Pure sodium metal explodes when it makes contact with water, and chlorine, in its natural state, is a deadly, poisonous gas. when these two chemicals combine, they form a harmless, white powder known as sodium chloride or table salt. which of the following statements does this information support? a. when substances are chemically combined, the properties of the new substances that are formed are often different from the properties of the original substances. b. heat must be added in order to change the chemical properties of substances. c. when substances are chemically combined, the properties of the new substances that are formed are the same as the properties of the original substances. d. the properties of substances change during chemical reactions but then later go back to their original condition.

Given the table below, what is the chemical formula for a compound between rb and the nitrate ion no3 -1? nitrate ion no3 -1 phosphate po4 -3 sulfate so4 -2 acetate c2h3o2 -1 ammonium nh4 +1 chromate cro4 -2 carbonate co3 -2 dichromate cr2o7 -2 permanganate mno4 -1 sulfite so3 -2 rbno3 rb2no3 rb(no3)2 rb2(no3)3

Silica, sio2, is formed on silicon as an electrically insulating layer for microelectronic devices. silica is formed when silicon is exposed to o2 gas at an elevated temperature. at 900˚c, it takes 90 minutes for the oxygen to diffuse from the surface to form a 0.06 micron (0.06 x 10-6 m) thick layer of sio2 on

7. using your knowledge of colligative properties explain whether sodium chloride or calcium chloride would be a more effective substance to melt the ice on a slick sidewalk. use 3 – 4 sentences in your explanation. 8. when a 2.5 mol of sugar (c12h22o11) are added to a certain amount of water the boiling point is raised by 1 celsius degree. if 2.5 mol of aluminum nitrate is added to the same amount of water, by how much will the boiling point be changed? show all calculations leading to your answer or use 3 – 4 sentences to explain your answer. 9. if 5.40 kcal of heat is added to 1.00 kg of water at 100⁰c, how much steam at 100⁰c is produced? show all calculations leading to an answer. 10. the freezing of water at 0⁰c can be represented as follows: h2o (l) ↔ h2o(s) the density of liquid water is 1.00 g/cm3. the density of ice is 0.92 g/cm3. in 3 – 4 sentences explain why applying pressure causes ice to melt.