lboogy

furthermore, if you look at this link http://en.wikipedia.org/wiki/Skewness and look at the introduction. they give a definition of positive skewness and a definition of negative skewness. but then they have 2 graphs which explain positive & negative skewness in the opposite way round. i.e. in the definition they say positive skewness is when the mass distribution is concentrated on the left. fair enough. but then under the graph that is positively skewed they say the most data is in the right. Am I really confused or has wikipedia got it wrong?

Hi everyone, I'm a little confused about positive & negative skewness. From what I've read, this is the picture I have, please tell me if it is correct: Positive Skewness This is when more data on a graph is towards the left of the graph (i.e. the lower values on horizontal axis). Even though the mass of the values are towards the left of the graph - the 'tail' is said to be greater on the right and the distribution is said to be right-skewed (if the majority of the data is on the left then wouldn't it make sense to think of the tail as being greater on the left and skewness to be left skewed?). Negative Skewness More data on a graph towards the right (i.e. the higher values on horizontal axis). More values to the right - but the 'tail' is said to be greater on the left and distribution is said to be left-skewed. thanks in advance! Gav

lol! ok thanks anyway

thanks for that Klaynos - I will have 15 groups, each increase by 1 letter to a maximum of 15 letters. Can I just ask one more thing? I'm not sure what the overall benefit of cumulative frquency analysis is. Is it the fact that it enables us to read upper and lower quartiles? So we can see if the data ranges between to data sets and maybe has a higher upper quartile in one set than in an other?

Hi everyone, I'm drawing a cumulative frequency table & graph for coursework on different lengths of words between an newspaper and magazine. I've read in my study guide that data must by grouped before it can be processed into a cumulative frequency table and graph. I understand the reason for this when the range of data is large - but my data ranges from 1 letter to the biggest word I found with 15 letters. Must I group this relatively small data set if I want to plot a frequency graph? Will I get lower marks if I don't? I could plot it in 5 groups of 3 letters - but I don't see the point of this considering that 1 - 15 isn't that large. I'd be grateful to know what you think when it comes to whether or not grouping data is necessary1 Thanks Gav

so how would i find the formula to calculated the nth number when the sequences are fractions?

Hi everyone, I have to do some coursework, and I am studying independant of school - so I have no tutor. I am doing some coursework on sequences of fractions. I'm just wondering, after finding the formula for the nth number, what else can you do with sequences? Here is what I have to do: 1/1 1/2 1/3 1/4 1/5 1/6 ... ... the difference from above is 1/2 1/6 1/12 1/20 1/30 ... ... the difference from above is 1/3 1/12 ... ... ... 'invesigate further' I'm not sure how to investigate further! I can find the formula, but then what? How can I investigate this further?

wow that's a lot of sugar - i never realised 1M was so much. thanks Fredrick Gav

also black people don't worship the sun like many white people do, avoiding skin cancer and damaged skin

Hi Fredrik - thanks for your help, so, just to confirm I have understood you correctly, 342.3g of dry normal table sugar mixed with enough water to equal a total of 1 liter will give me sucrose solution of 1M?

Hey...just 1 more question - I promise! If I know I want 1molar of sucrose solution, how would I measure that on a weighing scale in grams? I've get that 1 molar is 6.02 x (10)23 formula units, but how do weigh that? I'm stuck!

Yeah, so I think I get it now, One mole of a substance contains 6.02 x (10)23 formula units. thanks for your help guys.....I realise my questions must seem a bit daft, sorry.

From wikipedia: "The mole fraction Χ, (also called molar fraction) denotes the number of moles of solute as a proportion of the total number of moles in a solution. For instance: 1 mole of solute dissolved in 9 moles of solvent has a mole fraction of 1/10 or 0.1" I don't understand how this isn't 10%. I know I'm getting wrong, as you guys have told me, but my understanding from this is that the molar of a solution is a percentage the solute takes up of the whole solution. Please tell me what I'm getting wrong! thanks

yeah...but i though 1.0 would be the maximum i.e. 100%. could anyone help me please? p.s. if 0.1M was 10%, then 20M would be 2000% not 200% ;-)

Hi everyone, Can I just check with you, is 0.1M 10%? So to get from molar to % we just multiply by 100? Is that correct? thanks in advance...and sorry forthe simplicity

Hi everyone, I've been told by my tutor that this formula: Na2S2O3(aq) + 2HCl(aq) → S(s) + SO2(g) + 2NaCl(aq) + H2O is incomplete as it doesn't consider the effects of heat on the collisions of particles. I know what the effect is, but is she suggesting I represent heat in the equation itself? I've looked all over the net for something to give me a clue - but can't find it! Could anyone help? thanks Gav

thanks Fredrik

thanks Bluenoise & ecoli. I have just 1 further question if I may!? We all know osmosis is dependant on the semi permeable membrane - but can the concentration gradient be said to actually cause the osmosis?

so, even in a lab environment, when the potato will release water if the sucrose is strong, even to the extent that potato will be left weaker and flexible etc...is this an indication that it isn't capable of active transport?

Hi everyone, I hope this is the correct section of the forum - if it isn't please could someone advise which section is most appropriate? I have a few questions regarding active transport & osmosis. With potato pieces in sucrose, the water moves from the potato to the sucrose as there are fewer water molecules in the sucrose. Can we assume from this that the potato has no need for the water that it is releasing via osmosis? If it needed it, it could use active transport techniques to reatain it's own water plus acquire more from the sucrose? when we use a weaker sucrose we find that the potato does acquire extra water via osmosis. So, this it seems is determined by the concentration gradient - irrespective of what the potato actually needs itself? Thus if there is more water outside it will take it in, but if there is less water outside it will release some, and wont use active transport to get more? Please help! thanks

hello all, I was just wondering if anyone could give me some advice. I am doing a photsynthesis experiment using pond weed and varying light. What range of light in watts do you think is appropriate? I am doing this experiment at home and haven't got a device to change the light so will have to rely on different light bulbs with different watts. thanks

thanks D H & Insane_alien

Below is a quote from wikipedia refering to the factors that increase the rates of chemical reactions: "Temperature: The kinetic energy of particles follows the Maxwell-Boltzmann distribution. An increase in temperature not only increases the average speed of the reactant particles and the number of collisions, but also the fraction of particles having kinetic energy higher than the activation energy. Thus, the effective collision frequency increases" So, the above quote states there are 2 reasons why temp increases rate of reaction. 1) temp increases the average speed of particles. 2)increases the kinetic energy of particles. I'm a little confused at this distinction as I thought kinetic energy was the energy that a thing had due to its movement. therefore the first piont in the quote is about faster movement so doesn't this just mean an increase in kinetic energy and therefore is the same as the second point?

Hi everyone, In relation to another post about reaction rates, please could someone answer if it is conventional in chemistry to use significance tests like chi-squared? For example, would it be used in something like a rates of reaction test? If reaction rate is supposed to double as you increase temp by 10°C but you find the increase is 1.8 rather than 2 - could you use chi-squared to see if this is a significant relationship. What would the scientific community think of using suck techniques to test significance? thanks as always

sorry please ignore the above post, you lot must think i am crazy! hydrochloric acid + sodium thiosulphate= sodium chloride + sulphur dioxide + sulphur + water. 2HCl(aq) + Na2S2O3(aq) = 2NaCl(aq) + SO2(g) + S(s) + H2O The above is balanced and correct isn't it? Back to my original question, it is the acid that is breaking everything up?