Archive for December, 2008
ChemistryTutorsite.com-Chemistry Homework Help
A sample of 0.600 mol of metal M reacts completely with excess fluorine to form 46.8 gms of MF2 a) how many ?moles of F are in the sample of MF2 that forms? b) how many gms of M are in this sample of MF2? c) what element is represented by the symbol M?
ChemistryTutorsite.com-Chemistry Homework Answer
The chemical reaction between M and F2 can be written as:
M + F2 -> MF2
from the reaction above we know that 1 mole of M will be react completely with 1 mole of F2 to produce 1 mol of MF2 ( see the coefficient reaction). Thus 0.600 mol of M will be reacted with 0.600 mol of F2 to produce 0.600 of MF2.
thus the mass of F2
= mole x Mr
= 0.600 x 38
= 22.8 grams
thus the mass of M in the MF2
= mass of MF2 - mass of F2
= 46.8 - 22.8
= 24 gr
Mr of M can be calculate as:
mole = mass/Ar
Ar = mas/mol
Ar = 24/0.600
Ar = 40
when you check in the periodic table you will find that the atom that has Ar 40 is Ca
December 2nd, 2008
ChemistrytutorSite.com-Homework Chemistry Help
Can i find out if a substance is acid, base, or neutral without litmus paper?
ChemistrytutorSite.com-Homework Chemistry Answer
How to predict that a substance is acid, base, or neutral without using any indicator? the answer is you should examine the component that form the substance, check what is the cation and what is the anion of the substance, is the substance contains H+ or OH- or, what kind of base and acid that build the substance and the value of Ka and Kb will be necessary to consider too.
here i will be give you the examples:
1. does the substance have H+ or OH-?
substance that has H+ will be acid and that has OH- will be basic. thus:
H2SO4, HCl, H3PO4 are acids and NaOH, Ca(OH)2 and KOH are bases.
2. if the substance is a salt
salt that build from strong acid and strong base will be neutral in their solution, example NaCl will be neutral because it forms from stong acids HCl and NaOH. another example are NaNO3, K2SO4
Salt that build from strong acid and weak base will be acid and the reverse salt from weak acid and strong base will be basic.
example:
NH4Cl is acid in their solution
CH3COOK is basic in their solution
How about if the salt builds from weak acid and weak base? You should take a look for the Ka and Kb values, the greater one has to determine the properties of the salt.
December 2nd, 2008
ChemistryTutorSite - Homework Chemistry Help
What are the group trends for ionic radius?
ChemistryTutorSite - Homework Chemistry Answer
to answer this question i well give you example of the group IA the electron configuration of all atoms in this group are:
H 1s1
Li [He]2s1
Na [Ne]3s1
K [Ar]4s1
Rb [Kr]5s1
Cs [Xe]6s1
Fr [Rn]7s1
from H to Fr there are extra layers or sub shell that we add to the atoms thus from H to Fr or down to the group the atomic radius will be greater.
if they form ion the group IA will be release 1 electron each so the electron configuration will be:
H 1s0
Li [He]
Na [Ne]
K [Ar]
Rb [Kr]
Cs [Xe]
Fr [Rn]
the atomic radius of a metal is generally larger than the ionic radius of the same element for the example the radius of Na will be greater than Na+.
But if we go down in the same group they still have the same trend of radius with the atomic radius thus for the ionic radius in the same group the ionic radius will be greater if we go down in the same group.
December 2nd, 2008