1answer.
Ask question
Login Signup
Ask question
All categories
  • English
  • Mathematics
  • Social Studies
  • Business
  • History
  • Health
  • Geography
  • Biology
  • Physics
  • Chemistry
  • Computers and Technology
  • Arts
  • World Languages
  • Spanish
  • French
  • German
  • Advanced Placement (AP)
  • SAT
  • Medicine
  • Law
  • Engineering
lesya [120]
3 years ago
15

what mass of sodium fluoride (FW=42.0 g/mol) must be added to 3.50 x 10^2 mL of water to give a solution with pH = 8.40?

Chemistry
1 answer:
MaRussiya [10]3 years ago
7 0

Answer:

Explanation:

Sodium fluoride, being a salt, dissolves in water completely producing F ⁻ ions. Now  F⁻ is the conjugate base of the weak acid HF, so in water we will have the following equilibrium:

F⁻  +  H₂O ⇆ HF + OH⁻

Given this equilibrium, we need to calculate Kb from the Ka for HF,  the [ OH ⁻] from the given pH, and finally the mass needed to produce that  OH⁻ concentration.  

The equilibrium constant, Kb , can be calculated from Kw = Ka x Kb, where Kw = 10⁻¹⁴ and Ka for HF is  6.6 x 10⁻⁴ from reference tables.

Kb = 10⁻¹⁴ / 6.6 x 10⁻⁴ = 1.5 x 10⁻¹¹

pH + pOH = 14  ⇒ pOH = 14 - 8.40 = 5.60

[ OH⁻ ] = 10^-5.60 = 2.51 x 10⁻⁶

Now we have all the information :

                                   F⁻                    HF                        OH⁻

Equilibrium                 X                  2.51 x 10⁻⁶            2.51 x 10⁻⁶

(2.51 x 10⁻⁶)² / X  =  1.5 x 10⁻¹¹     ⇒  X =  (2.51 x 10⁻⁶)²  / 1.5 x 10⁻¹¹

X = [ F⁻ ] = 0.41 M

For 350 mL ( 0.35 L ) we need to add:

0.41 mol HF/ 1 L  *  0.35 L = 0.144 mol

and finally the mass will be:

0.144 mol NaF *  42.0 g/mol NaF = 6.03 g NaF

You might be interested in
GIVE ME ANSWERS
Shalnov [3]

Answer:

uh.. How many do you want done??

Explanation:

6 0
3 years ago
Read 2 more answers
Fill in the blanks: Electrons are ___ in an ionic bond, whereas they are___ in a polar covalent bond, and ___ in a nonpolar cova
NNADVOKAT [17]

Answer:

The correct answer is "transferred; unequally shared; equally shared".

Explanation:

Ionic bonding occurs when a positively charged atom (cation) interacts with a negatively charged atom (anion). In ionic bonding, the cation transfers its electron to the anion. In polar covalent bonding, electrons are unequally shared. This means that the electrons spend more time in an atom than the other, which gives partial positive and negative charges to the atoms. On the other hand in nonpolar covalent bonding, the electrons are equally shared and no charges are created.

3 0
3 years ago
I have my chemistry EOC tomorrow, and I need to know how to calculate the molar mass of a compound. Specifically ones set up lik
yuradex [85]

Answer:

357.475

Explanation:

First you need periodic table and you have to look for mass

Fe = 3 x 55.845 = 167.535

P = 2  x 30.97 = 61.94

o = 4 x 2 so 8 oxygen =  8 x 16 = 128

add all and you get 357.475

6 0
3 years ago
What is the formula of ideal gas law?
Debora [2.8K]
PV = nRT. Where P = pressure, V = volume, n = number of moles, R = universal gas constant and T = temperature. Hope this helps!
3 0
3 years ago
Read 2 more answers
What is the mass, in grams, of 1.58 mol of water, h2o?
inn [45]
Answer is: mass of 1,58 mol of water is 28,44 grams.
n(H₂O) = 1,58 mol.
M(H₂O) = 2 · 2 g/mol + 16 g/mol.
M(H₂O) = 18 g/mol.
m(H₂O) = n(H₂O) · M(H₂O).
m(H₂O) = 1,58 mol · 18 g/mol.
m(H₂O) = 28,44 g.
n - amount of substance.
M - molar mass.
3 0
3 years ago
Other questions:
  • What term defines a mass which is exactly equal to 1/12 the mass of one carbon-12 atom
    7·1 answer
  • How is synthesis and decomposition reaction related to each other???
    10·2 answers
  • How many atoms are in 1 mole of hydrogen
    14·1 answer
  • How many calories are required to raise the temperature of 105 g of water from 30.0°C to 70.0°C?
    9·1 answer
  • What types of materials are better at absorbing energy from radiation?
    8·1 answer
  • A gas was at STP. If the pressure increased to 3.5 atm, what would the new<br> temperature be?
    6·1 answer
  • HELP!!!!!! I will give you 15 points for this , please don’t guess
    13·1 answer
  • Substance A is mixed with water and donates 0.4% of its H+ ions. Which of the following BEST describes Substance A? (See picture
    14·1 answer
  • Use the following equation to answer the questions below:
    10·1 answer
  • What are the characteristics of nonvascular plants? (select all that apply) A . They don’t rely on roots to receive water.
    15·1 answer
Add answer
Login
Not registered? Fast signup
Signup
Login Signup
Ask question!