please check my answers. THANK YOU.
1) The percent by mass of carbon in acetone, C3H6O is.
Answer: 62.1%
2) What is the percent by mass of zinc, Zn, in ZnCO3?
Answer: 52.3%
3)What is the percentage of water in the compound BaCl2 * 2H2O?
Answer: 7.96%
4)How many atoms are in one mole of NO2?
Answer: 2.77 x 10^25
I looked on a "calculator" on the internet to help and they list 64.04% for C, 52.15% for Zn 14.74% for H2O (don't forget to multiply by 2 for mols H2O). 1 mol NO2 contains 3 atoms; therefore, 1 mol will contain 3 x 6.022 x 10^23 atoms. You don't say to what accuracy the percents should be known but i suspect your numbers are ok when rounded off (except for 3.)
My only options for numbers 1-3 are...
1. a) 20.7% b) 62.1% c) 1.61% d) 30.0%
2. a) 20.0% b) 47.7% c) 52.3% d) 65.4%
3. a) 33.3% b) 17.3% c) 7.96% d) 14.8%
1 is ok.
2 is ok.
3. BaCl2.2H2O
I will approximate.
Ba = 137.3
Cl = 35.5 x 2 = 71
H2O = 16 + 2 = 18 and 18 x 2 = 36
Total is 244.3
Then %H2O = (36/244.3) x 100 = 14.7% so I would pick d.