Question

I need help with both of these questions in the picture .

Answer 1

In order to answer question 4 we need to calculate how much 2.56x1024 molecules of water weight.

We know that 1 mol of water molecules (6.022x1023 molecules) weight 18g. This is because according to the periodic table 1 mol of hydrogen weights 1g and 1 mol of oxigen weights 16g. So knowing the chemical formula H2O we calculate:

`1mol_(H2O)=2x1(g)/(mol)+1x16(g)/(mol)=18(g)/(mol)`

Now we need to calculate how much 2.56x1024 molecules weight (mH2O):

`m_(H2O)=(2.56x10^(24)molecules)/(6.022x10^(23)(molecules)/(mol))x18(g)/(mol)=76.5g`

So we know that the mass of water is 76.5 g.

Now we calculate the total weight, given that the cup weights 5g:

`Total\text{ weight=}5g+76.5g=81.5g`

So the correct answer is B: 81.6g