Originally posted by UltimaOnline:

1) Weigh the anhydrous and hydrated salts. (the masses of both will be provided by the question.)

 

2) Calculate the molar mass of the anhydrous salts (from its formula).

 

3) Find the no. of moles of anhydrous salts. (no. of moles = sample mass / molar mass.)

 

4) Using algebra, equate mass of hyrated salts (by stoichiometry) with mass of hydrated salts (observed from experiment).

Come to think of it, I think my question goes something like this.

 

They give you a particular mass for the hydrated salt (eg 50.0g) and next they say water of crystallisation is removed by heating the salt to give the remaining anhydrous salt. They then tell you mass of anhydrous salt, say,28.0g.

 

Formula goes something like FeCl3.nH2O

 

question asks to find value of n. what i did was, i find the mass of the water that has been removed. in the case i created, the water that has evaporated is 22.0g. then i used 22 /18, where 18 is the Mr of H2O. i think i missed out some steps in between. do you know what they are?

there's this kind of question where they give you a hydrated salt, heat the salt to remove the water of crystallisation from it. I think the equation goes something like ____(salt's name)._H2O

 

How do you solve such questions? I did these questions before and looked through the required steps before the test today but I met with a hiccup midway throught the question. My answer was different from that of my friends'. could someone explain how you find out the "n" value of the H2O.

 

n is the unknown number, i think it's the mole ratio.

• if you don't mind ^tamago^, could you further explain how you solve the second question?  i mean part 2 of the question.

Originally posted by Tky35:

bonkysleuth  u mind sharing the answers for the listening comprehension?

sure. if you remember the questions, that is. i will try to recall the answers. ;DD

variables x and y are related by the equation y = ax / x-b. the graph y against y/x has gradient 3 and y-intercept 2.

 

(a) find value of a and b.

(b) find value of x for which x=y.

 

having a maths CT tomorrow, so please reply asap if you are able to help!

 

lastly thanks!

I will only be taking this november. i have heard a lot of talks going on about how diffcult the november paper will be compared to the may's paper. is it true or is this "rumour" unfounded? dead worried. anyway, the LC for this year was tricky. no one scored a perfect score in our class. the best was 18/20.

hydrogen bromide has a melting point of -87 deg celsius and a boiling point of -67 deg celsius. it dissolbes in water to form an acidic solution. describe what is seen when chlorine is bubbled through the solution.

 

the answer writes solution turns yellow. but i think it should be reddish brown. after all , isnt this a displacement reaction and chlorine displaces bromine? please check for discrepancies.

 

next. a student carried out some experiments to compare the relative strengths f dilute ethanoic acid and dilute hydrochloric acid. name a solid substance that will react with both acids. describe what you will see during the reaction.

what do you use? metal? if yes, then would the reaction be faster with HCl because it is a stronger acid and is fully ionised, thereby having a higher amount of H + ions.

 

please help ASAP because i still have got to clear my humans studying for tomorrow. thanks!

Originally posted by Maith:

walao,pri 6 got this alr ar?

i remember vividly learning this when i was in primary 6.

would you expect to take more time or less time to boil water in a saucepan if the outside curved surface of the saucepan were polished chrome rather than dull black? explain.

 

my guess is black takes a shorter time because it is a better absorber of heat. polished chrome is shiny which makes it a good reflector and a bad radiator. or does polished chrome take a shorter time since it does not radiate much heat? come to think of it, chrome seems to take a shorter time.

 

pretty perplexed by all these colours and stuff. can someone explain?

Originally posted by starmoonsun:

again, the graph x^2 + 2 does not intercept the x axis.

when x = 0, y =2. so you can expect that it is above the x-axis, but also intercepting the y-axis.

to find turning point, you can use dy/dx. at turning point, dy/dx = o. thus, find the value of x and sub it in the eqn y = x^2 +2 to find the corresponding y-value. if you have not learn differentiation, you can use the visual method to approach the question.

For example, y = x^2 +2 implies that a x^2 graph (centre at the 0,0 coordinate) moved 2 units up along the y-axis. so the turning point would be from (0,0) to (0,2).

for the next question, -x^2 graph implies that the graph is a x^2 graph, but reflected across the x-axis. i.e it is a x^2 graph that looks like you drawn it upside down and below the x-axis.

as the above question, the reflected x^2 graph should also cut the origin at (0,2). since the eqn given is y= -x^2 -3, this implies that the whole graph shifted 3 units down along the y-axis. thus the turning point of the graph is (0, -3). 

knowing the property of the graph, i.e the shape of the graph, you should be able to deduce that the line of symmetry is the x-coordinate of the turning point, i.e the line of symmetry is x=0.

How do you know the graph is centred at (0,0)?

state the turning point and sketch the graph of the following.

 

y = x^2 + 2

 

For this, you can't do the quadratic graph method like

when y =0. x =___

when x=0, y= ____

find turning point

find endpoints

 

when i sub y = 0. x^2 + 2 = 0

shift 2 to right-hand side and you get

x^2 = -2

 

i got stuck here cuz you cant square root a negative value. so what other method can i use?

 

the next question :

 

state the line of symmetry and sketch the graph of the following

 

y = -x^2 - 3. how do you get the line of symmetry? by looking at it, i can tell that it's 0 but is there anyone who can explain why?

Originally posted by starmoonsun:

you cant find the other point cuz the graph doesnt cut the x-axis

 

so you should just draw the min pt and y-intercept without the curve intercepting the x-axis.

also, note that b^2 - 4ac < 0 , which means it is either always positive or always negative. which in this case, it is always positive.

hope this helps :)

thanks all! may i know when i will know whether it is positive or negative when b^2 - 4ac < 0? i think i learnt this in A maths before cuz it seems so familiar.

(i)Express x^2 - 3x + 5 in the form (x-a)^2 + b

 

(ii) sketch the graph of y = x^2 - 3x + 5

 

For (i) i got (x-1.5)^2 + 11/4

 

I encountered some problems doing the second part(graph sketching). from the above equation, we can determine that the minimum point for the graph is (1.5, 2.75). now sub x = 0 into equation and you get y= 5. but when you sub y=0, you cant get any answer cuz it's a maths error. How do i go about drawin gthe graph since I've only had 2 points?

 

 

okay, suppose the question now wants me to find coordinates of D. can I use the fact that since the figure is a rectangle, the number of units for each opposite site is equal? Firstly, you get the coordinates of C. then you find coordinates of D by counting the number of units on the opposite site.

 

Is this method acceptable? or is there a way to find it? i got the answer. it's (16,6) and its correct. just wanna check whether there is any alternative to solve this question.

thanks so much!

in a rectangle ABCD, the coordinates of A and B are (4,2) and (2,8) respectively. given that the equation of AC is y = x - 2, find

 

(a)the equation of BC.

 

 

does anyone know where i can obtain such practical question? i desperately need help in this matter.

i screwed up the whole paper today. didnt even do the graph part and i might as well land myself a zero. lol. i misinterpreted the question and realise it nly 20-30 minutes later.

i need help with this. does anyone have an idea what are the questions SPA (for example, physics) would be? I need more exposure to such questions because my practical can be atrocious sometimes. where can i obtain the questons?

my teacher always advises us not to spot topics. would be great if you briefly try to understand the points. because humans is all about making logical sense.

 

for example what happens when the economy is on a downslide? naturally, unemployment comes into place, wages decrease, inflation comes in, food shortages, trade imbalances, and eventually people's quality of life takes a plunge. link all the facts up and you get the whole story/ idea.

given that ( 1 + kx)^n = 1-28x + 364x^2 +..., find the values of k and n. By expanding, I somehow got to know that nk = -28 and nC2(k)^2 is 364.

 

I dont know how to derive the correct answer but by trial and error i got n = 14 and k = -2. whats the proper way of doing this question?

 

the next question. in the expansion of ( 1 + x)^n, coefficient of x^4 and x^5 are the equal. find value of n.

 

Again by trial and error i got n = 9. but i do not know how to get the answer through proper presentation.

 

i wasnt in class today and my friend told me that some of the questions require some "new formula" besides the basic binomial statements. can someone help me identify whether these 2 questions are the ones that require the special formula or whatever it is.

Originally posted by Maith:

u siao ar 12...12 for what,dialouge isit? report writing just have:

para 1-intro

para 2-main body

para 3-knockout

para 4-conclusion and reliterate ur points

there are 2 types of report writing. one is the letter sent to a teacher or whichever person of a higher authority and you have to give the overview of say, a particular event, etc. but newspaper reports follow the newspapers writing style i guess. 1 to 2 lines in a paragraph. (you can look through the newspapers and you'llnotice that). so 12 paragraphs = a maximum of around 24 sentences (long and short sentences, of course)

Originally posted by Darkness_hacker99:

I feel that about 5~7 will do.

12 is definitely too much, in my opinion...

Then how about the size of the headlines? Do I fill words into two rows of spaces or just stick to using one row? I did newspaper report in school and wrote the headlines in large fonts. The teacher didn't tell us whether this is acceptable during the exams. It seems inapt to me.

Does anyone have an idea how many paragraphs must we write? My guide book follows a 3-paragraph system but what we do in school is totally worlds apart from what the guide book says. we usually go for 12 paragraphs and each paragraph consists of 2-3 line or even 1 line. so can anyone tell me the most appropriate number of paragraphs?

the table shows experimental values of variables x and y.

 

x - 0.25 | 0.5 | 1.0 | 1.5 | 2.5 | 6.0 | 9.0

 

y - 1.29 | 2.24 | 3.61 | 4.50 | 5.63 | 7.20 | 7.70 | 

 

it is known that x and y are related by an equation of the form xy + ay = bx/ using the vertical axis for y and horizontal axis for y / x, draw a straight line graph of y against y/x for given data. use graph to estimate

(a) value of a and b

(b) value of x for which y = 4x

 

please help with the second part of the question. thanks. anyway, a = 1.5 and b = 9, for your reference purposes.