open ended questions vg.ppt - lt scotland · blocked drains can be very unpleasant. common causes...

Open ended questions for Chemistry

Aims:} Rationale behind open ended questions} What do they look like?} How are they marked?} Techniques for answering} Practice Questions

Rationale} Open-ended question will be used to assess whether or not you

have truly understood a chemical concept.

} You are required to draw on your understanding of key chemical

principles in order to solve a problem or challenge.

} The ‘open-ended’ nature of these questions is such that there is no

unique correct answer. In addition to testing the extent of your

chemical insight, these questions promote and reward creativity and

analytical thinking.

} The marking instructions focus on rewarding you for your

understanding of chemistry.

What they look like} Open-ended questions will always be identified by the

wording ‘Using your knowledge of chemistry…’

} They are worth 3 marks.

} May be presented in a real-life context.

} All open-ended questions have more than one possible answer!

} Should be answered in around 5 minutes.

Marking

}Total of 3 marks available.

}Marks are awarded not deducted.

}There is no one “correct answer”. Do not be disheartened

if others have answered it differently.

0 Marks}The student has demonstrated no understanding of the science involved.

}There is no evidence that the student has recognised the area of science involved or has given any statement of a relevant science principle.

}This mark would also be given when the student merely restates the science given in the question.

1 mark: }The student has demonstrated a limited understandingof the science involved.

}The student has made some statement(s) that is(are) relevant to the situation, showing that at least a little of the science within the problem is understood.

2 marks: }The student has demonstrated a reasonable understanding of the science involved. The student makes some statement(s) that is(are) relevant to the situation, showing that the problem is understood.

}There might also be a statement of a science principle or of a relevant relationship between the variables involved in the problem.

3 marks}The maximum available mark will be awarded to a student who has demonstrated a good understandingof the science involved. }The student shows a good comprehension of the science of the situation and has provided a logically correct answer to the question posed. }This type of response might include a statement of the principles involved, a relationship or an equation, and the application of these to respond to the problem. }This does not mean the answer has to be what might be termed an ‘excellent’ answer or a ‘complete’ one.

Techniques for Success } Read the question carefully. } Pay attention to diagrams, structural formulae or equations

that have been included to help you answer the question. } Reflect on the information provided in the question. Make sure

that you answer exactly what the question is asking. } Show your understanding of chemistry by drawing structural

formulae, identifying functional groups, writing chemical equations or working out formulae.

} You may choose to present your answer as a paragraph, a set of bullet points or even as a labelled, annotated diagram.

} If you have time at the end of the examination, check to see if what you have written answers the question asked

Mrs Gilroy’s advice…} This is your chance to show off! Use the time to show off as

much of the relevant chemistry as you can. } Try to demonstrate your understanding by linking statements

and referring back to the question. } Don’t be afraid to take a minute to plan out your answer. } Come back to the question at least once! There may be

something else in the paper that jogs your memory.} If all else fails, play the word association game......

PRACTICE QUESTIONS

} You will now be given an Open Ended Question. } Together you have 5 minutes to come up with an answer.} I want you to do this in THREE STAGES!!!

1) Brainstorm ALL of the relevant higher chemistry you can think of. Everything. Don’t go into detail yet.

2) Put some explanation or understanding beside some of the chemistry from part 1.

3) Construct an answer to the question using what you have from part 1 and 2.

Open-ended Question Examples

Concentrated solutions of hydrogen peroxide are used in the propulsion systems of torpedoes. Hydrogen peroxide decomposes naturally to form water and oxygen:

2H2O2(aq) → 2H2O(ℓ) + O2(g) ΔH = −196·4 kJ mol–1

Transition metal oxides act as catalysts in the decomposition of the hydrogen peroxide.

Unfortunately, there are hazards associated with the use of hydrogen peroxide as a fuel in torpedoes. It is possible that a leak of hydrogen peroxide solution from a rusty torpedo may trigger an explosion.

Using your knowledge of chemistry, comment on why this could happen.

Titanium(IV) chloride is a colourless liquid at room temperature. It is used in the production of titanium metal and titanium dioxide.

Using your knowledge of chemistry, discuss the chemistry of titanium(IV) chloride and how you would determine the type of bonding present.



Graphene is a newly discovered form of carbon. Its structure is one-atom-thick planar sheets of carbon atoms that are densely packed in a honeycomb crystal lattice. It can be thought of atomic scale chicken wire and can be considered an indefinitely large aromatic molecule.

Using your knowledge of chemistry, compare graphenewith the other forms (allotropes) of carbon.


Oxygen gas speeds up the rate at which food is spoiled. To improve the shelf-life of foods, food manufacturers use several methods to remove oxygen from inside the food packaging. In one method, an enzyme is added that catalyses a reaction between oxygen and the glucose which is often present in foods.

glucose + oxygen + water → gluconic acid + hydrogen peroxide

Using your knowledge of chemistry, comment on why this method may not be suitable to improve the shelf-life of all foods.


Argon was discovered in 1890’s when samples of nitrogen prepared by different methods were compared. The element name was derived from the Greek argos, which means “lazy one”.Two samples of nitrogen can be prepared as shown.

Method 1 Removing carbon dioxide and oxygen from the air.


Method 2 Reaction of sodium nitrite with ammonium chloride

Heated magnesium metal can react with nitrogen gas to give magnesium nitride.3Mg(s) + N2(g) → Mg3N2(s)

Using your knowledge of chemistry, comment on the discovery and naming of argon.


A student makes the following statement:

‘Sugar can be used to produce alcohol, a carboxylic acid and the ester ethyl ethanoate’

Using your knowledge of chemistry, comment on the accuracy of the student’s statement.


Aspirin is a widely used medicine. It is advised that it is stored in dry, cool conditions.

Using your knowledge of chemistry, comment on the reasons why aspirin should be stored under these conditions.

CO OH

OC

CH3

O


Blocked drains can be very unpleasant. Common causes of blocked drains in homes are fats, hair and food waste.

Using your knowledge of chemistry, comment on chemical methods that might be used to unblock drains.


Hydrogen peroxide is used in gels to whiten teeth. The ion–electron equation for the oxidation of hydrogen peroxide is:

H2O2 → O2 + 2H+ + 2e−

Using your knowledge of chemistry, comment on possible methods for measuring and comparing the concentration of hydrogen peroxide present in two different gels.


The table below gives information about the percentage yield of ammonia obtained in the Haber process under different conditions.

Pressure/atmospheres

Temperature / oC200 300 400 500

10 50.7 14.7 3.9 1.2100 81.7 52.5 25.2 10.6200 89.0 66.7 38.8 18.3300 89.9 71 47.0 24.4400 94.6 79.7 55.4 21.9600 95.4 84.2 65.2 42.3

The equation for the main reaction in the Haber process is N2(g) + 3H2(g) 2NH3(g)

Conditions of around 400oC and 200 atmospheres are used rather than those that give the highest yield. Using your knowledge of chemistry, explain why these conditions are used.


From the information above, a pupil deduced that ionic bonding must be stronger than covalent bonding.

Using your knowledge of chemistry, explain whether you agree or disagree with this conclusion.

Melting point / oC Boiling point /oC

Sodium chloride 801 1417Carbon tetrachloride -23 77


Silicon and germanium both can join together with hydrogen to make homologous series similar to the alkanes.

Alkanes are good non polar solvents.

Using your knowledge of chemistry comment on the ability of silicon and germanium to form non polar solvents.

An internet discussion board on ‘Bad Chemistry’ has an entry referring to the TV drama ‘CSI: Miami’.

‘Last night’s episode showed the deceased victim floating in a swimmingpool contaminated with sodium hydroxide. The concentration was highenough to eat through glass. When the CSI guys realised it was an alkali,they needed to neutralise it to retrieve the body, so they sent one of theteam to the local grocery store for vinegar. They proceeded to pour thevinegar from four litre jugs into the pool, dropping the pH from 13 toexactly 7.0 – all within a few seconds, and without any stirring!’

Using your knowledge of chemistry, comment on whether the events described in CSI: Miami could take place.


Using your knowledge of chemistry, suggest a method of producing alcohols and how you could determine that you had produced this alcohol


Using you knowledge of chemistry, comment on two different elements comparing the properties

and position of your chosen elements?


} Aspirin is widely used as a medicine. The structure of aspirin is shown below.

} Using your knowledge of chemistry, comment on physical and chemical properties you would expect aspirin to demonstrate.


The labels have dropped off three bottles containing organic compounds. The chemistry technician has asked a chemistry class to identify these compounds.

Using your knowledge of chemistry, comment on how would the class could identify the alcohol, ester and carboxylic acid.


CARD SORT ACTIVITY

Instructions:1. You will now have a look at a series of cards. The pupils

response to the question is on one side and a comment on the mark actually awarded is on the other.

2. Put the cards on the table with the pupil response facing upwards.

3. Discuss in your pairs how many marks should be awarded using the marking scheme to help you.

4. Then turn the cards over and see how they have done.

Exemplars Question 1

Rasputin, often referred to as the ‘mad monk’, was a very powerful figure in the life of Alexandra, the last Tsarina of Russia. His enemies decided to kill him using a cyanide compound. Cyanide compounds are deadly poisons. Using a bottle of potassium cyanide, they attempted to poison a cake and some wine. Rasputin ate the cake and drank the wine and yet was not harmed. Although his followers claimed this was a sign of Rasputin’s supernatural powers, there are chemical explanations.

Using your knowledge of chemistry and the following information, comment on possible chemical reasons why the cake and wine did not poison Rasputin.

potassium cyanide + acid → potassium salt + hydrogen cyanide gas(white powder) (white powder)

Pupil response 1

0 marks

The student has tried to use ‘chemistry’ terms but the answer shows no understanding and, indeed, contains a lot of wrong information.

Pupil response 2

1 mark

This answer contains irrelevant information, but the student has recognised that the gaseous hydrogen cyanide would escape from the mixture, and therefore Rasputin would only be eating harmless potassium salt. This shows a limited understanding, and is enough to gain 1 mark.

Pupil response 33 marks

It is obvious from this answer that the student has a good understanding of chemistry.He/she has given a convincing explanation as to why Rasputin may not have been poisoned by the cake or the wine, and, indeed, has also brought in a suggestion of the effect of heat in the baking of the cake.The student has shown a good understanding of the chemical reaction producing potassium salt and hydrogen cyanide.

Exemplars Question 2

Hydrogen peroxide is used in gels to whiten teeth. The ion–electron equation for the oxidation of hydrogen peroxide is:

H2O2à O2 + 2H+ + 2e–

Using your knowledge of chemistry, comment on possible methods for measuring and comparing the concentration of hydrogen peroxide present in two different gels.

Pupil response 1

0 marks

student has shown no understanding of the chemistry involved. The student merely restates the chemistry given in the question.

Pupil response 2

1 mark

By suggesting measuring the pH, the student has suggested an indirect method of measuring the concentration of peroxide.Although limited understanding is shown, the student has recognised that H2O2 will react to produce H+ ions in the solution

Pupil response 3

1 mark

A full explanation of the procedure has not been provided, but the student has recognised that the oxygen being given off would produce ‘froth’, which could be quantified. This shows limited understanding.

Pupil response 42 marks

Although he/she has not really answered the question, his/her response shows a reasonable understanding of chemistry.They have correctly provided a method for measuring the average rate. They has interpreted the ion–electron equation to correctly predict the products of the electrolysis of H2O2. He/she has also proposed appropriate apparatus to use for the experiment, including the selection of carbon as a relatively inert electrode for the discharge of hydrogen.

Pupil response 5

2 marksStudent has provided three methods (two of which should work well in practice) that could be used to answer the question. However, the detail is vague and the response does not explain how these methods would be used to measure or compare concentrations. The answer shows a reasonable understanding of chemistry.

Pupil response 6

3 marks

This response absolutely answers the question. In the three methods discussed, the student has given detail and has brought in the idea that this is to compare and measure the concentration of hydrogen peroxide present. The student shows a good understanding of chemistry, and brings in areas of chemistry not provided in the question.

2017 Q3 Exemplars Question 3

Pupil Response

0 marks

Pupil Response

2 marks

Pupil Response

3 marks

Pupil Response

0 marks

Pupil Response

1 mark

Pupil Response

2017 Q8

open ended questions vg.ppt - lt scotland · blocked drains can be very unpleasant. common causes...

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