# Search results

1. ### Pauli's Contribution to the Atomic Theory?

The Exclusion Principle was the thing he got a Nobel Prize for, but he also came up with the idea of the neutrino i.e. during beta decay, a very tiny neutral particle was emitted - which explained why a beta ray can have a range of energies (e.g. when Carbon 14 decays into Nitrogen 14) - and not...
2. ### HELLLPPPPP me pls

A mass spectrometer is a machine that smashes molecules into bits and then weighs the pieces. Molecules break in predictable ways. For example, when the mass spectrum of ethane is taken (see http://webbook.nist.gov/cgi/cbook.cgi?Spec=C74840&Index=0&Type=Mass), there are a bunch of peaks at 30...
3. ### Bromine Water Prac PLZ HELP

I think in this case it is best to ignore any reaction between bromine (Br2) and water. It is an unnecessary complication. Most HSC Chemistry students will learn that the Br2 molecule simply "adds" onto the alkene, forming a dibromoalkane. Those with a bit more interest in the reaction will...
4. ### Combustion

Start with the delta H = mC delta T (delta h = mcat formula) How much energy is needed to raise the temperature of 350 grams of water by 77°C? delta H = 350 x 4.2 x 77 = 113190 Joules. So it takes 113190 Joules (113.190 kJ) of heat energy to raise the temp of 350 g of water by 77°C...
5. ### Equlibrium constant

Calculating an equilibrium constant (K) is a tricky thing, as there are a bunch of different equilibria which are covered in HSC Chemistry and they need to be looked at in slightly different ways. The usual K question in a HSC Chemistry exam involves a mixture of gases at a high temperature...
6. ### ACID + BASE equations...and H+ concentrations.

Polyprotic acid equations also apply to buffer solutions (9.2.4.2.9). Blood contains three buffers (bicarbonate, hydrogen phosphate and haemoglobin). The bicarbonate buffer being the most important. I would suggest learning all of the equations associate with the CO2 / bicarbonate buffer, and...
7. ### When to use these formulas?

CaVa = CbVb needs to be used carefully. It assumes that a monoprotic acid (e.g. HCl) is reacting with a monoprotic base (e.g. NaOH) - or diprotic with diprotic, or triprotic with triprotic. If you have a diprotic acid, then it takes twice as many moles of a monoprotic base to neutralise it...
8. ### Question on Special Relativity

This is a lot more complicated that it looks... a rocket travelling at 0.75 c will take 9 / 0.75 = 12 years to travel the distance. But let's pretend that someone on the "distant planet" shines a green light towards Earth when the rocket arrives - then that signal would take 9 years to get...
9. ### Conjugate Acid/Base pair

The Bronsted-Lowry definitions for this type of equilibrium say that an acid + base <> conjugate acid + conjugate base. So, in the equation as it is written, H2O is the acid, CO3 2- is the base, HCO3 - is the conjugate acid and OH- is the conjugate base. Speaking as a teacher, I won't be...
10. ### Quick question on Condensation Polymerisation

If you have a look at the chemistry of nylon you will find a condensation polymer which does not have an OH on both monomers. Water is still the by-product of the reaction. I have heard of condensation polymers which produce ammonia as a by-product (the "condensation", if you will), but those...
11. ### Just to confirm something

"Aromatics" is a general term for carbon compounds based on the benzene ring. There is only one direct reference to an "aromatic" compound in the syllabus - the styrene to polystyrene polymerisation.
12. ### URGENT!!! Sulfate content of lawn fertiliser question.

It sounds like you used some ammonium sulfate off the shelf from the chemical storeroom rather than a fertiliser mix from a supermarket or a hardware shop. If this is the case, then the ammonium sulfate would have all dissolved in the water pretty easily, so there would have been no need to add...
13. ### polystyrene question

There are three types of intermolecular forces which are discussed in HSC Chemistry: hydrogen bonding, dipole-dipole interactions and van der Waals (aka dispersion forces aka "London forces"). Polystyrene only contains carbon and hydrogen, so there is no possibility of hydrogen bonding (which...
14. ### Nuclear Chem help

YoloStudent is correct. An alpha particle is about 7350 times the mass of a beta particle. That's like comparing the mass of a really small car with the mass of a cricket ball. Your second question has me a bit puzzled. Cyclotrons and particle accelerators can produce radioisotopes by...
15. ### Calculate equilibrium constant help please!

Hey uart. Wish I had a dollar for every time i've stuffed up the arithmetic over the years. But I've checked it three more times and I keep getting 2518. ??? I can help with your question. Before the syllabus changed in 2000 equilibrium constant calculations were in the core, but these days...
16. ### Does the standard solution go into the burette or the conical flask?

It makes no difference at all, as long as you keep taking 25.0 mL aliquots from the same solution every time, and keep topping up the burette from the same solution every time. In fact, way back in the day, it was probably better to put acid in the burette as it was less likely to react with...
17. ### Calculate equilibrium constant help please!

Volume of container = 10 L Sulfur dioxide = SO2 Oxygen = O2 Sulfur trioxide = SO3 2SO2(g) + O2(g) <> 2SO3(g) Initial moles of SO2 = 1.903, number of moles of SO2 at equilibrium = 0.129, therefore (1.903 - 0.129) moles of SO2 has been converted into SO3. 1.903 - 0.129 = 1.774 moles of SO2 has...
18. ### HELP: Charges in Magnetic Field Question!

This is the correct method. But iheartOJ might have left something out when they retyped the question - remember force is a vector. So you might need to state both the size and the direction in order to fully answer the question. A positively charged object travelling into the page will...
19. ### hard industrial chem question help

The reaction is 2HI(g) = H2(g) + I2(g). If 4.00 moles of HI are put into a 2 L vessel and, once the above equilibrium has been established, 3.10 moles remain, then 0.90 moles of HI must have reacted with itself to produce 0.45 moles of H2 and 0.45 moles of I2. Imagine 2 HI molecules smashing...
20. ### HELP!

I am a bit puzzled by the original question. "Standard Model of the atom" is not a phrase you will find in the HSC syllabus. The Standard Model mostly relates to the tiniest things that science can measure - electrons, quarks, etc which are smaller than atoms. So the "Standard Model of the...