4 This question is about rusting.
(a) When iron rusts, it-reacts with oxygen in the air.
A student uses the rusting of iron to find the percentage of oxygen in a sample of air.
The diagram shows the apparatus.
100 80 60 40 20
cm
air
gas syringe
conical flask
wet iron
filings
These are the student's results.
volume of air in conical flask and connecting tube = 265 cm
volume of air in gas syringe at start = 100 cm
volume of air in gas syringe at end = 25 cm
Calculate the percentage of oxygen in the sample of air using the student's results.
(3)​

In any energy conversion, some of the energy is lost to the environment as question 5 options: electrical energy potential energy sound energy thermal energy

10. translate each of the following chemical equations into a sentence. a. 2 zns(s) + 3 o2(g) -> 2 zno(s) + 2 so2(g) b. cah2(s) + 2 h2o(l) -> ca(oh)2 (aq) + 2 h2(g)

A3.37-mg sample of protein was chemically digested to convert its nitrogen into ammonia and then diluted to 100.0 ml. then 10.0 ml of this solution was placed in a 50-ml volumetric flask and treated with 5 ml of phenol solution plus 2 ml of sodium hypochlorite solution. the sample was diluted to 50.0 ml, and the absorbance at 625 nm was measured in a 1.00-cm cuvette and found to be 0.486. for reference, a standard solution was prepared from 10.0 mg of nh4cl (molar mass = 53.49 grams/mole) dissolved in 1.00 l of water. then 10.0 ml of this standard was placed in a 50-ml volumetric flask, treated in the same manner as the unknown, and the absorbance found to be 0.323. finally, a reagent blank was prepared using distilled water in place of unknown, it was treated in the same manner as the unknown, and the absorbance found to be 0.076. calculate the weight percent of nitrogen in the protein.