Lux Aeterna Posted September 11, 2011 Share Posted September 11, 2011 CHEMISTRY HAS GOT ME BOGGED. I'M TWO QUESTIONS AWAY FROM FINISHING... but I can't figure out these. If anyone can help--and tell me how they figured it out (I need to show my work), pleeeease do. :< The first question... In the United States, water used for irrigation is measured in acre-feet. An acre-foot of water covers an acre to a depth of exactly 1 ft. An acre is 4840 yd2. An acre-foot is enough water to supply two typical households for 1 yr. Assume desalinated water costs about $3000 per acre-foot.(a) How much does desalinated water cost per liter? (b)How much would it cost one household per day if it were the only source of water? and the second: Gold is alloyed (mixed) with other metals to increase its hardness in making jewelry.(a) Consider a piece of gold jewelry that weighs 9.75 g and has a volume of 0.665 cm3. The jewelry contains only gold and silver, which have densities of 19.3 g/cm3 and 10.5 g/cm3, respectively. If the total volume of the jewelry is the sum of the volumes of the gold and silver that it contains, calculate the percentage of gold (by mass) in the jewelry. (b) The relative amount of gold in an alloy is commonly expressed in units of karats. Pure gold is 24-karat, and the percentage of gold in an alloy is given as a percentage of this value. For example, an alloy that is 50 percent gold is 12-karat. State the purity of the gold jewelry in karats. Thanks in advance. Quote Link to comment Share on other sites More sharing options...
Ansem Posted September 11, 2011 Share Posted September 11, 2011 http://gyazo.com/775b8531fcc9d954afbf5013fde558bf Quote Link to comment Share on other sites More sharing options...
Lux Aeterna Posted September 11, 2011 Author Share Posted September 11, 2011 (edited) ... Kai, if you seriously just did that yourself, my respect for you has soared. THANK YOU SO MUCH EDIT: But what about (b) of #1--/shot Edited September 11, 2011 by Lux Aeterna Quote Link to comment Share on other sites More sharing options...
Ansem Posted September 11, 2011 Share Posted September 11, 2011 (edited) b = # 2 no wait try using google once in a while Edited September 11, 2011 by Zack Fair Quote Link to comment Share on other sites More sharing options...
Original Alear Posted September 11, 2011 Share Posted September 11, 2011 (edited) 1B seems easy enough. The question states that An acre-foot is enough water to supply two typical households for 1 yr. Assume desalinated water costs about $3000 per acre-foot. We are trying to find out how much it costs to supply one household for a day, right? $3000/2=$1500 to supply one house with water for a year, $1500/365=$4.10whatever So assumimng non leap years, about $4.10 to get water to one household for one day, right? EDIT-SInce my answer didn't pop up in Kai's, lemme know what I did wrong. Edited September 11, 2011 by Blue Mars Quote Link to comment Share on other sites More sharing options...
Lux Aeterna Posted September 11, 2011 Author Share Posted September 11, 2011 b = # 2 no wait try using google once in a while I tried using google and they most certainly did not help. Quote Link to comment Share on other sites More sharing options...
Ansem Posted September 11, 2011 Share Posted September 11, 2011 Use Severlans answer? Quote Link to comment Share on other sites More sharing options...
Original Alear Posted September 11, 2011 Share Posted September 11, 2011 Check/discuss my logic and make sure it makes sense first, or doom yourself to potential foolishness. Where's all those math nerds? IEatTables and Lumi sure were good at stuff on that math challenge thread. RP too, though he's gone now. Quote Link to comment Share on other sites More sharing options...
Ansem Posted September 11, 2011 Share Posted September 11, 2011 Lumi's off :E Quote Link to comment Share on other sites More sharing options...
Psych Posted September 11, 2011 Share Posted September 11, 2011 This is why I take Earth Science. Quote Link to comment Share on other sites More sharing options...
Ansem Posted September 11, 2011 Share Posted September 11, 2011 You know some people dont have a choice ;_; Quote Link to comment Share on other sites More sharing options...
Original Alear Posted September 11, 2011 Share Posted September 11, 2011 This is why I take Earth Science. Hah. A class for those on the slow track to college in my district, anyway! And yes, of course you want to get into a competitive college for retarded reasons I can't fathom. Quote Link to comment Share on other sites More sharing options...
Lux Aeterna Posted September 11, 2011 Author Share Posted September 11, 2011 (edited) 1B seems easy enough. The question states that We are trying to find out how much it costs to supply one household for a day, right? $3000/2=$1500 to supply one house with water for a year, $1500/365=$4.10whatever So assumimng non leap years, about $4.10 to get water to one household for one day, right? EDIT-SInce my answer didn't pop up in Kai's, lemme know what I did wrong. I tried that before I looked at this. The webassign thing said it was wrong. EDIT: Well that is absolutely fucking retarded. It had me just say "4 dollars a day" and somehow that was right. Whatever. EDIT2: Actually, significant figures dictates that $3000 dollars only has one significant figure, which means that the answer should be $4, scientifically speaking. But that's not how much it actually costs... Edited September 11, 2011 by Lux Aeterna Quote Link to comment Share on other sites More sharing options...
Original Alear Posted September 11, 2011 Share Posted September 11, 2011 I tried that before I looked at this. The webassign thing said it was wrong. EDIT: Well that is absolutely fucking retarded. It had me just say "4 dollars a day" and somehow that was right. Whatever. Maybe it's a significnat digits thing. Quote Link to comment Share on other sites More sharing options...
Psych Posted September 11, 2011 Share Posted September 11, 2011 Hah. A class for those on the slow track to college in my district, anyway! And yes, of course you want to get into a competitive college for retarded reasons I can't fathom. Well, 1. It's Honors. And 2. My only other option would be AP Environmental. Quote Link to comment Share on other sites More sharing options...
Ansem Posted September 11, 2011 Share Posted September 11, 2011 Well, 1. It's Honors. And 2. My only other option would be AP Environmental. Those are all retarded classes here. lol Canada Quote Link to comment Share on other sites More sharing options...
Psych Posted September 11, 2011 Share Posted September 11, 2011 I have to have a Physical Science, either Chemistry or Physics, and Earth Science. There's Biology or AP Anatomy. Quote Link to comment Share on other sites More sharing options...
Agro Posted September 12, 2011 Share Posted September 12, 2011 (edited) Gold is alloyed (mixed) with other metals to increase its hardness in making jewelry.(a) Consider a piece of gold jewelry that weighs 9.75 g and has a volume of 0.665 cm3. The jewelry contains only gold and silver, which have densities of 19.3 g/cm3 and 10.5 g/cm3, respectively. If the total volume of the jewelry is the sum of the volumes of the gold and silver that it contains, calculate the percentage of gold (by mass) in the jewelry. (b) The relative amount of gold in an alloy is commonly expressed in units of karats. Pure gold is 24-karat, and the percentage of gold in an alloy is given as a percentage of this value. For example, an alloy that is 50 percent gold is 12-karat. State the purity of the gold jewelry in karats. I don't think there's enough information here to solve (a) :| Edit: I GOT IT Okay so to solve (a) we have to use our good old friend, simultaneous equations. I don't know how familiar you are with them so I'll just continue and hopefully you get it. So first of all, we have two unknowns: the volumes of gold and silver. So assign a variable to each; v(gold) = x, v(silver) = y. Now we know that the total volume has to be 0.665, so x + y = 0.665. Also, volume x density = mass, so mass(gold) = 19.3x and mass(silver) = 10.5y. They total to 0.75, so 19.3x + 10.5y = 9.75. Now, good old simultaneous equations comes in. We have two equations: 19.3x + 10.5y = 9.75 x + y = 0.665 Since we want to cancel out one pronumeral, multiply the bottom by 10.5 (you can do 19.3, but I like solving for x first) This gives the following: 1. 19.3x + 10.5y = 9.75 2. 10.5x + 10.5y = 6.983 Now we go 1. - 2., cancelling out y, and giving the following: 8.8x = 2.767 Solve for x. x = 0.3144 So we have the volume of gold. Substitute x back into x + y = 0.665 0.3144 + y = 0.665 Solve for y: y = 0.3506 Now that we have both our volumes and our densities, you can just use density x volume = mass 0.3144*19.3 = 6.07g. And m/m% = (6.07/9.75)*100 = 62.3% (3 s.f.) (b) is easy. It's just 62.3% of 24, so 0.623*24 = 15.0 (3 s.f. rounded from 14.95) carats (carat?) Edit 2: lol, beaten by first post Edited September 12, 2011 by Agromono Quote Link to comment Share on other sites More sharing options...
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