got 1 and 4

What was the first question?

the one where u had to estimate the value in the boxes how were u supposed to work it out i put the difference of the other 3 answers and whatever the difference was i just added it on to the unknown value would i get to marks also.:s-smilie:
Original post by mikyyyyy
can someone tell me the actual question for the empirical formulae please. i got ch3 its the simplest form of the equation i kept dividing them both by 2 until i got the simplest one for each one do u think ill get any marks it was 2 marks.
also in the movement of electrons the one where we had to draw the bonds i drew it properly but didn't add the brackets nor the charge just wrote the number of atoms and put arrows next to it. also the question where u had to draw the displayed formulae i drew it but had 3 carbons only 4 hydrogen and one oxygen when it was supposed to be 7 hydrogen s would i at least get 1 mark for each question?


I'm not completely sure what the question is something like 1.2g of carbon and 0.4g of hydrogen? m pretty sure it wasn't CH3 because just thinking of it chemically one carbon atom needs four bonds so one C atom will bond to 4 hydrogens, it was methane- CH4 i think.....maybe you got one mark ? :smile:

In marks schemes ive seen before if you added the arrows on the guidance part you could get 1 out of two marks.

i dont think you will get any marks for the next question, maybe if there generous and you drew the OH group.
Reply 97
Original post by elliot785
I'm not completely sure what the question is something like 1.2g of carbon and 0.4g of hydrogen? m pretty sure it wasn't CH3 because just thinking of it chemically one carbon atom needs four bonds so one C atom will bond to 4 hydrogens, it was methane- CH4 i think.....maybe you got one mark ? :smile:

In marks schemes ive seen before if you added the arrows on the guidance part you could get 1 out of two marks.

i dont think you will get any marks for the next question, maybe if there generous and you drew the OH group.

yeah but the question was out of 2 marks one for doing the hydrogen and the other for the carbon as u had to work it out
Reply 98
also what diagram would be best for measuring the volume of co2 i put the syringe and test tube method its the best way to check the vol. is it correct
also for the cfc question i put
cfcs contain chloride which react with the atmosphere
recently noted by scientists that it damages the atmosphere and makes it less concentrated this allows uv radiation to pass through as the atmosphere is weak.
replaced by hfcs as they dont contain chlorine sighned by 24 countries to replace cfcs some didnt replace as they cannot afford to but atmosphere is coming back.
how many out of three
Reply 99
Can anyone predict the grade boundaries please?

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