What is the amount of gold present in 15.5g of a pure gold ring? (Au=197)

.0787 moles

Explanation:

I'm assuming you mean moles of gold present as the "amount."

This is a moles to moles calculation, so we set it up as such:

*Note that 15.5g Au is given to us, and 197 g / mol of Au is gold's molar mass.

15.5g Au * (1 mol Au / 197 g Au) = ?

We can evaluate the equation to get 15.5 / 197 to get .0787 moles of Au.

X=240 g NaCl salt dissolves in solution.
Example: If we add 68 g sugar and 272 g water to 160 g solution having concentration 20 %, find final concentration of this solution.
Solution:
Mass of solution is 160 g before addition sugar and water.
100 g solution includes 20 g sugar
160 g solution includes X g sugar
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X=32 g sugar
Mass of solute after addition=32 + 68=100 g sugar
Mass of solution after addition=272 +68 + 160=500 g
500 g solution includes 100 g sugar
100 g solution includes X g sugar
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X= 20 % is concentration of final solution.