If the heat of vaporization of water is 539.5 calories per gram, how many calories of heat are needed to vaporize 3.14 kilograms of water. Express your answer in calories.

Alculate the concentration of h3o⁺in a solution that contains 5.5 × 10-5m oh⁻at 25°c. identify the solution as acidic, basic, or neutral. a) 1.8 × 10-10m, basicb) 1.8 × 10-10m, acidicc) 5.5 × 10-10m, neutrald) 9.2 × 10-1m, acidice) 9.2 × 10-1m, basic

The answer for #3 is c but i don't know why

Achemistry student needs to standardize a fresh solution of sodium hydroxide. he carefully weighs out of oxalic acid , a diprotic acid that can be purchased inexpensively in high purity, and dissolves it in of distilled water. the student then titrates the oxalic acid solution with his sodium hydroxide solution. when the titration reaches the equivalence point, the student finds he has used of sodium hydroxide solution. calculate the molarity of the student's sodium hydroxide solution. be sure your answer has the correct number of significant digits.