Q12 ,Q18 and Q20 2011 HSC (1 Viewer)

[NizDiz]

May someone please help? All help greatly appreciated! Thanks

 

[Menomaths]

Number of HCL=.0244x0.1 = 0.00244 moles
We know the ratio is 1:1 therefore number of moles of NaX= 0.00244 in the 20mL sample
We now want to convert this into 100 mL so it is equivalent to the HCL's volume so we multipy by 5. 5x0.00244 = 0.0122 in the 100 mL sample.
Applying the formula n=m/M we get;
0.0122=1/M
Rearranging M= 1/0.0122
M= 81.967g, or 82g 3 significant figures.

 

[Menomaths]

Since it says 'equal amounts are consumed' that means 200g is used for each reaction
200/12 =50/3 that is the number of moles. 50/3 x 16 = 800/3 that is the mass of half of an oxygen molecule
Now 50/3 x 32 = 1600/3 that is the mass of an oxygen molecule
Add up; 1600/3 + 800/3 + 400 = 1200 mg = 1.2kg

 

[Frie]

For 12, you arrange the metals in order of most reactive to least (decreasing order)

The numbers are their standard reduction potentials (given in question)
So similarly to the reduction potentials on the back of the periodic table, the most negative is the most reactive, apply the same concept here.

Hence if ranked in decreasing order it is: Cd (-0.40V), Ni (-0.24V), Ag (0.80V) and Pd (0.92V)
Which is the answer D.

 

[NizDiz]

Thanks guys, greatly appreciated!!!