How many moles are present in 10.5 grams of nacl?
0.180 mol
0.18 mol
0.457 mol

N(number of moles)=mass/molar mass

10.5=mass

Na=23 (rounded)

Cl=36 (rounded)

Add it together to get the molar mass

=59

Then refer back to the formula

10.5/59

=0.17796

Round that answer

=0.18 mol

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explanation:

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answer : third trial had the contaminated sample and the correct value for dhrxn should be 1000 kj/mol

explanation :

let us write down the given equations

equation 1 :

equation 2 :

equation 3 :

let us use hess's law to find out which 2 equations can be added to get the third equation.

let us reverse equation 2 and multiply it by 2. the new equation that we get is,

equation 4 :

let us add equation 1 & 4

the above equation is similar to equation 3 but has different value for dhrxn.

therefore third trial had the contaminated sample and the correct value for dhrxn should be 1000 kj/mol