Response Feedback (neutralisation) (1 Viewer)

[Ambility]

There is no marking guidelines for this past paper so I have come to BoS for opinions.

Is my response sufficient to gain 2 marks?
What is the question looking for?
How could I improve it?

http://i.imgur.com/95z1u8C.jpg

 

[porcupinetree]

As far as I can see from the paper, the question is out of 3 marks (is that right?). Assuming that's the case, you'd probably get 2 out of 3 - I think you need to put a little more emphasis on the use of HCl, rather than focusing on the use of an alternative compound (eg NaHCO3). You could mention the fact that it is impossible to tell when neutralisation is complete (when we use HCl), and also go into a little more depth about how the 6M HCl itself is dangerous.

 

[Ambility]

As far as I can see from the paper, the question is out of 3 marks (is that right?). Assuming that's the case, you'd probably get 2 out of 3 - I think you need to put a little more emphasis on the use of HCl, rather than focusing on the use of an alternative compound (eg NaHCO3). You could mention the fact that it is impossible to tell when neutralisation is complete (when we use HCl), and also go into a little more depth about how the 6M HCl itself is dangerous.

It's actually 2 marks, three is the total number of marks in that section on that page (confusing I know).
Thanks for your feedback!

 

[someth1ng]

I'd say it's a pretty average response but also a bit wrong. There's many problems with using HCl to neutralise NaOH spills:
1. Neutralisation is exothermic, strong acids and strong bases can have a violent reaction and produce a lot of heat (main problem).
2. Excess HCl is a problem since it's corrosive (as you mentioned).
3. You should always neutralise a strong base with a weak acid - some examples would be acetic acid, boric acid, NaHSO4, or NaHCO3.
4. The neutraliser being amphoteric is irrelevant.

 

[wu345]

I don't think it's a very good answer to be honest
-you haven't given a clear judgement (which is what the verb assess asks for) by explicitly saying 6M HCl is not good to use here
-you should say strong acids should not be used to neutralise strong bases since the reaction is highly exothermic and potentially explosive (as mentioned above by someth1ng)
-6M is a liquid reagent. I.e Instead of containing the spill, it will spread it and make it worse
-At my school with their strict marking, it is not sufficient to say 'HCl' is corrosive, rather you must explicitly state HCl can burn the eyes and skin
-The question does not ask for a better alternative so there is no need to mention one

Here's how I would answer the question:
6M HCl is definitely not the right reagent to use to neutralise a sodium hydroxide spill. HCl is highly corrosive, so it can burn the eyes and skin if mishandled. The reaction between the strong acid (HCl) and the strong base (NaOH) is highly exothermic and potentially explosive, so it could cause more damage to the surroundings instead of minimising it. Additionally, since 6M HCl is a liquid reagent, it would spread the spill instead of containing it, exacerbating the spill by widening its area of effect. Hence, 6M HCl is not a good reagent to use to neutralise a sodium hydroxide spill due to its dangerous effects.

Notice how I used a 'judgement sandwich structure' - judgement, evidence, judgement.
I suggest you use this structure for most 'assess' questions. You also may want to put the equation of the reaction, especially if this was worth more than 2 marks.

 

[leehuan]

I don't think it's a very good answer to be honest
-you haven't given a clear judgement (which is what the verb assess asks for) by explicitly saying 6M HCl is not good to use here
-you should say strong acids should not be used to neutralise strong bases since the reaction is highly exothermic and potentially explosive (as mentioned above my someth1ng)
-6M HCl is relatively concentrated, but it is not 'concentrated' in that it contains little to no water. Thus, 6M HCl is in aqueous solution so it is a liquid reagent. I.e Instead of containing the spill, it will spread it and make it worse
-At my school with their strict marking, it is not sufficient to say 'HCl' is corrosive, rather you must explicitly state HCl can burn the eyes and skin
-The question does not ask for a better alternative so there is no need to mention one

Here's how I would answer the question:
6M HCl is definitely not the right reagent to use to neutralise a sodium hydroxide spill. HCl is highly corrosive, so it can burn the eyes and skin if mishandled. The reaction between the strong acid (HCl) and the strong base (NaOH) is highly exothermic and potentially explosive, so it could cause more damage to the surroundings instead of minimising it. Additionally, since 6M HCl is a liquid reagent, it would spread the spill instead of containing it, exacerbating the spill by widening its area of effect. Hence, 6M HCl is not a good reagent to use to neutralise a sodium hydroxide spill due to its dangerous effects.

Notice how I used a 'judgement sandwich structure' - judgement, evidence, judgement.
I suggest you use this structure for most 'assess' questions. You also may want to put the equation of the reaction, especially if this was worth more than 2 marks.

Do you find it strange though, that the word assess was placed with a mere 2 mark question?

I think the mark allocation of the question itself was already wrong.

 

[wu345]

yeah it should have been at least three, i've never seen a 2 mark assess question

 

[leehuan]

Even 3 is dramatic. 3 is still at the explain/analyse level. (Although it's far more believable)

Requires 4.

 

[someth1ng]

6M HCl is definitely not the right reagent to use to neutralise a sodium hydroxide spill. HCl is highly corrosive, so it can burn the eyes and skin if mishandled. The reaction between the strong acid (HCl) and the strong base (NaOH) is highly exothermic and potentially explosive, so it could cause more damage to the surroundings instead of minimising it. Additionally, since 6M HCl is a liquid reagent, it would spread the spill instead of containing it, exacerbating the spill by widening its area of effect. Hence, 6M HCl is not a good reagent to use to neutralise a sodium hydroxide spill due to its dangerous effects.

Just be careful with words like "definitely" because the situation is not clear - they haven't said they have access to other reagents and hence, it's still possible that 6 M HCl is still their only choice or if they only had other strong acids.

 

[wu345]

Just be careful with words like "definitely" because the situation is not clear - they haven't said they have access to other reagents and hence, it's still possible that 6 M HCl is still their only choice or if they only had other strong acids.

I'll remember that! Thanks