Question

Not too great with chemistry :/... Any help/guidance is greatly appreciated.

1. Observe the following reaction:
NaOH + HCl → NaCl + H2O
If 8.00 mL of HCl requires 7.52 mL of 0.10 M NaOH to consume the HCl (or titrate to completion), what is the concentration of HCl?

2. A 1 cm cuvette was filled with a solution which contains only a solute with a molar absorbtivity coefficient of 4800 M-1cm-1 and solvent. After blanking with the pure solvent the absorbance of the solution is 0.543. What is the concentration of the solution?

Answer 1

1. lets write down all we have and all we need:

NaOH + HCl → NaCl + H2O

V(HCl)= 8 cm3
V(NaOH)= 7,52 cm3
c(NaOH)=0,10 M
------------------
c(HCl)=?

so lets start:

c=n/V -> n=c*V

now we calculate amount of NaOH in moles:

n(NaOH) = c(NaOH) * V(NaOH)
n(NaOH) = 0,10 mol dm-3 * 7,52 * 10-3 dm3
n(NaOH) = ???

now you calculate what amount of NaOH is needed to completely react with HCl with bearing in mind ratio from balanced chemical equation:

n(HCl) / n(NaOH) = 1/1 = 1
n(HCl) = n(NaOH)

and now just calculate the concentration:

c(HCl) = n(HCl) / V(HCl)

any questions?