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chem may/june 2010 p11 help
- Thread starter robinho10
- Start date
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Use Hess's law for this question. Follow this pathway: From iodinesolid to gas (+38) then to iodine tetrachloride (-214)
We then divided by 2 because the question is asking for the standard enthalpy change of formation of 1 mole of iodine tetrachloride not 2. So the ans is B
The oxidation number of nitrogen in NH4+ is -3 and in NO3- is +5. the oxidation number of nitrogen in N2O is +1 so from -3 to +1 the change is +4 and from +5 to +1 the change is -4
The mass of chlorine used is 2.367 which is 0.0333 moles of chlorine molecules.
The mole ratio of the metal atom to the chlorine molecule is 1:1
Therefore divide 2.920 by the Ar of the metals to get 0.0333
The number of moles of the gas required is 3/24 = 0.125
Divide the mass of the gass given by their Mr to get the specified number of moles.
8/64 = 0.125
Of course a pH of 6 is a weak acid.
You know that acids and alkalis dissociate in water forming H+ or OH-
At pH 7 there are no net H+ or OH-
If pH is closer to 7 this means that the substance dissociates slightly
pH 6 is closer to pH 7 than pH 9 so Y dissociates more than X regardless if it is an acid or alkali.
The important thing is the dissociation in this question
For this question write down the formulae of the oxides of the elements shown
Al2O3
MgO
P4O10
Na2O
From the first instance eliminate A and C because they require more oxygen atoms than the element itself
MgO has the same number of oxygens as magnesium
Only sodium is the one that requires least oxygens per mole.
I hope I was able to help,
Good Luck.
We then divided by 2 because the question is asking for the standard enthalpy change of formation of 1 mole of iodine tetrachloride not 2. So the ans is B
The oxidation number of nitrogen in NH4+ is -3 and in NO3- is +5. the oxidation number of nitrogen in N2O is +1 so from -3 to +1 the change is +4 and from +5 to +1 the change is -4
The mass of chlorine used is 2.367 which is 0.0333 moles of chlorine molecules.
The mole ratio of the metal atom to the chlorine molecule is 1:1
Therefore divide 2.920 by the Ar of the metals to get 0.0333
The number of moles of the gas required is 3/24 = 0.125
Divide the mass of the gass given by their Mr to get the specified number of moles.
8/64 = 0.125
Of course a pH of 6 is a weak acid.
You know that acids and alkalis dissociate in water forming H+ or OH-
At pH 7 there are no net H+ or OH-
If pH is closer to 7 this means that the substance dissociates slightly
pH 6 is closer to pH 7 than pH 9 so Y dissociates more than X regardless if it is an acid or alkali.
The important thing is the dissociation in this question
For this question write down the formulae of the oxides of the elements shown
Al2O3
MgO
P4O10
Na2O
From the first instance eliminate A and C because they require more oxygen atoms than the element itself
MgO has the same number of oxygens as magnesium
Only sodium is the one that requires least oxygens per mole.
I hope I was able to help,
Good Luck.
