HSC 2014 question wrong or I'm dumb? (1 Viewer)

[malcolm21]

The question asked if this experiment was valid. I said it wasn't because the environment wasn't controlled, the thermometer is touching the beaker and the beaker absorbs some of the heat. Apparently the boardofstudies marking guidelines said it's actually valid. Here's their answer:

Overall this is a valid investigation to show a relationship between
H and molecular mass.
This is supported by obtaining a similar trend in the theoretical and experimental data.
However, the quantitative values are inaccurate because of heat loss to the surroundings. The
error is systematic as shown by the consistent difference in experimental and theoretical
values, indicating variables were controlled.

 

[dan964]

The question asked if this experiment was valid. I said it wasn't because the environment wasn't controlled, the thermometer is touching the beaker and the beaker absorbs some of the heat. Apparently the boardofstudies marking guidelines said it's actually valid. Here's their answer:

Overall this is a valid investigation to show a relationship between H and molecular mass.
This is supported by obtaining a similar trend in the theoretical and experimental data.
However, the quantitative values are inaccurate because of heat loss to the surroundings. The
error is systematic as shown by the consistent difference in experimental and theoretical
values, indicating variables were controlled.

The experiment is valid but not accurate. A valid experiment is the method was conducted properly, i.e. other variables were controlled etc.

 

[BlueGas]

They keyword for this question is "Discuss", which means: Identify issues and provide points for and/or against

So basically you have to say why you think it was valid and at the same time provide reasons why it isn't valid. As you can see from the sample answer the experiment is valid however to a certain extent, because there was a heat loss to the surroundings and there wasn't anything to cover the beaker as shown in the diagram.

 

[malcolm21]

The experiment is valid but not accurate. A valid experiment is the method was conducted properly, i.e. other variables were controlled etc.

Isn't uncontrolled conditions (the environment) and the thermometer touching the beaker enough to say these impacting variables aren't controlled properly?

 

[DepressedPenguino]

The question asked if this experiment was valid. I said it wasn't because the environment wasn't controlled, the thermometer is touching the beaker and the beaker absorbs some of the heat. Apparently the boardofstudies marking guidelines said it's actually valid. Here's their answer:

Overall this is a valid investigation to show a relationship between H and molecular mass.
This is supported by obtaining a similar trend in the theoretical and experimental data.
However, the quantitative values are inaccurate because of heat loss to the surroundings. The
error is systematic as shown by the consistent difference in experimental and theoretical
values, indicating variables were controlled.

It is valid because the heat loss due all those factors applied to all of the alkanols that was experimented with. So all the heat loss that is 'controlled' throughout the expierment hence making it valid. Also for this question it may be good to define what is mean by validity to show your knowledge.

 

[Mr_Kap]

it is valid for reasons stated by other people above. My chem teacher marked this question last year in HSC and said it threw a lot of people off. The fact that the lines are parallel on the graph (in the part before) mean same trends between experimental and accepted values are the same, showin that this is valid. Although there were accuracy problems due to the reasons you stated, the fact that those accuracy problems applied to ALL of the alkanols tested, meant this variable was controlled, hence it was still valid.

Remember, validity is if you meet your aim, which can be done by controlling variables. The aim here is to determine quantitative relationship between Heat of Combustion and Molar Mass of alkanols, and because the relationship is the same then it is valid, despite the inacuracies.

 

[sy37]

First determine if it is valid. If it is valid then it will ALWAYS be reliable and that's usually enough to talk about for these type of questions.