Blood alcohol levels are usually reported in mass percentages: A level of 0.10 means that 0.10 g of alcohol (C₂H₅OH) was present in 100 g of blood. This is just one way of expressing the concentration of alcohol dissolved in the blood. Other concentration units could be used. Find the molarity of alcohol in the blood of a person with a blood alcohol level of 0.12. (The density of blood is 1.2 g/mL.)