Question

A total of 20.0 mL of sodiutm hydroxide (NaOH) was neutalized by 30.0 mL of 0.250 M hydrogen bromide (HBr). What was the concentration of the sodium hydroxide? ****** I need help filling out the chart. please help me through it

Answer 1

@imqwerty

Answer 2

The balanced reaction of the two chemicals will be this-

\(NaOH + HBr \) ----> \(NaBr+H_2O\)

here \(\color{orangered}{1 ~mole~ of~ HBr~neutralizes~ 1 ~mole~ of ~NaOH}\)

so we are given all this info-
the concentration of \(HBr\) =0.25M
volume of \(HBr\) = 30mL
and
volume of \(NaOH\)=20mL

and it says that A total of 20.0 mL of sodiutm hydroxide (NaOH) was neutalized by 30.0 mL of 0.250 M hydrogen bromide (HBr)

^here the number of moles of \(NaOH\) will be equal to the number of moles of \(HBr\) because \(HBr\) is completely neutralizing the \(NaOH\)

so we find the number of moles of \(HBr\) with the given info

\(\large Molarity =\frac{moles_{of~HBr}}{volume_{in ~mL}} \times 1000\)
\(0.25= \frac{moles}{30} \times 1000 \)
\(moles= \frac{0.25 \times 30}{1000}\)


okay so we have the number of moles of \(HBr\)
the number of moles of \(NaOH\) will also be this much
so

\(Molarity= \frac{moles}{volume_{in~mL} } \times 1000\)

\(Molarity= \frac{\frac{0.25 \times 30}{1000}}{20} \times 1000\)

\(Molarity= \frac{0.25 \times 30}{1000 \times 20} \times 1000\)

\(Molarity= \frac{0.25 \times 30}{20}\)

\(Molarity=0.375M\)

Answer 3

im a little confused on the molar ratio would it be 1 for HBr and 1 for NaOH?

Answer 4

you mean why will be the moles equal? :)

Answer 5

yes

Answer 6

okay
see the reaction-

\(\color{orangered}{1}HBr+\color{orangered}{1}NaOH\) -----------> \(\color{orangered}{1}NaBr+\color{orangered}{1}H_2O\)

^this is a balanced stoichiometric reaction
and in a balanced stoichiometric reaction the stoichiometric coefficients[the numbers in the red :) ] of each chemical denote the ratio of the moles of the chemicals reacting or being produced.

so here 1 mole of \(NaOH\) reacts with 1 mole of \(HBr\) and neutralizes completely
so since the number of moles reacting to complete the neutralization reaction are same for both we equaled them

suppose if 5 moles of \(NaOH\) react then correspondingly 5 moles of \(HBr\) will be needed to complete the neutralization reaction :)

Answer 7

oh okay that makes sense.

Answer 8

:)

Answer 9

how do i find the concentration of NaOH now?

Answer 10

concentration is nothing but the molarity

molarity is given by this expression-

\(molarity= \frac{moles}{Volume} \times 1000\)

here the volume must be taken in mL.


alright
so if we wish to find the molarity of \(NaOH\) -
we know the volume but we donno the moles
so we can't find it rn

but we know that since the NaOH is getting completely neutralized its moles must be equal to the moles of HBr

so next step is to find the moles of HBr

Answer 11

and how do we do that?

Answer 12

we know the molarity and the volume of HBr
try to put these values into that molarity equation to get the number of moles :)

Answer 13

im not sure what numbers i need to put in for the equation

Answer 14

sorry i really suck at chemistry

Answer 15

okay this is our equation-

\(molarity = \frac{moles}{volume} \times 1000\)

read the question
its given that the molarity of HBr is \(0.25M\)
and the volume of HBr is \(30mL\)

we can plug this info into that equation to get moles?