Chemistry Talk Chemistry Talk    FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  plz someone help with this problem relating to chemical reac Goto page 1, 2  Next          Chemistry Talk Forum Index -> Chemistry Talk View previous topic :: View next topic   Author Message reactionhelp Guest Posted: Tue May 29, 2007 1:36 am    Post subject: plz someone help with this problem relating to chemical reac What mass of magnesium, in reaction with an excess of hydrochloric acid, is needed to produce 128 ml of hydrogen (h2) gas? The h2 is collected over water at a temperature of 25c and a total pressure of 762 mmhg. Back to top   Ads Advertising Sponsor Salmon Egg Guest Posted: Tue May 29, 2007 5:46 am    Post subject: Re: plz someone help with this problem relating to chemical On 5/28/07 1:36 PM, in article 1180384568.972935.107110@u30g2000hsc.googlegroups.com, "reactionhelp" <nisarahmed86@gmail.com> wrote: Quote: What mass of magnesium, in reaction with an excess of hydrochloric acid, is needed to produce 128 ml of hydrogen (h2) gas? The h2 is collected over water at a temperature of 25c and a total pressure of 762 mmhg. This sure looks like a homework problem. If you are taking chemistry, you should consider dropping the course. Bill -- Fermez le Bush--less than two years to go. Back to top   Ads Advertising Sponsor Bob Guest Posted: Tue May 29, 2007 8:36 am    Post subject: Re: plz someone help with this problem relating to chemical On 28 May 2007 13:36:09 -0700, reactionhelp <nisarahmed86@gmail.com> wrote: Quote: What mass of magnesium, in reaction with an excess of hydrochloric acid, is needed to produce 128 ml of hydrogen (h2) gas? The h2 is collected over water at a temperature of 25c and a total pressure of 762 mmhg. Show us what you have done so far, and then we can focus on where you are stuck. This question involves several steps, each of which is individually straightforward. So jump in and get started, show us what you have done, and we can help as needed. No one here just wants to do your work for you; you would learn nothing from that.(And hint... if you just jump in and do it, you may well figure it out yourself. It often happens.) bob Back to top   Ads Advertising Sponsor Marvin Guest Posted: Tue May 29, 2007 7:26 pm    Post subject: Re: plz someone help with this problem relating to chemical Salmon Egg wrote: Quote: On 5/28/07 1:36 PM, in article 1180384568.972935.107110@u30g2000hsc.googlegroups.com, "reactionhelp" nisarahmed86@gmail.com> wrote: What mass of magnesium, in reaction with an excess of hydrochloric acid, is needed to produce 128 ml of hydrogen (h2) gas? The h2 is collected over water at a temperature of 25c and a total pressure of 762 mmhg. This sure looks like a homework problem. If you are taking chemistry, you should consider dropping the course. Bill -- Fermez le Bush--less than two years to go. It is too late for that. Most schools won't let you drop a course this late in the term. Every year we get postings like this from students who haven't opened the textbook yet. It usually involves freshman chemistry, and the students might be better off to drop college completely. Back to top   Ads Advertising Sponsor Salmon Egg Guest Posted: Wed May 30, 2007 1:52 am    Post subject: Re: plz someone help with this problem relating to chemical On 5/29/07 7:26 AM, in article 135odvv96e4ltdf@corp.supernews.com, "Marvin" <physchem@cloud9.net> wrote: Quote: It is too late for that. Most schools won't let you drop a course this late in the term. Every year we get postings like this from students who haven't opened the textbook yet. It usually involves freshman chemistry, and the students might be better off to drop college completely. One problem, these days, is that you have to go to college to get a decent high school education. Bill -- Fermez le Bush--less than two years to go. Back to top   Ads Advertising Sponsor The_Man Guest Posted: Wed May 30, 2007 3:48 am    Post subject: Re: plz someone help with this problem relating to chemical On May 28, 4:36 pm, reactionhelp <nisarahme...@gmail.com> wrote: Quote: What mass of magnesium, in reaction with an excess of hydrochloric acid, is needed to produce 128 ml of hydrogen (h2) gas? The h2 is collected over water at a temperature of 25c and a total pressure of 762 mmhg. HInts (for an obvious homework problem) 1) Write (and balance) the reaction of Mg with HCl to give H2. 2) Look up the partial pressure of water at 25C. The pressure of H2 is the total pressure (762 Torr) MINUS the partial pressure of water (Dalton's Law of partial pressures) 3) Find the number of moles of H2 by using the ideal gas law (PV=nRT). Make sure you use the PARTIAL pressure of H2, and NOT the total pressure 4) Use the number of moles of H2 (from the gas law) to find the number of moles of Mg (from step 1). 5) Use the atomic weight of Mg (look this up in periodic table) to find the mass of Mg needed. Don't worry about the amount of HCl, since the problem tells you it is excess. You are either a high school student, or a college student taking the course in summer I. If so, go to the tutor! This isn't a hard problem, but it takes practice to put all the pieces together. Back to top   Ads Advertising Sponsor Marcus Fox Guest Posted: Wed May 30, 2007 7:00 am    Post subject: Re: plz someone help with this problem relating to chemical "The_Man" <me_so_horneeeee@yahoo.com> wrote in message news:1180478889.702508.233990@o5g2000hsb.googlegroups.com... Quote: On May 28, 4:36 pm, reactionhelp <nisarahme...@gmail.com> wrote: What mass of magnesium, in reaction with an excess of hydrochloric acid, is needed to produce 128 ml of hydrogen (h2) gas? The h2 is collected over water at a temperature of 25c and a total pressure of 762 mmhg. HInts (for an obvious homework problem) 1) Write (and balance) the reaction of Mg with HCl to give H2. 2) Look up the partial pressure of water at 25C. The pressure of H2 is the total pressure (762 Torr) MINUS the partial pressure of water (Dalton's Law of partial pressures) 3) Find the number of moles of H2 by using the ideal gas law (PV=nRT). Make sure you use the PARTIAL pressure of H2, and NOT the total pressure 4) Use the number of moles of H2 (from the gas law) to find the number of moles of Mg (from step 1). 5) Use the atomic weight of Mg (look this up in periodic table) to find the mass of Mg needed. Don't worry about the amount of HCl, since the problem tells you it is excess. Can you not just calculate how many moles of H2 there are in 128ml of gas, as one mole of gas occupies a certain volume at STP, and then use your balanced equation to work out the mass of magnesium? Marcus Back to top   Ads Advertising Sponsor Marcus Fox Guest Posted: Wed May 30, 2007 7:03 am    Post subject: Re: plz someone help with this problem relating to chemical "Marcus Fox" <please-reply-via-newsgroup-th@-i-posted-to.com> wrote in message news:cPidnf-q1sM2R8HbnZ2dnUVZ8qKvnZ2d@bt.com... Quote: "The_Man" <me_so_horneeeee@yahoo.com> wrote in message news:1180478889.702508.233990@o5g2000hsb.googlegroups.com... On May 28, 4:36 pm, reactionhelp <nisarahme...@gmail.com> wrote: What mass of magnesium, in reaction with an excess of hydrochloric acid, is needed to produce 128 ml of hydrogen (h2) gas? The h2 is collected over water at a temperature of 25c and a total pressure of 762 mmhg. HInts (for an obvious homework problem) 1) Write (and balance) the reaction of Mg with HCl to give H2. 2) Look up the partial pressure of water at 25C. The pressure of H2 is the total pressure (762 Torr) MINUS the partial pressure of water (Dalton's Law of partial pressures) 3) Find the number of moles of H2 by using the ideal gas law (PV=nRT). Make sure you use the PARTIAL pressure of H2, and NOT the total pressure 4) Use the number of moles of H2 (from the gas law) to find the number of moles of Mg (from step 1). 5) Use the atomic weight of Mg (look this up in periodic table) to find the mass of Mg needed. Don't worry about the amount of HCl, since the problem tells you it is excess. Can you not just calculate how many moles of H2 there are in 128ml of gas, as one mole of gas occupies a certain volume at STP, and then use your balanced equation to work out the mass of magnesium? OK, my bad, it's at 25 C. Marcus Back to top   Ads Advertising Sponsor Bob Guest Posted: Wed May 30, 2007 9:58 am    Post subject: Re: plz someone help with this problem relating to chemical On Wed, 30 May 2007 03:03:45 +0100, "Marcus Fox" <please-reply-via-newsgroup-th@-i-posted-to.com> wrote: Quote: "Marcus Fox" <please-reply-via-newsgroup-th@-i-posted-to.com> wrote in message news:cPidnf-q1sM2R8HbnZ2dnUVZ8qKvnZ2d@bt.com... "The_Man" <me_so_horneeeee@yahoo.com> wrote in message news:1180478889.702508.233990@o5g2000hsb.googlegroups.com... On May 28, 4:36 pm, reactionhelp <nisarahme...@gmail.com> wrote: What mass of magnesium, in reaction with an excess of hydrochloric acid, is needed to produce 128 ml of hydrogen (h2) gas? The h2 is collected over water at a temperature of 25c and a total pressure of 762 mmhg. HInts (for an obvious homework problem) 1) Write (and balance) the reaction of Mg with HCl to give H2. 2) Look up the partial pressure of water at 25C. The pressure of H2 is the total pressure (762 Torr) MINUS the partial pressure of water (Dalton's Law of partial pressures) 3) Find the number of moles of H2 by using the ideal gas law (PV=nRT). Make sure you use the PARTIAL pressure of H2, and NOT the total pressure 4) Use the number of moles of H2 (from the gas law) to find the number of moles of Mg (from step 1). 5) Use the atomic weight of Mg (look this up in periodic table) to find the mass of Mg needed. Don't worry about the amount of HCl, since the problem tells you it is excess. Can you not just calculate how many moles of H2 there are in 128ml of gas, as one mole of gas occupies a certain volume at STP, and then use your balanced equation to work out the mass of magnesium? OK, my bad, it's at 25 C. and has water vapor in it bob Back to top   Ads Advertising Sponsor The_Man Guest Posted: Wed May 30, 2007 11:01 am    Post subject: Re: plz someone help with this problem relating to chemical On May 30, 5:53 am, Borek <m.borkow...@delete.chembuddy.whats.com.invalid> wrote: Quote: On Wed, 30 May 2007 11:04:56 +0200, The_Man <me_so_hornee...@yahoo.com wrote: OK, my bad, it's at 25 C. and has water vapor in it My take is that partial pressure of water is to be ignored. NO!!!!!!!!!!!!!!! Figuring out the partial pressure of water is an IMPORTANT part of the problem. In general you are right, but it all depends on the level. Most of the people asking these questions are HS students and they are struggling with the very idea of stoichiometric calculations. You think they have heard about partial pressures in HS? You have a point. Students come to college or university, and say that they had both chemistry and "AP chemistry", and they can't even name the compounds :-( Quote: Borek --http://www.chembuddy.com/?left=BATE&right=pH-calculatorhttp://www.ph-meter.info/pH-electrodehttp://www.bpp.com.pl/?left=dysleksja&right=dysleksjahttp://www.terapia-kregoslupa.waw.pl Back to top   Ads Advertising Sponsor Borek Guest Posted: Wed May 30, 2007 11:01 am    Post subject: Re: plz someone help with this problem relating to chemical On Wed, 30 May 2007 11:04:56 +0200, The_Man <me_so_horneeeee@yahoo.com> wrote: Quote: OK, my bad, it's at 25 C. and has water vapor in it My take is that partial pressure of water is to be ignored. NO!!!!!!!!!!!!!!! Figuring out the partial pressure of water is an IMPORTANT part of the problem. In general you are right, but it all depends on the level. Most of the people asking these questions are HS students and they are struggling with the very idea of stoichiometric calculations. You think they have heard about partial pressures in HS? Borek -- http://www.chembuddy.com/?left=BATE&right=pH-calculator http://www.ph-meter.info/pH-electrode http://www.bpp.com.pl/?left=dysleksja&right=dysleksja http://www.terapia-kregoslupa.waw.pl Back to top   Ads Advertising Sponsor The_Man Guest Posted: Wed May 30, 2007 11:01 am    Post subject: Re: plz someone help with this problem relating to chemical On May 30, 3:18 am, Borek <m.borkow...@delete.chembuddy.whats.com.invalid> wrote: Quote: On Wed, 30 May 2007 06:58:21 +0200, Bob <bbx107....@excite.XYZ.com> wrote: OK, my bad, it's at 25 C. and has water vapor in it My take is that partial pressure of water is to be ignored. NO!!!!!!!!!!!!!!! Figuring out the partial pressure of water is an IMPORTANT part of the problem. Another hint: I am a professor of chemistry - I've taught the solution to exactly this type of problem. Students often DO ignore the partial pressure of water, and they lose lots of points for doing so. Quote: Seems like basic pV=nRT question. Borek --http://www.chembuddy.com/?left=BATE&right=pH-calculatorhttp://www.ph-meter.info/pH-electrodehttp://www.bpp.com.pl/?left=dysleksja&right=dysleksjahttp://www.terapia-kregoslupa.waw.pl Back to top   Ads Advertising Sponsor Borek Guest Posted: Wed May 30, 2007 11:01 am    Post subject: Re: plz someone help with this problem relating to chemical On Wed, 30 May 2007 06:58:21 +0200, Bob <bbx107.XYZ@excite.XYZ.com> wrote: Quote: OK, my bad, it's at 25 C. and has water vapor in it My take is that partial pressure of water is to be ignored. Seems like basic pV=nRT question. Borek -- http://www.chembuddy.com/?left=BATE&right=pH-calculator http://www.ph-meter.info/pH-electrode http://www.bpp.com.pl/?left=dysleksja&right=dysleksja http://www.terapia-kregoslupa.waw.pl Back to top   Ads Advertising Sponsor Marvin Guest Posted: Wed May 30, 2007 9:03 pm    Post subject: Re: plz someone help with this problem relating to chemical The_Man wrote: Quote: On May 30, 5:53 am, Borek m.borkow...@delete.chembuddy.whats.com.invalid> wrote: On Wed, 30 May 2007 11:04:56 +0200, The_Man <me_so_hornee...@yahoo.com wrote: OK, my bad, it's at 25 C. and has water vapor in it My take is that partial pressure of water is to be ignored. NO!!!!!!!!!!!!!!! Figuring out the partial pressure of water is an IMPORTANT part of the problem. In general you are right, but it all depends on the level. Most of the people asking these questions are HS students and they are struggling with the very idea of stoichiometric calculations. You think they have heard about partial pressures in HS? You have a point. Students come to college or university, and say that they had both chemistry and "AP chemistry", and they can't even name the compounds :-( Borek --http://www.chembuddy.com/?left=BATE&right=pH-calculatorhttp://www.ph-meter.info/pH-electrodehttp://www.bpp.com.pl/?left=dysleksja&right=dysleksjahttp://www.terapia-kregoslupa.waw.pl There's nothing new there. When I was a grad student at Iowa State (1950-53), the students had to have had high school math through algebra, but most of didn't know logarithms. And the commonly misspelled words on exam papers - even words that were in the question. In the Iowa small towns, the main functions of high school were football and dances. I know a Ph.D. scientist who went through Iowa State as an undergrad, and came from a small town. He and I see it the same way, so it isn't my Eastern prejudice. His family valued education, unlike most in town. Back to top   Ads Advertising Sponsor Stephan Bird Guest Posted: Thu May 31, 2007 2:42 am    Post subject: Re: plz someone help with this problem relating to chemical On Wed, 30 May 2007 11:53:55 +0200, in op.ts4wf5iyu0t02r@borek Borek <m.borkowski@delete.chembuddy.whats.com.invalid> wrote: Quote: In general you are right, but it all depends on the level. Most of the people asking these questions are HS students and they are struggling with the very idea of stoichiometric calculations. You think they have heard about partial pressures in HS? Well, that very much depends on location and possibly the actual syllabus. Thumbing through my old A-Level (last course before university) notes we certainly covered it to an extent here in the UK. Stephan -- Stephan Bird MChem(Hons) AMRSC Currently in Caernarfon, Wales Back to top   Ads Advertising Sponsor Display posts from previous: All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year Oldest FirstNewest First         Chemistry Talk Forum Index -> Chemistry Talk All times are GMT Goto page 1, 2  Next Page 1 of 2   Jump to: Select a forum Chemistry Talk----------------Chemistry Talk  You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum 97 Attacks blocked Powered by phpBB © 2001, 2005 phpBB Group