Final answer:
To find the percentage by mass of alcohol in the solution, we need to calculate the mass of alcohol and the total mass of the solution. The mass of water is 180g, and the total mass of the solution is given as 200g. So the percentage by mass of alcohol is 10%.
Step-by-step explanation:
To find the percentage by mass of alcohol in the solution, we need to calculate the mass of alcohol and the total mass of the solution. Given that the solution contains 180mL of water, we can calculate its mass by multiplying the volume by the density of water, which is 1.00 g/mL. So the mass of water is 180g.
To find the mass of alcohol, we subtract the mass of water from the total mass of the solution. The total mass of the solution is given as 200g. Therefore, the mass of alcohol is 200g - 180g, which is 20g.
The percentage by mass of alcohol can now be calculated by dividing the mass of alcohol by the total mass of the solution and multiplying by 100. So the percentage by mass of alcohol is (20g / 200g) x 100, which is 10%.