Calculate the mass percent of a nacl solution in which 140g of nacl is dissolved in 4.50l of water at 25c (density = 0.997g/ml).

Large helium-filled balloons are used to lift scientific equipment to high altitudes. what is the pressure inside such a balloon if it starts out at sea level with a temperature of 10.0ºc and rises to an altitude where its volume is twenty times the original volume and its temperature is – 50.0ºc ?