Q: Molarity expresses the relationship between the number of moles of a solute per liters of solution, or the volume of that solution. In formula form, molarity is expressed as: molarity = moles of solute / liters of solution Example problem: What is the molarity of a solution made by dissolving 3.4 g of KMnO4 in 5.2 liters of water? Finding molarity demands that you have the number of moles and the number of liters. If you are not provided with the number of moles but you do have the volume and mass of the solution, you will need to use these two figures to calculate the number of moles before continuing on. Example problem: Mass = 3.4 g KMnO4 Volume = 5.2 L To calculate the number of moles from the mass or grams of solute used, you must first determine the molar mass of the solute. This can be done by adding together the separate molar masses of each element found in the solution. Find the molar mass of each element using the periodic table of elements. Make sure that you count the atoms for each element and calculate the molar mass of each of the atoms. Example problem: Molar mass of K = 39.1 g Molar mass of Mn = 54.9 g Molar mass of O = 16.0 g (The solute contains 4 O atoms, so count the 16g 4 times.) Total molar mass = K + Mn + O + O + O + O = 39.1 + 54.9 + 16 + 16 + 16 + 16 = 158.0 g Now that you have the molar mass of the solute, you need to multiply the number of grams of solute in the solution by a conversion factor of 1 mole over the formula weight (molar mass) of the solute. This will give you the number of moles of the solute for this equation. Example problem: grams of solute * (1/molar mass of solute) = 3.4 g * (1 mol / 158 g) = 0.0215 mol The grams units of the solute and solute mass cancel each other out so you are left with mol units. Now that you have the number of moles, you can divide this value by the number of liters of solution in order to find the molarity. Example problem: molarity = moles of solute / liters of solution = 0.0215 mol / 5.2 L = 0.004134615 You should round off the number of digits after the decimal point to the place requested by your instructor. Usually, this will be two or three places after the decimal point. Additionally, when you write out the answer, abbreviate "molarity" with "M" and state the solute involved. Example problem: 0.004 M KMnO4
A: Know the basic formula for calculating molarity. Examine the problem. Find the molar mass of the solute. Convert the grams into moles. Divide the number of moles by the number of liters. Write your answer.

Q: As with other retinal surgeries, you will be required to abstain from eating or drinking anything for between two and eight hours before the procedure. You may also be instructed to use eye drops to dilate the pupils before surgery. In a vitrectomy, your doctor will remove the vitreous fluid from inside the eyeball, and will remove any tissue that may be preventing the retina from healing. Your doctor will then fill the eye with air, gas, or liquid to replace the vitreous, allowing the retina to reattach and heal. This procedure is the most commonly-performed type of retinal surgery. Over time, the substance (air, gas, or liquid) your doctor injected is absorbed by the eye, and your body will produce fluid that will fill the vitreous cavity. If your doctor used silicone oil, however, he will need to surgically remove the oil after several months have passed and the eye has healed. After a vitrectomy, your doctor will send you home with specific care instructions for your eye to help ensure a full recovery. Follow your doctor's instructions carefully, and ask him if you're uncertain of what to do. Your doctor may instruct you to: Take a pain reliever, like acetaminophen Use prescription-strength eye drops or ointments After a vitrectomy, most patients are instructed to keep the head stable in a specific position. This is known as "posturing," and it is vital to allow the bubble to settle into the correct position. It can also be helpful in maintaining the eye's shape after surgery. Follow your doctor's instructions on posturing to allow the retina to heal. Do not travel by airplane until the gas bubble is fully absorbed. Your doctor will tell you when it is safe to fly again. Having gas bubbles in the eye may cause complications in other surgeries. Let your doctor know about the gas bubbles before any subsequent surgeries, and before being administered general anesthetic, especially nitrous oxide. Your doctor may give you an eye box to help your eye heal. He will instruct you on how to use the eye box, and will let you know how long to continue using it. Wash your hands thoroughly with soap and water before handling any eye equipment. Soak cotton balls in the prescribed eyewash solution. Loosen any crust that may have formed on your eye, then wipe gently from the inside of your eye across to the outside. If you are treating both eyes, use separate cotton balls for each eye. Your doctor may give you an eye patch and an eye shield to help your eye heal. These tools will help you protect your eye while sleeping and whenever you are outdoors. Wear the eye shield for at least a week, or for as long as your doctor instructs you to continue use. The eyepatch will help protect your eye from bright lights, like the sun, and will help prevent dirt and debris from entering your healing eye.
A:
Prepare for surgery. Have a vitrectomy. Recover from surgery. Stay in position. Use an eye box. Wear a shield and patch.