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OCR F321 - 23rd May

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Reply 100

voices1

Original post by *QueenBeee

Calcium dissolves ( could get away with saying it disappears)
A gas is produced

Hope that helps!! xx

fizz, bubbles of gas
solid disappears
colorless solution formed.....

Reply 101

786girl

Original post by TrampingRampage

The excess Ca reacts with water which forms calcium hydroxide and hydrogen gas.

In the equation Ca(s) + 2HCl (aq) ----> CaCl2 (aq) + H2 (g),

what would a student observe?

fizzing
solid dissapears

Reply 102

voices1

if you get a solution containing a group 2 element is the solution colourless?

Reply 103

INeedToRevise

Original post by *QueenBeee

Hey guys, been looking for this thread and was just wondering whether someone could help me out :smile:

i did jun09 paper and their is a question that i am confused about for 3a)(ii) i got 177.6 but mark scheme say 180 exact.could anyone help me out??.......Major rep for life!! xx

Hey.

So they give you the moles of CaCO3 as 7.5x10-3. If you look at the equation you have the same number moles of CO2. To find volume you multiply moles by 24. In this case, you have to find the answer in cm3, so you multiply by 24000.

Reply 104

voices1

guys does only greater nuclear charge and smaller shieldin increase nuclear attraction?? and increase n of proton increase the attractive force on outer electrons which pulls them in towrds the nucleus?? correct?

Reply 105

broken_glass_heart

Original post by INeedToRevise

Are you an AS student or an A2 student?
Because I was in the same position as you and I had a U last year for my AS practical. My overall grade for AS was a D and now, with a resit of F322 and the practicals, I'm just a couple UMS of an A which is why I'm resitting this module tomorrow.

Its possible, just requires a lot of work.

Hi i am an A2 student, my overall mark last year was a D and it still is a D as my college wouldn't allow us to resit AS practicals. I just scraped very low C in both my AS exams (1 mark away from a D, so the lowest C available) therefore, my overall grade was a D. I need a B overall AS+A2 to get into my uni course. but at the moment it looks impossible as the A2 exams r very very hard and am resitting F321 tomoro, hoping to get an A (unlikely though). Plus having got 20/40 (low grade E when u convert it out of 60 according to last years boundaries) in A2 practicals doesn't help with pulling the grade up! so my only way is to get an A in every single chemistry exam in AS and A2.. god help me... am so scared for tomoro!! :fight:

Reply 106

786girl

can someone explain the diff between nuclear charge and nuclear attractioon
i always mix them up

Reply 107

786girl

Original post by TrampingRampage

The excess Ca reacts with water which forms calcium hydroxide and hydrogen gas.

In the equation Ca(s) + 2HCl (aq) ----> CaCl2 (aq) + H2 (g),

what would a student observe?

but where does the water come from? theres no Oxygen in the equation

Reply 108

intellectual1

Relative isotopic mass

-Mass of the isotope compared to 1/12th
-Of the mass of a carbon-12 atom

Original post by 786girl

but where does the water come from? theres no Oxygen in the equation

There's no water its H2 (g) :tongue:

Reply 111

TrampingRampage

Original post by 786girl

but where does the water come from? theres no Oxygen in the equation

The aqueous solution. There's a question in one of the past papers which was exactly the same as that one where the mark scheme states
"Ca reacts with water
Ca + 2H2O ---------> Ca(OH)2 + H2"

Reply 112

ilovedubstep

Original post by TrampingRampage

The excess Ca reacts with water which forms calcium hydroxide and hydrogen gas.

In the equation Ca(s) + 2HCl (aq) ----> CaCl2 (aq) + H2 (g),

what would a student observe?

Ca seems to dissolve and effervescence occurs.

Why does the ionisation energy decrease as you go along a period?

Original post by intellectual1

There's no water its H2 (g) :tongue:

i knooo but he said it reacts with water to form calcium hydroxide,
where does the water come from? loll

Reply 115

ilovedubstep

Original post by 786girl

i knooo but he said it reacts with water to form calcium hydroxide,
where does the water come from? loll

It was in aqueous solution. I.e. dissolved in water.

Reply 116

TrampingRampage

Original post by 786girl

i knooo but he said it reacts with water to form calcium hydroxide,
where does the water come from? loll

I wondered the same thing when I was doing the past paper (the old syllabus Foundation Chemistry January 2005 Q2eiii) but the mark scheme says the Ca continues to react with water forming calcium hydroxide and hydrogen gas and the water is from the aqueous solution

Reply 117

voices1

ok guys, why is chlorine the strongest oxidisin agent???

Reply 118

TrampingRampage

Original post by ilovedubstep

Ca seems to dissolve and effervescence occurs.

Why does the ionisation energy decrease as you go along a period?

Don't you mean increase?

As you move across a period, there are more protons thus there is increased nuclear charge. The increased nuclear charge pulls in the electrons thus the atomic radius is smaller. The extra electrons as you move across a period fill in on the same shell so there is similar shielding. The nuclear attraction experienced by the outer electrons increase and thus more energy is required to remove the electrons.

How does a base neutralise an acid?

Reply 119

intellectual1

Explain why Xenon has a lower first ionisation energy than Xenon [3 marks] Jan 10 Q1 F321

Neon +2081kj mol^-1
Xenon + 1170 kj mol^-1

1. Xe has a bigger atomic radius OR Xe has more shells

2. Xe has more shielding

3. The nucler attraction decreases

OR

Outermost electrons of Xe experience less attraction to the nucleus

OR

Increased shielding/distance outweighs the increased nuclear charge

The mark schemes tend to allow various forms of the answer, but there are key words that always must be included in the answer. Also remember, if there are 6 lines given, and 3 marks, it does'nt mean you must fill all the lines. Some people have considerably larger handwriting and that is the purpose of those lines. If you look at the mark schemes, sometimes just 2.5 to 3.5 lines are sufficient for a 3 mark question, even though there may well be 6 or 7 lines of space. Also this is a Chemistry examination, not an English Literature essay. The examiners keep stating how they're annoyed each year by candidates writing too much and trying to fill up all the lines when it is not neccessary.