Hi, I really need some help on a question...

The volume of seawater on Earth is about 330,000,000 cu mi. If seawater is 3.5% sodium chloride by mass and has a density of 1.03 g/mL, what is the aproximate mass of sodium chloride, in tons, dissolved in the seawater on Earth (1 ton =2000 lb)?


First, I converted the 330,000,000 cu mi into mL.
Then, I multiplied that by the density to find ? g of seawater.
Then, I multiplied that amount by 0.035 to find mass of dissolved NaCl in grams.
Finally, convert that amount into tons..

The answer in the key is 5.5 x 10^16 tons.. but I always get something different.

Your logical steps look fine.
( 2.54 cm/in * 12 in/ft *5280 ft/mi)^3 = 4.168E15 cubic centimeters/cubic mile.
*330000000 cubic miles=1.3755E24 cm3 total volume
*1.03 g/cm3 = 1.417E24 g total mass
*0.035 fraction sodium= 4.957E22 g NaCl
/1000 g/kg = 4.957E19 kg NaCl
*2.2046 lb/kg =1.0932E20 lbs NaCL
/2000 lb/ton = 5.466E16 tons of Sodium chloride.

Significant figures 330000000 has only 2 significant figures.
5.5E13 tons of sodium chloride.

It's probably just a case of 'happy fingers'
(that's what a co-worker calls typos and miss keys on the calculator).