Tips for Chemistry Practicals (P3)

[Nisa Mirza]

if only i can like this twice thanks a lot man !
just one question tho.. what is the excess stuff when doing anions and cations.. hw can i kno whether or not a solution disolves in excess or not? i dont understand it :/

well when u add excess of a hydroxide or ammonia to its salt, a complex compound is made which might be soluble.
For example Zn2+ (aq) + 2OH-(aq)

Zn(OH)2(s). But when u add excess to this salt u get : Zn(OH)2(s) + 2OH- (aq)

[Zn(OH)4]2-(aq). Thats a zincate ion which is soluble.

 

[MindStealth]

if only i can like this twice thanks a lot man !
just one question tho.. what is the excess stuff when doing anions and cations.. hw can i kno whether or not a solution disolves in excess or not? i dont understand it :/

Usually you just have to add 10-15 drops more. But if you're not sure just to be safe just keep adding until the solution has doubled, by that I mean if you took 1 cm of solution A and you're testing with another solution then keep adding until it becomes 2 cm. You're probably not going to see any change after that.

 

[MindStealth]

A burette has an accuracy of 0.05 cm^3. The graduations are after every 0.10 cm^3 but you can read up to an accuracy of 0.05 cm^3.
So the maximum accepted error in the titre is 0.10 cm^3 and that's how close the two readings we pick should be.

I guess it's kinda late to reply but for others who are confused, yes this is right, that's what the accuracy should be practically BUT you're not being judged so strictly, if you just read the marking scheme you will know how much leverage they give you for such reading. What I said was regarding how you will be graded, not what is right. Besides, even if you think about errors, you're not counting errors due to the lab temperature/pressure, parallax error, error in the dilution of the solutions made, there are many to list. The point is, they give you a lot of room for stuff like this.

 

[binder]

Haha nice question...They way I see it is that when a person knows in-depth, everything leads to something that it beyond on imaginations something that is not explained by our science. For example, the big bang if you what it is, according to which the Universe was once in an extremely hot and dense state which expanded rapidly, now if you study in detail you will know that the time itself started when the big bang happened so when there was no time, no forces, nothing; then what could have caused the big bang? There so many questions like this that point toward one super power, that is GOD.
Thanks for the complement =D

hey i m not annoying you but it is just an advice that bilieving in god is good thing but saying that this bang bang it is sort of bull shit you have said... i say is god but releating science and god.... its not balanced.... i hope you dont take it seriously... btw your tips are very helpful i appreciate you and thankx...

 

[binder]

can you say about the triangle method of gradient

 

[MindStealth]

hey i m not annoying you but it is just an advice that bilieving in god is good thing but saying that this bang bang it is sort of bull shit you have said... i say is god but releating science and god.... its not balanced.... i hope you dont take it seriously... btw your tips are very helpful i appreciate you and thankx...

One would say what you just said is bullshit, just read what you wrote. No offence, but who are you stop me from saying what I want? I'm not writing this on your wall, in fact you're coming to my thread and asking me to not say something. Really?

 

[binder]

One would say what you just said is bullshit, just read what you wrote. No offence, but who are you stop me from saying what I want? I'm not writing this on your wall, in fact you're coming to my thread and asking me to not say something. Really?

dont take it seriously i told you man.....

 

[tottybee3]

Do u h

• Just keep you mind cool and read everything on the paper, mostly students just don't read long paragraphs of text carefully. Practicals are not that hard so try to score most here, the best solution to this is try as many practicals as many possible.
• Don't perform unnecessary titrations, if you did two and got results close to each other then there's no need for a third one.
• Always draw a triangle on the graph to find the gradient, if you are asked to find it.
• Latest salt analysis sections contain a trick with aluminium and lead(II) ions because they have the same results with ammonia and sodium hydroxide. The test that distinguished them is addition of HCL, it will form a precipitate with lead(II) ions but not with aluminum ions. (Lead(II) ions can be distinguished from aluminium ions by the insolubility of lead(II) chloride.)
• Always read carefully the names of the solutions before working with them, 1 small mistake and you might have to start from the beginning.
• Always heat solutions in a boiling tube and not the test tube.
• Make sure the burette is closed before adding solutions to it.
• If you're quick at experiments then I recommend washing the apparatus with distill water before using.(But only if you're sure you can complete the experiment in time.)
• Don't spend more than 45 mins on Salt Analysis.
• When you write the observation for some gas that is released, always include a confirmatory test. You should actually never perform these confirmatory tests (to save time) just use your knowledge of chemistry to find which gas is released but always include the test in the observations. E.g. when a carbonate is reacted with an acid, you should write the observation; "Colorless gas released which turns lime water milky."
• Remember some gases are hard to see when released in a test tube, so where you expect some gases to be released, look carefully for the observation. A good idea is to use the white tile or if you're not provided with it then use your paper as the background when looking at the test tube.
• Try to memorize the smell of ammonia. I know its very disturbing to smell it but you need to identify it from others when they ask you so just smell it enough that you can distinguish it form other gases.
• In the paper you want both speed and accuracy, so do the easy parts fast like pouring solutions and stuff and use the time saved on important parts like observing changes and stuff.
• In the exam if you think some solution has some impurity or you put something into it by mistake then just ask them to replace it, don't use it.
• Remember to not to use the same dropper for two different solutions.
• If some solution involves heating and then heating strongly then you really need to heat it strongly so don't write no change too fast.
• Always wash the thermometer before using, and make sure its working before using, when not dipped into any solution, it should give a constant reading of 25-30 °C.
• Some solutions need shaking to mix them and sometime you will need to shake it really hard to work it out. Just wash your hands and close the top of the test-tube with your thumb and shake.
• Be careful with the amount of solutions you use, you need to finish all the experiments in the amount of solutions provided don't think that you can get more if you're empty because some examiners might be strict.
• Try to work in a clean and objective oriented environment, what I mean is when you're working with 1 part of the paper then just keep the solutions needed for that part to yourself and keep the others away. This helps a lot.
• Always draw tables(similar to how they give you in the questions) to represent results and observations, don't just write them down in lines.
• One last thing and this is really important; understand the question before doing it, if you can't then try drawing diagrams on a paper to help you visualize what you are going to do and if you still don't get it then skip that part you can do it in the end unless it is related to any other part, if so then just try to copy whatever is instructed in the question.

If you have anything else to add feel free to do so. =)

EDIT [24/05/2012]​

Tips for drawing the graphs:

• Think carefully before choosing scales for the axes, you need to keep in mind that the scale needs your values to cover at least half of the page and should is sensible, by that I mean you should be able to easily find values on the axes without needing to calculate what value some point on the axes represent.
• Sharp your pencil, the last thing you want is to lose marks because your line was too thick.
• Double check when marking the points, 1 mistake and in some cases you might mess up the whole graph.
• "Line of best fit." Doesn't necessarily mean that its a straight line. Although rarely, it could be a curve too that fits most of the points.
• In graphs of experiments like heating and then cooling, you need to draw two lines, 1 representing cooling and the other one representing heating instead of a curve.
• Whenever they ask you to find gradient, ALWAYS draw a triangle, and the bigger the triangle, the more accurate your gradient.
• If you have doubt about your gradient, just take any point that is close to the line and find (y/x), this value should be very close to the gradient found using the triangle. But remember this only works when the graph is starting from origin or near it.
• Try to never break your graph but if you do, REMEMBER that the y-intercept needs to be calculated using the equation "y = mx + c" where m is the gradient you found, c is the y-intercept and can be found using the y and x value of any point on the lane.
• Try to keep your graph clean and visible. If you need multiple lines to find gradient and other value, make sure they're distinguishable.
• ALWAYS write what each axis represents with its unit.
• To determine which quantity goes on the x and y axis, you need to find which quantity is dependent and which one is independent. Independent is usually the one you are changing and dependent is the one you measure.
• If you draw multiple graphs, make sure to label them.
• Don't spend more than 15 minutes on the graph. The graph is usually simple, and if its not then you've done probably something wrong and instead of wasting time on it, try to score marks in other parts first and then come in the end to figure out what's the problem with the graph.
• If you're good at salt analysis, then do it first and finish it fast so you can do the graphing without any tension.
• REMEMBER even if you draw the graph wrong due to some wrong measurements or something, don't lose hope on it, you can still workout the rest of the questions for the wrong graph and score most of those marks like gradient and stuff.
• When they ask you to prove some relationship like T=kV or something, write that since the graph is a straight line, the value of the K is constant and therefore the relationship is true...unless emm...your line is not straight.
• If you don't have time to draw the graph, try to do as much as you can like plotting two or three values and then making the line instead of all the points or even writing the quantities on the axes can gain your marks.

Do u have any chemistry equation sheet? if so pls send to me

 

[Muslimah98]

• Just keep you mind cool and read everything on the paper, mostly students just don't read long paragraphs of text carefully. Practicals are not that hard so try to score most here, the best solution to this is try as many practicals as many possible.
• Don't perform unnecessary titrations, if you did two and got results close to each other then there's no need for a third one.
• Always draw a triangle on the graph to find the gradient, if you are asked to find it.
• ......

• If you don't have time to draw the graph, try to do as much as you can like plotting two or three values and then making the line instead of all the points or even writing the quantities on the axes can gain your marks.

I was wondering if we have to identify the sources of error and improvements in chemistry practical like we do in physics and bio.... URGENT REPLY PLEASE!!

 

[Danny_Chang]

I would like to thanks you for the tips! Though I copied some of them, with your name on it so don't worry. And I shall NOT distribute it. Sorry if it seems a little bad there.

 

[FranticAmaze]

a_wiserME!! awesomaholic101 ruby_fern

 

[awesomaholic101]

Mimick if u haven't completed ur practical paper yet

 

[FranticAmaze]

Midnight dream

 

[Midnight dream]

Midnight dream

Thanks for the tag

 

[Midnight dream]

Wkhan860

 

[Xaptor16]

okay question, should i perform all the practical things first and then do all the calculations at the very end or do it question by question like the practical question 1 and its calculations and so on?

 

[Mimick]

Mimick if u haven't completed ur practical paper yet

Yeah i havent, thanks babe :*

 

[awesomaholic101]

Yeah i havent, thanks babe :*

yea welcome

 

[awesomaholic101]

okay question, should i perform all the practical things first and then do all the calculations at the very end or do it question by question like the practical question 1 and its calculations and so on?

i felt it is more time-saving to do calc after question coz u dont have to come back and read the whole question again ... but u shud time urself ...
for example try to finish titration exp within 25 mins and its calculations in not more than 10 mins ... and keep 45 mins for salt analysis and before that, finish of the other question. In that way you will actually have some time left if u want to make corrections or double check nd stuff ...

 

[Maayee]

hello, i am just new to this community
i have one question pls
what happens if for titration u don't get ur results the same as the teacher's or it is not within the range of the teacher's? Do u get the whole titration wrong or will there be any error carrried forward marks?
My cousin just took her exam and she is freaking out as she didn't get the same results as the teacher's