//11/18/02-update netscape 7
thepage="Buffers Comp.(77)"
refnumber=119
attempts=0
pK=0
pH=0
theacid=""
thebase=""
acidconc=0
baseconc=0
ratio=0
askit=""
newone=""
totl=0
corrt=0
function dataset(acid,base,Ka,formacid,formbase){
	this.acid=acid
	this.base=base
	this.Ka=Ka
	this.formacid=formacid
	this.formbase=formbase
}
function question(p1,p2,p3,p4,p5){
	this.p1=p1
	this.p2=p2
	this.p3=p3
	this.p4=p4
	this.p5=p5
}
HH=new Array("pH=pKa+log([base]/[acid])","pH-pKa=log([base]/[acid])")
quest=new Array(10)
quest[1]=new question("A buffer solution contains "," and "," ion with concentrations of ","<b>M</b> and ","<b>M</b>, respectively. What is the pH of the buffer?")
quest[2]=new question("What is the base/acid ratio in a buffer containing "," and "," ion, if the buffer has a pH of ","?")
quest[3]=new question("A buffer has a pH of "," and a "," concentration of ","<b>M</b>. What is the "," concentration?")
ansphrase=new Array()
ansphrase[1]=new Array("The Henderson-Hasselbach equation has the form:<br>","<br>The pKa for "," is ",".<br> Substituting the ratio into the equation yields:<br>")
ansphrase[2]=new Array("The pKa for "," is ",". Rearranging the Henderson-Hasselbach equation yields:<br>")
ansphrase[3]=new Array("The pKa for "," is ",". Rearranging the Henderson-Hasselbach equation yields the following:<br>","<br>Since "," is given, one can readily solve for the needed concentration.")
species=new Array(50)
species[1]=new dataset("acetic acid","acetate",1.75e-5,"CH<SUB>3</SUB>COOH","CH<SUB>3</SUB>COO<SUP>-</SUP>")
species[2]=new dataset("acrylic acid","acrylate",5.5e-5,"C<SUB>3</SUB>H<SUB>4</SUB>O<SUB>2</SUB>","C<SUB>3</SUB>H<SUB>3</SUB>O<SUB>2</SUB><SUP>-</SUP>")
species[3]=new dataset("arsenous acid","arsenate",6.6e-10,"H<SUB>3</SUB>AsO<SUB>3</SUB>","H<SUB>2</SUB>AsO<SUB>3</SUB><SUP>-</SUP>")
species[4]=new dataset("benzoic acid","benzoate",6.3e-5,"C<SUB>7</SUB>H<SUB>5</SUB>O<SUB>2</SUB>","C<SUB>7</SUB>H<SUB>4</SUB>O<SUB>2</SUB><SUP>-</SUP>")
species[5]=new dataset("bromoacetic acid","bromoacetate",1.3e-3,"C<SUB>2</SUB>H<SUB>3</SUB>BrO<SUB>2</SUB>","C<SUB>2</SUB>H<SUB>2</SUB>BrO<SUB>2</SUB><SUP>-</SUP>")
species[6]=new dataset("butyric acid","butyrate",1.5e-5,"C<SUB>4</SUB>H<SUB>8</SUB>O<SUB>2</SUB>","C<SUB>2</SUB>H<SUB>7</SUB>O<SUB>2</SUB><SUP>-</SUP>")
species[7]=new dataset("chloroacetic acid","chloroacetate",1.4e-3,"C<SUB>2</SUB>H<SUB>3</SUB>ClO<SUB>2</SUB>","C<SUB>2</SUB>H<SUB>2</SUB>ClO<SUB>2</SUB><SUP>-</SUP>")
species[8]=new dataset("cyanic acid","cyanate",3.5e-4,"HOCN","OCN<SUP>-</SUP>")
species[9]=new dataset("formic","formate",1.8e-4,"H<SUB>2</SUB>CO<SUB>2</SUB>","HCO<SUB>2</SUB><SUP>-</SUP>")
species[10]=new dataset("hydrofluoric acid","fluoride",6.6e-4,"HF","F-")
species[11]=new dataset("nitrous acid","nitrite",7.2e-4,"HNO<SUB>2</SUB>","NO<SUB>2</SUB><SUP>-</SUP>")
species[12]=new dataset("propionic acid","propionate",1.3e-5,"C<SUB>3</SUB>H<SUB>6</SUB>O<SUB>2</SUB>","C<SUB>3</SUB>H<SUB>5</SUB>O<SUB>2</SUB><SUP>-</SUP>")

function startit(){
	clear()
	totl++
	document.forms[0].total.value=totl
	which=Math.ceil(12*Math.random())
	theacid=species[which]['acid']
	thebase=species[which]['base']
	ratio=0
	while(ratio<.5 || ratio>5){ratio=10*Math.random()}
	ratio=number(ratio,3,3)
	acidconc=0
	while(acidconc<.1)acidconc=Math.random()
	baseconc=acidconc*ratio
	acidconc=number(acidconc,2,3)
	baseconc=number(baseconc,2,3)
	pK=-Math.log(1*species[which]['Ka'])/2.303
	pK=number(pK,3,3)
	pH=1*pK+Math.log(1*ratio)/2.303
	pH=number(pH,3,3)
	whichask=Math.ceil(4*Math.random())
	makequestion(whichask)
	buildanswer(whichask)
}
function makequestion(f){
if(f==1){thequest=quest[1]['p1']+theacid+quest[1]['p2']+thebase+quest[1]['p3']+acidconc+quest[1]['p4']+baseconc+quest[1].p5;ansr=pH}
if(f==2){thequest=quest[2]['p1']+theacid+quest[2]['p2']+thebase+quest[2]['p3']+pH+quest[2]['p4'];ansr=ratio}
if(f==3){thequest=quest[3]['p1']+pH+quest[3]['p2']+theacid+quest[3]['p3']+acidconc+quest[3]['p4']+thebase+" ion "+quest[3]['p5'];ansr=baseconc}
if(f==4){thequest=quest[3]['p1']+pH+quest[3]['p2']+thebase+quest[3]['p3']+baseconc+quest[3]['p4']+theacid+quest[3]['p5'];ansr=acidconc}
thequest+=("(pKa="+pK+")")
showquest(thequest)
}
function buildanswer(f){
	if(f==1)theanswer=ansphrase[1][0]+HH[0]+ansphrase[1][1]+theacid+ansphrase[1][2]+pK+ansphrase[1][3]+"pH="+pK+"+log("+baseconc+"/"+acidconc+")="+pH;
	if(f>1)theanswer=ansphrase[2][0]+theacid+ansphrase[2][1]+pK+ansphrase[2][2]+HH[1]+"<br>"+pH+"-"+pK+"="+number((pH-pK),2,3)+"=log(base/acid)<br>Taking the antilog yields<br>base/acid="+ratio;
	if(f==3)theanswer+=("<br>Since the acid concentration is given as "+acidconc+"<br>base="+ratio+"*"+acidconc+"="+baseconc);
	if(f==4)theanswer+=("<br>Since the base concentration is given as "+baseconc+"<br>acid="+baseconc+"/"+ratio+"="+acidconc);
	}
function answer(f){
	if(tried==1)alert("You've already done this one! Get a new problem");
	else{
		if(tried==2){totl++;document.forms[0].total.value=totl};
		if(f>.95*ansr & f<1.05*ansr){
			document.forms[0].results.value="correct"
			corrt++
			document.forms[0].correct.value=corrt
		}
	else{
		document.forms[0].results.value="incorrect"
		tried=2
		}
	}
}