Hi, im terrible at maths and need a dumbed down explanation of something simple

Hi guys, im working through some chemistry problems and i have zero math ability. Part of my problem requires me to Work out two values

for e.g

0.616 = A / B

A + B = 0.3

Its to work out the concentrations of an acid and a base in a chemical reaction. This is the part im stuck on. I know A divided by B = 0.616 and i know that if you add A + B together it comes to 0.3

Is there a method to work this out. In the book it gives this but i don't under stand where it gets some of the numbers from.

HPO4 (is just the chemical name)

0.616 x (0.3m -[HPO4] = [HPO4])

0.185 - 0.616 x [HPO4] = [HPO4]

0.185 = 1.616 x [HPO4]

0.114m = HPO4

So A = 0.114 and B = 0.186

I dont understand what they are doing to get the concentration....Can someone explain in simple terms?

Thanks

Re: Hi, im terrible at maths and need a dumbed down explanation of something simple

I am going to make some assumptions here. A is the concentration of the HPO4 and B is the concentration of something else. Let's start with the equation A+B = 0.3 and subtract A from both sides:

Next, for the equation , we will multiply both sides of the equation by :

Since , we can rewrite the equation: .

This simplifies to .

So, now we have two different equations (Equation 1 and Equation 2):

The first equation tells us that wherever we see , we can replace that by because the two values are equal. So, in the second equation, we will make this replacement:

. That is where the book writes (This is why I assume that ).

Now, on the left hand side of the equation, we need to distribute the multiplication. So, we have:

This works out to (again, replace by and you have what the book wrote).

Now, we will add to both sides of the equation:

(replace by and you again have what you saw in the book).

Finally, divide both sides of the equation by 1.616 to get . Now that you have , you can plug that into (Equation 1) to get .

Re: Hi, im terrible at maths and need a dumbed down explanation of something simple

You have explained this amazingly, yet i still am struggling to understand it. Thats just a reflection on my awful maths tho. Thanks alot for this, i suspect if i read over it enough everything will become clear.

Re: Hi, im terrible at maths and need a dumbed down explanation of something simple

Hi, sorry i am just reading over it, i have a few questions.

Where did the 1.616A come from? You had 0.185 - 0.616A + 0.616A = A + 0.616A Then that equals 0.185 = 1.616A - Where did that 1 come from?

Re: Hi, im terrible at maths and need a dumbed down explanation of something simple

From A + 0.616A

You can factor out the A so it becomes A(1+0.616)

Hence 1.616A

Re: Hi, im terrible at maths and need a dumbed down explanation of something simple

Thanks, Again im a maths noob, is that a general rule?

Everytime i have

A + num x A

Can i factor out the A's and put a one in front? Seems weird!

Re: Hi, im terrible at maths and need a dumbed down explanation of something simple

Well A is equal to 1 x A

So A + num x A= 1 x A + num x A= A(1+num)

Re: Hi, im terrible at maths and need a dumbed down explanation of something simple

Are you familiar with the distributive property?

for any numbers a, b, and c:

a picture to demonstrate:

http://s23.postimg.org/tlgupje97/distributive.png

The area of the left rectangle, a*b, plus the area of the right rectangle, a*c, is equal to the entire big rectangle, a * (b+c)

Re: Hi, im terrible at maths and need a dumbed down explanation of something simple

Ah thanks, that explains the concept well.