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Relative strength of an unknown acid
Ok-here's the situation...
I am provided with a sample of unknown acid (12.56g) made up to 250cm3. The Mr of the sample if 50.
50cm3 of this acid solution is placed in a polystyrene cup, and 50cm3 of NaOH is added. The temperature rise is 3.6.
The specific heat capacity of water is 4.18
Heat given out in joules is q=mcdeltaT
Is the molar enthalpy change of neutralisaion -29.93kJmol-1?
I am provided with a sample of unknown acid (12.56g) made up to 250cm3. The Mr of the sample if 50.
50cm3 of this acid solution is placed in a polystyrene cup, and 50cm3 of NaOH is added. The temperature rise is 3.6.
The specific heat capacity of water is 4.18
Heat given out in joules is q=mcdeltaT
Is the molar enthalpy change of neutralisaion -29.93kJmol-1?
remind me what is m again ?
Here are my calculations: someone plz check for errors:
moles acid = mass/Mr = 12.57/50 = 0.2514moldm-3
moles acid = molarity x volume/1000
0.2514 = molarity x 250/1000
molarity = 0.2514x1000/250
molarity = 1.0056
q = mcdeltaT
q = 100 x 4.18 x 3.6
q = 1504.8 J
kJ/mol = 1.5048kJ/(0.2514/5) = 29.93, but since it is exothermic, it must be -ve
moles acid = mass/Mr = 12.57/50 = 0.2514moldm-3
moles acid = molarity x volume/1000
0.2514 = molarity x 250/1000
molarity = 0.2514x1000/250
molarity = 1.0056
q = mcdeltaT
q = 100 x 4.18 x 3.6
q = 1504.8 J
kJ/mol = 1.5048kJ/(0.2514/5) = 29.93, but since it is exothermic, it must be -ve
yeah your calculation seems right 
and ok to me just put it into my calc sorry about asking you what m was forgot cause i did it in AS last year this year all i can think about is equlibria in unit 4 chem !. but yeah your correct and yes negatvie because energy is given out so exothermic
and ok to me just put it into my calc sorry about asking you what m was forgot cause i did it in AS last year this year all i can think about is equlibria in unit 4 chem !. but yeah your correct and yes negatvie because energy is given out so exothermicmolar enthalpy of neautralisation is to produce 1 mole water not to neautralise 1 mole acid - i dunno if u have done this or not i cant be ****ed workin it out
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